CUI in Austenitic and Duplex Stainless Steels

CUI damage in austenitic and duplex stainless steels is a form of external chloride stress corrosion cracking (ECSCC). As with all forms of SCC, cracking occurs when a susceptible metallurgy is exposed to the combined action of a corrosive environment and an applied/residual tensile stress. Susceptible materials include Type 300-series austenitic stainless steels. Duplex stainless steels, though more resistant than austenitic stainless steels, are not immune. A corrosive environment occurs when chlorides concentrate under the insulation at the surface of the austenitic stainless or duplex steel when the insulation becomes wet. Residual cold work from fabrication or residual welding stresses provide the tensile stresses necessary promote cracking.
Most CUI damage in austenitic stainless steels occurs at metal temperatures between 140°F and 350°F (60°C and 175°C) although exceptions have been reported at lower temperatures. Below 120°F (50°C), it is difficult to concentrate significant amounts of chlorides; while above 350°F (175°C), water is not normally present and CUI damage is infrequent. It should be noted that even austenitic stainless steel piping that normally operate above 500°F (260°C) can suffer severe ECSCC during start up after insulation gets soaked from deluge system testing or rain during
downtime.
Typically, CUI damage in austenitic and duplex stainless steels goes unnoticed until insulation is removed or a leak occurs.
CUI damage in duplex stainless steels occurs at higher temperatures than observed for austenitic stainless steels.  It is experienced that SCC of duplex stainless steels does not occur until about 285°F (140°C) at very high chloride concentration levels. In general, there have been few reported cases of cracking in the industry. Those that have been reported have been under severe conditions where SCC could be predicted. Some of the failures reported have been on offshore facilities, and were attributed to ECSCC on relatively hot equipment.

CUI in Carbon and Low Alloy Steels

Corrosion under insulation (CUI) is defined as the external corrosion of piping and vessels that occurs when water gets trapped beneath insulation. CUI damage takes the form of localized external corrosion in carbon and low alloy steels. The  factors that affect the amount of CUI damage under insulation include:
a)  Duration of the exposure to moisture,
b)  Frequency of the exposure to moisture,
c)  Corrosivity of the aqueous environment, and
d) Condition of protective barriers (e.g. coating and  jacketing),
e) Equipment design issues,
f) Service exposure temperature,
g) Insulation type,
h) Condition of weather barriers and caulking.
i) Type of climate,
j) Site maintenance practices, and
k) Leaking steam tracing systems.

CUI in carbon and low alloy steels is a form of oxygen corrosion. CUI damage is characterized by either general metal wastage or pitting due to the localized breakdown of passivity. For damage to occur, water  should be either absorbed by the insulation or collected beneath the insulation due to breaks in the  insulation or cladding (jacketing). Water ingress may occur from numerous sources such as rainwater, a deluge system, spillage from process operations, or condensation on the metal surface in humid environments. Contaminants in the insulation such as chlorides and sulfides may contribute to the corrosivity of the environment.
CUI damage occurs on carbon and low alloy steel when exposed to moisture and oxygen. This occurs when moisture is allowed to penetrate the insulation and contact exposed  steel at metal temperatures between 32°F (0°C) and 212°F (100°C). When determining CUI susceptibility, a much broader operating temperature range should be considered, typically from 10°F to 350°F (-12 C to 175 C) due to fluctuations in operating temperature, ineffective insulation maintenance, temperature gradients within the equipment considered (long pipe runs, fractionation columns, heat exchangers, etc.), and various operating modes.
In some instances, these differences arise because users have reported actual metal temperature for CUI incidents, other users have reported actual process temperature in reports of CUI damage, and some have introduced a margin of safety. This has led to an expanding of the range where CUI damage may occur. CUI damage is most severe at metal temperatures between the 170°F and 230°F (77°C and 110°C),
All operating conditions should be considered, including the out-of-service state, for equipment which is offline at ambient temperatures for significant periods of time. Equipment which cycles in and out of the CUI range during regeneration cycles, or is frequently out-of-service at ambient conditions, can experience aggressive CUI damage even though when in normal operation it is outside the CUI temperature range.
 CUI Damage Below 32°F (0°C) and Above 212°F (100°C)
The user will sometimes note that the temperature range quoted for CUI varies from one document to another depending upon field experiences. Normally, liquid water would not be predicted at temperatures below 32°F (0°C) and above 212°F (100°C). In some instances, this is because users  report damage based on the process operating temperature rather than the actual metal surface temperature. Typically, the metal surface temperature of an insulated component will be close to or at the process operating temperature. There are situations where the metal surface temperature will vary somewhat from the process operating temperature.

 In some instances, this is because users report damage based on the process operating temperature rather than the actual metal surface temperature. The key factor for CUI damage to occur is that a corrosive aqueous layer be present on the insulated metal surface during any operating period or during downtime.
One possible situation is where water breaches the insulation on piping with the metal surface temperature between 212°F to 300°F (100°C to 149°C). CUI damage could be occurring as the result of continual flashing of water at the hot metal surface. Even at surface metal temperatures up to 600°F (316°C), CUI could occur during operation if water reaches the metal surface during a shutdown period and flashes off during startup. Another instance where CUI can occur at process temperatures above 212°F (100°C) is where deposits in a deadleg reduce the surface metal temperature sufficiently to allow CUI to take place. CUI damage may also occur at process temperatures below 32°F (0°C) as the result of cyclic exposure conditions above 32°F (0°C), or frequent unit shutdown. It is more important to determine whether water is breaching the insulation system rather than dwelling on what the exact temperature of the insulated metal surface during normal operation. It should be noted that it is very difficult for insulation jacketing/cladding systems to be leak tight. Refer to API RP 571 for further information on CUI inspection practices.

