Repair for a Thermowell

[engrpiper]

Can you weld a 6" sch40 pipe cap over a hole (removed thermowell) in a 10" Sch40 pipe. Area reinforcement for a branch connection per B31.1 is provided without adding a reinforcement pad.

Is a branch spool piece required between the 10" pipe and the 6" cap?

Thanks for your replies!

 

[hacksaw]

better to address this to the ASME Codes forum, B31.1 is strictly interpreted especially where pipe repairs are involved

 

[pennpiper]

Engrpiper,
Why don't you give us some background on this question.

What is the material?
What kind of TW was it (welded, threaded or flanged)
Why is the TW being removed?

We can be of more help if we know some of the details.

 

[engrpiper]

Material: A335 P11
Weldolet with threaded TW
Service: steam 300psig 835F
The TW is redundant.

The fillet weld on the weldolet to pipe cracked. After removing the weldolet dye penetrant showed cracks extending out into the 10" pipe. Cutting a 5.5" hole will remove these cracks. I am planning on making a 6" branch connection (6" length) with a pipe cap to dead-end the branch. I am being asked if we can simply attach the pipe cap.

Thanks for your replies.

 

[BigInch]

Did anybody look into the line stresses at that point to try to figure out why the weldolet cracked and the cracks extended into the 10" pipe. Unless you're PDS its a low stress point, you need to cut out about a 1 meter section of the 10" pipe and replace that completely. Otherwise I think you'll just be looking at cracks extending into the repair quite soon.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[metengr]

Was this a stainless steel thermowell seal welded and threaded into a Cr-Mo weldolet?

 

[hacksaw]

if the weldolet is F11 it is difficult to see how thermal mismatch would cause cracking in the adjacent pipe.

As a redundant well installation, if the primary well is hazard free, then it sounds like a weldment issue.

 

[engrpiper]

Let me catch up.

BigInch
Yes - a stress model has been completed and three new hangers are being installed. The original design (30 years old) had a rigid rod on top of an elbow that wanted to lift up. Someone at the plant saw the bent rod and determined that a new "bigger - better" rod (2" pipe) needed to be installed to keep the line down.

metengr
it is cr-mo - No disimilar thermal expansion

hacksaw
The other well crack earlier (late last year). Conducted a stress review then and designed the three new hangers. Before the unit came offline the second TW crack open and leaked steam for a week or two.

I am comfortable with replacing the TW with a branch connection (small spool piece and a pipe cap). Just not sure if a pipe cap only is acceptable under B31.1.

Thanks for all the replies.

 

[BigInch]

Well that's a bit of a red flag (the kind we have here in Spain, not the forum red flag).

A bigger support, stronger rod, bigger whatever, reduces deflection AND in the process often increases internal stresses, since internal stresses are no longer relieved by expansion.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[metengr]

engrpiper;
Originally, I quickly read your OP thinking you might have had a fatigue problem, DMW problem or defective weld.

Well, after seeing the statement below....

The fillet weld on the weldolet to pipe cracked. After removing the weldolet dye penetrant showed cracks extending out into the 10" pipe. Cutting a 5.5" hole will remove these cracks. I am planning on making a 6" branch connection (6" length) with a pipe cap to dead-end the branch. I am being asked if we can simply attach the pipe cap.

...you may bee seeing creep damage in this line. I get very suspicious of P11 pipe material at RT, inspection plugs or TW attachments where multiple cracks radiate out into the pipe base material. This could be early warning signs of impending advanced creep damage.

I would strongly recommend you check the pipe diameter using a set of calipers or pi tape just to see if the pipe OD has increased in size by 5%.

 

[BigInch]

Uh huh!

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/