[MW:1811] Re: Pre heat requirement for split welding procedures from combined PQR.

Your AI is correct. You may not use the 24C preheat recorded for the
SMAW process as a basis for FCAW. Each process is qualified
independently as far as essential variables is concerned. QW-200.2(b)
states, in part: "The completed PQR shall document all essential
variables of QW-250 through QW-280 for each welding process used
during the welding of the test coupon". QW-406.1 is an essential
variable for the FCAW process and therefore the minimum temperature
used during the welding of the FCAW pass(es) becomes the "preheat"
value used for the WPS. Of course, the WPS may have a preheat 100F or
55C less than the lowest recorded temperature for the process per
QW-406.1.

Thickness of base metals, thickness of the deposited weld metal have
no bearing on this - you have two welding processes and the essential
variables shall be recorded for each seperate process and the WPS
shall be based on those values.

In your case, the WPS for the FCAW process (PQR minimum preheat
recorded 87C) may have a minimum preheat of 32C.

If you think about it this makes sense. Assume you were to use GTAW
for the root pass and FCAW for the fill and the material was carbon
steel with a carbon equivalent of, say, 0.55. This material would
have some sensitivity to hydrogen induced cracking. GTAW has very low
hydrogen potential, <H4, and would probably require no preheat above
ambient in order to prevent HIC. However, standard FCAW with a
hydrogen content of >H8 may require preheat to prevent HIC. Would you
want to assign no preheat to a WPS of FCAW only?

We will see what the other pundits have to say. Cheers.

J

On Mar 26, 5:49 am, Muhammed Ibrahim <ibrat...@gmail.com> wrote:
> Hi friends,
>
> I would like to clarify one important thing about preheat. My PQR is
> qualified with SMAW+FCAW. When I start the welding I preheated to 24 degree
> C. After root and hot pass compleated with SMAW before starting FCAW the
> plate temperature is 87 degreeC. If I split this PQR to make a WPS only for
> FCAW, Is it required to preheat the plate to 87 degree C or can I give 24
> degree celcius as preheated in the starting of PQR test coupon?. Your
> response will be highly appreciated.
>
> The AI insisting to put preheat of 87 degree shall be considered when we
> split the PQR for FCAW because when FCAW process starts the temperature of
> the plate to be considered as the preheat temperature (87 degreeC).
>
> Thanks & Regards
> Muhammed Ibrahim PK

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