Fillet weld size in a Gate valve´s vent line.

Date 07-17-2015 17:54

Without specifics of code, materials, etc, this is going to be the best wag.
http://www.twi-global.com/technical-knowledge/faqs/process-faqs/faq-how-do-you-determine-the-minimum-size-of-a-fillet-weld/

By Superflux (****)

Date 07-17-2015 20:13

Octavio,
WHY do you think this is a fault of the weld size?
WHO welded the 1" line??
Was it from the factory or a field modification.
It's more of an engineering question that is a bit beyond simple weld size.
For instance,
1) How thick is the valve body and pipe wall?
2) Are there any thickness variations near the weld?
   A) Is this just a piece of pipe stabbed into a hole on a valve body?
B) Is there an integrally reinforce fitting involved?
   If "A" above, then the missing material from the hole has to be replaced and is sometimes accomplished with an oversized fillet weld.
Which is why some clever engineer invented the IRBC fitting.
Crack in center of fillet weld... hmmm...
WAY too many variables involved and my questions are:
1) is weld profile correct?
2) fit up tolerances OK?
   3) is proper filler metal used?
4) preheat and innerpass temps correct?
   5) Impurities/contamination in the weld?

BUT! The real issue is your question and the addressing of the crack. And that IS NOT due to an improperly sized weld. When a weld cracks, there are forces fighting each other. It is most likely either a process/procedure problem or welder skill problem.

By Octavio Date 07-17-2015 23:00

Hi Superflux,
you have giving me a lot of things to think of, and I am very grateful for people like you.

Yeah, the failure might not be just due to the fillet size, and you mention the other probable root causes. You might agree with me that the fillet weld size has something to do with its resistance to internal pressure, I mean, a formula or equation should exist to calculate the fillet size based on the internal pressure.

On the valve. It is a 36" class 600, double expansion gate valve, trademark is valvitalia. The niple is socket welded to the body or shell of the valve. The shell (A105) is about 2.88" wall thickness and the 1" niple (a106) is 0.250" wall thickness. the fillet weld was produced with a SMAW process using E7018-1 rod.

I would love to send you my report if you let me know you email adress. in that report I have put several pictures of the crack...yuo would like the pics in it...

Any further help will be highly appreciated.

Octavio.