PWHT - B31.1 vs ASME IX 2

[pattimelt]

On a P1 to P1 pipe l, we have a weld to make on material with NWT of 1.375. Our WPS covers to basemetal thickness range of 1.875 to 9.00". The GTAW maximum is 1" and the SMAW maximum is 8". The WPS does not make mention of PWHT, permissible under Section IX, QW 407.1. However, under B31.1, Table 132 indicates that PWHT is required, only receiving exemption based on the carbon equivalent. We are trying to locate the MTRs, and will perform a PMI should our hunt be unsuccessful. Is this the correct approach? Am I looking at an essential variable here? I have not come up on this thickness and this situation in a P1 before, and the two codes seem to contradict each other to an extent. Thanks for any help.

 

[metengr]

First, in lieu of PMI, if you know the material specification, SA 105 or SA 106, etc., you can use the stated maximum chemical composition ranges to determine CE. To determine CE you need to know the carbon content and PMI will not work. To determine carbon content you either need to remove a sample for lab analysis or use a portable OES.

If the CE exceeds the value for exemption for PWHT under B31.1, you will need to have a WPS that is qualified with PWHT.

 

[weldstan]

The requirements for PWHT are defined in the design Code or Engineering Specifications ASME I, VIII, B31.1, etc. ASME IX does not address when PWHT is required; it only addresses the PWHT requirements for WPS qualification.

 

[Guest102023]

metengr,
Using CE based on element maxima in the standard will yield unreasonably high numbers that I am confident would trigger the PWHT requirement, although I haven't checked B31.1.

pattiment,
Section IX is not really at issue, other than that heat treatment condition is an essential variable. Specific requirements are given in the various construction codes.
1" GTAW + 8" SMAW deposited metal(?) on the WPS strikes me as being a bit fishy. Is this based on more than one PQR?


"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[pattimelt]

I have my answer - ASME B31.1, 2014 edition, states in Table 132.2 'Exemptions to Mandatory Postweld Heat Treatment'(pg 99) that P no 1 all groups, all types of weld, that if a preheat of 200 degrees is applied prior to welding on any nominal material thickness greater than 1" no PWHT is necessary. We were all looking at B31.1, 2012 edition. Thanks to all

 

[weldstan]

pattimelt,
While the B31.1 2014 exemptions are ideal for your situation, one should have many second thoughts applying the exemptions for all thicknesses.

 

[DekDee]

weldstan,
I agree with your comment re:all thicknesses but if the code committee includes these exemptions then people will obviously take advantage of the exemptions - whether it is right or wrong is a different story.
I only have a 2004 edition (haven't worked to B31.1 in years) and the exemption was for less than or equal to 3/4" with a 200 degree F preheat - seems very strange it is now "all thicknesses" with the same preheat ?

brimstoner,
Would not a single PQR on 2" thick material (1/2" GTAW / 1 1/2" SMAW) give you a WPS with deposited weld metal of GTAW 1" max and SMAW 8" max ?

pattimelt,
Was your initial posting a typo ?
"Our WPS covers to basemetal thickness range of 1.875 to 9.00"."

You want to production weld something that is 1.375" thick ?
Where does the 1.875 minimum come from ?
Your WPS is qualified to 8" max parent metal, not 9" - you cannot add the 1" and 8" deposited weld metal together to give you 9" (unless your PQR is qualified on over 6" parent metal)

Cheers,
DD

 

[weldstan]

DekDee,
Both B31.1 and B31.3 have been harmonized regarding Exemptions to PWHT of P-1 materials. I would have preferred that they would have limited the exemption to ASME VIII, Div.1 or somewhat heavier wall. And you are absolutely correct that the exemption will be used indiscriminately with unfortunate consequences.

One would have thought that low hydrogen welding processes would have been mandated for the exemption. But Not!

 

[metengr]

@brimstoner

Using CE based on element maxima in the standard will yield unreasonably high numbers that I am confident would trigger the PWHT requirement, although I haven't checked B31.1.

That is the intent if you have nothing else to rely on.