Ball Valve Seat of Pigged Pipeline

I always specify soft seat for barrel-isolation valves. In fact, I have to have a really compelling chemical reason to ever specify a metal-to-metal seat.

I've never purchased a "double piston effect" valve (had to look that one up, it doesn't seem to have much traction in the US), not sure how far I'd rely on the alternate seat.

Nope, never put a bypass on a barrel-isolation valve (the kicker or process bypass serve that function), I suppose you could put a PSV on the body cavity, but I'm not sure why you'd bother.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

I would go for a soft seat as well on this service. Normally these valves don't close against flow or open with differential pressure which is what ruins soft seats.

Double piston is not universally accepted as double block in the same way as a split gate or expanding plug so normally you need double ball valves to get your double block.

Nothing extra is normally needed, but if you do specify double piston then you needed a cavity relief, especially for liquid lines.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

I'd say
1) soft seats are OK for a trap
2) Maybe not use a trunnion valve for sizes of 6", or 8", or less
3) and I'd change "normally you would need double ball valves" to "you would not need double" valves

There is no design code, standard practice, recommended practice, or anything else, except a few company standards and those companies that like to copy other company standards and make them thier own, that require doubled ball valves for isolation (in non-poisonous, hydrocarbon service), although a few oil/gas production companies (I personally only know of about 4, maybe 5, in the whole world) who do seem to think that they need it for some reason.

To make it clear, what I'm talking about is shown here in this PID, the two valves being the ones at the end of the launcher barrel, with the operator notation "NC", and "HV".


Interestingly enough those companies that do use doubled valves do not agree even to the slightest extent about when they need double valves. Some say everything over 10 barg, another not until 100 barg.

While there may be a few oil and gas production companies that do use doubled valves, I don't know of any "pipeline" transmission companies (in any country) that would even think of using double valves at a launcher, or anywhere else for that matter. Does anyone know of any pipeline companies that work to a double-valve isolation standard ie. putting two valves between launcher and pipeline? I'd be interested in knowing what others might think. Which companies (production, or pipeline) do this?

As far as that PID goes, any other comments about this PID?
I would not think a PSV is necessary for a gas line, although the bypass to flare might be helpful sometimes. A thermal expansion relief could be needed for a liquid line, but only if the trap barrel was left in a full condition. Why it would, I don't know.
I don't think balancing lines are necessary.
Why two drains?
The PSV might be a good idea, if someone hooked up a high pressure source to the purge connection. There was a fatal accident like that 2 years ago.
I've never had a necessity to put a check valve in the bypass line.
The second XT, assume it's a pig sig, on the pipeline, might be underground in many onshore configurations.
I would not normally put an ESD on the pipeline (the third valve there), as I know that ESD valves should isolate station from pipeline, but in production situations, especially offshore, an ESD "emergency shut down", or SDV "shut down valve" for those not willing to admit to the possibility of an emergency situation, is often placed on the pipeline riser to try to stop gas backflow near the topside decks.




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Weko, sorry if I'm hijacking your thread. Are you interested in continuing, or should I start anew?

I hate Windowz 8!!!!

Thanks all for your response.

@big inch:
Please continue, interesting

Thanks.

API 6D spec, of course.

The "balancing line" might be helpful, if this trap design were to be installed as a launcher, or a receiver, or both launcher and receiver, in which case you'd want to remove that check valve.

The spec blinds?
I've been told recently that I don't know anything about spec blinds. So,
why on the vent to atmosphere?
Why on the kicker and drains, but not on the balancing line?
Why are they needed here at all?


I hate Windowz 8!!!!

BigInch,
I've been looking at your drawing and I have couple of comments about it.
[ul]
[li]Like you, I also have never seen a check between the side valve and the tee, and I would strongly resist it being there. If you ever need to change a receiver into a launcher (and vice versa) then that check would make it really difficult.[/li]
[li]Doubling the barrel isolation valve is not something that I would ever sanction (and two valves without a vent between them is just asking for trouble)[/li]
[li]The third valve in line with the barrel (on the pipeline side of the tee) doesn't seem to have a purpose.[/li]
[li]PSV between the side valve and the side valve check is not needed and doesn't add any value at all.[/li]
[li]I put a PSV on the barrel because I've had receivers isolated liquid full and it doesn't take much heat to expand a line full of water to break something. I put a tiny thermal relief there.[/li]
[li]I make the point where the purge connection is into a vent (so that slight leakage from the barrel isolation valves will not push the pig out of the barrel throat while trying to load the pig).[/li]
[/ul] I sure wouldn't put that check valve on the purge line.
Spectacle blinds in the drains seem like more than a bit of overkill.
The PSV bypass looks odd to me, but I don't see that it is "wrong"
I've never built a launcher with that much instrumentation. Don't know that it is "wrong", just never seen it.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

Yes, not everything is wrong, but many of the things that are not wrong do seem to also be NOT necessary. Mostly a lot of instruments that are just waiting to get plugged up with pig gunk.

I hate Windowz 8!!!!

