Pig Valves Experiences in Low Pressures Natural Gas Pipelines 1

[hianbotech]

Right now, We are designing a Natural Gas Gathering Pipelines from different oil produced clusters. In the actual design we are considering use pig traps in the main trunklines, but we are thinking to use pig valves for some branches (economical reasons). However we have not had experience with these kind of Valves, only vendors references.

The question is knowing the experience with this kind of pig valves in similar services, instead using pig traps. These valves are safety?. How is the recommended instalation?. There are some pressure restriction for using?.

The conditions of the Gas Pipelines will be: 58-100 psig and 67 - 131°F. The fluid will be Natural Gas. the pipe sizes are between 4 and 10 inches.

I will apreciate your help on this issue.

Best Regard, Hianbo

 

[jsummerfield]

The pig valves that I usually see are full-port ball-valves.

John

 

[hianbotech]

Thanks Jhon for your answer. We are considering the use of this full-bore-valves in the gas pipelines as you said in your message. However when I said pig valves, I refered a special kind of valves that can be used instead pig traps (launch and receiving).

This kind of specialty item permits a double block & bleed valve that can send or receive pigs, all in one only piece.

You can see the detail in this Weg page:

http://www.girardind.com/valves.htm

Best Regards,

Hianbo

 

[zdas04]

I've installed over 20 pairs of the Argus Pigging Valves. In the proper application I love them.

There are a few important points:
- the 8-inch valve costs more than fabricating a traditional pig launcher/receiver. The closure is so heavy that the davits never work right. 6-inch and smaller they work very well
- Try to install the receiver on a vertical-down orientation to allow the liquid to fully drain into the trunk line (that is also piggable).
- I've installed receivers with and without bypass valves and have found the bypass adds cost without adding much value.
- The launchers have zero dP. The receiver dP is flow dependent. If your gathering line superficial gas velocity is less than 100 ft/sec then it will be difficult to measure the dP across the receiver plate.

After everyone complaining about the first version, Argus changed the design to include a 1/2 inch vent valve and really improved the closure. In the early version the hammer closure tended to be really hard on the 1/4 valve (that we installed on the closure instead of on the back). Removing the closure without a vent valve gets too exciting.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[hianbotech]

I really apreciated your answer. It was very valuable for our design.

For the case of 8" pigging valves, Did you implement any special design for the closure like hinge, etc.....

Thanks againg..


Hianbo

 

[zdas04]

When I installed the 8-inch, Argus only had a rail system for moving the heavy closure. The rail system had to be installed in a horizontal orientation (which meant that the valve had to be put on a horizontal pipe run). Shortly after I bought 4 pairs they came out with a davit system that allows it to be put on a vertical pipe run, but I've never run one.

Regardless of which version, the closure is very heavy and it is impossible for most mere mortals to start the threads without a support system. Other than that I would install them just like the 6-inch.

For the price of the 8-inch pigging valves I would stick-build a conventional launcher and get the added ability of being able to run a wider variety of pigs (including smart pigs). I'm not real excited about smart-pigging 6-inch and smaller lines, but I've had a couple of instances where a smart pig in an 8-inch would have been worthwhile.

As an aside, last month a crew put a 4-inch receiver in backwards. It was the first time that I had failed to mark the flow direction with a magic marker (I wish Argus would stamp the flow direction or the plate location on the recievers). Generally I mark all of the launchers and receivers with a flow arrow but I got busy this time. On the launchers, if you get it backwards the operator has to remember to install the pig back first (no big deal), but in the receiver it is a big deal. We had a bunch of fun getting the line blown back down with a poly-pig in the line between the gas and the best vent.

David

 

[BigMac23]

All the Argus Pig Valves that I have seen had the flow direction right on the nameplate.

 

[zdas04]

I just looked at a nameplate on a 4-inch launcher and if there is a flow direction on it then it is written in some obscure Canadian hidden writing and I don't have the decoder light.

David

 

[BigMac23]

The nameplate on the valve has a box where they indicate flow direction. Your 4in launcher must be on an Argus 4" valve. It is indicated by FLOW: L--->R or L<---R.

 

[hianbotech]

We will ask to pig valves manufacturer the problem that you mentioned. Our Piping group is taking care of this issue.

Thanks again to Aavid and Bigmac23 for share your experiences.

Hianbo