Operating Limits (Operating windows) and IOWs ?

In order to operate any process unit, a set of operating ranges and

limits needs to be established for key process variables, to achieve the

desired results (i.e. product within specification, safe operation, reliability,

etc.).  These limits are generally called operating limits (windows) or

operating envelopes.   

However, IOW’s are a specific subset of these key operating limits that

focus only on maintaining the integrity or reliability of process

equipment. 

Integrity operating windows (IOWs) are those preset limits on process

variables that need to be established and implemented in order to prevent

potential breaches of containment that might occur as a result of not

controlling the process sufficiently to avoid unexpected or unplanned

deterioration or damage to pressure equipment.    

Typically IOW’s address issues that involve process variables that, when not

adequately monitored or controlled, can impact the likelihood and rates of

damage mechanisms, which may result in a loss of containment which is an

incident not acceptable in any process industry.  

Good Practice of inspecting Flange joints prior to Bolting

Flange surfaces shall be finished in accordance with the flange finish description referred to by the Piping Class. Gasket surfaces shall be inspected by the fit up crew, and shall not show evidence of damage, or Contaminants. The bolt or nut seating surface shall be flat and provide a low friction, full contact area for Bolt head or nut. Discrepancies shall be addressed to Field Engineering for evaluation. Note: Cast firewater Valves / flanges are an exception to this rule. In extreme case, the flange may require re-machining.

1. Gasket surface areas shall be cleaned in accordance with the gasket manufacturer’s installation instructions. Typically previous gasket materials and contaminants such as dirt, oil, and grease. Thin, uniform preservative coatings are generally acceptable. Provided they do not fill seating finish or show evidence of build up or runs. When using a wire brush for cleaning, ensure the wire brush is compatible with the flange material i.e. do not use carbon steel bristles on stainless steel flanges. The direction of

brushing shall also follow the seating surface grooves or finish. Take care not to over smooth the finish, and use only Hand brushes. Depending on gasket type, minimum profiles are required for optimum gasket performance. Power brushes shall only be used, if approved by Field Engineering.

2. Flange gasket seating surfaces shall be inspected for scratches, dents, scoring, and other damage. Depending on the gasket type, pipe size, and extent of imperfections, some deviation can be accommodated, without flanged joint degradation. Contact Field Engineering if further interpretation is required.

3. Flange seating surfaces shall also be monitored for flatness, around their circumference

Thermal Gradient at the Flange Bolts

For un-insulated flanged joints, the bolts are assumed to be a different temperature from the flanges, causing differential thermal expansion across the bolted joint. For systems operating above installation temperatures, this differential will tend to tighten the joint. For systems operating below the installation temperature this differential will tend to open the joints.

Additionally if the flange joint will be subjected to high temperatures, the initial calculated bolt load shall be increased by the amount necessary to ensure an adequate working life for the joint, considering loss of bolt load due to the effect of "creep and relaxation" on the bolts. Gasket relaxation should be incorporated as well.

The hydrostatic test condition shall be also considered.

For mechanical equipment stresses are compared against the lowest minimum yield stress determined

for bolting materials found in the ASME VIII, Div-1

Visual Inspection: A Necessary Component of Infrared Inspections

Visual inspections are a very valuable by-product of an infrared (IR)  survey of electrical switchgear. Many electrical panel interiors have not seen the light of day since installation. Since one must remove the panel covers in order to do a proper survey, when they are opened during an IR inspection, two opportunities present themselves: The infrared inspection and the visual inspection.

1. The infrared inspection: The reason for performing this type of survey is to find electrical problems so maintenance personnel can repair them before failure and/or damage to the component and the resulting downtime. Many times, critical problems are obvious and other times they are not so obvious without some due diligence.
2. The visual inspection: Visual inspection can be just as important as infrared. There are many things visually that can’t be detected with infrared as the examples in this article demonstrate.

It may seem that visual inspection goes beyond what thermographers are hired to do, but conscientious thermographers include notes and even images in their reports when they see code violations, broken equipment, incorrectly sized fuses, bad wiring, etc. Whether the inspection is insurance driven or a proactive stance, an infrared inspection and a visual inspection complement each other

Predictive Maintenance Has 3 Main Elements: Detection, Analysis, and Correction

Oftentimes, when there is a prominent 1X vibration level present in the collected data and displayed as a spectral plot, it is easy to attribute the problem to an unbalance condition. In most cases, this will actually be the root-cause problem about 40% of the time. However, before sending out the balancing crew to make a correction, the analyst might go a step beyond the initial detection of the problem, and jump into a bit more analysis work. A prominent 1X component could be due to several faults, including bent shaft, mechanical looseness, resonance, etc. There are some tools available to the analyst to help isolate and pinpoint the root cause of the 1X reading. These include making a few cross-channel phase measurements to note machine components movement and performing some bump tests to note natural frequencies. These extra steps will prove useful and actually save some time and resources in making the right call for correction.

