Bellows seals -Material of construction for Thermic fluid application

Selection of  AISI 316Ti  Vs AISI 321 as materials of construction for bellows seals for Thermic fluid application (such as Santhotherm-66, dow therm ,therminol etc) for high temperature application +200 to +300 Degree C)

Generally both the materials are recommended for selection of bellows seals so long maximum temperature is below the creep range.
AISI 321 is Titanium stabilized Austenetic Stainless steel. It is very good corrosion resistant material for high temperature environment where presence of chloride is negligible.Presence of Ti has tendency  to suppress the formation of Chromium carbide under elevated temperature specially at welded construction .Thus depletion of Cr is avoided due to presence of Ti.
But it has less resistance to Pitting-Corrosion as compared to AISI 316 Ti

On the other hand AISI 316 Ti is having 'Mo' in addition to 'Ti:'. Therefore it has very good resistance to Pitting corrosion and has all property of AISI 321.


Obviously AISI 316 Ti shall be comparatively costlier than AISI 321   

Why No-Load Testing is important in Reciprocating compressors after complete overhaul ?

Why No-Load Testing is important in Reciprocating compressors after complete overhaul ?

After complete overhaul (i.e. replacement of worn out bearings -main bearings,conn rod big end bearings,small end bearings,cross head shoe replacements,piston rings and rider rings ,stuffing box pair of rings,etc etc) following should be checked during idle run (no-load ) test for establishing soundness of assembly .
Prior to start up for idle run:
1.Check and ensure that CE (Crank end  or BDC) and Cylinder Head End (TDC) clearances are measured correctly by lead wire and micrometer and values maintained as per OEM recommendation.
2.Check piston rod run out (vertical and horizontal) to ensure correctness of piston and cylinder assembly with respect to slide body or distance pieces wherever applicable.
3.Start auxiliary oil pump and observe that oil is going to all the bearing locations as well as cross head pin and crank shaft main bearings through oil passages .
4. keep barring the crank shaft while oil is flowing to all required locations. Lube oil pressure should not be less than 2.5 kg/cm2 (g).
5.Close all the doors of cross-head guide .
6.Ensure valve and valve covers from cylinders are removed prior to No load Testing.

Observations during No-load Testing

1.Run the compressor for 15 minutes and stop to measure/observe  followings:
  - Temperatures at crank shaft main bearings and intermediate bearings if provided.
  - Temperatures at all conn rod big end bearings and small end bush bearings.
  - Lube oil pressure and Temperature before and after oil cooler.
  - Water temperature at in let and outlet of oil cooler.
  -Temperatures at all cross heads shoes.
  - Piston rod temperatures at stuffing box packing locations.
  - Gear box bearing temperatures
  -Any other abnormality if any.

2. If all the readings in step 1 above are within satisfactory range, run the compressor for next one hour and repeat all those readings mentioned in step 1 above.
3.If all the readings in step 2 above are satisfactory within acceptable range ,run the compressor for next two hours and repeat the readings mentioned in step 1 above..
4 If the readings in step 3 above are within acceptable range run the compressor for next one hour and repeat the readings mentioned in step 1 above.
5. If readings in step 3 and 4 are almost steady ,stop further running. This completes the satisfactory idle run test for minimum 4 hours.In case readings are not steady even after 4 hours of no load  trial , repeating the running further is not advisable rather we should check  for cause of increasing trend of temperature .It could be the misalignment or  poor workmanship which needs attention to be addressed / fixed the problem. After correction , repeat the fresh no load trial as per step 1 to 5 above till the parameters are steady within 4 hours of cumulative running.

Many end users are not following above procedures .They directly start the compressor for load trial .There are two main disadvantages in this case :
1. It may result in catastrophic failure of compressor or bearing seizure because of  possibility of  poor
    workmanship/practices which could have been noticed in first 15 minutes no load trial run.
2.Very fast wear rate of rider rings and piston rings resulting in their low MTBF. As most of the rider rings
   are made of PTFE with graphite filler,during no load a layer of PTFE is formed on sliding surfaces of
   cylinder liners which further reduces the coefficient of friction during load testing or load trial.

What is risk based inspection (RBI)?

 

The inspection of plant and machinery has traditionally been based on statutary requirement  backed up by local health & safety legislation. The type of equipment has determined inspection frequency, methods employed and locations examined - with little focus given to its age, specific duty or likely condition. Increased operational experience and a greater appreciation of the hazards are now leading some parts of industry to adopt a more informed approach to inspection planning, targeting the inspection required to reduce the risk as low as reasonably practicable.
Risk based inspection is the process of developing an inspection plan based on knowledge of the risk of failure of the equipment. The essential element is a risk analysis. This is the combination of an assessment of the likelihood (probability) of failure due to damage, deterioration or degradation mechanism with an assessment of the consequences of such failure.
The information gained from this process is used to identify
1.The type and rate of damage that may potentially be present and
2.The equipment or locations where failure would give rise to danger of different degrees.
 Higher risk equipment may have active damage mechanisms or high consequences of failure, or a combination of the two. A suitable inspection scheme is then planned to increase confidence about the equipment's current and future condition, taking account of the potential damage mechanisms and the reliability of the inspection techniques used.
Risk based inspection may be applied in any industry, but there has been most interest from the power and petrochemical sectors.  The American Petroleum Institute has published guidance for risk based inspection relevant to refineries. ^[1]
Industry sees RBI as a means of using inspection resources more effectively which can result in economic benefits from extended run lengths or from the use of advanced NDT or non-invasive schemes. Regulatory pressure will ensure that the process of RBI is carried out rigorously so that non-prescriptive inspection decisions are based on adequate information and expertise. .

Reference

1. API Recommended Practice 580 and Base Resource Document 581

How to keep copper and aluminum apart to avoid corrosion ?

Guidelines for how best to keep copper and aluminum apart to avoid corrosion?

In many industrial installation use of aluminium and copper combination can not be ruled out completely.
To minimize galvanic corrosion,  always attempt  to maximize the size of the anode and minimize the
size of the cathode. In an aluminum/copper couple, copper is the cathode and aluminum is the anode. If
you paint the copper and the paint gets scratched, then you have a small cathode and a very large anode
which is exactly what you want. We must know that in a cathode-anode combination, larger is the anodic area lesser will be the corrosion rate.
On the other hand If you  paint the aluminum and it gets scratched, then you have a small anode and a very large cathode, which is not what you want.This will accelerate the corrosion rate.

Tips on Belts drives for better performance and reliability

1.Maximum speed that a drive belt can safely handle:
Pulley rim speed is the limiting factor, rather than the belt. This limiting speed depends on the
pulley material and design.
For gray iron casting and statically balanced, pulley  rim speeds up to 6,500 fpm is normally satisfactory. A pulley running at more than 6,500 fpm may cause vibration, noise, poor bearing life, and high fatigue stresses. Therefore, pulleys that exceed 6,500 fpm should be dynamically balanced.

2.Causes of vibrations in belt-drive and corrective measures.
 Drive belts experience both vertical and lateral vibrations when their natural frequencies coincide with excitation frequency of connected equipment.Belt tension can affect the amplitude of this vibration. Therefore, to correct the problem, first check for proper tension.
If this does not work, consider changing other drive parameters to reduce the amplitude of vibration or alter its frequency. Such parameters include span length, belt type, misalignment, inertia of driving or driven machinery,pulley diameter and weight (inertia), speed, and the number of belts. In some cases (where original unit was oversized), it may be possible to downsize the drive by reducing the number of belts or belt width, and increasing the static tension to alter the belt’s natural frequency so it doesn’t coincide with the excitation frequency of the machinery. When it can be done safely, it is preferable to reduce the static tension to keep the operating belt tension below the belt’s natural frequency range.
To reduce lateral vibration, increase flexural rigidity in the lateral direction. This can be accomplished by using joined belts.

