Pig Launcher/Receiver Kicker Line

[DGrayPPD]

All,

I have a question regarding pig trap kicker lines. I'm getting ready to design my first pig launcher/receiver, and I'm trying to review my practices and standards before I get started. As I understand it, for pig launchers, the kicker line should be placed as close as possible to the end closure. For pig receivers, the kicker line should be placed as close as possible to the reducer.

My question is, if the pig launcher/receiver is to be bi-directional, where is the optimal placement for the kicker line? My first thought would be closer to the end closure to be sure that the kicker line can assist in launching the pig from either direction, but I've seen some articles that state the kicker line should be placed in the middle of the barrel.

Thoughts?

Thanks for the help.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[LittleInch]

I've come to the conclusion after decades of doing this that it really doesn't make much difference and the quantity of opinion about where to place a kicker line is vastly in excess of any actual testing, reality or operational experience.

I tend to design all mine now with the kicker line in the middle. One design suitable for every possible option.

On launching if the first cup isn't tight into the reducer then it matters not a jot if the kicker line is one end or the other, the pig still won't go anywhere.

ditto on arrival the pig will either stop dead as soon as the last cup escapes the reducer or it won't if the velocity is too high. Having your kicker line at one end or the other also makes no difference.

Please please please make sure the pig traps are designed flat. Slopes on pig traps are the work of the devil.

and try and get your kicker line to be 50% of the size of the main pipe. absolute minimum 30%.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DGrayPPD]

LI, thanks for the input.

I've got 2 pairs of launchers/receivers to design. One is a Class 600 system with a 16"x12" major to minor barrel transition and the other is a Class 900 system with a 24"x20" major to minor barrel transition. Both will definitely be designed flat. The kicker line for the 16" is 6" and the kicker for the 24" is 10".

On similar designs in the past (when I was still a newbie and didn't assist on) they placed the kicker line roughly in the middle too it seems, so I think I'll follow a similar approach.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[georgeverghese]

Good that you are thinking about these things most people wouldnt. Guess a lot depends on the length of the pig device. If it is short, kicker line tie in at the middle of the barrel would be okay. If you have a long linalog intelligent pig, you may have to make the barrel longer if you want the kicker line tee off at the middle if you want this barrel to be in bidirectional service.

 

[PMaginot]

I concur with LittleInch, I typically leave at least a 1.5 foot pup between the kicker and the trap door, on which I install a high point vent and low point drain. I also install a high point vent and low point drain as near the trap inlet valve as practical, so that both sides of the pig can be confirmed to be depressurized before opening the trap.

 

[DGrayPPD]

georgeverghese,

Thank you. The questions are currently out on what type of pig, how long is the pig, and how many pigs do they anticipate at once. Once I know that, I'll be able to verify if my barrels are long enough.

PMaginot,

My current design follows a similar approach, with a 2'-0" pup piece between kicker tee and closure, along with all other vents and drains.

Thanks for the input.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[SunnyOaks]

Don't forget to verify there is nothing between the launch and catch that the pig won't fit through in the P&ID!

 

[georgeverghese]

This point re installing vents on both sides of the pig from @pmaginot is a safety critical - I recall an incident many years ago which resulted in a fatality in SPDC, Nigeria where a pig shot out of the barrel due to trapped gas on the upstream side of the pig.

 

[itsmoked]

where a pig shot out of the barrel due to trapped gas

Rather like opening a torpedo tube hatch without running a drip-spigot test.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LittleInch]

Unfortunately these incidents keep happening.

I have knowledge of more than this, but its often difficult to get good information out of operating companies.
for design you need to be able to de-pressurize all parts of the trap regardless of where a pig might be.

https://www.ncbi.nlm.nih.gov/pubmed/15553280

First incident here:

http://www.pngrb.gov.in/pdf/ERDMP/Analysis of incidents reported to PNGRB from april to june2015.pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DGrayPPD]

The current P&ID layout for the launcher is shown below. Still waiting on answers regarding the pigs themselves.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[LittleInch]

You really need have a pressure balance line from as close to the motorized valve as possible to somewhere on the major barrel.

