6 replies to this topic

[R NESAMANI]

Dear all,
I am working in Natural gas pipeline. In one of the pipeline flange (20'' dia) gas leakage exist for the last 6 years. Leak is in between 3 bolts of the flange.
Leak increases with the increase in pressure. Gasket is spiral gasket.
Operating pr. is from 55 to 75 Kg/cm2.
My doubt is we are planning to tighten (slowly) the flange bolts.
Whether the leak will stop...? any risk in doing so...?

[kkala]

Look at http://www.furmanite.com/services/on-line-leak-sealing-repair/on-line-leak-sealing-repair/, reporting the possibility of on-line repair but not saying how!
There are numerous specialized companies to repair leaking flanges on-line, e.g. http://www.tapmasterinc.com/NaturalGas.html, probably all over the world where gas pipelines can be; however no tangible explanation has been seen.
Googling can reveal more companies and probably specific explanations. Sorry for not having experience, hopefully experienced members could be specific. Possibility of on-line repair seems to exist.

Edited by kkala, 17 August 2012 - 10:59 AM.

[ankur2061]

Nesamani,

If the gasket is unevenly pressed or is damaged, tightening will not help. It will worsen the leakage. If you plan to tighten the flange do it using a torque wrench using the right torque settings. The sure way of rectifying the leakage is to isolate the pipe section containing the flange, depressurize, unbolt the flange, remove the old gasket, clean the flange faces to remove sticking pieces of the old gasket, provide a new gasket and tighten the bolts (cross- bolts i.e bolts 180 deg apart) using a torque wrench with the correct torque settings.

Regards,
Ankur.

[breizh]

Nesamani,

No option ,you need to stop and fix the problem by replacing the gasket before damaging the flanges !

Hope this helps

Breizh

Edited by breizh, 17 August 2012 - 08:17 PM.

[Art Montemayor]

Nesamani:

Pay careful attention to the information offered by Ankur and Breizh, and heed their advice.

I can tell you from personal field experience that it is a very dangerous procedure to apply torque to pipeline flange bolts in excess of that prescribed for the load. More things can go wrong than can go right.

When you apply additional torque to the flange bolts in the field, you are assuming that the correct bolt and nut were installed on the flange initially and that the alloys involved can take the applied stress. While you may be correct in your assumption, there is always a possibility that the quality of the bolts and nuts on the flange are not appropriate for the application or are defective. You have no available way of proving otherwise. Therefore, the situation is one of "trust" in whoever it was that installed the flange assembly and torqued it initially. And I am willing to bet that you have no way of knowing who that person, entity, or organization was - and what's more, you probably do not have the installation report together with all commissioning and testing certifications on that joint.

One potential reason that you are experiencing leaks may be that the bolts/nuts are not the correct alloy and the applied stress has deformed them and that is causing the leak. If you apply further stress to the bolt/nut threads, you could provoke a material failure and rupture.

Therefore, I cannot allow myself to stand by and not alert you to the fact that doing what you propose is a calculated risk that is not worth taking and that it could result in a major, fatal accident. Please don't do it. Heed the warnings.

[kkala]

The flange leaking has been occuring for 6 years, indicating trouble in isolating the flow in that part of the 20" line to replace the gasket. Is it online leak repair / sealing impossible? Or probably not practically feasible? Furmanite and others report this possibility (post No 2), but I do not have experience to assess it, having actually no idea on how it could be realized.
Advertised "special bypass capabilities without system shutdown" makes me think of isolating a short pipe around the flange, but is it possible without preinstalled valves? This might not be the only way of online flange leak repair (if any).
Local Natural Gas Company can theoretically stop gas supply for 24 hours yearly, yet this would have serious implications. Local high pressure pipeline does not have loops. I suppose an online repair of some leakage could be a way out, even if it were expensive.
Any advice on this possibility (positive or negative) from experienced members would be welcomed. It could also be a way out concerning this query.

[ankur2061]

Nesamani,

In most long distance gas pipelines there is a phenomenon called as line packing where the line packing time determines the availability of gas for a certain duration of time albeit at a reduced pressure. Recently I encountered a long distance gas pipelines of approximately 100 km length and 32" sizewith operating pressures of 55-60 barg with a calculated line packing of 8 hours.

Line packing allows depressurizing of section of pipeline having sectionalizing valves to be depressurized for short periods of time to do any maintenance work without stopping gas supply such as correcting flange leakages.

Hope this helps.

Regards,
Ankur.