PWHT Process in High Pressure Piping

You are describing mild steel pipe Sched. 160. There are tons of these welds in service that never saw PWHT. But if you have a procedure specified in the contract, then it is the obligation of the contractor to MIL-TFP4-1.

A53 Gr B a P1 CS material be PWHT to B31.1 power piping? The normal pwht temperature 1100 to 1200 degrees. 600 to 648 C How did you determine that the chart temperature did not agree with the pipe temperature? The PWHT area consisting of the weld, the soak band (SB), the gradient control band are covered with heaters and insulation that extends for some length beyond the heaters, so how did and where did you read 324 degrees C? If the temperatures that you stated were true then you have the wrong people doing your heat treating. I believe that the chart would be correct in fact I would bet on it!! The WPS should give these perimeters as well as preheat and inter pass temperatures. The PQR should have been completed showing that the results wanted are obtained using the welding rod, the type of welding SMAW, GTAW and the PWHT guidelines. NDE/NDT is covered in the code book and directed by the welding Engineer and or QA QC.. Hardness is covered in the ASME Code Book. P1 CS before PWHT will usually be below 200BHN. It seems that while you are not qualified to be QC or a welding engineer you are trying to act in that capacity. Away well. Most everything is covered under code, schooling, and experience. I am glad you are working under B31.1 and not B31.3. Lots of luck but get qualified.

Hi Sir,

Temp reading on pipe - Read thru a calibrated laser temperature gun shooted in side the pipe, exactly on welding joint.

If what you is true, then there could have been something wrong with PWHT procedure (or) it could have been poor insulation covering. The difference in temp. can not be that much. But the graph records the actual temp. through thermocouples fixed on the weld.

The contractor has to give proper explanation for the difference.Pl. check the hardness of the Weld & HAZ and you can repeat the SR again if required for that particular joint and it has to be done in the presence of an inspection agency.

sridhar.

Optical temperature guns often give the wrong reading. They have to be calibrated to the emisibilty of the material being read. Take a reading on ground metal and then on the metal just one inch away that has not been ground, The difference is amazing! Also the angle that you point the gun will give you a false reading as will distance. Run a test. Have thermocouples installed on the inside of a pipe befoe the weld is fitted. Then do a PWHT, check readings on recorder interior verus exterior. Then take a reading with your temperature gun. The thermocouple reading will not agree with your gun. There remains the question of how your thermocouples are attached. Most PWHT companys use capacater welded thermocouple wire to get an accurate reading. However if they are using sheathed TCs, OR if they are twisting the thermocouple wire and wiring or taping them to the pipe you may be right. Thermocoupless attached this way avarage the temperature of the pipe and the heater. Thermocouples that are attached useing capaciter welding are very accruate. Wireing or taping thermocouples MAY give you an highly inaccruate reading!

Hi sir,

Thanks for the best Answer. Many thanks for the support.

Thank you.

sridhar.

Observations.

1, Temperature difference between Pipe 324 deg C and Chart 620 deg C.

I ask again how you could determind what the temperature was at the weld and soak band during PWHT soak?!