3 Things Every Maintenance Reliability Professional Needs.

From Heinz Bloch workshop at Lube -2011 at the Reliability Performance Institute:

1) A clear role statement

2) A formal long range training plan

3) A journal that includes monthly summary of tasks and accomplishments

Explaining Impact of Reliability to Bottom Line

Education is one of the most important tools to explain how Reliability delivers to bottom line. Many organizations lack understanding and commitment to delivering Reliable Capacity. Start by showing everyone the cost of reactive vs. proactive Maintenance: downtime, maintenance and operational cost for critical assets. Proactive Maintenance cost is 3-5 times less. Then, complete an assessment comparing current practices to known Reliability best practices to develop an improvement plan for the future.

The Impact of Language on RCA Investigations

How many times have you read an incident report and have been left wondering what was being investigated, or what the causal relationships were all about?  You are often required to interpret the information, using your own knowledge to fill in the gaps. If you didn’t have any of the information or knowledge necessary to be able to understand the incident, then you would have had little clarification by reading the report.
This often occurs when vague or nebulous descriptors are used to explain causal relationships.
It would be an indication that the actual causes, causal relationships have not been clearly understood. By using a descriptor such as “poor” to describe say maintenance for example, I would have satisfied the need to find a cause for an effect, which in this instance may have been a “lack of lubrication”.
The use of this word in fact has a twofold effect.  Firstly it leads easily into the categorising of causes for one. We are easily led to “Human error” in this instance, by making subjective assessments of the maintenance which is driven by the “poor” reference to it, and we are then moving quickly down a blame path. The results of this are typically some sort of sanction or warning, some retraining might be perceived to be warranted or a new procedure is written and added to the multitude of other such procedures that already exist. One or all of these actions may occur. When categorical thinking, like “human error” eventuates, we will tend to end up with the same generic types of solutions for each category.
It is categorical thinking, the pigeon holing of causes into common themes, that also allows subjective assessments and judgements to be made and this may happen in the complete absence of any facts. It is based on opinion and in the lack of any clear description is hard to deter or argue against.
A secondary effect of using words like” poor”, “inadequate”, “ineffective” , “insufficient” is that they are often emotive, inflammatory, and can lead to conflict.
When effective, unbiased communication is needed to understand an event, it is the advent of conflict or the perception of blame that are primary reasons why little progress is made in understanding causal relationships.
e.g. if I were to describe the maintenance of a machine as “poor” then the maintainers would arguably take offence to this and will react accordingly.
Now let’s examine the word “poor” itself. If I were to say that the word “POOR” is such a “poor” word, what is it that I would be trying to say? To someone it means one thing, to someone else it means something completely different and yet both are entitled to their understanding because the word itself is inclusive of everything. In fact you could take all of the possible reasons why it is poor, wrap them up into one huge collective bundle and just throw it out there by saying that it is “poor”.
“Poor maintenance” for example……what does this term actually describe? And the answer is everything that could possibly be poor about maintenance. It is imprecise, vague, and allows people to hide behind a cloak of communal misunderstanding. i.e. Almost everyone accepts it (because they do it themselves).
 You will often find reference in a chart to faults or failures. i.e. the machine was laid up because of a mechanical failure. This is another example of an imprecise description of causes. I mean how many different types of mechanical failure are there? If you were to start listing them for any particular machine, the list would be a long one. The term “mechanical failure” in the initial context actually refers to only one of these, not all of them. This represents either a failure to understand the event or a failure to describe it in a way that other people can understand.
Either way it can lead to assumptions and misinterpretations, to subjective assessments of problems, to categorical thinking and more generic solutions.
As a facilitator, whilst accepting the “imprecise” description in the first pass at finding and unearthing causes, I am aware that it is not right. I know I need to get back to it and challenge it. As a means of clarification I will ask something to the effect of …”what is it that makes the maintenance poor?” The answers to this question need to be in the chart. By challenging the imprecise words consistently you will create CLARITY where previously there was none. Do this for all of those “imprecise” words that so frequently are littered throughout a chart and the report that follows.
Then you have causes that are characterised by what I would call “non description”.  Causes which are simply referred to, but understanding relies completely on how you interpret them. Examples of this would be ……
 “Time”…it was “the shaft was worn” because of “wearing” over “time”.
 “Speed”….”car crashed” because the person didn’t see the other car” and “speed”.
  “Age”……the pipe “corroded” because it was a “metal pipe” and “age”.
 “Weight”……we couldn’t stop it because it was “rolling” and its “weight”.
Another example of a different context would be “maintenance”….i.e..the machine failed because of “maintenance”. The intent of this very vague reference would be to suggest that some aspect of the maintenance has been less than adequate but if we take this reference literally it would simply fail to make any sense. In other words what you are saying is that the “maintenance has caused the machine to fail”.  Now I will agree that this is not the intent of the causal connection to say this, but it actually is what is being stated literally. It is the absence of a suitable description, a “non-description” if you like, that leads to this interpretation.
Now whilst all of these causes probably have some specific relevance within the causal pathways in which you find them they all create confusion as there is no clear descriptor to explain the relationship. This will again lead to subjective assessments. People will interpret the reference in their own way. Speed will mean different things to different people, as will weight, age and time. Typically what is required is to quantify each of these words. In other words
 “How much time are you talking about?”
 “What was the speed?”
”How old is it?”    
 “How heavy is it?”  and
“What is it about the maintenance that was less than adequate?”
It is this information that the chart requires. Try to be as precise as possible here. This will create a far better understanding. By simply referring to a cause, without accurately describing it, you demand that the reader interpret it in the same way that you do. But this is an assumption. Everyone is different. There is not one of us, as humans, that is exactly the same as anyone else. It is the human condition. Everyone is unique, the sum total of all of their life experiences to date. So it would be erroneous to assume that all people think the same way. Then why do we ask them to do so?
Now I would suggest that this is not so. That this is not what we are trying to do. That this is not a deliberate expectation, but it is the result, none the less, when we present information in this fashion.
Another area in which language plays a significant role in the understanding of a particular causal factor is where the descriptor makes a judgement call. Words like “wrong, or “incorrect” are used to describe causes. This sort of description is purely subjective, opinionated and may not be based in fact. If what we are trying to do is to present the facts then these types of words would fail to achieve that. Your task as a facilitator is to seek clarification of these words. Why is it wrong? What makes it wrong or incorrect?  When these questions are asked the responses to them need to be recorded and added to the chart. The original reference has been replaced by something far more factual and meaningful. It also makes your charts easier to understand. The chart will become more transparent. Remember that you are trying to tell the story, rather than ask people to guess, or infer what has happened with vague or imprecise descriptions of causes.
The task of charting the incident is also made easier because it is now easier to find and arrange causes that have a precise description rather than a vague one.
The logic will become clearer and the chart easier to follow and understand.
Understanding our problems is the cornerstone to finding effective solutions that will prevent reoccurrence. It is our ability to apply our understanding of the impact of clear and precise communication that will have a tremendously positive impact in this pursuit.

Operator Driven Reliability (ODR) ?

A system of involving the equipment operators in improving reliability by having them identify potential equipment problems and failures early. The operator fixes them if they are minor and issues a repair request if they are major to maintenanace department. 

Best Practice on Turnaround

There are mainly six stages for Turnaround Planning

Stage-1. Sub-process - Analyze Business plan (24 Months prior) :

Shut down is a business Decision .The major activities are listed & mapped in Multi    year

Planning Process for 10 year (Minimum 5-6 years) horizon & “Dominant reasons

/constraints “are identified for deciding the “Major shut down event “or "Short shutdown

Event." Following various aspects are reviewed while taking this decision.

• Market Demand

• Operational Requirements which cannot be postponed (e.g. Catalyst exhaustion,

Statutory which is must etc)

• Plant performance deterioration due to fouling /cleanouts

• Statutory requirements

• Project Integration

• Critical overhauls & Corrective repair plans

• Inspection Intervals.

• Fit the company's overall business & budget plans

• Check Seasonal adjustments

• Other Company shutdown coinciding

To understand the cost impacts associated with turnaround timing decisions, & to simplify

Their analysis, four distinct cost components can be identified. Each represents a group of

Costs that typically are affected when a turnaround date is changed. These factors are:

• Probable cost of failure (potential cost associated with the risk of an unplanned

Outage due to reliability issues)

• Planning & execution cost of turnaround

• Life cycle cost impact on the facility

• Business environment related costs (differential margins, cash flows etc)

The cost impact over time for each of these factors is distinctly different.

The probable cost of failure generally increases with time from the last turnaround.

The planning & execution costs generally increase with a change in either direction from

Target turnaround date (given sufficient planning time was allowed to begin with).

Life cycle costs increase (interval <baseline) or decrease (interval >baseline) linearly from the

defined optimum baseline reliability –driven turnaround interval.

And the business environment costs are irregular & dependent on business conditions at the

points in time under consideration.

Considering all above, Proposal for Shut down with Justification indicating Date, Size,

Purpose & Objective of shutdown. (E.g. High Pay Back modifications, Reduce the probability

of breakdown between shutdowns, Increase intervals between shutdowns, Catalyst

Replacement etc) is prepared & put up for approval of the Management.

Stage-2. Sub-process - Conceptual planning (18 Months Prior) :

This is a one page Mile stone plan. The cross functional core team is formed. Conceptual

planning focuses on establishing critical dates required to execute the process for any given

event. The initial process timeline includes key dates such as unit shutdown & start up periods,

basic dependencies among units & the target mechanical windows including critical jobs.

Previous lessons learned are also addressed in conceptual planning. Contracting Strategies are

firmed up

• Cross Functional team formed

• Define basic dependencies between units.

• Previous lessons learnt

• Major /Critical Job Window.

• Key time frame indicating unit shut down & start up periods including the time line

for Major Job window.

• Firming the contracting strategies

• Level 1 Budget (+/- 30%)

Stage-3. Sub-process - Detail planning (12 months prior):

Detail work tasks are reviewed, sequenced & steps required to complete each work package

are logically laid out. The in-detail job steps & resources are reviewed by knowledgeable who

will execute the job in field & document the final steps & resources as required. The critical

path job is identified & risk analysis is performed. Level 2 budget (+/- 10%) is prepared &

budget approval is initiated. Procurement action for long lead time items initiated. Contractor

Mobilization Plan is prepared. With approved budget, Material ordering & awarding the

contracts initiated. Contractor Mobilization Plan is prepared. Identifying tools &

consumables needs, packaging the materials, developing definitive crew assignment plans,

etc. are firmed up.

• Logical Mapping of Detail work task, steps to complete the work task & sequencing

the work task

• Review & revalidation of resources required to carry out the job.

• Identification of tools & consumables.

• Optimize schedule with different work approaches & final activity chart indicating the

critical path as well as indicating the predecessors & successors for all the activities.

• Level 2 budget: More Precise (plus minus 10 %)

• Defining the contractor’s scope.

• Contractor Mobilization Plan

• Material Ordering for long lead time items 12 Months prior.

Stage-4 Sub-process - Pre Turnaround activities & Audit:

With approved budget, Material ordering & awarding of the contracts are initiated.

Communicating & familiarizing the scope to executing parties are also triggered. This

familiarization will help the contractors understand the scope as clearly as originator and help

control the scope during the execution phase. This familiarization phase is most important of

establishing contractor staffing & craft mobilization plan.

All the activities which can be executed prior to shutdown are listed & completed in advance.

The Permit Issue Plan, Isolation Plan, Decommissioning & decontamination plan, Electrical

isolation Plan, Crane routes & rigging plan , Safety plan, Prefabrication Jobs, Working shifts

& shift manning plan etc. are typical activities which can be completed during this phase .

Peripheral Infrastructure like Contactor site office, Contractor’s Canteen, Rest room, Sign

Boards & Hoardings, Material Handling arrangements, Placements of materials at the

required location by schedulers etc are completed during this phase.

Audits are conducted to ensure the availability of all required resources. Inspection & quality

checks of receipts and follow up of pending if any, brings the confidence to zero date shut

down execution phase.

Validation of crane routes & rigging plans ensures the safe material handling during

Plans 12 to Zero Months Prior

Stage-5. Sub-process -Turnaround Execution:

All resources are mobilized as per the mobilization plan & the work should begin as soon as

possible following the shutdown plan.

Safe decommissioning, proper & positive physical isolations, Electrical Isolations are very

critical to hand over the equipments for maintenance. Timely issuing the permit to work

eliminates the idle time.

Detail maintenance tasks are carried out as per the scheduled sequence of activities. The final

recommendations, during inspection if any, should come as early as possible to ensure enough

time for correction.

Create feed back loop to monitor progress & update the plan. The quality plan & embedded

mini plans must be audited on a continual basis to confirm that the things are happening as

they are planned to. Shut down progress charts should be prominently displayed at strategic

locations. The Planner must update & highlight significant issues which imply deviation from

plan and need to be resolved. Daily schedules derived from the master schedule helps to bring

the effectiveness in monitoring shutdown. The shutdown manager should hold a daily

communication meeting with the shutdown team including contractor’s representatives.

Deviation in the plan due to changing priorities, progress, potential problems & all other

relevant issues should be discussed during the meeting. Job completion clearance should be conducted as per the authorization matrix.

Pre start up audits should be conducted to ensure smooth start up. Preparation of start up with

pre start up safety review should begin as a parallel activity, the moment the equipments are

boxed up.

• Safe Decommissioning

• Daily meeting to Monitor progress & Update plan

• Quality checks & audits

• Daily Schedules from Master Schedule

• Deviation Plan due to changing priorities

• Job Completion review Planned & actual.

• Prestart up safety review

• Preparation of start up

Stage-6. Sub-process - Post Turnaround activity:

All aspects like Managing work scope, Job Planning, Cost Performance, Work Schedule,

Contractor Performance; Safety & Environmental Compliances etc. should be reviewed to

find out Learning points identified during the course of shutdown & identifying the actions

for future improvement. Shut Down reports should be released as soon as possible but not

later than 3 months after start up. The report should contain brief but precise record of

inspection findings, operational & technological findings, the shutdown observations &

forecast of the inspection work list for the next shut down. The report should have headings

like Executive Summary, Performance statistics, Duration/Delays/Safety , Organization &

Manning, Contracts & Contractor Performance. The report should indicate the learning’s from

Turnaround (seek improvement and not guilt).

• Waste/ Scrap Management

• Brief but precise documentation of inspection findings

• Review all parameters to indicate learning & to measure the shutdown performance

• Compliance & Variance report on various parameters like Schedule, Cost , Safety,

Environment, etc

• Publish Consolidated Shutdown report within 3 Months (Max)

• Work list for next Shutdown

• Job Benefit analysis after six Months of start up to access Performance.

Best Practices of Condition Monitoring of Centrifugal Compressors

High equipment availability can be obtained cost-effective by the implementation of a

Predictive Maintenance strategy .Therefore a well-balanced monitoring program

should be implemented related to the criticality classification of the equipment. It

should combine periodic inspection (Off-stream) of easily accessible parts of major

equipment with the day to day on-line inspection and monitoring results.

The basis of the condition-monitoring program is comparing the current performance

with a reference (past) performance. This comparison is done for equipment on a

selective basis on a number of typical selected parameters:

Typical Condition Monitoring Parameters:

• Vibrations , frequency , phase and transient analysis such as bode and polar plots

• Thermodynamic performance (pressures, temperatures, efficiency, flow etc.)

• Oil analysis

• Wear Particle analysis

• Seal oil consumption/ leakage over the seals/ lube oil leakage's/ excessive venting

• Seal gas system i.e. flows and pressures in the supply and leak off lines

• Balance line leak offs

• Radial and axial shaft positions

• Bearing temperatures

• Motor winding temperatures

• Foundations NDT

• Inspection results of previous overhauls

The trends need to be analyzed to determine the 'health' status of the equipment.

Deviations beyond set limits of the parameters should be reported to management and

appropriate action taken.

Do not operate the plant at conditions (feed stock quality, flow rates, process

temperatures/ pressures) beyond the approved operating envelope. Any changes and

deviations in upper and lower design limits shall be thoroughly discussed and

evaluated for machine integrity. Based on this, approved window should be

established.

Ensure that the agreed/ approved operating envelope is clearly known and properly

documented. Make operating staff responsible and accountable for maintaining the

operating conditions of the plant systems and equipment within their respective

envelopes

Regularly measure and evaluate the performance in critical areas by comparing the

results with the Performance Indicator target values and analyze the differences.

Determine the reasons for the variances and identify and apply corrective action, as

and when required and report via monthly and/or quarterly site management reports.

Widely publicize the current performance indicators against the agreed target values

and the results.

In all cases, any foreseen operating deviation must be reported to allow for proper

monitoring of the equipment. Any operation outside the operating envelop of the

plant/equipment must be subjected to a complete review including the safeguarding

system, start-up and shutdown procedures.

After each overhaul it is necessary to log a new base-line reading of operating data to

verify mechanical and thermodynamic performance and to establish whether the

maintenance job has been executed successfully.

Predictive or Preventive ?

There was a time when Preventive Maintenance (PM) was the answer to increasing reliability of systems and equipment. However, PM is usually intrusive and sometimes even harmful to equipment because it may actually introduce a failure mechanism.
Predictive Maintenance (PdM) on the other hand is typically non-intrusive, is easier to schedule because shutdown is not required and actually should be the basis for most of your existing PM work.
Which is better for you personally, surgery to see if you are healthy or some x-rays, blood work or even an MRI to determine what is really going on?

Why is equipment any different? The technology is out there, lets start using it

Testing Bearings With Ultrasound

When collecting bearing data consistent placement of the contact probe is critical to repeatability. Care should be taken to position the probe at the same place each time. Wherever possible a ninety degree angle between probe and bearing should be realized. Modern ultra sound systems are less subject to hand pressure then older systems. However a firm and consistent hand pressure should be applied. Better still, use a magnetic mount with a RS1 threaded sensor. Measurement should be taken in the following sequence.
1.) Position probe on bearing
2.) Set amplification
3.) Set acquisition sample time
4.) Listen with headset
5.) Begin capture and store
6.) If alarm is triggered capture dynamic data for time waveform analysis.

When It Comes To RCA…Listen To Your Operators/Plant Engineers

When it comes to looking for failures during a Reliability Study or for causes during a Root Cause Analysis investigation, ‘Listen to your operators’.
They are the eyes and ears of your production facility. It doesn’t matter if you are running a chocolate factory, bottling beer, or drilling for oil, they all have one thing in common - operators on the front line.
These valuable members of your team are often the first to notice problems occurring; these problems may only stop the machine once a shift for a few minutes while they go and hit the reset button. These ‘high frequency short duration’ issues often get reported but are not seen or considered as critical because we have not yet witnessed a major stoppage. After all, we hit the reset button and the machine starts again.
A few things start to naturally happen at this stage.
• Operators stop reporting faults because nobody does anything about them
• Operators start to change the operating practice of the machine to allow for these issues during their shift. This then becomes normal operating practice, without any form of risk assessment having been performed. These changes are usually only identified following a major incident investigation. When it is often too late.
Reliability is like Safety - Ignore the little things and before log it could be something major.
Typical comments used by operators during Reliability Studies and RCA investigations are:
• ‘We’ve been doing it that way for years’
• ‘We kept reporting it to management’
• ‘I used to do that task but we removed it from our check list because we never found anything’
Great examples exist like the operator who used to carry out torque checks on a rotating piece of equipment at the end of shift, only to be told it was no longer required. Two years later the Reliability investigation into downtime on the machine revealed ‘sheared bolts’ as the number one failure mode on the machine. We re-introduce the torque checks and the problem disappears.
Or the Root Cause Analysis performed on a ‘light curtain trip’ that stopped the machine once a shift for five minutes. The downtime lost on this ‘insignificant’ problem was quantified to be worth over $1million in losses to the business. The solution identified during the Root Cause Analysis equalled $34,000! The problem solved.
So during Reliability Studies and Root Cause Analysis, listen to your plant engineers, equipment specialists and OEMs, but, whatever you do, don’t forget to ‘Listen to your operators’

Is Soft Foot in Rotary Equipment drive Train Really Important?

Soft Foot has often been noted as the most inexact science portion of Shaft Alignment. Historically, when people think of Soft Foot, they often want to neglect, ignore, or otherwise do everything possible to not deal with it. This is one of the traps that leads down the path of bad habits, bad alignments, and more problems down the line.
Shaft alignment can be thought of as two things: 1) Aligning the couplings and 2) Checking for and correcting Soft Foot. Soft Foot, in fact, plays so much of a role in shaft alignment, that if one were to analyze the 6-Step Alignment Procedure below, one can see that Soft Foot actually appears in 3 out of the 6 steps. Therefore, Soft Foot can be thought of as half the alignment job.

