Leaks on underground pipe flanges 2

[Tumza12]

I've been recruited to conduct pressure test at a site. During the tests it was clear that we were loosing pressure at all the sections we tested. The was leaks on all flanges (i.e on the bolts). I need to know which method to use in order to stop the leaks permanently. One other problem is that I have no idea what causes the nuts to loosen. NB the flanges are not wlded... Help.

 

[pennpiper]

The subject of your posting is"
"Leaks on underground pipe flanges"

And you wrote:
"I need to know which method to use in order to stop the leaks permanently."

This is really very easy. It is never a good idea to have Flanges buried underground. Cut out all the underground flanges and replace them with pipe butt welded in place.

 

[cvg]

come on, flanges are used in buried service all the time and replacing them with welded is not necessarily the best solution. However without knowing anything about the project, not the pressure, type of pipe, product in the pipeline, type of flange or any particular QA/QC measures that were already followed in either the manufacture or the installation of the pipeline, it would be very difficult to recommend a method for repairs. I doubt that "nuts are loosening" is the cause of the leaks. Perhaps more likely the nuts were never properly tightened?

 

[DLite30]

I'm going to make a wild assumption and say that you're really talking about "flanges" on below-ground bolted-body valves (such as Grove valvles), Or you're talking about Dresser couplings.

 

[11echo]

Buried flanges are leaks waiting to happen! ...Unless they are accessible for maintenance. I've been in this business 35 yr.s now and I see it all the time.

 

[BigInch]

I could say the same for above ground flanges too. Actually no flange is highly desireable, but for some idiotic reason, manufacturers won't stop making them.

In other words,

All flanges are a necessary evil. Sometimes the evil is above ground, sometimes below. Wishing away the evil usually doesn't work.

 

[11echo]

YEAH BUT ...when they are above ground, you know where they are, you can quickly determine "IF" they are leaking, and normally they can be fixed fairly easily! I can't say the same for them underground.

 

[rconner]

Basic concepts and applications of bolted flanged joints are of course now hundreds of years old. I am even aware that one sizable and lengthy cast iron pipeline, with a great many flanged joints, has serviced pretty much uninterrupted and well in France for more than 300 years! That being said, the assembly of flanged joints has always been labor-intensive, and for much of their general service history their performance also somewhat labor and effort reliant. This is particularly true when rather unforgiving flat (and not "special sealing design" gaskets were employed). I have read an old dusty, published book entitled “Cast Iron Pipe” dated 1914 from United States Cast Iron Pipe and Foundry Company that additionally made the following statements in discussions of buried piping joint types, “Flanged joints were found unsuitable for underground use because the connecting bolts had but a limited life and because the line when bolted up proved too rigid, for pipe lines laid in earth must possess a certain degree of flexibility to compensate for subsidence of the supporting soil. In a long line of pipe, provision must also be made for expansion and contraction due to variations in temperature.”
I’m not really sure what has changed in the last near 100 years since this was written, unless it is that gray cast iron pipes have not been furnished in the USA for more than three decades, and some folks have attempted to use in more recent years for buried service some quite expensive stainless steel HHHN bolting in place of old wrought iron etc. (and some of these SS bolts have exhibited thread “galling”, characteristic of some such materials, that even exacerbates leakage problems due to imperfect assembly and/or alignment/soil support conditions etc!)

 

[BigInch]

11echo

No argument, however you appear to assume that there is some choice involved in selecting to use, or not to use, flanged joints under ground and that choice (not to) somehow depends on the difficulty of seeing a leak when they are UG. In my experience, there is not a choice involved when a flanged joint is used underground (or above ground for that matter). You use flanged joints simply because you have no other practical alternative for that particular joint. If you need a flanged joint AG, or UG, then that's where a flanged joint goes, so I think it's kind of irrelavent if its more difficult to determine if a leak exists, no matter where the flange happens to be. I've never put a flanged joint above ground just so I could more easily see it leak ... if you get my drift.

 

[zdas04]

I've operated gathering systems for a couple of decades and I don't hate buried flanges. Yes they do serve as an anchor point, so I want a few joints of pipe on either side of them to allow for expansion and contraction (every pipeline I've ever laid has had a large number of overbends and underbends to match terrain, so I have no concern about expansion and contraction putting the pipe in compression or tension).

I've dug up flanges that have been in the ground for 30+ years without leaking. They have long-lived spiral wound gaskets, but I wouldn't be terribly worried about other sorts of gaskets. I've never repaired a buried flange-face leak on a gathering system (but one time I had a leak that was in the body of a tee that had flanges on two sides, the flanges were fine, the tee was junk). I make sure that the to-be-buried flanges are exposed during the static test, I've found a few that leaked until they were properly made up.

I work with a lot of companies that have hard and fast proscriptions against buried flanges. Their reasoning is always "policy". People don't question policy decisions today like they did in my day, so I bastardize my designs to accommodate the policy and grumble all the way to the bank.

David

 

[BigInch]

I don't know of a petro/gas pipeline company that prohibits UG flanges. They know that sometimes you don't have a choice.

zdas, Instead of using joining flanges for anchors, use an anchor flange. Its just a double weld-neck flange. No face to face and no bolts.

 

[unclesyd]

We have 3 of the Mark Helium Detectors that have been used to detect leaks. Inside our manufacturing area we use Ultrasonic for detection.
There are a number of portable He detector's on the mark now. We subbed out the Ultrasonic leak detection to a testing service.

http://www.ashtead-technology.com/us/Environmental/Content

/LeakDetectorSG.html

 

[BigInch]

Good point. You don't necessarily have to even see them to know.

BTW I can't access that link.

 

[rconner]

I first heard of the “helium” method more than 30 years ago (I was told then it was used very successfully on a project along with a “sniffer” to find leak on a deep line in porous soil, when leak would not “come up”. Have heard more contemporarily it can now be some pricy. Link that worked for me, to apparently a detector used for same, is

http://www.ashtead-technology.com/us/Environmental/Content/LeakDetectorSG.html

).

 

[unclesyd]

You can use the Mark for tests of other components on a routine basis,like some of our large jacketed SS equipment that undergoes high cyclic stress. After we ok the vessel with a mass spec, Edwards, Leybold-Heraeus, high dollar machines. From this point on we use the Mark He detector at each overhaul We use Therminol heat fluid vaporized at 290° C to heat the system. Since we started using the Mark in 1995 we have not had a Therminol leak to the process side.