effect of re welding on stress analysis

[irfan202]

Dear All

Did cutting & re welding is effecting stress analysis of steam line ASTM A335 weld P91. if you have any standard reference for cutting & re welding of piping system kindly specify.

Regards

 

[pennpiper]

Your question does not give enough information for us to offer an answer.
1). What size and schedule of this line?

2). What is this line connected to on the upstream end?

3). What is this line connected to on the down stream end?

4). What is the normal and maximum Operating Temperature of this line?

5). Was the routing/configuration changed?

6). Was the one or more dimensions altered? If so, how many and by how much? Were these dimensions increased or decreased?

7). What was the reason for this alteration?

 

[irfan202]

1). What size and schedule of this line? Line Size 200 Sch 80.

2). What is this line connected to on the upstream end? turbine main stop valve.

3). What is this line connected to on the down stream end? for HRSG Boiler

4). What is the normal and maximum Operating Temperature of this line? 132 BAR, 567 Deg C

5). Was the routing/configuration changed? No

6). Was the one or more dimensions altered? If so, how many and by how much? Were these dimensions increased or decreased? by cutting 3 Meter portion shall be removed for steam blowing and re instate after steam blowing by welding.

7). What was the reason for this alteration? Steam blowing purpose.

 

[pennpiper]

If I understand the situation correctly you will be blowing the steam to atmosphere and then you will return the piping to it's original configuration. Is that correct?

If it is correct then I would say that you do not need a new Stress Analysis and I don't think there is any standard reference beyond common sense for cutting & re welding of piping system.

 

[BigInch]

If the repair was made within the approved methods of repairs provided in the design code, no additonal stress analysis is reqired.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[StevenHPerry]

It is conceivable that the engineer may have considered a derate at girth welds since the temperature makes creep a significant factor. I believe such a derate is or was required by ASME B31.3, but I haven't seen it required in B31.1. Just because it is not required doesn't mean it was not done though. Other piping codes may have similar requirements.

So, adding a girth weld may affect the stress calculations.

What's the harm of notifying the engineer of the change? What's the risk of withholding the information on a 132bar steam line?

Communication is not a bad thing.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[irfan202]

Again, Another Issue is if we cut the joint and make the bevel again for re welding than our gap for welding is going to be increased by 4-3mm. it means inertial we maintain 2mm gap, but after cutting and re welding gap is going to be increased and it become 6mm normally.

this will effect the piping integrity or this may cause to increase the stress in piping system?

 

[BigInch]

Most owners won't accept such a repair, even if the code would, and require that the segment containing the weld be cut out on both sides and replaced with a new section in its entirety.

If it ain't broke, don't fix it. If it's not safe ... make it that way.