What causes a squealing belt?
 A V-belt squealing is usually caused by belt slip, often due to under tensioning. When a new belt replaces one belt in a multi belt drive, the new belt may be tensioned properly, but all of the old ones are undertensioned. To avoid this problem, replace all belts in a multibelt drive at the same time, and with belts of the same construction from the same manufacturer.
Replace worn sheaves, which can lead to noise and belt rollover, as well as worn or damaged belts.
Sudden, high startup torques or peak loads also cause belt slip. Usually, this condition lasts only a few seconds.But, it can lead to heat build-up which reduces belt life. If belt slip and heat build-up is suspected, turn off the drive and place a gloved hand on the belt to feel if the belt is too hot.
Grit, oil, or grease cause belts to slip. Therefore, keep the drive components clean. And don’t use belt dressing.
This only masks the real problem of inadequate tension.
Large pitch, wide synchronous drives may generate noise at high speeds. This can be caused by too-high or too low belt tension, or misalignment, which prevents the belt teeth from smoothly entering or leaving the sprocket grooves. Because of this, alignment requirements are tighter for synchronous belts than standard V-belts.
Note:: when inspecting a problem drive, review all components. Noise can be caused by nonbelt sources,
such as bearings, guard vibration, and loose mounts.

Enhanced Shelf Life of V-Belts- By Good Storage practices.

Under proper storage conditions, belts can be used for many years without appreciable deterioration of quality and service life.Shelf life can be enhanced between 4-6 years provided following guidelines are followed as a good preservation practices:

1. Store belts in a cool, dry, dust-free area, away from radiators and direct sunlight.
2. Temperatures ideally between 5 degree C and 30 degree C and relative humidity below 70
    percentage are recommended near storage location of material stores
3. Store belts away from ozone producing unguarded fluorescent lights, mercury vapor lamps, and high
   voltage electrical equipment.
4. Do not store belts near chemicals, oils, solvents, lubricants and acids.
5. Belts can be coiled on shelves or hung on pegs having diameter not less than minimum diameter sheave
    recommended for the belt cross section.
6. However, avoid sharp bends and stresses that can cause deformation, cracks or any other damage to the
   belts.
7. Stack belts no higher than 12" to prevent damage to the belts at the bottom of the pile.
8. When hanging, coil longer belts to prevent distortion due to belt weight
9.Do not store belts on the floor unless they are in a protective container. Floor locations are exposed to
   traffic that may damage the belts.
10.When the belts are stored, they must not be bent to diameters smaller than the minimum recommended
sheave or sprocket diameter for that cross section.

Tips to install "V"-Belts in belt drive system to prevent premature failure.

Following minimum check points should be checked to ensure reliability of V-Belt power transmission.

 1. Ensure LOTO (Lock out Tag out ) compliance prior to start the job on belt drive system inspection.
     Observe all other safety procedures.
 2. Remove belt guard.
 3. Loosen motor mounts.
 4. Shorten center distance.
 5. Remove old belts.
 6. Inspect belt wear patterns for possible troubleshooting.
 7. Inspect drive elements–bearings, shaft, etc.
 8. Inspect sheaves for wear and clean.
 9. Check sheave alignment. (preliminary)
10. Select proper replacement belts.
11. Install new belts.
12. Tension belts.
13. Check sheave alignment. (final)
14. Replace guard.
15. Start drive (look & listen).
16. Re-tension after 12 to 24  hours of running.

Advantages and disadvantges of belt drives over direct coupling or gear drives

Belt drives are occasionally used on trains involving small reciprocating equipment having speed preferably below 500 RPM . The advantages of  belt drive of coupling mechanism include relatively low cost, ease of mechanical assembly, reduced maintenance complexity, and less likelihood of damaging the attached equipment during failure. In addition, the belt will typically accommodate much more misalignment than traditional couplings or gear drives.
However, disadvantages of  belt coupling mechanism  presents significant uncertainties in determining the
torsional behavior, as the belt stiffness tends to be nonlinear and highly dependent on belt tension
(preload). In addition, it is sometimes difficult to obtain an accurate estimate of the torsional damping
associated with the belt.

Tips for preservation of rotating equipment installed but idling in field for longer duration

Long Term Perspective : ( Idle  from 6 months  to 2 years and above)

 PUMPS (CENTRIFUGAL, ROTARY & RECIPROCATING )

1. Pump casing should be flushed & drained.
2. If service is acidic or alkali, the same should be neutralized.
3. All cooling jackets should be flushed by fresh water followed by air drying.
4. Pump casing should be filled with mineral oil containing 5 percent rust preventive 
   concentrate.
5. Cooling water jackets, bearing housing and stuffing box should be plugged; low point drain
    valve should be cracked open slightly.
6. Approved preservative coating should be applied on parts which protrude through bearing or
   stuffing box housings like shaft end and cover with tape.
7. All exposed machined surfaces and coupling parts except elastomers should be coated with
    preservative.
8. Bearing housing should be completely filled with mineral oil containing 5 percent rust
   preventive concentrate.
9. Pump suction and discharge valves should be kept closed.
10.The equipment should be given few hand rotations (4 to 6) every 6 months (or during P.M).

 LARGE FANS
1. Approved preservative coating should be applied on coupling and all external machined
   surfaces.
2. Rust preventive spray should be applied on fan wheel.
3. Casing low point drain valve should be crack opened. The equipment should be given few
hand rotations once in 6 Months (or during P.M).
 GEARBOXES
1. Gearbox and piping should be completely filled with oil containing 5 percent rust preventive
concentrate. Some space should be left for thermal expansion.
2. All vents should be plugged.
3. The equipment should be given few hand rotations every 6 Months (or during P.M).

RECIPROCATING COMPRESSORS
1. Compressor casing should be made free of hydrocarbons and purged.
2. Compressor suction and discharge valves should be removed and separately preserved in 
    store .Valve ports should be closed with valve covers after spraying with anti rust 
    preservative inside the cylinders.
3.Start auxilliary lube oil pump and give barring to compressor for 4 to 6 rotation periodically 
    every 4 months
4. All exposed machined parts should be coated with approved preservative.
5. After flushing & drying of cooling jacket, oil can be filled.
6. If the equipment is not in operation for more than one year, all soft packings, elastomers
   should be inspected & replaced (if required).

CENTRIFUGAL PROCESS COMPRESSORS
1. Compressor casing should be made free of hydrocarbons and purged.
2. Machine internals should be flushed with solvent to remove heavy polymers.
3. Casing should be pressurized with nitrogen or bone dry air (25 mm water column gauge just
     positive pressure above atm.)
4. After mixing 5 percent rust preventive concentrate to existing lube and seal oil, it should be
    circulated through the entire system for one hour through auxilliary oil pump and should be
   given hand rotation few turns periodically every 4 months.
5. Upon the above exercise, oil return header should be closed. Shaft openings should be
   sealed with silicone rubber caulking and tape.
6. Oil console should be filled with mineral oil containing 5 percent rust preventive concentrate.
7. Filling should be done when compressor is at ambient temperature. All heat tracers should
   be turned off.
8. All exposed machined parts; including couplings (except elastomer) should be coated with
    approved preservative.