The double valve thing is of course linked to the particular companies isolation philosophy. I've seen single and double valves in these sorts of locations, but for new build, double isolation for ball valves is more common than not for #600+ gas lines. I agree that there is no standard or code, but most "majors" seem to have gone this way. Some try to use the double piston arrangement to create a DBB valve out of a ball valve, but this is a different subject and is not universally accepted.

The issue is of course risk of leaks from a single seat and as time has gone on, the level of risk acceptable to many operators has diminished. For single valve isolations on a pig trap I would strongly recommend a double acting gate valve - WKM used to make some really good ones if a bit pricey - when you're staring down the barrel of a pig trap you don't want anything coming your way. I think the national UK gas pipeline company does this (double valve) and the multi-products pipeline operating company I worked for always used double acting gate valves on the pig trap valves.

I disagree strongly about the balancing line - I believe they are a vital requirement, especially for gas and I would insist on one in any design or HAZOP I was involved in. If it's not there you risk crushing the pig against the valve as you pressure up for a launcher and the pig is forced further into the minor barrel (assuming you have a good fit of course) as the gas or liquid pressure builds and compresses the gas in front of the pig. This can damage both pig and ball. For a receiver, you risk a high pressure pocket of gas remaining downstream the pig propelling it forward when the debris is removed as the door is opened or just if the pig has got a bit stuck in the last section. This has happened and resulted in serious injury to the operator clearing debris from in front of the pig and for the sake of an additional nozzle and a bit of pipe the risk can be eliminated.

The PT should be on the main barrel with direct connections to stop it fouling

I hate intrusive pig signallers so would remove the flanged XTs, but the magnetic non intrusive ones now are much better.

I agree about the spectacle blinds and the NRV and I've not often seen a PRV line to flare at that point on the pipeline.

A PRV on the trap is pretty standard in my experience - liquid ones especially can become trapped volumes and generate large pressure if left filled but isolated in the sun.

I'm glad the drawing doesn't show a slope - I'm on a mission to remove all slopes on every pig trap drawing that passes my way so it doesn't just get repeated on the next one...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

Thousands of launchers with no balancing lines would suggest that the risk of squashing pigs against valves is negligible.

If double valves are not required (by at least one major) until you reach 100 barg (1450 psig), it's pretty easy to justify ... never.

It also seems strange that you need double valves at 100 barg (1450 psig) just before reaching the FULL rating of ANSI#600 = 102 barg (1480 psig) you jump to double the number of valves required. Does the probability of failure of a 600# valve between 100 and 102 barg dramatically increase as you reach the supposed 600# limit of 1480 psig? They will hold 1450 psig, but not 1480? One could also argue that these valves should be able to hold 10% more than their full rating across the seat as well. What do the valve manufacturers say about that. I'm sure they like the double valve policy, but what do they say about the ability of their valves to fully hold their rated pressure? Or is it that this policy is designed for poor maintenance practices? Is poor maintenance a characteristic of the majors?





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"Negligible" is putting it to mildly. I'd say non-existent and a total failure of Engineering Judgement to even take the suggestion seriously. Long before a pig would crush, you would get leakage around it to balance the pressures. The balance line is simply a waste of a dozen welds and a handful of fittings on the altar of "what if" that only exists in the rarefied air of a HazOp meeting where every hare-brained idea seems to have exactly the same weight as real risks.

As for ever double valving a barrel-isolation valve, kicker valve, or bypass valve I would quit a gig before I would design a launcher or receiver that way. For any pressure. I simply don't need the money from a company stupid enough to have that pointless and wasteful a design requirement.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

zdas, do you know of anywhere that BP uses doubled valves in the USA?

Launchers with no balance lines no doubled valves in California
Running smart pig, Rosen & SoCal Gas
Launching / Receiving TDW video

Animations, but none actually show double valves or balance lines

I hate Windowz 8!!!!

NOTE! Relief valves on traps are required by Minerals Management Service, MMS - the US Gov office having former design approval authority for offshore production systems.

BP safety alert
Not a photo, however their diagram shows no doubled valves, or balance lines.
Probably a good reason to have a PSV, if any ole pressure sources can be attached.


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I have had my hands on that launcher and no, it doesn't have double valves. I don't think that a PSV would have been a lot of help in that incident, it looked to me like a complete failure of Engineering.

I've been to a very large number of Amoco and BP locations and I've never seen doubled valves or balance lines. While I was their Technical Authority on gathering system no one ever proposed that foolishness to me.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

Gents,

You're concentrating on the wrong thing here. It's making this inherently risky operation as safe as possible and that's all about making sure you don't accidentally turn your pig tap into a artillery device. See the attached file and link below, both of which refer to gas trapped behind pigs as a key safety aspect.

Sure, the vast majority of pigging operation are safe and three is no incident, just like the vast majority of car journeys are safe, but would you not agree that seat belts and air bags have saved lives?. A balance line has one small nozzle and a bit of 2" pipe. Not really going to break the budget there.

