Time between Welding and PWHT
Time between Welding and PWHT
(OP)
Hi All,
Can any body tell me to where I can find time between welding and PWHT for P91 materials especially for Power Piping. Thanks
Regards
Muhammad
Can any body tell me to where I can find time between welding and PWHT for P91 materials especially for Power Piping. Thanks
Regards
Muhammad





RE: Time between Welding and PWHT
However,there are a lot of factors here.
- How big are the spool pieces?
- How many spool pieces are involved?
- How big is the PWHT oven?
- How full is the oven?
- What does it cost to heat that oven up and run it at required temperature for the required duration?
- What day of the week is it?
prognosis: Lead or Lag
RE: Time between Welding and PWHT
RE: Time between Welding and PWHT
Not sure if this is applicable (I only have the 2004 edition of B31.1 and P5B is now P15E)
131.6 Interruption of Welding
131.6.1 After welding commences, the minimum
preheat temperature shall be maintained until any
required PWHT is performed on P-Nos. 3, 4, 5A, 5B,
and 6, except when all of the following conditions are
satisfied.
(A) A minimum of at least 3⁄8 in. thickness of weld is
deposited or 25% of the welding groove is filled, whichever
is less (theweldment shall be sufficiently supported
to prevent overstressing the weld if the weldment is to
be moved or otherwise loaded).
81
(B) For P-Nos. 3, 4, and 5A (with a chromium content
of 3.0% maximum) materials, the weld is allowed to cool
slowly to room temperature.
(C) For P-No. 5B (with a chromium content greater
than 3.0%) and P-No. 6 materials, the weld is subjected
to an adequate intermediate heat treatment with a controlled
rate of cooling.
(D) After cooling and before welding is resumed,
visual examination of the weld shall be performed to
assure that no cracks have formed.
(E) Required preheat shall be applied before welding
is resumed.
Regards,
DD
RE: Time between Welding and PWHT
Most shop purchased P91 filler has more nickel than does the parent metal which implies the weld must be cooled down to 200 F prior to PWHT ( in order to form 95% martensite prior to PWHT).The only exception may be welds thicker than 4" thk and true matching filler. The higher nickel filler is more ductile than matching filler and thus reduces the likelihood of cracking in the shop prior to PWHT due to handling stresses ( ie pushing the bundle into the oven).
If the shop uses space heaters that burn nat gas which has suphur bearing odorant, then condensation of the heater's combustion products leads to concentrations of H2SO3 on the weld , which can lead to SCC if the weld is not kept hot enough to avoid nightime dew condensation. So keep the weld s hot enough to preclued nightime dew condensation.
"Whom the gods would destroy, they first make mad "
RE: Time between Welding and PWHT
According to Babcock & Wilcox, the time between completion of welding and PWHT should be limited to 14 days maximum to minimize the risk of SCC:
Gold M, Hainsworth J, Tanzosh J M, ‘Service experience with design and manufacturing approaches with T/P91 materials’, Proc. EPRI Conf. ‘9Cr Materials Fabrication and Joining Technologies’, 10-11 July 2001, Myrtle Beach, South Carolina, USA
According to Vallourec & Mannesmann, the time between completion of welding and PWHT should be limited to 7 days maximum: Vallourec & Mannesmann Tubes, ‘The T91/P91 Book’, 1999
More recently, I have heard some people refer to a limit of 3 days or so, but I’ve not seen this in any document.
But these all I did not study in any quality procedures or in any standard/Code.
RE: Time between Welding and PWHT
From that experience it is advised to preheat, then weld and imediately after welding cool down to between 80 and 100 degree Celsius for martensite forming, and after that the heat treatment will be followed by a predetermined time which can be calculated according Larson Miller Parameter at a temperature approximately 20 degree Celsius below the heat treatment of the pipe material itself. After that cool down slowly. After complete cooling down + 2 days do a traverse hardness test across the weld, the HAZ and the base pipe material.
I do not know the exact details, but this is what I remember.
RE: Time between Welding and PWHT
http://www.psimedia.info/Industry%20Alert.pdf
RE: Time between Welding and PWHT
I am aware all of above techniques. What I am asking, there is some time limit between P91 welding and PWHT, say 3, 7 or Max 29 days, if we do not organise PWHT within 29 days, it will lead us SCC crack. I am wondering to where I can get aforementioned info i.e time between Welding and PWHT. Thank you
RE: Time between Welding and PWHT
This is how we do it here, but then again: I am not a metallurgist and do not know all the details.
RE: Time between Welding and PWHT
RE: Time between Welding and PWHT
RE: Time between Welding and PWHT
RE: Time between Welding and PWHT
We answered your post - NO there is no time limit.
RE: Time between Welding and PWHT
Did you use a dehydrogenation heat treatment after discontinuing the weld?
RE: Time between Welding and PWHT
"Whom the gods would destroy, they first make mad "