Why there is a need for different maintenance philosophies in a process industry specially in energy sector ?

The answers would be :

• To keep the plant equipments functional for the intended service
• To prevent premature failures or break down
• To mitigate the consequences of failure
The different maintenance philosophies should also be technically appropriate, feasible and economically justified.
We must realize that Breakdowns in continuous running process plants e.g. petrochemicals /Energy sector industry can have significant impact on the profitability of a business.No business can sustain for longer time without profit. Whether we are producing or not , our fixed cost of labor /employee remains same. Ratio of fixed costs to product output is negatively affected if plant equipments are not available for production when required.
Frequent  repair of break down equipment is critical to business success.The process of  addressing equipment breakdowns after its occurrence is known as Reactive type Corrective Maintenance.This Reactive approach exists in some form almost in all manufacturing companies. However, when equipment breakdowns occur the cost of repair can go much  beyond the cost of period of repair. The reason is obvious : production process lines require significant run-time after startup to begin producing quality product, and the manufactured products in process at breakdown as well as the products manufactured for a period after breakdown may either be unusable or of less value (off-specs or poor quality). Because of the impact both during and beyond the immediate downtime, modern maintenance business process have sought a methodology  to prevent equipment breakdown by a process known as Preventive Maintenance . With preventative maintenance, equipment is routinely inspected and serviced in an effort to prevent breakdowns from occurring. Such inspections frequency are based on either calendar periods or equipment run time. Corrective Maintenance and Preventive Maintenance  approaches are being adopted  for decades, but each have some important merits/demerits.We all  appreciate that Break down Maintenance or Run to failure maintenance approach shall not be acceptable now days where HSEF (Health,Safety,Environment and Fire) is an issue. Therefore there is need to go for Proactive approach which is feasible by Condition Monitoring (CM)  of equipment for enabling condition based maintenance to get maximum ROI.
Condition based Maintenance (CBM) means to maintain and correct the equipment at the right time.
 Observing the state of the system is known as condition monitoring which will determine the equipment's health, and act only when corrective maintenance is actually needed.
Advancement in recent years have allowed extensive instrumentation of equipment, and together with better tools for analyzing condition data, the maintenance personnel of modern age are more comfortable than in past decades to decide what is the right time to perform maintenance on some piece of equipment. Ideally condition-based maintenance will allow the maintenance personnel to do only the right things, minimizing
spare parts cost, system downtime and time spent on maintenance (MTTR).

The current scenario is that a higher percentage of organizations are practicing reactive maintenance than scheduled maintenance.This unplanned/unscheduled reactive maintenance should not exceed 20 % of total maintenance activities.Condition based maintenance should preferably be up to 60% and scheduled maintenance to 20% as maintenance options.
The objective of maintenance function is to optimize maintenance cost and improve reliability.
A maintenance function is considered to be more effective when it:
•  increases the Mean Time Between Failures (MTBF) of the equipment
•  reduces the consequence of failure
•  reduces the risk of multiple failures

Why design of Condition Monitoring (CM) Schedule of an equipment is Important in Process Industries?

Condition Based Maintenance Strategy technically is of great challenge in modern age. Even if the state of some types of equipment can easily be observed by measuring simple values as vibration, temperature or pressure, it is not an easy task  to turn this measured data into actionable knowledge about health of the equipment.
Although many failure modes are not age-related, most of them give some sort of indication or warning that they are in the process of occurring or are about to occur. If evidence can be found that something is in the final stage of failure, it may be possible to take action to prevent it from failing completely and/or to
avoid the consequences of failure.The modern condition monitoring tools are capable to determine the time when Potential Failure starts in a component and if not corrected in time and allowed to be deteriorated up to the point of Functional Failure, then it becomes expensive break down Maintenance. Therefore
Condition based maintenance entails monitoring for potential failures, so that actions can be taken to prevent the functional failure or to avoid the consequences of the functional failure.This is called Proactive Approach of Good Maintenance System.
The P-F (Potential Failure-Functional Failure) interval is the interval between occurrence of a potential failure and its deterioration into a functional failure. It is also known as the warning period, the lead time to failure (LTF) or the failure development period. If we want to detect the potential failure before it becomes a
functional failure.The time interval between monitoring checks must be less than the P-F interval. For different failure modes, it could vary from fractions of a second to several years. So there could be different frequency of CM schedule for same type of equipment depending upon failure modes and damage mechanism in the system.

Integrity Strategy Frame work-From reactive to Proactive

1.Integrity Assurance is delivered through an Integrity Management Framework

(Key elements cover all equipment types, standards and practices, inspection, maintenance and remedial works addressing business risks)

• Purpose of systems & Goals
• Asset register / Description.
• Business Risks
• Main Processes/ activities.
• Roles & responsibilities.
• Interfaces – Inputs/Outputs
• Performance measurement.
• Anomaly flagging / Tracking.
• Continuous Improvement Process

2.Integrity Strategy focuses on moving from reactive to proactive via calculative approach

• Risk identification and mitigation is addressed
• Develop strategy to Identify all the critical weak links
• Focus on Risks: Remove dead legs, replace/repair Piping
• Improve inspection and corrosion inhibition
• Implement reliability studies and failure analysis

3.Integrity Division Organization is updated to deliver the integrity assurance requirements

• Operational, Technical assessment and Projects support identified

Practical and reliable approach in carrying out maintenance activities

Applicable for Process/Hydrocarbon Industries :
In order to ensure reliability in any Maintenance activities in the context of  process industries, the SOP are:
1.Prepare SMP (Standard Maintenance Procedures) for each maintenance activities.This should be prepared by  an engineer having minimum 4-5 years of maintenance experience in the field for which he is going to write SMP.The content of SMP shall be:
- Description of Potential risk in executing the actvities and their mitigation plan.
-Mention of necessary tools and tackles to be used
-Mention a caution for Receiving the PTW along with LOTO/RA sheet prior to commence the maintenance job.
-Description of sequential procedure in form of check list in which the activities shall be carried out.This also mention the data/clearances /tolerances/Fits to be maintained wherever necessary.
2.The technician who is executing the activities must also record  the observation data prior to correction/repair in annexure sheet of SMP document
3.The technician should write the corrected dimensions/clearances/alignment in the annexure sheet of SMP document.
4. After closing the job and handing over the work permit,technician should incorporate all maintenance history data in CMMS (SAP-PM module) for future reference.

Can Reliability be considered as subset of Maintenance System ?

 Maintenance is execution of all PM,PdM and corrective repair activities based on CM (condition monitoring) results as per SMP. An effective and efficient maintenance team will result in decreased MTTR which will enhance the Availability of equipment.
Reliability function is basically a function of thinker group who is responsible for developing procedures and checklist, analysing root cause failure analysis (RCFA) ,Optimizing Preventive and Predictive maintenance programme in order to optimize maintenance cost based on improved MTBF.
In my understanding Maintenance and Reliability both are complementary to each other.
As Reliability, Availability and Maintainability are components of Maintenance Effectiveness equation and Reliability is subset of Availability,we may consider Reliability is subset of Effective Maintenance System.

Availability of equipment or system refers to MTTR and defined as ratio of UP-Time /(UP-time + Down Time) assuming yearly calender hours as total of up-time and down-time.
On the other hand Reliability refers to MTBF and defined as probability that an equipment or system shall perform its intended service under given duty point or operating conditions,given environmental conditions under given time period ( In this case budgeted production hours are normally taken as given time period)

The above explanation shall be more accurate if both the business objective terms MTBF and MTTR are accurately quantified to the extent possible.

