Leaks on threaded fittings.
Leaks on threaded fittings.
(OP)
Is anyone familiar with the code implications of welding over threads as a means of leak control? It obviuosly limits reuse but I have seen it done. I have an application with a SS tank with 2" inspection ports that are a problem. The pressure is 550PSI and the temperature cycles from 20°C to 220°C.
Thanks for any help.
Thanks for any help.





RE: Leaks on threaded fittings.
RE: Leaks on threaded fittings.
If you do have to weld the threads make sure you cover any threads, don’t leave a notch. Make the transition as smooth as possible. The AI has always concurred though at times he has suggested a complete rework of the connection eliminating the threads.
SS threads don’t like high pressure if there is a temperature cycle as in your case
RE: Leaks on threaded fittings.
We require all threaded connections to be seal welded where I work. There are a few issues to be aware of with B31.3, such as noting that the seal weld shall not be considered a strength weld, no thread compound should be used on joints intended to be seal welded, etc. Look up "seal weld" in the index for specifics. As long as you stay away from high pressure piping (sections K...), which you are, you should be ok.
If you have a situation such as a threaded half coupling nozzle on a heat exchanger with an extended body valve screwed into it then you could get into an argument regarding the seal weld and Section VIII vessel repairs/alterations. Our perspective, seconded by our local AI, is that the joined threads are the sealing surface which define the Section VIII - B31.3 interface. The threads (and edge of the coupling) which are being seal welded are considered to be in the domain of B31.3.
jt
RE: Leaks on threaded fittings.
As I mentioned in my previous post, its worthwhile to go to the index and read the noted sections... Thats part of why I like to participate in this forum - it forces me to go back and research and understand more about things which we just consider a standard procedure.
jt
RE: Leaks on threaded fittings.
From your 2 posts you seem to be implying that seal welding threads is REQUIRED by B31.3. What the code says is that if you're GOING to seal weld threads, then all threads have to be sealed.
RE: Leaks on threaded fittings.
RE: Leaks on threaded fittings.
I did not mean to imply that seal welding is required. I agree that B31.3 simply puts some guidelines on seal welding if that is what you choose to do.
jt