Pig Receiver/Launcher Non Operational State

[Brnmcgn]

Hopefully posted within the correct forum to get the most. Iews, replies and experiences.

I am currently working on a new build on-shore gas processing facility. As part of the build, a large pipeline transporting mainly clean gas with some liquids (c5+)is being attached. It is expected that the pipeline will require to be pigged once a week to ensure liquid slugs are brought through.

Obviously as part of the design we have an appropriate pig receiverbeing installed and this is wheremy question is.

The pig receiver in question is an appropriate rated pressure vessel with a bandlock door seal. Due to the make upof the new facility it is actually located in the middle of the plant (slightly different from other facilites).

In your experiences, in what state would people normally leave the pig receiver? Isolated, Depressurised and inertered or isolated and left at pressure with hydrocarbons?

The current design (as I believe with most pig receivers) does not have a relief valve but is rated for the maximum pipeline pressure. However, a design has been made to fireproof the vessel.

Really appreciate any comments.

 

[zdas04]

First off, no PSV on the receiver barrel is a major mistake. It doesn't take much leakage to end up with the barrel liquid full in the sun. I've seen it happen in 2-3 days. It doesn't take much of a PSV, but you need something for thermal protection.

Second, there really isn't a standard way to leave receivers, and if you assume one, an operator will figure out a reason to ignore you. I've had good luck with purging the barrel through the bypass line and leaving the barrel isolated at around 1 barg. That way you can check the pressure before starting the process to see if valves are leaking in (i.e., barrel at line pressure) or leaking out (i.e., barrel at atmospheric pressure). Going to the trouble of inerting it is simply a waste of resources, it does not add to safety in any tangible way. A lot of people are happy leaving the barrel vented, but I have a problem with that--if the bypass or barrel-isolation valves leak through then you don't really have any indication.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

A receiver would probably be isolated (receiver barrel valve certainly closed), depressurised and quite possibly containing air, but you should assume that hydrocarbons (from a leaking barrel valve), or HC + N2, or HC + air are present and always drain, vent and purge before opening again, which you would most likely do anyway, if it is a receiver.

You're asking because it doesn't have a thermal relief, correct?

What would you be doing, if you knew that you could not fail? Ans. Gov lobbyist.

 

[BigInch]

BTW yes, it should have thermal relief.

What would you be doing, if you knew that you could not fail? Ans. Gov lobbyist.

 

[Brnmcgn]

Gents,

Thanks for the replies.

You are correct it does not have thermal relief as the designer has designed it like they would (i.e it is a pig receiver within a field) others they have designed. The problem it is in the middle of gas plant but it does have a tie in/blow down line to the flare system, manual only. I felt that an operational procedure, stating that it is depressurised and isolated would provide adequate safeguards in case of thermal relief. Thermal relief is only a problem in the event of a pool fire underneath it.

 

[zdas04]

Not even close. A barrel that is liquid full will overpressure in a few minutes in the sun. Nothing to do with a fire case.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

A procedure is NOT sufficient. The design codes REQUIRE PRESSURE RELIEF in the event of overpressure. A procedure will never be able to meet that requirement.

What would you be doing, if you knew that you could not fail? Ans. Gov lobbyist.

 

[SJones]

A thermal relief valve shall be installed where the shut-in pressure of trapped fluid could
exceed the design pressure as a result of thermal expansion of the static fluid. Thermal
relief valves are not normally required for gas or multiphase pipelines, but should be
considered for liquid pipeline systems. The relief valve capacity and setting shall comply
with the pipeline design code and DEP 80.45.10.11-Gen.
NOTE: Where operating procedures restrict isolation of the pig trap to the period of loading or retrieving pigs,
it may be possible to eliminate the thermal relief valve.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[BigInch]

That's just fine if it's a SHELL plant, but B31.8 itself doesn't recognize Shell DEPs.

B31.8
845.2.1 Control and Limiting of Gas Pressure in Holders, Pipelines, and All Facilities That Might at Times be Bottle Tight.

Suitable types of protective devices to prevent overpresuring of such facilities include,
(a) spring-loaded relief valves of types meeting BPV Code, Section VIII
(b) pilot-loaded back-pressure regulators used as relief valves, so designed that failure of the pilot system or control lines will cause the regulator to open
(c) rupture disk of the type meeting the provisions of BPV Code, Section VIII, Divsion 1

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SJones]

Who said it was B31.8? There's more to the world than 31.8!

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[BigInch]

Well that's just it isn't it. Nobody said anything about any specific code, Shell included (or actually not). Given the preponderence of codes and company standards in the world, most based on B31 series anyway in one way or another, even the Chinese code is a virtual copy, it is reasonable to mention their requirements. I've been working outside the USA for 20 years and I never have been able to escape ASME (even as much as I'd like to at times). What's the problem anyway? I never said he had to use them.