Reliability,Availability and Maintainability (RAM)

Maintenance is execution of all PM,PdM and corrective repair activities based on CM (Condition monitoring ) results as per SMP.An effective and efficient maintenance team will result in decreased MTTR which will enhance the Availability of equipment.
Reliability function is basically a function of thinker group who is responsible for developing procedures and checklist, analysing root cause failure analysis (RCFA) ,Optimizing Preventive and Predictive maintenance programme in order to optimize maintenance cost based on improved MTBF.
In my understanding Maintenance and Reliability both are complementary to each other.
As Reliability, Availability and Maintainability are components of Overall Maintenance Effectiveness equation and Reliability is subset of Availability,we may consider Reliability is subset of Effective Maintenance System.
Availability of equipment or system deals with MTTR and can be defined as ratio of  UP-Time /(UP-time + Down Time) assuming yearly calender hours as total of up-time and down-time.
On the other hand Reliability deals with MTBF and can be defined as probability that an equipment or system shall perform its intended service under given duty point or operating conditions, given environmental conditions and under given time frame ( In this case budgeted production hours are normally  taken as given time period).
Maintainability deals with ease and rapidity at which the repair /maintenance activities are carried out as per SMP.This will have impact on MTTR. Higher MTTR will reduce the availability and low MTTR will enhance the availability.

Overall Effectiveness = Reliability X Availability X Maintainability
Its value varies between 0 to 1 in a 0---1 point scale.

Tips to Maintenance Engineers to become successful in Career

I am sure the 7 points habits of Maintenance Engineers shall be the key for their success in their career.


1. Know the Standard Maintenance Procedures of each maintenance activities.

2. Focus Only on the Most Important Things

3. Document the Baselines (example: Existing MTBF/MTTR/MTBM, past failure history etc)

4. Use Tools to be More Effective (Use Check lists as a tool)

5. Discuss and Communicate Results ( post maintenance equipment performance) to all concerned
   preferably in business terms (e.g Improved MTBF, Decreased MTTR, Increased Up-Time ,% age 
   increase in reliability/availability)

6. Keep Learning (Never Stop learning).

7. Share Your Knowledge with others (Sharing your knowledge with others can help to make you and them more effective.For your own success, if people understand what you do, they will have a better
appreciation of the value you bring to the company. It’s hard to downsize someone that
brings a lot of value..

Frequent loosening of nuts caused by system vibration - becomes a Reliability issue

  

Checks points to prevent loosening of nuts/ bolts:

1. Ensure nuts don't have appreciable lateral play on bolts. This could be judged by visual inspection.

2. Nuts should sit on perfect flat surface .Avoid point or line contact between nuts and seating surface.

3. In case seating surface is not machined face, use of spring washers beneath the nuts can help.

4. In case spring washers cannot accommodate on seating surface because of increased size of bolt hole dia, place suitably machined flat washers on seating surface and then place spring washers on top of it beneath the nuts..  

Asset Management as an Enterprise Strategy For Profitability-A Methodical Approach

A methodical systematic approach for  measuring a company’s current reliability performance and establishing  “Asset Management Opportunity” in terms of dollars is very much necessary for  long term sustenance of an Enterprise or an Organization.

In the context of fast growing global competitions, major manufacturing companies in many industries
(including process industries) have started to realize the importance of  Enterprise Asset Management (EAM) as an enterprise strategy, if  correctly implemented, will definetely improve financial performance. Typical results of an effective EAM Strategy include a 20% - 50% reduction in repair and maintenance expenses accompanied by a 5% - 10% increase in real production volume, with no significant investment in production equipment.
Profitability is the return on an investment. Measurements of return include cash flow and net income while measurements of investment include operating assets, total assets and equity. Typical measures that affect Senior Management  premium are Return on Net Assets (RONA), Economic Value Add (EVA), and Earnings Per Share (EPS), etc. Each of these can be directly correlated to Asset Utilization, the effective measure of a Strategic Asset Management Program.

CATEGORIES OF OPPORTUNITY FOR POTENTIAL RETURN ON INVESTMENT
There are mainly four categories that offer significant potential return from an Asset Management Program:
1. Fixed Cost Expense Reduction
2. Increased Product Throughput
3. Capital Spending Avoidance
4. Reduction of Inventory Investment

The easiest of these to achieve is the reduction of fixed costs in terms of maintenance expense, a waste elimination mechanism. It is critical to identify the inefficient business processes and infrastructures that create the waste and to replace them with well designed processes and structures. This mechanism is employed by reducing the amount of unplanned equipment outage or down time and becoming more effective in managing the resource allocation function.
Increasing product throughput by developing a more reliable operation, while more challenging, has a double impact on financial performance. It significantly reduces the unit cost of the product while reducing the level of maintenance repair required on the equipment. This is a particularly effective mechanism in industries where fixed costs represent a significant per cent of the total cost of making product as all additional units produced are made at a total cost equal to the variable cost of production, yielding the highest profit.
In an industry where product demand is high and Capital Investment is needed to increase plant capacity, a strong Asset Management Program can often achieve the required additional throughput, avoiding the requirement for capital spending. This mechanism often provides the greatest thrill in terms of financial improvement as it prevents the cost of borrowed money for investment in facilities as well as the increase of asset values on the company’s books. (Remember that profitability is a measure of return on assets employed.)
Raw material, finished product, and spares parts  inventories are held to account for unreliability in the manufacturing process. In a Lean Manufacturing environment where inventories of raw materials and finished product are minimized, it is critical that the company establish and maintain an effective Asset Management Strategy. As the manufacturing process and associated assets become more reliable, inventories of both of these as well as spares parts supplies can be significantly reduced with little risk.
FIXED COST EXPENSE REDUCTION
According to A.T. Kearney, Maintenance Cost to Equipment Replacement Value Ratio (ERV) in the early 80’s were used as determining  a benchmarking during survey for DuPont. It is calculated as:

ERV ratio = Maintenance Cost/Equipment (Asset) Replacement Value

-expressed as a per cent. Industry experience has shown that maintenance expenses can be considered to be genuinely justified if it is lower than  1.5% - 2.5% of ERV depending on the industry type and complexity of manufacturing process.

INCREASED PRODUCT THROUGHPUT
It is generally believed that shareholder return is a result of three factors:
• Asset Growth: Compounded Asset Growth Rate
• Cash Flow Margin: Ratio of Cash Flow to Sales
• Asset Productivity: Ratio of Sales to Asset
The most effective way to increase Fixed Asset Productivity is to maximize asset utilization by increasing the Reliability of the Assets through an effective Asset Management Program.
To calculate  current level of Fixed Asset Productivity (FAP) or Asset Utilization (AU) one can use the following formula:
FAP = Sales Volume x Selling Price/Net Fixed Assets
 Sales Volume= Max Daily Rate x Asset Utilization x 365 days

Where utilization is calculated as:
AU = Actual Annual Production / Max Daily Rate X 365 days
Max Daily Rate = Demonstrated Capacity

A company can look for opportunity for improvement up to the difference between current AU and AU = 100%.

