Your explanation is correct regarding the problem with hydrogen cracks
but you call them HIC cracks and in my opinion you only get typical
HIC cracks (better known as stepwise cracking) when a sensitive
material is exposed to a H2S containing gas. Cracks will start
anywhere in the microstructure on dislocations and/or MnS inclusions
because of hydrogen collecting at such location and building op
internal pressure by which the crack will find his way through the
microstructure by following the path with the lowest resistance.
The typical cracks due to Hydrogen during welding mostly called cold
cracking.
Hope this information is useful.
Best Regards,
Herman Pieper
On 26 mrt, 14:56, jhenn...@deltak.com wrote:
> 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- Tekst uit oorspronkelijk bericht niet weergeven -
>
> - Tekst uit oorspronkelijk bericht weergeven -
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