Thanks for the good discussion we had in below mails from J and Sayee. I
would just like to add the following from my experience.
When we discuss the Code, we have to judiciously follow the
provisions/limitiations therein. The explanation by J is the most
appropriate so far as the ASME is concerned. In case, the lower preheat
temperature are required to be used, the new qualification may be executed.
That is the only way. This doesnot mean that if we do not follow, there
would be really some problem of the sort we discussed in below mail.
It is something like this. When you are going on a highway, you have to
follow the maximum speed limit specified for the same even though by
exceeding the limit. This may be due to a no. of reasons, as we all know.
Similarly, when we need to follow certain standard, specification, code,
etc. we may have to make the best use of the provisions for our situation
before qualification of procedures and use the worst situation in
qualification so that during actual production welding, there would be
minimum problems.
Best regards,
Prasad
"Sayee
Raghunathan"
<Sayee.Raghunatha To
n@twi.co.uk> <materials-welding@googlegroups.com
Sent by: >
materials-welding cc
@googlegroups.com
Subject
[MW:1819] RE: 1812] Re: Pre heat
27/03/09 11:01 AM requirement for split welding
procedures from combined PQR.
Please respond to
materials-welding
@googlegroups.com
On a code basis, the explanation given by others limiting the decrease of
preheat on WPS to 55Deg C below that of the PQR is correct, and I agree
that the preheat shall be the minimum interpass temperature recorded for
the FCAW process-55Deg C, purely from a perspective of
application/interpretation of ASME Section IX code requirements.
For a more comprehensive answer, the preheat is determined by the combined
thickness, the carbon equivalent of the material(s), the level of
diffusible hydrogen in the weld metal and the heat input or arc energy of
the process. These factors either affect the cooling rate(s) or the
hardenability of the material and the susceptibility to hydrogen induced
cracking. Higher the hardness in the HAZ and higher the diffusible hydrogen
content in the wm, greater is the susceptibility to cracking. The method of
calculating the preheat temperatures is explained very clearly in EN
1011-2, which can be downloaded from the BSI website.
Therefore in my personal opinion, I would be looking at which has the lower
susceptibility to cracking, the FCAW process with potentially high weld
metal hydrogen, 24Deg preheat or with 32Deg preheat and compare with the
TIG process with diffusible hydrogen levels <5ml/100gm weld metal, 24Deg
preheat and lower arc energy(?). In my personal opinion the change in
preheat temperature will hardly be critical for welding C-Mn steels with
less than 0.43CEQ (IIW) and thicknesses lower than typically 25mm. I
mention this thickness and CEQ limit because from the level of preheat
specified by you, I would assume this is the case.
Regards
Sayee
-----Original Message-----
From: materials-welding@googlegroups.com
[mailto:materials-welding@googlegroups.com] On Behalf Of
pieper-qsi@kpnmail.nl
Sent: 26 March 2009 21:09
To: Materials & Welding
Subject: [MW:1812] Re: Pre heat requirement for split welding procedures
from combined PQR.
Dear J,
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 -
TWI Ltd
Registered Number: 3859442 England
Registered Office: Granta Park, Great Abington, Cambridge, CB21 6AL, UK
_______________________________________________________________________
The information in this e-mail is confidential, and may be legally
privileged. It is intended only for the person(s) specified in the
above address. Access to this e-mail by anyone else is unauthorised,
and any disclosure, copying, distribution or other use of this e-mail
is prohibited and may be unlawful. We will not under any circumstances
have any responsibility or liability arising out of or in connection
with any unauthorised use of this e-mail. Please inform us if this
message has gone astray before deleting it.
Please note that all e-mail is monitored.
When sending e-mails to TWI, please help us by including your name,
company, and details in your e-mail signature.
Seeking Technical Information? Industrial Members can access data as
JoinIT registrants on http://www.twi.co.uk
_______________________________________________________________________
Save a tree...please don't print this e-mail unless you really need to.
Save a tree...please don't print this e-mail unless you really need to.
This email and any attached files ("Message") may contain confidential and/or privileged information. It is intended solely for the addressee(s). If you receive this Message in error, inform the sender by reply email, delete the Message and destroy any printed copy.
Any unauthorized use, distribution, or copying of this Message or any part thereof is prohibited. Emails are susceptible to alteration. Neither Technip nor any of its affiliates shall be liable for the Message if altered or falsified nor shall they be liable for any damage caused by any virus that might be transmitted with this Message.
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding-unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
-~----------~----~----~----~------~----~------~--~---
No comments:
Post a Comment