CAPITAL SPENDING AVOIDANCE
When demand for a product of a manufacturing unit is strong, there is often a significant motivation to raise Capex for expanding capacity of the facility.Thus a proposal is put up before Top Management for seeking approval for enhancing capacity with justified capital investment.It has been experienced that if  current AU is less than 70%, the generally accepted strong probability is that one can achieve the desired enhanced capacity by implementing an Asset Management Program that raises AU to the 90% range.

REDUCTION OF INVENTORY INVESTMENT
Various manufacturing industries hold raw material and finished product inventories as insurance against manufacturing delays and unexpected demand. They maintain large spares parts Inventories (parts and maintenance supplies) for similar reasons. These inventories can amount to a significant portion of the Asset Value carried on Corporate Balance sheets, negatively impacting profitability. The objective of Lean Manufacturing concepts is the reduction or total elimination of these inventories. Poor reliability resulting from ineffective Asset Management will destroy any Lean Manufacturing benefits.
The Opportunity in this case is the total value of Raw Material and Finished Product Inventory that is maintained to account for unplanned manufacturing outage as well as a significant piece of the spares parts Inventory.
CHANGING THE PROCESS
Once opportunity is defined, one must be able to address the question of how one can achieve all or part of this opportunity. This means changing the existing business processes. The first step is to evaluate the current state; the second is to identify the process changes that will yield the expected financial benefits. Remember, without change in processes, one cannot achieve the future state that will deliver the benefits. 

Steps for effective lubrication for improved reliability

 Oil monitoring system is a positive step to achieve proper

 Lubrication. There are two methods:

1 .Performing routine periodical oil analysis and trending the results to determine quality of oil.

2. Using condition monitoring devices. There are many available devices in the market that provide moisture/water levels, viscosity levels, vibration analysis, etc.

 Using one or both of above methods to determine when oil

Changes are required should be based more on need basis rather than routine to achieve long term benefit from  cost and reliability point of view...

Steps for effective lubrication for improved longevity:

•  Evaluate current lubrication methods and procedure
•  Set target cleanliness levels
•  Identify sources of contaminations & degradation mechanism
•  Take specific actions to achieve targets
•  Analyze lubricant health frequently
•  Distribute the results - increase visibility

What Makes Bearing Housing Pressures Rise?- A Reliability Issue

Most bearing-housing breather vents, and especially small vents, offer a restriction that might allow a small amount of pressure build-up in bearing housings. It is also reasonable to expect that some oil will get flung into the close clearance region, typically fitted with lip seals or labyrinth seals, where the shaft penetrates the bearing housing. The oil has film strength, which makes it cling to surfaces. This oil now tends to bridge the gap between the rotating shaft and the surrounding stationary components.

In that event, the trapped air above the oil level will constitute a closed volume. As this volume of air is warmed by sun exposure or by frictional heat generated in the bearings, its pressure will increase in accordance with the perfect gas law:

(P2) = (P1)(T2/T1)

Using Rankine (absolute) temperatures and absolute pressures, it is easy to see how relatively minor temperature increases may cause pressures to rise by amounts that cannot be ignored. As pressures go up beyond the rupture strength of oil films, the sealing oil film will be temporarily interrupted. The bearing housing seal will open up for a fraction of a second.However, rising bearing housing pressure may lead to one of two undesirable events:

• During a pressure rise, the oil level will go down in the bearing housing and will rise in the lower surge chamber supporting the lubricator bottle (Bernoulli’s law).If the housing level drops sufficiently, the bottom of the bearing may be deprived of oil, or slinger ring immersion may no longer be sufficient for satisfactory lubrication.

• If oil overflows the surge chamber during a pressure rise, it is lost from the system, while the pressure in the lubricator adjusts to the new housing pressure. Oil from the bottle refills the housing when the system re- equilibrates with each“burp.” As the cycle repeats itself, more and more oil will be lost. These problems are caused by system features that allow for pressure differentials between the housing interior and the environment. There is evidence that installing bearing isolators and other narrow-gap housing closures increases the likelihood of potential problems with lubricators that had served perfectly well as long as not-so-close fitting labyrinth seals were being used. Fortunately, the pressure-balanced constant-level lubricator does not introduce the same risk. As mentioned earlier, the oil levels “x” at locations inside the bearing housing and inside the lubricator are always exposed to identical pressures. The problem is solved, and another step towards increased equipment reliability has been implemented. Only Pressure equilibrated level and not OTA-type lubricators should be used in reliability-minded plants. By providing a piping connection between the lubricator and bearing housing, lubricator port “x” and the bearing housing operate at the same pressure and the risk of oil leakage or unintended lowering of oil levels due to pressure buildup in bearing housings is eliminated. This approach provides protection from airborne contaminants, as well. Disadvantages? The pressure-balanced constant-level lubricator probably costs more, but the resulting reduction in the risk of failure far outweighs any disadvantages, both perceived and real.

Do we know how a constant level oiler works?

The Basic Principle (Based on Bernoulli’s law)

When rotary equipment is under rest, the constant level oiler very much resembles a simple, mercury barometer. As long as the neck of the filler bottle (reservoir) is immersed in the pool of lubricating oil, preventing air intrusion, the column of liquid in the bottle is supported by the atmosphere. The pressure in the air/vapor space at the top of the bottle, plus the head of fluid, exactly balances ambient air pressure (p).

If depletion of lubricant causes the level (x) to drop below the bottleneck, it allows air to enter. As air bubbles up into the bottle, it displaces lubricant, which pours down into the pool below.

 When the pool surface rises sufficiently to again seal the bottle from air, lubricant flow stops. The vapor space and new, lower, liquid height have re-equilibrated with ambient pressure. Figures are self-explanatory.

Equipment Performance is "Predictable" and Risk is "Manageable"

Ask any maintenance engineer  working in a reactive maintenance environment if they believe equipment performance is predictable and risk manageable and they will almost always answer, ?No, those statements are not true!? Even those who do agree will usually add the disclaimer that they simply don't have the time to do anything about either of them.
For those who claim they don't have the time to implement a reliability program, I ask them this question, ?Why is it you can always find time to fix the equipment, but never the time to engineer out the problems and prevent them from recurring ?? For as many times as I've asked this question, I've yet to hear a good answer.
The reality is equipment performance is predictable, risk is manageable and maintenance organizations can and should set forth the necessary time and effort to do something about it. It is the only way a maintenance organization will ever break out of its reactive maintenance environment.

