Can removing fillet weld from outside a pipe cause stress concentration?

[invent11]

In our plant there is an anchor support that we would like to convert it to a guide. Support is made of a vertical HSS254x254x8 welded to a base plate which itself is bolted to concrete floor. A 6" CS standard horizontal pipe going through this HSS (thru 2 holes) and welded all around to it by a 5 mm fillet weld. I suggested that we cut the fillet weld (by grinding or cutting) and remove the HSS and change it to a guide support. However concerns raised that fillet weld removal can take some of the wall thickness and therefore would be a source of stress concentration. I would like to know how much this concern is valid and if so how we can address this concern. Pipe carries water at 800kPa(g)/ 0-35 deg C.
Finally due to other limitations cutting and replacing that section of pipe can be very difficult and expensive task.
Thank you in advance for your inputs.

 

[racookpe1978]

Please provide a sketch or photo of the current installation.
It is unfortunately not clear from your description.

Grinding out a fillet can be done with little effect on the pipe wall IF - big IF - there! - it is does carefully by a competent fitter or welder. Done poorly by a bad welder or fitter, yes, it can scar the pipe walls. I have supervised many such cuts properly. Have done many myself properly.

 

[danschwind]

I agree with racookpe1978. If done by a competent worker, it can be done.

You could also remove the existing support (without actually grinding down the existing welds) and offset the installation of the new support upstream or downstream of the existing support if you have available space for that.

 

[Rputvin]

racookpe1978 - it sounds like a 6" pipe is passing through an 8mm (0.31") thick plate and has a circumferential fillet weld at the penetration.

What is the pipe schedule and corrosion allowance? 800kPa = 116psi, 35°C = 95°F. If this is Schedule 40 6" pipe you should be well enough above minimum wall thickness, even with a moderate corrosion allowance.

Is the service actually inclusive of 0°C water?

 

[racookpe1978]

Now, the unstated "other option" - and it may not be valid since we don't have a photo yet of the actual pipe and pipe weld! - is to cut out the support plate around the fillet (away from the pipe itself) leaving a ring on the pipe that is not connected to anything at all. Use a plasma cutter or oxy-acetelyne torch.

Requires the replacement support be already built, or a temporary support be used during fabrication, but that's probably not a big issue.

 

[invent11]

Thanks to all the feedbacks the last response to leave a ring round the pipe and not grinding off the weld will work for me

 

[Dhurjati Sen]

Dear invent11,

A thumb rule - if the welding did not require PWHT, weld removal is NOT an issue.

If you think the grinder has inadvertently removed excess material, weld build up to the desired thickness would be required.

Leaving anything unnecessary on the piping has the potential to cause future external corrosion. Be sure that this does not take place in your case.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen