Fitness For Service Decisions

FITNESS FOR SERVICE ASSESSMENTS (FFSAs)

R-R-R-R DECISIONS

We see lots of FFSAs during our training and consultancy activities at WILKINSON COUTTS. With the best of intentions, things sometimes get more complicated than they need to be. Let’s simplify things….

There are only possible output decisions of a FFSA, as shown in table 1 below;

• Run (as-is)
• Re-rate
• Repair
• Replace

Several decisions may be viable, so you have to choose which one(s) to use. The frequency of their use depends on industry and plant type, but for large structural or pressure equipment items, things tend to end up looking like the pie-chart Figure 1. Each outcome has benefits and downsides, so you must balance them when deciding which to choose.

Fig.1

BRING ON INTUITION

Okay it’d be better to quantity everything, then a computer could do it. Sorry, it won’t work — you’d have to tell it what to decide. There are two sides to most R-R-R-R decisions

• Technical risk considerations
• Added value considerations

These act together, complementing or contradicting each other, so there’s no algorithm to help you choose. The danger is that your interpretation of FFSA results gets biased by your preference towards one or the other. You see what you want to see and decide your R-R-R-R option accordingly. That’s reality — but let’s dig open the arguments —and see what’s behind them.

TECHNICAL RISK CONSIDERATIONS

It’s all about the risk of failure (catastrophic or leaks); causing downtime or risk to people. Timescale is important; the longer you take a risk, the greater the chance of that dreaded undesired event. Here are some considerations

• ‘Run’ or ‘re-rate’ times grow longer (not shorter) —temporary becomes permanent
• Repairs can introduce new risks due to poor welding access or rogue materials
• Cheap replacements (watch your purchasing department) mean bigger risks
• Re-rating may not be possible, for process reasons

You can see it’s not straightforward. There are technical (failure) risks hiding behind every R-R-R-R decision. They differ for each situation, but watch out for one of the biggest

NEW MAY NOT MEAN BETTER

Solid engineering arguments valid across many industries conclude that how you treat equipment (i.e. its lifestyle) has a much greater influence on its failure risk than its age. For some equipment, it means two or three times. You’ll have to weather early-life failures of replaced complex equipment (the bathtub curve), and if you buy cheaply, you’ll buy new problems also.

On the positive side, you won’t get too much opposition from people if you justify your R-R-R-R decision based on risk reduction (health & safety and all that stuff). It’s never the full story, though.

THINK ADDED VALUE

These lurk in the background. Integrity engineers often ignore them as it’s ‘not their job’ (like management relegating technical risk arguments to second place behind production targets).

Start with the concept of added value and see how each of the R-R-R-R decisions affects it. If implementing your decision adds value, the value of the asset goes up (obviously), and vice-versa. Because value needs time to show itself you need to think about the lifetime of the asset into the future — will it produce more revenue, suffer less downtime, or cost more for future repairs, and so on. There’s a rule of thumb blowing around

IF A REPAIR COSTS LESS THAN 50% OF A REPLACEMENT

IT’S WORTH DOING

Could be true. It lives off a supporting rule that new assets (from a replacement) give more (not fewer) problems than existing repaired ones more than 50% of the time. Replacement does not guarantee fewer problems and less downtime, which skews the balance. It depends on the equipment and its lifestyle of course. You might conclude that added value is a factor in R-R-R-R decisions, but consider technical risk more important. Lifetime cost models are fine but rarely break the ice into day-to-day R-R-R-R decisions. You’ll hear convincing arguments either way;

• It’s easier to get capital to replace obsolete equipment than a maintenance budget
• New equipment is an investment. Repairing old stuff is a ‘sunk cost’
• Repairs add value also…you get a new item for half-price
• It’s cheaper to buy a new item than find someone to repair an old one

Listening too much to these results in strange behavioural decisions. IT’S YOUR CALL

At Wilkinson Coutts, we offer various courses that deal with these subjects:

• API 579 FFS ASSESSMENT: We take a practical approach, not baffle you with complex maths, so you feel the need to use fancy software. (We don’t sell software)

• ASME PCC-2 REPAIRS contains excellent engineering detail on welded and non-metallic repairs. It’s broadly compatible with API codes also.

• LIFE ASSESSMENT/EXTENSION: Mainly for high temperature and boiler plants, but it applies to other plants as well…in fact, it’s easier

• CODE COMPLIANCE of all types of pressure/static plant

We provide them as in-house courses, tailored to just what you need.

For info, contact [email protected]