Testing of Pipe/Final Weld

[pmover]

Fellow engr's,

I'm headed to a seminar now and not able to look into the matter now. But . . .

A power plant is replacing existing flanged steam butterfly valves with flanged gate valves of a length greater than the butterfly valves. the system pressure/temp is 600 psig/800°F respectively. (As such, a portion of existing piping will need be cut and removed. Thus, there will be a new flange and perhaps a pup (short length of replacement pipe) welded to new flange prior to final installation. The final weld testing/examination is the unknown. Assuming the pup is from a section of pipe that has already been hydrotested, what are and where can i locate the criteria for testing/examining the final weld? Should the pipe NOT be pre-tested and the pipe installed, then the final weld and section of piping does need to be hydrotested; thus ASME B31.1, Section 137 (Pressure Tests)applies.
Also, are there minimum lengths between welds on power plant piping (i.e. min length of pipe must be xyz-feet)?

Thanks!
-pmover

 

[metengr]

what are and where can i locate the criteria for testing/examining the final weld?

ASME B31.1, Table 136.4 Mandatory Nondestructive Examination for Pressure Welds ot Attachments to Pressure Welds

For 600 psig and 800 deg F

NDT; RT or UT butt welds, greater than 2 NPS in size and VT

Should the pipe NOT be pre-tested and the pipe installed, then the final weld and section of piping does need to be hydrotested; thus ASME B31.1, Section 137 (Pressure Tests)applies.

Have the pipe supplied in accordance with an ASME pipe specification. Hydrotesting after it is installed is NOT required. Perform NDT on all installation welds in accordance with B31.1.

Also, are there minimum lengths between welds on power plant piping (i.e. min length of pipe must be xyz-feet)?

The axial distance between butt welds should be such that RT can be performed on only one weld at a time. Normally, I like to use 2 x PD.