why was this a cut out?

[sftyvlv]

I have a 20"condensate line that terminates in the main condensor of a 500mw steam turbine. The pipe is A106 sch 40 20". The wps calls for a gtaw root pass with Er70s-2 wire and smaw 7018 root, fill and cap.
The service temp and pressure are 50 psig and 350 deg F.
A hydrostatic test was required but could not be done due to isolation points in the line. Instead an mpi was done on the root pass and Rt on the remainder of the joint,the weld failed due to "suck back" on the root pass.
My question is instead of using an Rt procedure could not an mpi of the entire weld have been done instead? The condensate line met none of the requirements for Rt testing in service pressure, temp or wall thickness.
What is the limit of "suck back" allowed?
sftyvlv

 

[vesselfab]

MPI is not a good inspection tool for thick welds. I really only locates cracks and surface discontinuities.

RT examines the whole weld a and looks for porosity, slag inclusions, lack of fusion and full penetration (suck back)

No suck back of lack of fusion is disireable

 

[metengr]

My question is instead of using an Rt procedure could not an mpi of the entire weld have been done instead? The condensate line met none of the requirements for Rt testing in service pressure, temp or wall thickness.

Great question. In my opinion, the code of construction would be ASME B31.1, and using the requirements for NDT in Table 136.4,you are correct, the only requirement for NDT would have been only a VT based on a temperature at 350 deg F but your pressure is below 1025 psig.

Since someone wanted an RT, and you have no linear, crack-like indications and only suckback, you could attempt to disposition "as-is" or fit for service. There is really no obligation for RT at this pressure unless the owner specified it and contractually it must be done.

 

[metengr]

Forgot to mention, was the basis of rejection based on ASME B31.1, 136.4.5? If not, the rejection criteria should be based on (A.5).

 

[sftyvlv]

Yes this is to B31.1
Sftyvlv

 

[metengr]

sftyvlv;
Why was the RT selected for NDT? Was this the owners requirement or what?

 

[rmw]

Let's see, main condenser, condensate line, LSTG unit. So far I'm OK. Service temperature 50 PSIG and 350F? What is wrong with this picture? If this were an extraction drain line or a emergency vent line, I'd say maybe yes and especially to the temperature, but if this joint ever sees 50 PSIG, the condenser will have long since launched itself into the next county. Why are the service conditions specified thusly?

Now, don't for one minute think I am minimizing the need for proper welds at the joints of terminations into the condenser. I've repaired too many and beefed too many up beyond their original specification to do that. The service conditions just raise a red flat with me.

rmw