No Pain, No Gain

Make no mistake about it, implementing a Reliability-Centered Risk Management program will require time, additional effort, cultural changes and an increase in short-term maintenance costs. It makes me cringe when I hear so-called experts tell maintenance organizations otherwise because it paints an unrealistic picture and companies become completely disillusioned when they find out it is not the case.
The old adage of ?no pain, no gain? is very much applicable to implementing a Reliability-Centered Risk Management program, as is the case with any major program implementation. However, the pain is short-lived and the gain is well worth the upfront investment of time, money and effort. Let me explain?
An Implementation Will Take Time ? Depending on the starting point a maintenance organization must elevate itself from, it can take upwards of two years to establish a credible Reliability-Centered Risk Management program. That's not to say benefits won't be realized during the start-up period, because they will. Results generally materialize in as little as 3-6 months. Of course, this is somewhat dependent on the amount of time and effort a maintenance organization is willing to invest in the implementation? the more focused and concentrated the effort, the quicker the results.
An Implementation Will Require Additional Effort ? There's no doubt that implementing a Reliability-Centered Risk Management program will require additional upfront effort. After all, a maintenance organization can't forego its responsibilities to maintain plant equipment during the implementation. Maintenance organizations often must choose how they will assimilate the additional work during the start-up phase of the program. Some choose to mandate overtime, some reorganize trying to free up key maintenance personnel, while others bring in temporary contractors to assume some of the workload.
An Implementation Will Require Cultural Changes ? There will be shifts in responsibilities, either within the maintenance organization itself or between maintenance and operations during the implementation of a Reliability-Centered Risk Management program. These cultural changes will need to be well managed to overcome the fear of change, keeping a clear vision of the end result in mind. Handled correctly, the cultural changes will be accepted and embraced. Handled incorrectly, and it can become a political hot potato.
An Implementation Will Increase Short-Term Costs ? There are always upfront costs when implementing any program with proven long-term rewards and benefits. That's also true of implementing a Reliability-Centered Risk Management program. Typical upfront costs include purchasing new Predictive Maintenance equipment, training, higher labor costs because of increased overtime and/or supplemental contract labor and the costs of refurbishing older equipment to return them to a like-new condition again.
Maintenance costs may well increase during the first 12-18 months of the program as it ramps up and begins to gain momentum. After that, costs will quickly fall, dipping well below what they were before the onset of the implementation.
It has been my experience that the return on investment (ROI) from any upfront investment in a Reliability-Centered Risk Management program will be realized within 2-3 years. Of course, this is dependent on the level of commitment a maintenance organization demonstrates toward achieving a successful implementation

Today's Maintenance Organizations Can't Afford to Turn Blind Eye on "Asset Reliability"

In present economic scenario of competitive market, maintenance organizations of any manufacturing organization can't afford not to implement a Reliability-Centered Risk Management program. Maintenance is one of the last frontiers in a company's battle to improve bottom line profitability and gain a competitive advantage in their respective market segments.
Increasing reliability and reducing risk lowers the total cost of asset  maintenance, lowers production costs and increases plant capacity and increases contribution margin  exactly what today's companies need.

Is Reliability Without Risk?

Everyone considers Reliability-Centered Maintenance must do to effectively manage  asset repair costs and increase overall plant efficiency. Reliability-Centered Maintenance has long been recognized as the most proactive maintenance method because it incorporates all of the best practices of traditional maintenance into a single, harmonious and complimentary program.

In spite of this, maintenance organizations often don't include Risk Management as part of their overall reliability program even though it's considered a sub component of Reliability-Centered Maintenance. Usually this is because organizations either don't understand its concepts or fully appreciate what Risk Management can do for them.
Risk Management compliments Reliability-Centered Maintenance by helping classify the criticality of equipment for example - PSM Critical equipment in the context of process industry; the most likely modes of failure; the effects these failures might have on equipment, the environment, and personnel; and what critical spares will be required in the event of a failure. It would be nearly impossible to develop a sound maintenance strategy without taking risk into consideration. Therefore managing risk is an essential component of a reliability program.
Reliability-Centered Risk Management strives to restore the balance between managing reliability and risk.
Reliability-Centered Risk Management program helps organizations achieve all of the benefits and potential of a well-rounded, comprehensive proactive maintenance program, including:
•  Increased equipment availability
•  Increased production capacity
•  Reduced spare parts inventory
•  Reduced work in process inventory
•  Extended equipment life
•  Reduced risk of failure
•  Lowest total cost of equipment 
•  Increased morale
•  Equal focus on production, the environment, and worker health and safety
•  And more?

Six stages of crevice corrosion

1.Formation of crevice by crevice former which can be either man made by design or by nature -oversight.
Some examples of man made ( desigh basis) crevice formers are : stationary "O" ring in "O" ring groove,Gasket surfaces,Tube to tube sheet joint of heat exchangers etc.
Some examples of man made by oversight are: poor root pass of pipe weld joint ,roughened surfaces,natural sediments and deposits.
2.Oxygen depletion. It has been recognized that oxygen is depleted in well shielded crevices creating an oxygen concentration cell between crevice and area out side the crevice.
3.Hydrolysis of metal ions and decrease in pH. The few metal ions entering the moist environment of crevice hydrolyze depleting the hydroxyl ions.The pH decreases.
4.Migration of chloride ions in to the crevice from outside of crevice region to balance the charge resulting from depletion of hydroxyl ions.
5.Initiation of crevice corrosion if pH decreases sufficiently and chloride ion concentration increases sufficiently to a critical values (Threshhold value) at which film break down  and corrosion initiation will occur
6.Propagation.

Asset Integrity is a journey not a destination

Points to remember :
•At this stage of aging refinery/petrochemical /oil industry’s facilities Integrity implementation is not an option, it is our safe guard from catastrophic failures
•Integrity is not about new standards , it is how to apply the existing standards effectively
•Integrity is a change case to any organization, leaders mind set, the way we manage our business and the competencies of our workforces
•Integrity is a journey not a destination, it need committed leaders to keep sailing it steadily. The question is Can we do it? The answer should be "Yes"


Six steps approach to assure MI (Mechanical Integrity) in a process or oil/gas industries:

1.Establish the EAM system in place after several round of brain storming sessions /reviews with experienced and working level executives at corporate and site level.
2.Imparting Training and provision of necessary tools.
3.Pilot Implementation.
4.Integrity assurance
5.Full Implementation across all units of Enterprise
6.Improvement

Equipment failure because of High Temperature Corrosion

High Temperature Corrosion : High temperature corrosions are named as follows:
- sulfidic corrosion
- sulfidic corrosion without hydrogen present
- sulfudic corrosion with hydrogen present
- naphthenic acids
- fuel ash
- oxidation
1. Sulfidic corrosion:
Corrosion by various sulfur compounds at temperatures between 260 and 540°C is a common
problem in many petroleum-refining processes and  in petrochemical processes. Corrosion is in the form of uniform thining, localized attack, or errosion corrosion. Nickel and nickel rich alloys are rapidly attacked by sulfur compounds at elevated temperatures, while chromium containing steels provide excellent corrosion resistance (as does aluminum). The combinations of hydrogen sulfide and hydrogen can be particularly corrosive, and as a rule, austenitic stainless steels are required for effective corrosion control.
2. Sulfidic corrosion without hydrogen present:
This type of corrosion occurs in various components of crude distillation units, catalytic cracking
units, hydrotreating and hydrocracking units upstream of hydrogen injection line.
Preheat-exchanger tubes, furnace tubes, and transfer lines are generally made from carbon steel,
as is corresponding equipment in the vacuum distillation section. The lower shall of distillation
towers, where temperatures are above 230°C is usually lined with stainless steel containing 12% Cr
such as Type 405.
 Metal skin temperature, rather than flow stream temperatures, shall be used to predict corrosion rates when significant differences between the two arise. For example metal temperatures of
furnace tubes are typically 85 to 110°C higher than the temperature of the hydrocarbon stream
passing through the tubes. Furnace tubes normally corrode at a higher rate on the hot side (fire
side) than on the cool side (wall side).
3. Sulfidic corrosion with hydrogen present:
The presence of hydrogen in, for example, hydrotreating and hydrocracking operations, increases
the severity of hightemperature sulfidic corrosion. Hydrogen converts organic sulfur compounds in
feed stocks to hydrogen sulfide; corrosion becomes a function of H2S concentration.
Down stream of hydrogen injection line, low-alloy steel piping usually requires aluminizing in order
to minimize sulfidic corrosion. Alternatively Type 321 (S32100) stainless steel can be used. Tubes
in the preheat furnace are aluminized low-alloy steel, aluminized 12% Cr stainless steel.
Reactors are usually made of 2.25 Cr-1 Mo steel, either with a Type 347 (S34700) stainless steel
weld overlay or an internal factory lining. Reactor internals are often Type 321 stainless steel.
4. Naphthenic acids:
These organic acids are present in many crude oils. The general formula may be written as R(CH2)n
COOH, where R is usually cyclopentane ring.. This acid is corrosive only at temperature above 230°C in the range of 1 to 6 neutralization number encountered with crude oil and various side-cuts. At any given temperature, corrosion rate is proportional to neutralization number. Corrosion rate triples with each 55°C increase in temperature. In contrast to high-temperature sulfidic corrosion, no protective scale is formed, and low-alloy and stainless steels containing up to 12% Cr provide no benefits
whatsoever over carbon steel. The presence of naphthenic acids may accelerate high-temperature
sulfidic corrosion that occurs at furnace headers, elbows, and tees of crude distillation units because
of unfavorable flow conditions.
Severe naphthenic acid corrosion (in the form of pitting) has been experienced in the vacuum
towers of crude distillation units in the temperature zone of 290 to 345°C and sometimes as low as
230°C. Attack is often limited to the inside and very top of the outside surfaces of bubble caps.
Alloy 20 (N08020) and titanium Grade 2 (R50400) are also resistant to naphthenic
acid corrosion. In contrast, aluminized carbon steel tray components, such as bubble caps, have
performed poorly.

