lap joint - can I weld the stub end to a socket weld fitting?

[rafal2015]

Hi,

I've got an application with a limited space. I wonder if it isn't against any design rules to weld the butt weld end of a stub-end of a lap joint fitting directly into a socket weld fitting (instead of normal butt weld to a pipe)? This is a 1'' size connection in 700psig steam service.

Thanks for any advice

 

[racookpe1978]

Draw a section view of your proposed solution - To scale. Include the welds as physical sizes.

 

[moltenmetal]

Depends on the length of the stub end and the thickness of the backing flange. Yes, you need to draw it to scale- then plot it to scale and show it to your welder and ask them if they can fit their TIG torch into the gap at the correct angle to actually complete the weld.

 

[rafal2015]

Thanks moltenmetal, so there is no rules in B31.3 or B31,1 against doing that?

 

[moltenmetal]

None that I'm aware of. It's more a practical matter which depends on the factors I've noted. I would want to see the lap joint stub end long enough so it can be inserted fully into the socket, then pulled back the required amount just prior to welding- that pre-welding gap is, unless I'm mistaken, a code required minimum. There is no code requirement for a gap to exist after welding though- that has been discussed here before many times...

This is different, say, than inserting a plain butt-welding elbow or tee into a socket-welding fitting, where the radii of the fitting results in an asymmetrical weld when the part is inserted into the socket to the correct depth and hence is considered bad practice. Again I'm aware of no prohibition against doing what I just mentioned in a particular section of B31.3, but it's not something I'd ever do in code piping personally. In those cases, special "long-land" elbows and tees can be procured for the job, or else a pup piece of pipe would need to be added to the fitting.

 

[rafal2015]

Thanks for your advice moltenmetal
Regards,
Rafal