Inspectioneering Journal

Introduction to the 99 Diseases of Pressure Equipment

By John Reynolds, Principal Consultant at Intertek. This article appears in the January/February 2003 issue of Inspectioneering Journal.
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Welcome to a new series of articles about the ninety-nine leading types of degradation, flaws and failure that can and do happen to pressure equipment in the hydrocarbon process industry. Imagine for a moment, a world free of unexpected pressure equipment failures due to degradation and failure of the construction materials? Pipe dream? I say not! It is possible and doable that we can eliminate a lot of unexpected failures if all the right people know about and understand the “afflictions” of pressure equipment, why they happen, and how to prevent them from resulting in failure. The key is clearly prevention, and we can’t prevent what we don’t know about. But in the case of the “99 most common diseases of pressure equipment”, there is no excuse for not knowing. Most of these things have been known to a few of us subject matter experts (SMEs) for decades. It’s now time that more people knew about them.

This series of articles is not aimed at the experienced corrosion/materials specialist who should be routinely involved in corrosion control and inspection planning, but rather it is aimed at the others who should or may be involved with pressure equipment, including inspectors, operators, maintenance crafts, process engineers, maintenance engineers and foremen. In this series of articles, I will simply identify the issues and some questions that should be asked determine if any particular degradation mechanism is “possible or probable” in each operating environment.

I mentioned the RBI team in the last sentence. Yes, one of the most important aspects of conducting RBI Planning is understanding what types of degradation can cause deterioration and therefore eventual failure of pressure equipment. We can’t do a valid risk assessment or a good job of inspection planning unless we know all the possible and probable causes of failure in each piece of equipment in each operating environment. So this series of articles will outline the 99 most common of our pressure equipment “afflictions”. Hopefully the information in this series will help the entire RBI team to understand every potential failure mode that should be considered when trying to determine the probability of failure side of the risk equation. Eventually all these degradation by the entire RBI (Risk-Based Inspection) team in order to phenomena will be covered in much more detail in the forthcoming API RP 571 on Deterioration Mechanisms in Hydrocarbon Processing, when it is published next year. Hopefully this series of articles will just “wet your appetite” for knowing much more about each phenomena when API RP 571 is available.

Another source of information that is being compiled is a new operator training series on pressure equipment integrity issues. The API has issued a contract for the compilation of a training manual for this series, which should also be ready for publication early next year. Watch for it; as it will be one of several tools available to us to transfer knowledge about corrosion and materials degradation issues to those who really need to know. Another tool that we’re having great success with is the compilation of Corrosion Control Documents (CCDs) for each of our process units. These CCDs have become the basis for transfer of knowledge about all the corrosion/materials issues in each process unit from the knowledgeable SMEs to the rest of the RBI team and to all operators, engineers, and craftsmen who need to know. They contain a wealth of information on potential degradation mechanisms, operating windows, materials of construction, operating environments, etc. that are also handy for doing effective Process Hazards Analysis (PHAs or HAZOPs).

There are certainly other important reasons why other folks outside of our profession need to have some limited knowledge of all the potential degradation mechanisms in the equipment with which they are associated. In my 35 years in the business, time and time again I see and hear about failures that are not new to me or to the site corrosion and materials engineer. Usually when a failure occurs, the corrosion and materials specialist already had the knowledge that could have prevented the failure. But unfortunately, the other folks who are closer to daily operations and maintenance of our equipment don’t always have the minimal information they need to understand what it takes to protect and preserve it, and thereby prevent unexpected failures. A good example, which nearly everyone has seen, is when equipment that contains a mildly caustic environment is eventually “steamed out” during clean out procedures, exposing it to the potential for caustic cracking. I’d be rich if I had a dollar for every time I heard about that happening because the responsible operating folks were not aware of the issue. This stuff is not rocket science! It’s actually much more important than rocket science to those of us who make a living working in the hydrocarbon process industry.

Another reason why operating folks and process engineers need to know about the “99 diseases of pressure equipment” is that this knowledge will help them understand why it is so important for us to set the limits (and stay within them) in our operating windows. Each potential threat to the safety of our pressure equipment (and the people who operate it) should have a clearly designated operating window (typically upper and lower limits), within which the equipment can be safely operated without exposure to unexpected degradation and failure. The more people understand the reasons behind these standard and critical operating limits, the more likely they are to adhere to and respect them. Do you have an operating window established for each of the potential and probable materials degradation variables in your pressure equipment? Far too often, I find that the operating windows don’t focus on causes of failure as much as they do operating quality issues or operating reliability issues.

Why do I call them the “99 diseases”? Because there is an analogy to the medical profession with regards to prevention and cure. Certainly in both cases, it’s much easier, much less expensive, and healthier (safer) to prevent such diseases than it is to cure them. I’m sure we would all rather know and practice the necessary lifestyles that will prevent us from having cancer or heart disease than it is to cure either after we contract them. The same is largely true with the diseases of pressure equipment. Preventing cracks, high corrosion rates, and metallurgical degradation is usually easier, much less expensive, and safer than coping with the aftermath of unexpected vessel and piping failures. Often it only takes shared knowledge and good operating practices to avoid many of the afflictions.

There’s another analogy in the prevention of unexpected failures in pressure equipment. It’s with our automobiles. We’ve all heard about people who do such a good job with preventive maintenance and operating care on their vehicle that it runs very well to 200,000+ miles. The same is true with vessels, tanks, heat exchangers, columns, and piping in the hydrocarbon process industry. If we take care of them, understand what can make them “break down” (i.e., fail unexpectedly), and “drive them” with care (i.e. operate them within the preset operating window), they will provide reliable, safe service throughout the life of our process plant. What prevents us from doing it?

So, what are those 99 diseases of pressure equipment? I’m sure that many of the IJ readers have heard about most, if not all of them. So, be sure to pass this article along to others who may not know about all of them, but may need to know more in order to help you protect and preserve your pressure equipment. These articles will not convert them into corrosion/materials engineers, but perhaps will make them aware of the important flaws and degradation issues, so they can be our “eyes and ears” in the field, so they can be better members of the RBI team, so they can understand the importance of the operating window, so they can help us prevent unanticipated pressure equipment failures.

I’ll start with a very common one (caustic cracking) and a very uncommon one (green rot), and share some information on high hardness fittings then try to fill in everything in between during the next few editions of the Inspectioneering Journal.

Continue to Caustic Cracking

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