Overall Alignment Procedure1. Pre-alignment checks
2. Rough alignment to “eyeball clean” (with bolts loose).
3. Rough soft foot: Loosen all bolts and “fill any obvious gaps”.
4. Initial alignment. Get to within 5 to 15 mils (0.125 mm to 0.375 mm) at coupling or less than 20 mils (0.5 mm) at feet.
5. Final soft foot. All feet less than 2.0 (0.05 mm)
6. Final alignment within tolerances.
Note: Step # 1 includes shim inspection and cleaning of machine supports

What is Soft Foot?
Soft Foot is Machine Frame Distortion.

How does it happen?
Soft Foot can happen from a number of things, including:
• Bent Feet
• Bad Bases (warped, uneven, flimsy)
• Dirt, rust, corrosion under feet
• Excessive number of shims
• And many more…

What should be done about it?
A full and extensive diagnosis should be done on every machine foot to determine whether or not the tightening of that particular bolt is causing machine frame distortion, and thereby adding coupling misalignment or machine frame strain. A few helpful tips to remember are:
• Minimize total number of shims under each machine foot to no more than 4 shims per foot.
• Make sure the area is clean, including machine feet, bases, shim packs, etc.
• Any jacking bolts that may be causing force against the machine frame should be backed off, so as to not interfere with the soft foot check.
• When checking for soft foot, only one machine foot should be loosened at a time, and the deflection or movement at the shaft noted.

With advancements in technology,  laser alignment tools can help diagnose whether a machine has a soft foot. The newest addition to the tools available , not only diagnoses the soft foot condition of the entire machine, but tells the user exactly how much to shim each foot, in order to correct the soft foot condition.
So the next time someone tries to pass off a bad Soft Foot problem as not being “that bad”, be aware that it is 50% of the alignment. Your machine’s Soft Foot condition should be taken care of, because if it has not, neither has your Shaft Alignment.

Shaft Alignment Check

Check for flat bases. Check for soft foot and correct. Do “rough” alignment first. Train aligners to current alignment techniques. Educate technical people about misconceptions on how much misalignment is acceptable with flexible couplings. Use alignment tolerances that are speed related. Compensate for thermal growth. Check for pipe strain. Use accurate alignment tools such as laser alignment systems. Check the vibration levels before and after alignment to determine if alignment was done properly

OEM - Maintenance Recommendations, Does it Work ?

Original Equipment Manufacturer (OEM) maintenance tips are not always the best solution to maintain your equipment. Some manufacturers tend to overreact with maintenance routines to guarantee their machines to pass warranty period or to sell more spare parts that are sometimes more profitable than the machine itself. I recall my car manufacturer advises in the manual to replace the engine oil filling cap every time I replace the engine oil!
On the other hand, ignoring the OEM check list completely is not the solution! Then what should we do to maintain our equipments?
If you have a new type of equipment or if you are just starting to create your maintenance routine, it’s advisable to use your OEM recommendation as a start, check your list; eliminate the illogic and unnecessary operations. Study your equipment maintenance manual; add operations that you see the OEM may have missed. Re-engineer some operations to be condition based instead of time based. Now you have your primary maintenance routine.

Second step is simply after running your machine and after several maintenance activities, you may face some failures, record them, study, and add the counter measures in your maintenance routine. That could be an additional operation in your PM list, or a condition monitoring solution, etc…. In the mean time, you have to monitor the gain or value added of each operation in your primary maintenance routine, you may find some operations that have no value added to the equipment condition as it never generates a corrective action. These types of operations should be eliminated from your maintenance routine.

By this time, you will have an optimum maintenance routine that is adapted to your equipment under your operating conditions and environment. This is by continuously eliminating and adding different operations in your maintenance routines according to your recent operating conditions.
There is no one perfect maintenance routine that suits your equipment all the time. Your equipment ages, new maintenance technologies arise, and operating conditions differ. Unless you continuously improve, regulate, and enhance your maintenance routines, you will have no perfect one

Monitoring Reciprocating Compressors

Advanced ultrasound inspection of reciprocal compressors.
When it comes to recips the opportunities for failure are many. Seal integrity around the piston cylinder wall reduces efficiency of compression. Dirty and worn valves do not seat properly due to corrosion and debris built up around the valve head. Wear and tear leads to broken valves and permanent component damage.
There are equal opportunities to win back uptime by applying advance ultrasound inspections. Recording dynamic signals at frequent intervals and performing simple time waveform analysis opens our senses to failures with an early enough warning to avoid a catastrophic shutdown.
Using simple UAS software, it is easy to expand 1/10th or even 1/100th of a second of data to see a valve open, exhaust and close. During that blink of an eye, we can see if there is complete sealing of the valve seat, and we can even assess the strength of the valve spring.

What is Splash Lubrication ?

A system of lubrication in which parts of a mechanism  dip into and splash the lubricant onto themselves and/or other parts of the mechanism.

Condition Based Maintenance and ROI

When considering a condition based maintenance process (CBM), a manager should first review their calendar based preventive maintenance tasks to see which tasks could become CBM tasks. If the equipment has automated control systems with electronic counters, it would be a candidate for integrating it into their CMMS/EAM system to automatically produce a PM service or inspection. This insures the PM will not be performed too often or missed when due.

