welding pre-straint pipe

[millimeters]

I am working on a project that underground gas pipe strained less than %1 due to ground movement. In order to weld an sleeve, do we need to due stress relief? Thanks for your inputs

 

[racookpe1978]

How do you know it is strained 1%, and where is that "strain" located?
Why do think the strain will not re-occur after continued ground movement, if it has already happened once?
And where would you propose doing the stress relief?

 

[millimeters]

Thanks Racookpe, analyzing data by FEA reveals that we have deformation and axial strain is less than %1 and close to tensile strain capacity. Deformation caused compression in top and tension in bottom. Deformation located in girth welded area but it passed the inspection and no defect reported. In order to get certain level of insurance we may reinforce the area by sleeve. Welding on strained area concerns me and I am thinking to stress relief only the area we want to fillet weld the sleeve ( to the width of 5 inch each side). just wondering if stress relief is common in pipeline system? any reference for the time and temperature?
Thanks

 

[LittleInch]

I'm struggling to understand what you're doing. You analyse a piece of pipe by fea, presumably because it has moved down due to some sort of ground movement and you've calculated less than 1% strain. This is less than you get for a 40D cold bend and no one cares about that. I've never seen a normal pipe be stress relieved by heating and then cooling slowly unless you have quite thick pipe. You need to make sure the weld was properly ndt tested and if so I would just make sure the pipe can't move again and leave it be. 10% strain maybe, but doing this for 1% seems completely unnecessary and welding a sleeve just creates a stress Change at the sleeve weld and could lead to a different failure if ground movement occurred again.

In short I think you're solving a problem which doesn't exist and in the process creating some real problems.

Just my view, but from the low amount of info offered so far that would be my input.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[millimeters]

thanks littleinch. we were told by consultant that this amount of tensile strain might be close to tensile strain capacity depends on the size of flaw in girth welded area and they agree to weld a reinforcement sleeve. Pipe is 414 grade, 30"OD X 9.5 mm.

 

[BigInch]

B31.4 strain limit is 2%

Independent events are seldomly independent.

 

[LittleInch]

I still think you're creating a bigger problem by creating a stress point at the ends of your sleeve. If they are that worried about it you are far better to cut it out and either re-weld or put a pup piece in.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way