On a launcher this is so that as you pressure up the trap, both sides of the pig ( which is jammed into the neck of the trap) pressure up at the same rate and have the same pressure. Otherwise your pig can start to move down inside the minor barrel and end up jammed against the valve. This is not good.

Just remember to close the balance line before you start to pig.....



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DGrayPPD]

LI,

I will bring this up and see what the higher ups have to say.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[LittleInch]

Hmmm,

Unfortunately there is no standard for these items and you will see many and various ways to design them unfortunately.

However if you can explain why something is done a certain way then it hopefully makes sense to those who review and approve.

Also missed it first time around, but I've never seen a barred tee inside a pig trap before.

I realize this is for a launcher, but a 2" drain is quite small. It will take a long time to drain under gravity only and on a receiver could very easily become blocked with debris. Min 4" is much better.

Do you have a pressurizing loop somewhere? Just having a 6" valve on the kicker is a bit brutal when it comes to filling it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DGrayPPD]

Here is pretty much the entire P&ID besides the pipeline going off the page.

I asked about the barred tee inside the pig trap, but they seem to have concerns that the pig could somehow get snagged a little in the branch without the barred tee. I also asked about the balancing lines and was told the intent is to hook up temporary connections to the 1" valves around the MOV's and balanace out the pressure that way. The company we're doing this for seems to try and keep all their pig traps in a similar layout to what you see below. I also don't really have much impact on the sizing of the 2" drain.

All other questions above, I'm still waiting on answers for.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[LittleInch]

Hmmm,

Like I said there are as many different ways of doing this as there are pig traps, but this seems to be a particularly poor design.

Relying on make and break to install hoses and valves is not good practice and I can't quite work out how the drain line connects to the relief or vent lines?

Is this liquid or gas?

The barred tee thing is pure nonsense, how anything will get into a nozzle which is pouring gas or liquid into the trap is beyond me.

The equalization of pressure or filling with liquid across the pig is a key issue - how are they planning to do that?? Asking for the operations procedures might shed some light on it. Or asking a few operators.

I'm sure they will say "we've been doing it this way for xx centuries and it works fine", but that doesn't mean it is the safest and operationally correct way to do it.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DGrayPPD]

You nailed it with that last sentence. "We always do it this way" or "We just copied what they had out there" seem to be the responses I get for most of my questions.

I sat down with the lead process engineer to walk through the P&IDs and get a better understanding of what each line and branch was doing so that I could design it properly and half the branches, when asked what they were for, the response was "Um, I'm not sure. We just copied their existing P&IDs and they had them on there." At which point I respond with, "Well how do you expect me to design this system without knowing what each line is for and knowing the correct way to orient the branches?" The process design and operation philosophy may be flawed, but that doesn't mean my piping should be.

From what I am told, the project consists of traps for liquid ethane, butane, and ngl lines. I think they're expecting the ethane and butane to flash when they open the valves. NGL they're still working out.

I agree with the barred tee issue. I don't understand their logic on that one. Especially when the pig should be getting shoved past the tee to the reducer to begin with.

This is probably why you've seen me ask so many questions over the years on here.

"Thinking is the hardest work there is, which is probably the reason why so few engage in it."

-Henry Ford

 

[LittleInch]

You have my sympathy.

A good place to bring up these issues if you can't sort them is often the HAZOP, especially if you can get an operations person in there to explain how they do it in practice.

Will probably raise a few actions....

I'm at the point where I can tell people how it should be done and impose my will on the design. It takes time.

Pigging is a misunderstood process a lot of the time but needs to be looked at closely.

My opening gambit in a HAZOP is that this is a potential full bore rupture which you are intentionally doing. Get it wrong and people die.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Vaguely recall there is a max nozzle size limit beyond which a barred tee is required for piggable lines, but I dont recall it now. Could be DN100??. Agreed, we used to have a kicker line bypass for pressurisation purposes also. Where the pipeline is in 2phase operation with a slugcatcher downstream of the the pig receiver, a slug control valve is installed on the kicker bypass for slugcatcher level control. Obvioulsy, LTCS would be in order as MOC for these pig launchers / receivers for unstabilised NGL, ethane, propane. maybe not required for C4.

 

[LittleInch]

The usual ROT is 50% branch size to main line when you need a barred tee but I've never seen one on a pig trap before now.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.