Vibration Route Frequency

How often do you collect vibration data on your equipment? Is it monthly, quarterly or even yearly? Most of the time Management will allow data collection frequencies based upon the importance they assign to vibration analysis or available resources at the time. Management may actually ask that vibration data be collected every month or even more frequently if the machine has failed recently. Different companies and managers use different means to determine how often to collect vibration data or any other CM data for that matter.
Assigning arbitrary data collection frequencies (routes) to your equipment may actually do your reliability efforts a disservice. The best method is to determine the failure intervals of the failure modes (bearing defects, etc) in the equipment. Assign data collection intervals short enough to identify these failures.
For example, a bearing may develop a failure on day one and run for ninety days before it causes the machine to fail. If the machine is monitored with vibration analysis every ninety days, then your analyst may never identify the bearing failure condition in the machine. The result is that your machine will most likely fail without anyone being aware of the issue. If the same machine is monitored monthly with vibration analysis, then the bearing failure condition would most likely be identified with your vibration monitoring program. This would alert the maintenance department of the issue and allow appropriate repair efforts to be budgeted and scheduled.

What is PM and PdM Yield ?

A measure of corrective work that results directly from preventive maintenance (PM) and predictive maintenance (PdM) tasks in place. The measure is the amount of repair and replacement work that is identified when performing PM or PdM work compared to the amount of PM or PdM work being done.

Tips to Sustain Reliability Culture in a Maintenance Organisation

Cultural change is an outcome of developing a proactive environment and transferring knowledge and competency to drive behaviors towards a reliability mindset. Maintaining focus after the project is in place involves transitioning carefully from a project phase to an operational phase where activities are incorporated into daily life.
Things to consider:
• Developing a control plan - what should be included (ensure you consider personnel attrition, focus lapses, etc.)?
• Measuring and managing the proactive process (very different than managing a reactive process)
• Putting in place effective rewards and recognition.
• Celebrating success.

Corrosion under Insulation -CUI

 

CUI is a particularly severe form of localized corrosion that has been plaguing chemical process industries. Intruding water is the key problem in CUI. Special care must be taken during design not to promote corrosion by permitting water to enter a system either directly or indirectly by capillary action. Moisture may be external or may be present in the insulation material itself. Corrosion may attack the jacketing, the insulation hardware, or the underlying equipment.
For high temperature equipment, water entering an insulation material and diffusing inward will eventually reach a region of dryout at the hot pipe or equipment wall. Next to this dryout region is a zone in which the pores of the insulation are filled with a saturated salt solution. When a shutdown or process change occurs and the metal-wall temperature falls, the zone of saturated salt solution moves into the metal wall.
Upon reheating, the wall will temporarily be in contact with the saturated solution, and stress-corrosion cracking may begin. The drying/wetting cycles in CUI associated problems are a strong accelerator of corrosion damage since they provoke the formation of an increasingly aggressive chemistry that can lead to the worst corrosion problems possible, e.g. stress corrosion cracking, and premature catastrophic equipment failures.

Types of Corrosion Under Insulation

By understanding the types of corrosion that can occur under insulation, the proper materials and construction can be employed to prevent them. Intruding water is the key problem in CUI. Special care must be taken during design not to promote corrosion by permitting water to enter a system either directly or indirectly by capillary action. Moisture may be external or may be present in insulation.

What is the Mechanism of Corrosion Under Insulation?

The mechanism of corrosion under insulation involves three requirements:

1. Availability of oxygen.
2. High temperature.
3. Concentration of dissolved species.

Normally, as the temperature increases, the amount of oxygen dissolved in solution decreases as the boiling point is reached resulting in reduced corrosion rates. However, on the surface covered by insulation, a poultice effect is created which holds in the moisture which essentially makes it s closed system. In fact the measured corrosion rates associated with corrosion under insulation follow trends to higher corrosion rates commonly associated with only pressurized systems. Furthermore, in cases where precipitation becomes trapped on the metal surface by insulation, corrosive atmospheric constituents such as chlorides and sulfuric acid can concentration to also accelerate corrosion. In some cases, chlorides are present in the insulation which greatly promotes corrosion of the underlying surface which it becomes laden with moisture.

How do I Inspect for Corrosion Under Insulation?

The most common and straightforward way to inspect for corrosion under insulation is to cut plugs in the insulation that can be removed to allow for ultrasonic testing. However, many times such plugs can be the source of moisture leakage. The main problem with this technique is that corrosion under insulation tends to be localized and unless the inspection plug is positions in the right spot the sites of corrosion can be missed. Other techniques that are available include special eddy current techniques, x-ray, remote TV monitoring and electro-magnetic devices.

How do I Prevent Corrosion Under Insulation?

The most serious problem is the system already in service with a know corrosion under insulation problem. Inhibitors have been tried with varying success since repeated wet / dry cycles may make inhibitors ineffective. This is an area of opportunity. However, long terms performance and efficacy must be proven. Water proofing to prevent the ingress of water from outside sources is another method. However, it has been shown that sometimes these techniques tend to lock in moisture which can also increase corrosivity. Careful selection of insulation materials to prevent those that contain high levels of corrosive impurities such as chlorides is critical to reducing corrosion under insulation.
One of the best but most expensive options to prevent corrosion under insulation is the use of protective coating systems. Unfortunately, in most cases, coatings that have been successful for atmospheric service are used under insulation with disastrous results. In it often a surprise that under-insulation service is a more severe condition than straight atmospheric service. Special coating system must be utilized that have proven performance. In some applications inorganic zinc has worked well, but not in others. Anticorrosion and inhibitive coatings are being are also being proposed or considered for longer term performance.