Now, since you brought up this Shell, let's talk about it.

Given the circumstances of this question, specifically directed towards pig launchers and receivers in slug clearing service run once per week, I would not follow the Shell DP, even if I worked for Shell. While I would agree that a relief valve might not be needed on a pipeline in gas or multiphase service, this case is not discussing the pipeline, it is a localized bottle-tight device that could easily be full of liquids. Furthermore it is not way out on the edge of a plant or on the pipeline somewhere, it is in the MIDDLE of the plant. If there is anywhere you would want to have a relief valve on any part, or component, of a gas or multiphase pipeline, especially on a LAUNCHER/REVEIVER, and even the DP allows for it, I will requote you, "not NORMALLY required", this is one of those cases where it needs to be given a whole lot of thought. IMO, the Shell DP does not give a safe practice in this circumstance. I would not follow it. The B31.8 code is far superior in the degree of safety provided and .... costs relatively nothing. They are handling the liquids in some manner at present anyway.



If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SJones]

The Shell DEP simply provides a contextual response framework to the original statement

The current design (as I believe with most pig receivers) does not have a relief valve

]Whether it is right or not will have to be determined by HAZID, HAZOP and other process safety activities.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[zdas04]

Codes and company specs ONLY describe a minimum level of performance. If an engineer has a reasonable expectation that the code provides inadequate protection for a given situation then he needs to go beyond the code or company spec for that particular situation. That is what Engineering Judgement is all about.

This may become moot anyway. I am starting to see regulations (starting with Norway, but others are following) that reject the idea that pigging facilities are "pipeline accessories" as defined in B31.8 et al and requiring them to be treated as pressure vessels. I don't agree with this trend, but I understand where it is coming from. If a receiver barrel is a pressure vessel then this whole discussion becomes moot because there is no way to say that thermal relief is not required under the BPVC.

I started noticing 4-5 years ago that the horrible pre-fabricated pigging facilities that you can purchase from folks such as the old Tube Turns (they have changed their name) now have code stamps and include pressure relief on the barrels. This is recent, but it is a response to some pretty dramatic failures.

What you do with the PSV exhaust is another issue. A thermal relief generally dumps a couple of tablespoons of liquid and reseats until next time. Piping that to a flare is a really bad idea. Mostly people don't pipe it at all, and just let it splash the pipeworks. I support that approach, but in the middle of a plant that would probably be seen as wrong. If I had to pipe it somewhere it would be into a sump or waste water collection system.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Brnmcgn]

Firstly a big thank you for taking the time for reply to my original query. Obviously some differing approaches and sound justification for both stances. I think I will be pushing our pig receiver/pipeline EPC to design with a thermal relief valve included. While the stream is gas/multi phase and not totally liquid, any HAZOP would push for a TRV due to the potential for an operator not getting the isolations right.

In terms of relief route, it will be fed through to our flare which has a liquid knock drum before the actual flare which will be suitable.

Thanks again

 

[zdas04]

The problem with piping a thermal relief to flare is RUST. These stupid things spit a few ml of liquid that will wet down the piping and never get very far down the pipe. I don't like taking any PSV on predominantly water service to a flare stack (even with a knockout), but nothing says you can't do it.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

you were really saying wonderful things and I was saying, "Great! I agree with THAT!!!", then you got to this one. "Mostly people don't pipe it at all, and just let it splash the pipeworks. I support that approach,", then I said ...

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[Brnmcgn]

Again thanks for the replies. Rust won't be a problem as it will be a mix of hydrocarbon liquids, MEG and corrosion (no free water) and our flare header and knock out drums are stainless steel. Our knock out drum also has a pumping system to reclaim liquids.

 

[zdas04]

I've always been more of a cowboy than you could tolerate BigInch, I understand that. In the middle of an undeveloped field in New Mexico 20 miles from the nearest house, letting a thermal relief vent locally (i.e., splash the pipeworks) is not (in my opinion) unreasonable.

In a plant (even on the edge) I'll pipe it to a sump of some sort, but putting a stream that will be exclusively water into a flare header is a problem for me.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[BigInch]

zdas, I really just don't know where you come with those things. I think, hey he's kidding, right. Right?? Fortunately Brnmcgn's engineers are mostly on top of the situation, granted they missed the PSV, but the STAINLESS flare was a good move... water keeps the flare cooler, so they say. Venting to atmosphere, even in New Mexico, contributes to global warming for all of us. It's hot enough here as it is thanks. Also might be one more reason you got so many forest fires around U this year.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[zdas04]

Releasing a few mL of water is a contribution to climate change??? On that note I'll bow out.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.