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