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I remember once interviewing for a job during one of the many industry downturns. The guy doing the interviewing hit me with this question: “When is it OK to defer maintenance?” I didn’t have an answer ready for that one, at least not a short answer. 

A young, altruistic engineer might have answered, “Never!” However, I had been through enough oil price swings that I knew there were times when tough decisions had to be made. Well I’m a bit older now, and hopefully wiser—and I’ve had some time to think about it. So, now I have a concise answer. When is it OK to defer maintenance? “It depends–on risk assessment.”

You’ve guessed it; there is no short answer. It really depends on a lot of variables that require evaluation of risk.

First, I want to define what I broadly consider to be maintenance for plant and wells. For the purposes of this discussion, we’re going to include the following as “maintenance:” 1) Repair or replacement of failed equipment; 2) Planned Preventative Maintenance that is performed to prevent the failure of equipment or the process system (including instrument calibrations); 3) Integrity Inspections that are aimed at preventing structural failures or Loss of Containment; 4) Fabric Maintenance, such as painting, fixing loose or broken decking or gratings, repairing signage, repairing lighting, and general housekeeping.

So, how do we prioritize all of these types of activities, to choose which ones are OK to defer? My answer is “Risk Assessment.” Even if it’s just qualitative, the discussion should be around risk.

Risk is defined as probability x consequence. Two questions must be asked: “How likely is it to fail if maintenance is deferred?” and “What happens if it fails?”

Let’s look at each of these four types of maintenance individually.

Repair or replacement of failed equipment. The easy answer is you’re going to repair it, if the failed equipment affects safety, health, or environmental protection—unless it makes more economic sense to shut in the well or the plant. If the failed equipment affects production, then the repair is a simple economic decision. 

There is a more subtle possibility. If the failed equipment is an online spare, the economic logic changes. For example, if a plant has 2 x 100% export pumps, and one fails while the online spare is performing the duty, it has no spare. When facilities are designed, various methods of achieving facility availability are evaluated—including online sparing. The cost of availability is compared to the value of availability, and the optimum design is selected. Obviously, the value of availability is based on an assumed product price. If there has been a significant drop in product price, the point of optimum availability changes. So, it may be OK not to repair this export pump and to accept a lower availability.

Planned Preventative Maintenance (PPMs). Again, with PPMs, there is no single decision strategy. Here, risk asessment and engineering judgement need to be combined. If the PPMs are on safety equipment, be careful about deferring them. For example, I would be very hesitant to defer calibrations of equipment, such as gas detectors or pressure safety valves.

However, it might be appropriate to study the results of past PPMs on a piece of rotating equipment. If it had been operating normally when the last PPM was performed, and any removed parts looked okay, it might be reasonable to re-think PPM frequency.

Integrity inspections. There is no simple answer to decisions regarding integrity inspections. Since these are usually done on structural components and pressure containment equipment, the consequence of failure must be looked at closely. For piping and vessels, what kind of fluid is being contained? Is it toxic, flammable or explosive? What pressure and temperature does it have? What is the volume of fluid that might be released? Generally, the answers to these questions point to a fairly serious consequence.

Decisions about deferring integrity are, therefore, based heavily on probability of failure estimations, as consequences are usually high. This is more straightforward than one might think—at least for pressure containment equipment.

If your inspection strategy is time-based, you must incorporate some form of risk assessment to justify deferring inspection. This risk assessment must address potential failure consequences, as well as probability of failure. One of the inputs into the probability of failure estimation is the results of past inspections to determine a rate of metal loss.

If your inspection strategy is already risk-based, using API Recommend Practice 580, then you already have a risk model in place that can be consulted. In fact, the requirement to make a decision, about deferring inspection, can serve as an impetus to convert from a time-based inspection strategy to a risk-based one.

Fabric maintenance usually can be deferred, unless there are safety implications. There was an instance in the past, when fabric maintenance in the North Sea got so bad, that the U.K. Health and Safety Executive became concerned that the abysmal condition of some platforms gave a subconscious message to workers that operators weren’t concerned about safety. In other words, don’t let things get too bad.

In summary, there are occasions when it is OK to defer maintenance. In fact, you don’t need to wait for low oil prices to optimize your maintenance and inspection programs. However, these decisions should be based on science and pragmatic risk assessments.