P91 and inspection nozzles
P91 and inspection nozzles
(OP)
I am involves with a project that has superheater outlet headers and pipes made from P91.
The headers have inspection nozzles that are also made of P91. There are some reservations regarding the cleanliness of these headers and the contractor has been asked to remove the end caps on the inspection nozzles for a borscope inspection.
The contractor has responded to this request by saying that it is not practical to remove the end caps because rewelding the end caps after the inspection will need the nozzles to be filled with argon backing gas which would mean filling the boiler with argon.
I would be pleased to hear of other peoples experience with the problem.
Last week I was in a meeting with another contractor on another project, so I asked him the same question. His response was that backing gas is not requred so I am really confused now.
Regards,
athomas236





RE: P91 and inspection nozzles
In this situation, backing gas for GTAW welding is NOT required.
RE: P91 and inspection nozzles
Thanks for the information, but why is backing gas required.
Regards,
athomas236
RE: P91 and inspection nozzles
The purpose of the boroscope inpsection nozzle is, well, inspection by boroscope, or to allow surveilance of the interior of a major weld during initial assembly ( in EU codes, such surveilance allows use of a more liberal weld fatigue life curve), or to allow insertion of a source for X-ray. Small component P91 welds are often made without having the entire pressure part pressurized with argon.
Maybe the contractor suspects some debirs is inside. I can recall a steam blow of a new plant- the initial lift steam blow sent large rocks thru the main steam line which launched the steam silencer like a rocket . Inspection of the duplicate unit main steam line revealed lots of debris placed inside by disgruntled workers.
RE: P91 and inspection nozzles
RE: P91 and inspection nozzles
I would suggest using a water soluble purge dam and a football needle to purge through the root opening. I have also heard of some success with SMAW root passes. Pat Patrick of Fluor published a good paper in the AWS Welding Journal on this.