Should the two isolation valves fot the pig barrel be DB&B valve? If yes, does any code state th 1

[CALGARY007]

I am working at an EPC firm. Just found some project use DBB ball valves for the isolation of pig barrel, and some project just use regular ball valves. I want know if this is regulated by any code or just by the client preference.

The pig launcher or receiver can see this link:

http://www.act-on.ca/acton/Product/pig_launching_&_receiving_trap.htm#top

 

[brimmer]

I don't believe there is a code requirement for these, in CSA Z662 for example, it is a matter of client specifications, but this has become the norm in Canada. I believe there is a clause for steam oilfield lines, section 14 that may require double block, always a good poractice to have these.

 

[zdas04]

What drek. Positive energy isolation is required for personnel protection during high risk activities (hot work, confined space entry, hot work in a confined space). That is it. To open a launcher barrel and have wisps of gas is not a horrible thing. I use trunnion ball valves for barrel isolation and kicker valves, and I've often argued that they satisfied the letter and intent of DBB, but that isn't why I use them. I use them because they work better in that application than floating ball valves. Adding a second valve and a vent (on both the barrel isolation and kicker valves) is just a waste of money.

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.

 

[CALGARY007]

Thanks for all the answers.
Carl

 

[SNORGY]

In Alberta, the "rules" by OHSA regarding confined space entry and positive isolation are, to some Owner / Operators, not perfectly clear. Most of the Clients I have worked for want the DBB valves, especially for isolation on the pipeline side, and a single ball valve designed and constructed as a "DBB" valve is typically specified. However, some Clients *interpret* that such valves do not satisfy either OHSA or their own (often more rigorous) requirements for double block and bleed and, as a consequence, they install two independent valves with the bleed in between. Even then, an exception is invariably made at the pig barrel because of the physical space and cost required for such an arrangement.

Other valves are sometimes used for pig barrel isolation: special plug valves and slab gates come to mind. These are not always DBB.

A lot of the gas we deal with is pretty sour and it doesn't take much of a leak across a valve to knock you down; but by that argument, the gas will be coming out the "bleed" anyway, and the Operator won't be more than ten feet away from it.

The most common arrangement that I have seen is a single DBB ball valve; whenther or not it is a trunnion or a floater ends up having as much to do with line size and pressure as with the DBB function.

 

[zdas04]

SNORGY,
Nothing I have ever said about DBB or pig launchers/receivers applies to your situation. I visited a plant outside of Calgary once and was amazed at the mountains of sulfur that used to be H2S. If I had pigging facilities on sour gas lines, the OSHA regulations would be the least of my considerations. It seems that everything an Engineer does in that stuff should have very careful consideration and checking, I'm really scared of that stuff.

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.

 

[SNORGY]

Hi David (zdas04).

Would that plant you visited have been Crossfield or Lone Pine Creek, by any chance?

In the '80s, just about every gas plant in central and southern Alberta blocked sulphur and subsequently remelted the blocks for truck and rail transportation. The view from the air looked like some gigantic child had tossed his yellow alphabet blocks all across the Province.

Agreeing with you, sour gas pig barrels and their operation are probably among the most risky pieces of equipment Operators face. Our typical sour gas composition, when sour, ranges from 10% to 35% H2S-in-gas (i.e., 100,000 ppm to 350,000 ppm). Probably the most dicey operation in these pipeline gathering systems occurs when people are trying to dislodge and move a hydrate plug through a section of line, creating an instant oilfield potato cannon effect. I have even heard of some folks who open up the closure, park a D-9 Caterpillar with blade at the now open end of the barrel, and open the pipeline isolation valve. To their credit, they *did* use a D-9, as opposed to something smaller.

 

[zdas04]

It would be Crossfield. Worked for Amoco in those days. I've done the "catch the pig in the air" trick with a track hoe bucket and a 20-inch mandrel pig. Hoe came off the ground on one side, and the $3000 pig madrel was bent like a kangroo's hind leg, but the pig missed the compressor station.

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.

 

[Krausen]

I believe this an area clouded with confusion in industry. I've worked with 25-yr experienced oil & gas PEs that do not clearly understand the nuances between DBB vs. non-DBB vs. DIB (Double Isolation & Bleed) valves. To make matters worse, some valve manufacturers will stamp "DBB" onto their valve bodies just to satisfy purchasers and sell more product it seems.

The latest API 6D spec defines the differences between these designations very clearly for anyone who will take the time to read it.

 

[BigInch]

It is client preference, unless different products on either side are incompatible and may be dangerous if mixed, or if there is a reason that no product should ever leak across the valve when it is closed (when it is going to a meter statin for example). No code specifies when DBB is required, or when it is not.

Independent events are seldomly independent.

 

[Aamir3354]

A DBB (Double Block & Bleed valve) which has 2 x Ball valve can used to suit your requirement.

These DBB comply to ANSI B16.10 Face to Face Sizes while providing double-block-bleed. Apparently, Oliver Valves has a DBB pig launcher and receing system which has minimal foot print.

Regards,

Aamir

 

[zdas04]

Aamir,
Every one of those I've ever seen has had reduced port valves in the body--not good for pigging. I've also seen a few that had the ball offset from the centerline to reduce space--again not very desirable for pigigng.

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.

 

[Aamir3354]

Zdas04,

These are true full bore and ball are inline for pigging applications.

I guess sizes are limited to 8" 2500# full bore with manufacturer.

I can send some literature , if u wish!!

Regards,

Aamir