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lethal service revisited

lethal service revisited

lethal service revisited

(OP)
I was recently asked to look at commercial terms for ordering of some pressure vessels but I found a bit of a problem. The service conditions range from extremely high concentrations of H2S to high wet CO2 with pressures ranging from 150psig to 1500psig but specific operating condtions cannot be planned ahead of time during design so there is no opportunity to pick protective films or calculate partial pressures. The vessels are assumed to be actively corroding when any bare metal is showing and if present, polymer internal coatings exacerbate the problem if they are torn. Sometimes acid that is not spent is moved through these tanks so they really get a workout even in the case of overlays. Apparently it is not unusual to have the vessel filled with ice so service conditions are definitely cold and -50°F is a realistic service condition. I was a bit surprised to see all the vessels are RT2 and although the unwritten standard is that H2S is not considered lethal, it was reported that some of the past process fluid was dry gas with high concentrations of H2S which really changes the entrained by wet gas argument. Any major failure would be pretty lethal but so far the industry incident rate has been low (low probability, high consequence). Reportedly, the primary causes of scrapping these types of vessels is from sand erosion and pitting corrosion but there have been temperature/weldquality related fracture as well but nothing catastrophic. The pressure vessel owners are typically not understanding of the code requirements as no juristiction seems to be very concerned about this application but they want to be informed as I go through the process. How does an engineer in good conscience techncally/morally justify not recommending the owner into lethal service with the price consequence when the "industry standard" does not reflect the need under UW2 for proper consideration of what lethal service is.

RE: lethal service revisited

Equality;
I am a bit surprised by your question because this seems like it is being asked by a lawyer instead of an engineer since you prefaced this by "commercial terms". Leave the commercial terms out and lets roll up our sleeves to discuss engineering specifications. Was there a detailed engineering specification developed for these vessels? If so, this question needs to be directed to the Design Engineer or firm assuming responsibility for the design of the vessels. All of this should have been evaluated during the design phase of the vessel.

RE: lethal service revisited

Equality,
Per U-2 (a) "The user or his designated agent shall establish the design requirements...Such considerations shall include...
(2) the definition of lethal services..."

In the Oil/Gas/Petrochemical industries, the services defined by you have not been been considered meeting the definition of Lethal provided in UW-2 (a). While I have not been engaged in defining lethal service during the past 20 years, only one of those companies, by no means one of the majors, defined such service as Lethal.

RE: lethal service revisited

(OP)

Sorry about sounding like a lawyer but due dillegence and ethical practice certainly require that we understand code and regulation before we make decisions. These basic section VIII Div 1 vessels are unique in service as you cannot plan for the corrosion environment like you can in facitilites. I was only brought in to look at a commercial problem but did not expect to find an engineering standard problem as no regulatory juristiction requires that well production testing have an owner user program but owner user problems are still there. Many of the vessels are bought off the shelf, bought used etc and my short review showed that typically the lowest standard of quality of ASME BPVC section VIII Div1 was adopted. When I looked at the service conditions, I was surprised that little in the way of due dillegence was excercised and the regulation was pretty relaxed. Being as the vessels are used on both sides of 49, CSA B 51 applies as do all the USA antidumping rulings.

As expected, the commercial problem were really just a manifestation of not having an engineering specification when the contract was written. To make a proper specification, the diversity of the production enviroments makes it hard to make a factual descision on lethal service whereas a requirement such as notch toughness is very clearly defined by service temperatures.

I polled some pressure vessel manufacturers and got different answers but most of the answers are based on past service experience not true engineering judgement (back to low probability, high consequence) There was one that was pretty clear about how to define what was lethal based on partial pressure.
while it appears that most of industry feels that H2S is not a lethal fluid but some do and heither B51 or ASME talk about degreees of revival ater exposure as a criteria for a lethal fluid. I have not found a single regulator that has weighed in with an opinin. If a person dies, whomever makes this decision has to defend it and I never did like the "Industry Standard" defence. Addopting NACE requirements does solve a lot of problems that Lethal service addresses. Reviving after H2S exposure is harder to do that a person would like to admit and I personally know one person that did not make it. H2S is not Sarin or phosgene but it is still very quiet and deadly.

RE: lethal service revisited

Equality,
If you are the User or the User's designated agent, you make the Lethal decision under ASME VIII. If the Jurisdiction defines H2S as Lethal in the facilities described, the decision is made and the User must comply.

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