5. Fuel ash:
Corrosion by fuel ash deposits can be one of the most serious operating problems with boiler and
preheat furnaces. All fuels except natural gas contain certain inorganic contaminants that leave the
furnace with products of combustion.These will deposit on heat-receiving surfaces, such as
superheater tubes, and after melting can cause severe liquid-phase corrosion. Contaminant of this
type include various combinations of vanadium, sulfur, and sodium compounds. Fuel ash corrosion
is most likely to occur when residual fuel oil (Bunker C fuel) is burned.
In particular, vanadium pentoxide vapor (V2O5) reacts with sodium sulfate (Na2SO4) to form sodium
vanadate (Na2O-6 V2O5). The latter compound reacts with steel, forming a molten slag that runs off
and exposes fresh metal to attack.
Corrosion increases sharply with increasing temperature and vanadium content of fuel. If the
vanadium content in the fuel oil exceeds 150 ppm, the maximum tube wall temperature should be
limited to 650°C. Between 20 and 150 ppm V, maximum tube wall temperatures can be between
650 and 845°C depending on sulfur content and the sodium-vanadium ratio of the fuel oil. With 5 to
20 ppm V, the maximum tube wall temperature can exceed 845°C.
In general, most alloys are likely suffer from fuel ash corrosion. However, alloys with high chromium
and nickel contents provide the best resistance to this type of attack. Sodium vanadate corrosion
can be reduced by firing boilers with low excess air (<1%). This minimizes formation of sulfur
trioxide in the firebox and produces high-melting slages containing vanadium tetroxide and trioxide
rather than pentoxide. In the temperature range of 400 to 480°C boiler tubes are corroded by alkali
pyrosulfates such as sodium pyrosulfate and potassium pyrosulfate, when appreciable
concentrations of sulfur trioxide are present.
6. Oxidation:
Carbon steels, low-alloy steels and stainless steels react at elevated temperatures with oxygen in
the surrounding air and become scaled. Nickel alloys can also become oxidized, especially if
spalling of scale occur. The oxydation of copper alloys usually is not a problem, because these are
rarely used where operating temperatures exceed 260°C. Alloying with both chromium and nickel
increases scaling resistance. Stainless steels or nickel alloys except alloy 400 (N04400), are
required to provide satisfactory oxidation resistance at temperatures above 705°C.
Thermal cycling, applied stresses, moisture and sulfur-bearing gases will decrease scaling
resistance.
High temperature oxidation is limited to the outside surfaces of furnace tubes, tube hangers and
other parts that are exposed to combustion gases containing excess air.
At elevated temperatures, steam decomposes at metal surfaces to hydrogen and oxygen and may
cause steam oxidation which is more severe than air oxidation at the same temperature. Fluctuating
steam temperatures tend to increase the rate of oxidation by causing scale to spall and thus expose
fresh metal to further attack.

Low Temperature Corrosion in petroleum refinery and petrochemical plants.

 Most corrosion problems are not caused by hydrocarbons but by various inorganic compounds such
 as water, hydrogen sulfide (H2S), hydrochloric acid (HCl), hydrofluoric acid , sulfuric acid (H2SO4 )
 and caustic. There are two main sources of these compounds:
- feed-stock contaminants and
- process chemicals.

1. Low temperature corrosion by feed-stock contaminants
The cause of the refinery corrosion is the presence of contaminants in crude oil as it is produced.
Corrosive hydrogen chloride evolves in crude preheat furnaces from relatively harmless magnesium
and calcium chloride entrained in crude oil. In petrochemical plants, certain corrosives may have
been introduced from upstream refinery and other process operations, other corrosives can form
from corrosion products after exposure to air during shut-down: polythionic acids fall into this
category. Corrosive contaminants are as follows:
- air
- water
- hydrogen sulfide
- hydrogen chloride
- nitrogen compounds
- sour water
- polythionic acids
Air:
Air may enter to many potential inlets equipments of  during prolong shutdown of plant. In general, the air contamination of hydrocarbon streams has been more detrimental with regard to fouling than corrosion. However, air contaminant has been sited as a cause of accelerated corrosion in vacuum towers and vacuum transfer lines, also accelerate overhead corrosion of crude distillation towers.
Water:
Water content of crude oils and water originated with stripping steam for fractionation towers
hydrolyses certain inorganic chlorides to hydrogen chloride, and is responsible for various forms of
corrosion in fractionation tower overhead systems. It is a good practice to keep equipment dry in
order to minimize corrosion.
Combination of moisture and air enters into storage tanks during normal breathing as a result of
pumping and changes in temperature. Corrosion of tank bottoms occurs mostly with crude oil tanks
which is caused by water and salt entrained in the crude oil. A layer of water usually settles out and
can become highly corrosive.

Hydrogen sulfide is the main constituent of refinery sour waters and can cause severe corrosion
problems in overhead of certain fractionation towers, in hydrocracker and hydrotreater effluent
streams in vapor recovery of Fluid Catalytic Cracking (F.C.C) Units, in sour water stripping units and
in sulfur recovery units. Carbon steel has fairly good resistance to aqueous sulfide corrosion
because a protective film of FeS is formed to avoid hydrogen stress cracking (sulfide cracking),
hard welds (above 200 HB) must be avoided, if necessary, through suitable postweld heat
treatment. Excessive localized corrosion in vessels can be resolved by selective lining with alloy
400 , but this alloy can be less resistant than carbon steel to aqueous sulfide corrosion at
temperatures above 150°C. If significant amounts of chlorides are not present, lining vessels with
 Type 304 (S30400) stainless steel can be considered.
In refineries, corrosion by hydrogen chloride is primarily a problem in crude distillation units, and to
lesser degree in reforming and hydrotreating units. In petrochemical plants, HCl contamination can
be present in certain feed stocks