Where did anyone say a single valve wouldn't hold the pressure? The issue is about leakage. Very few ball valves after a few operations are bubble tight, so when you have a single valve, the risk is always there. I've seen arguments both ways and for infrequently used systems, single valves will predominate, but as said, the appetite for accepting risk has fallen over the last decade. At the end of the day it's a judgement call and we all have different views on this - I respect yours and I hope you respect mine.


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

The link is interesting. Eight incidents 10 years, not close to the league of vehicle incidents. Should it be zero. Maybe. The incident you linked was all about line-of-fire and we have had that training and have had for 40 years that I know of. You train people to look at what is going on and try to anticipate the line of fire so they can stand somewhere else. This isn't a pigging incident, this is a training incident. I think you have more risk of injury just installing the second valves than you would ever mitigate by their existence. In my experience, safe operations come from hiring competent people and ensuring that you have not tied their hands with stupid procedures to the point that they forget to think. I've done nearly 40 projects that were each over $2 million. I was accounatbale for day to day operations on 125 wells and 200 miles of gathering for 12 years. I had zero reportable accidents/injuries. Zero reportable spills. The people who took over that operation from me have had 1-2 reportable injuries a year and 3-4 reportable spills a year--but they have all the PSM/nanny-society processes and procedures. I like my way better.

The .pdf is mostly just a support document for my way of operating pigging equipment. I've seen the circumstances of the first incident a dozen times (but didn't ever write up a "loss prevention bulletin" my god). When you open the closure you stand out of the way (like these guys obviously did) and if you can't see the pig then you crack open the barrel isolation valve an remove the pig--happens dozens of times a month with no big drama until someone writes a report. Adding a vent is just a band aide that will rarely be exercised (I put the vent that they call for on launchers, but I do it so that I can seat a pig in the throat when the barrel isolation valve is leaking by a little bit). The second one is kind of silly, he should have put the loader bucket head on to the pig instead of side on, or just let the pig run free. I've done the loader bucket thing a couple of times and the loader lifts up a bit, but doesn't flip. The contractor paid attention in those line-of-fire classes. The last one is complex, but it is clear to me that the supply air to the actuated valve had been locked out (else it wouldn't have taken "several minutes" to open it) in an over abundance of caution.

I have been looking at your signature for a few weeks and I'd change "Also: There's usually a good reason why everyone does it that way" to "Also: There once was a good reason why everyone did it that way, that reason is not necessarily still valid". In my practice I see hundreds of "that's the company policy" techniques that are inappropriate for a given reservoir or downright dangerous in extant conditions.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

Now that you mention it, I also feel that "company policy" and even design codes, are in many cases all too often blindly misapplied to inappropriate situations, especially where knowledge, experience and understanding are lacking. By nature, standard methods of any kind can only apply to the most general situations. Design codes at least state that they give the minimum requirements and are not a substitute for good engineering design practice, knowledge and experience, but I don't see that statement on company standards. They are all to often applied to all situations that might just happen to look similar, without the help of even a seeing eye dog.

LittleInch, I can (usually) believe that 2 of anything is safer. I'm only saying IMO, 2 valves may be one too many safe. And yes, anytime a pathway to pressure is (almost or nearly) open, one should be expecting gas, no matter how many valves you have in line. More valves, more packing leak possibilities. In fact, most of the "closed" gas systems I have been around, gas has always been leaking from one source or another. Back in the day, it was the control valves and gas operated actuators that were powered directly by natural gas taken from a regulator attached directly to the line they were connected into that were the biggest sources of gas clouds. Once they used that gas power, they vented it in place. Most of that was eliminated in the late 80s, early 90s to reduce sources of lost gas, and supposedly ie. greenhouse gas emissions; not really having anything to do with safety, although that was obviously a complementary result. I think the real driver was the cost of gas lost in that manner, as it was a bit expensive at the time.

Agreed that balance lines won't often break the budget, but let's leave that argument to the bean counters and concentrate on technical reasons.

As always, I do respect everyone's opinion, but I am not going to want to conform to a philosophy if I don't understand and believe the logic behind it. I'm pushing this thread to the max, so I and all readers can get the benefit of experience, including yours, from all that want to contribute.

I asked zdas what BP is doing in the USA, because I know of his extensive experience there with BP and his answer now allows me to deduce that BP could be using double valves in some places, because they think they are required to do so in the North Sea, rather than actually being the result of some analysis that they developed on their own accord. Why else would they be doing this in the North Sea, but not in the US?

The problem just got bigger for me because now it appears that the wide variations in implementation of the "10-100 bar double valve policy" across companies is even worse than I thought previously, not even being standardized across the same company. Now that I'm pretty sure that the logic is not applied uniformly in the same company, this is becoming a hole so large that I don't think I will be able to understand at all. In fact, the farther I go with this, the less logic there appears to be.


I hate Windowz 8!!!!

If they are going to put the spec blinds in, at least put them in the open position.

Snorgy ... that's a good one.

I think I saw yesterday that the BP standard wants hard-seated valves too.

I hate Windowz 8!!!!