With all the recent changes in the Process Safety community within the USA, I have been getting a lot of questions regarding pressure vessels and what to expect when it comes to how they play a role in PSM/RMP programs. These vessels pose our greatest risk within our process as they contain the majority of our HHCs/EHSs. Now I am not saying that these vessel’s failing is a “high risk” because Risk is both probability and severity; however, if these vessels are not operated properly nor cared for properly, the risk of their failure is increased. In this article, I hope to break the ice for many who have never been through a pressure vessel inspection.
Our first step in any mechanical integrity program is to decide which RAGAGEP is best suited for our process equipment. When we consider pressure vessels, the two (2) most common RARAGEP for their inspection are:
- API 510, and
- NB-23, Part II
API 510 is by far the most widely used RAGAGEP in the process industry and NB-23 seems to be popular in businesses where the vessel is a free standing such as Air Receivers and Hot Water Heaters. But in their totality, both RAGAGEPS follow very similar methodologies and schedules. So I will not mention any specific one in this article unless there is something critical that needs mentioning. I would also like to point out that SAFTENG does NOT perform any MI inspections so this is NOT an ad for services!
How much will an inspection cost?
The biggest question I get is how much will a vessel inspection cost. Since we do not do these inspections I can only speak from our experiences in helping clients manage their inspection programs (its been 13 years since I have managed a functioning MI program of my own and prices have changed drastically over those 13 years based on supply and demand!). Of course, the costs can vary HUGELY from vessel to vessel and although size is a major driver of price, there are other drivers that can have as big of an impact as size. For a 10,000 – 20,000 gallon vessel you should probably budget around $5,000-$10,000. This is a BASELINE cost and depending on several factors the price could be less OR more. For example, if the vessel is older than 10 years old and has never had an inspection and the owner/operator does not have the full-service history of the vessel (e.g. bought it used) then there is a very good chance the inspector will request an internal inspection and this will INCREASE the costs. Another huge factor that will INCREASE cost is the lack of vessel data. If we do not have a nameplate or U-1 form for the inspector, the inspector will be facing a huge challenge in his/her inspection of our vessel. In many cases, this will require us to perform a Fitness for Service (FFS) inspection and this can get very pricey.
The location of your facility could increase costs. This means if your facility is remote from hotels then travel costs will increase.
The accessibility of your vessel could increase the costs. This means that if an aerial lift is needed to access the vessel then, of course, this will increase the costs; some situations will call for scaffolding to be built for inspection access.
What’s the inspection schedule for my vessel?
There is no one set schedule for any single vessel, but a rule of thumb we should use for budgeting purposes is a plan to have the vessel inspected every ten years. There is also a 5-year external visual that is usually required, ESPECIALLY on insulated vessels, but these 5-year visuals tend to be much less costly as long as we have no Corrosion Under Insulation (CUI) issues. The 10-year, as a baseline, is where we often times have to have the vessel “off-line” and at some point through the service life of the vessel we will need to perform an INTERNAL inspection which will increase inspection cost AND incur downtime costs as well. But schedules may actually never be the same for like vessels within a single process. There are so many factors that go into establishing the “remaining service life” that vessels sitting side by side may have different schedules even though they are the same age, materials of construction, etc. Once we have inspection data, schedules are based on what is called Risk Based Inspection (RBI) protocols which mean based on the condition of the vessel and how it is faring in our process, the environment it resides in, and the chemical(s) it is handling the inspector will calculate the next necessary inspection. Of course, if our 5-year external visual finds issues, then the schedule will be revised to something more frequent. Here are passages from API 510 regarding frequency/schedules…
An RBI assessment may be used to establish the appropriate inspection intervals for internal, on-stream, and external inspections, as well as inspection and testing intervals for pressure-relieving devices. The RBI assessment may allow previously established inspection intervals to be exceeded from limits specified in 6.4 and 6.5 including the 10-year inspection and one-half remaining life limits for internal and on-stream inspections and the 5-year inspection limit for the external inspections.
…
Unless justified by an RBI assessment, the period between internal or on-stream inspections and thickness measurement inspections shall not exceed one-half the remaining life of the vessel or 10 years, whichever is less. Whenever the remaining life is less than four years, the inspection interval may be the full remaining life up to a maximum of two years. The interval is established by the inspector or engineer in accordance with the owner/user’s QA system.
One thing we need to recognize about our inspection schedule for any pressure vessel… the older it gets the more frequent our inspections will become. RBI or not, as our vessel ages it is going to require we keep a closer eye on how it’s performing, thus increased inspections and this means increased costs. Most businesses learn the hard way about when it’s best to replace a vessel and how NOT to push our luck, but seeing how most pressure vessels will out live most of us we may never have to replace one during our entire career.
Why do insulated vessels have more concerns?
There is a failure mode called “Corrosion Under Insulation” and this mode impacts BOTH vessels and piping. Most people believe that corrosion begins internally and works it damage from inside-out when in reality most failures occur from EXTERNAL CORROSION working outside-in. Insulation will expedite this process as once it becomes wet, from either water or chemical, it creates a very corrosive environment against the wall of the vessel (or pipe). For vessel and pipe that operate at colder than ambient temperatures, the process temperatures will even condense the humidity in the air and saturate the insulation with moisture. This process can be so efficient that I have seen insulation dripping it was so wet and this moisture is constantly against the vessel or pipe spells TROUBLE with a capital T.
NOTE: For Carbon Steel vessels, API calls out vessels that operate between 10°F (–12°C) and 350°F (175°C) as an increased risk such that the inspection plan should include a CUI inspection.
Another driver of costs may be the need to strip vessels of their insulation if CUI is identified as a problem. This will not significantly increase the cost of the actual inspection, but there will be increased costs in the form of removing the insulation, increased downtime, and of course the cost associated with re-insulating the vessel. If there are no CUI concerns noted during the inspection, the inspector will most likely create inspection ports through the insulation. These inspection ports MUST be done correctly as they can become avenues for moisture to find a way to the vessel (or piping).
Can my vessel “fail” its inspection?
Oh YES and when that day comes, mechanical integrity will be a four letter word (if you get my drift)! MI is usually not a popular topic in most processing plants as this single element is usually the most costly of all the PSM/RMP elements. But when faced with a vessel that has failed its inspection and can not be “re-rated” for some interim use, the business finds itself in a major bind. These “failing” inspections are usually a result of a business not properly caring for their vessels over their service life. Items like skipping inspections, changing the service the vessel is used in, changing the operating parameters for items such as pressure and temperature can ALL play a role in shortening the service life of the vessel. So when the business finds the $ and downtime to do an inspection they can be sorely surprised and caught completely off-guard. In fact in ALL my cases where I have seen vessels fail their inspection we can trace the issues back to IMPROPER inspections and inspection frequency. The facility tried to save money when business was slow so they fell into the trap of having unqualified inspectors do inferior inspections that missed warning signs. In most cases it was NOT the inspectors fault but the facility’s decision to not strip the insulation even though CUI was found or to skip the internal inspection so the unit could stay on-line. Making these changes once in a while is bad enough, but when the facility gets used to saving the $ and falls into the practice of short-cutting inspections and delaying the inspections that they actual do, it will come back to haunt them. It is one of those old sayings… Pay me now or Pay me later! That is the business side; the safety side is as shameful as we are not respecting one of our biggest risks!