Ammonia is also produced in ammonia plants to become a raw material for the manufacture of urea
and other nitrogenbase fertilizers. Ammonia in synthesis gas at temperatures between 450 and
500°C causes nitriding of steel components. When synthesis gas is compressed to up to 34.5 MPa
(5000 psig) prior to conversion, corrosive ammonium carbonate is formed, requiring various
stainless steels for critical components. Condensed ammonia is also corrosive and can cause SCC
of stressed carbon steel and low-alloy steel components.
Polythionic acids:
Combustion of H2S in refinery flares can produce polythionic acids of type H2SxOy (including
sulfurous acid) and cause severe intergranular corrosion of flare tips made of stainless steels and
high-nickel alloys. Corrosion can be minimized by using nickel alloys such as alloy 825  or
alloy 625
2. Low temperature corrosion by process chemicals:
Severe corrosion problems can be caused by process chemicals, such as various alkylation
catalysts, certain alkylation by-products, organic acid solvents used in certain petrochemical
process, hydrogen chloride stripped off reformer catalyst, and caustic and other neutralizers that
ironically, are added to control acid corrosion.  Another group of process chemicals
that are corrosive, or become corrosive, is solvents used in treating and gas-scrubbing operations.
These chemicals are as follows:
- acetic acid
- aluminum chloride
- organic chloride
- hydrogen fluoride
- sulfuric acid
- caustic
- amine
- phenol

Acetic acid :
Corrosion by acetic acid can be a problem in petrochemical process units for the manufacture of
certain organic intermediates such as terephthalic acid. Various types of austenitic stainless steels
are used, as well as alloy C-4 , alloy C-276 and titanium, to control corrosion by acetic acid in the presence of small amount of hydrogen bromide or hydrogen chloride.Small amount of water in acetic acid can have a significant influence on corrosion. Type 304 (S30400) stainless steel has sufficient resistance to the lower concentration of acetic acid up to the boiling point. Higher concentration can be handled by type 304 stainless steel if the temperature is below 90°C.Corrosion by acetic acid increases with temperature. Bromide and chloride contamination causes pitting and SCC, while addition of oxidizing agents, including air, can reduce corrosion rates by several orders of magnitude.
Aluminum chloride :
Certain refining and petrochemical processes such as butane, isomerization, ethylbenzene
production and polybutene production, use aluminum chloride as a catalyst. Aluminum chloride is
not corrosive if it is kept absolutely dry otherwise it hydrolyzes to hydrochloric acid. During shutdown
equipment shall be opened for the shortest possible time. Upon closing, the system shall be
dried with hot air followed by inert gas blanketing. Equipment that is exposed to hydrchloric acid
may require extensive lining with nickel alloys, such as alloy 400 (N04400), B-2 (N10665), C-4
(N06455), or C-276 (N10276).
Hydrogen fluoride:
Some alkylation processes use concentrated HF instead of H2SO4 as the catalyst. In general, HF is
less corrosive than HCl because it passivates most metals by the formation of protective fluoride
films. If these films are destroyed by diluted acid, severe corrosion occurs. Therefore as long as
feed stocks are dry, carbon steel-with various corrosion allowances-can be used for vessels, piping,
and valve bodies of hydrofluoric acid alkylation units. All carbon steel welds that contact HF, shall be PWHT (postweld heat treated).
Fractionation towers shall have Type 410 (S41000) stainless steel tray valves and bolting for
desiobutanizer tower tray valve and bolting, alloy 400 (N04400) is recommended. Corrosion
problems in HF alkylation units occur after shutdown because pockets of water have been left in the
equipment. It is very important that equipment be thoroughly dried by draining all low spots and by
circulating hydrocarbon before the introduction of HF catalyst at start-up.
Sulfuric acid :
Certain alkylation units use essentially concentrated sulfuric acid as the catalyst; some of this acid
is entrained in reactor effluent and must be removed by neutralization with caustic and scrubbing
with water. Acid removal may not be complete, however, and trace of acid-at various concentrations
(in terms of water)-remain in the stream.
Dilute sulfuric acid can be highly corrosive to carbon steel, which is the principal material of
construction for sulfuric acid alkylation units. Because the boiling point of sulfuric acid depending on
concentration ranges from 165 to 315°C, depending on concentration entrained acid usually ends
up in the bottom of the first fractionation tower and reboiler following the reactor; this is where the
entrained acid becomes concentrated.
Acid concentration above 85% by weight are not corrosive to carbon steel if temperatures are below
40°C. Cold-worked metal (usually bends) shall be stress relieved. Under ideal operating conditions,
few, if any, corrosion and fouling problems occur.
Carbon steel depends on a film of iron sulfate for corrosion resistance, and if its film is destroyed by
high velocities and flow turbulence, corrosion can be quite severe.
Phenol
Phenol (carbolic acid) is used in refineries to convert heavy, waxy distillates obtained by crude oil
distillation into lubricating oils. As a rule, all components in the treating and raffinate recovery
sections, except tubes in water-cooled heat exchangers, are made from carbon steel. If water is not
present, few significant corrosion problems can be expected to occur in these sections. In the exact
recovery section severe corrosion can occur, especially where high flow turbulence is encountered.
As a result, certain components require selective alloying with Type 316 (S31600) stainless steel.
Typically stainless steel liners are required for the top of the dryer tower, the entire phenol flash
tower, and various condenser shells and separator drums that handle phenolic water.
Tubes and headers in the extract furnace shall also be made of Type 316 (S31600) stainless steel
with U-bends sleeved with alloy C-4 (N06455) on the outlet side to minimize velocity accelerated
corrosion.

Combating crevice corrosion and pitting corrosion in engineering installations

Crevice Corrosion
Intensive localized corrosion frequently occurs within crevices and other shielded areas on
metal surfaces exposed to corrosives. The attack associated with small volumes of stagnant
solution caused by holes, gasket surfaces, lap joints, surface deposits, and crevices under bolt and
rivet heads.
Methods and procedures for combating crevice corrosion are as follows:

- Use welded butt joints instead of  bolted joints in new equipment if system permits for maintainability
- Close crevices in existing lap joints by continuous welding, caulking or soldering.Example:Pipe in SORF
  flange joint should be fillet welded from inside of flange bore and from out side at flange socket end to
  avoid crevice
- Design vessels for complete drainage; avoid sharp corners and stagnant areas.
- Inspect equipment and remove deposits frequently.
- Remove solids in suspension early in the process or plant flow sheet, if possible.
- Remove wet packing materials during long shutdowns.
- Provide uniform environments, if possible, as in the case of back-filling a pipeline trench.
- Use "solid"Spiral wound metallic gaskets with inner ring of MOC compatible with corrosive media or other
  suitable metallic gasket where ever possible so  as to avoid formation of crevice.
- Seal weld instead of pure rolling joint  in tubes, in tube sheets of heat exchangers.
 Pitting Corrosion
Pitting is a form of extremely localized attack. That results in holes in the metal. It is a cavity
or hole with the surface diameter about the same as or less than the depth.
Pitting is one of the most destructive form of corrosion, it causes equipment to fail because of
perforation with only a small percent weight loss of the entire structure. Pitting may be considered
as the intermediate stage between general overall corrosion and complete corrosion resistance.
Oxidizing metal ions with chlorides are aggressive pitters. Cupric, ferric and mercuric
halides are extremely aggressive even our most corrosion resistant alloys can be pitted by CuCl2
and FeCl3.
 Prevention
The methods suggested for combating crevice corrosion generally apply also for pitting. Materials
that show tendencies to pit, shall not be used to build the plant under consideration. For example the addition of 2% molybdenum to 18-8S (Type 304) to produce 18-8S
Mo (Type 316) results a very large increase in resistance to pitting.