How to specify preheat on a WPS? 2

[ethan18]

A welder is making a test coupon for procedure qualification. The provisional WPS used for making the coupon specifies preheat of 150°C. Welder aims for 150°C, however – after a few passes the actually observed preheat rises to 200°C. Overall, preheat is observed to be in the range of 150°C – 200°C over the course of test coupon welding.

1. What temperature should be recorded on the PQR? 150°C? 200°C? Or, 150° to 200°C?

2. What minimum temperature can be specified on WPS? QW-406.1 says that ‘A decrease of more than 100°F (55°C) in the preheat temperature qualified’ attracts re-qualification. Can one specify preheat of ‘minimum 95°C’ on the production WPS then? (I am guessing this is not how QW-406.1 is intended to be used. If not, QW-406.1 needs rewording).

Similar questions exist for QW-406.3 too – for inter pass temperature.

 

[DekDee]

406.1 is based on minimum preheat temperature - you can increase what you like on the WPS but cannot decrease more than 55 degrees C.
406.3 is based on maximum interpass temperature - you can decrease what you like (as long as above preheat minimum) but you cannot increase more than 55 degrees C.
PQR should list preheat of 150 degrees C and Interpass of whatever was the recorded maximum interpass temperature.
WPS can list 95 degrees C for preheat minimum.

 

[ethan18]

@DekDee, thanks for your response. Although, i have to disagree with you a bit. You are right that PQR should show 150°C as the preheat; however, it is not Section IX's intent that in the case cited above, WPS can specify a preheat of 95°C. This is not how QW-406.1 is intended to be used.

The actual preheat temperature inevitably rises during test coupon welding. Section IX intends that - provided this increase is not more than 55°C, one can specify the starting preheat temperature (during coupon welding) as the minimum preheat required, on the WPS. This is sensible - actual temperature might have been 205°C during most of the coupon welding, but you would end up fulfilling Sec IX's expectation if simply specify 150°C (which is 55°C below 205°C) on the WPS. Specifying 95°C is patently wrong.

QW-406.1 falls short of communicating this intent, however.

 

[DekDee]

Looks like you and I are on totally different pages Ethan.
I do not agree preheat rises - preheat is the temperature recorded prior to commencement of welding.
Lets say 100 degrees C preheat.
That is then the minimum preheat to be shown on the PQR.
All other temperature readings are interpass temperatures unless welding is interrupted.
After interruption and prior to recommencement the temperature is 8o degrees C - minimum preheat is now 80 degrees C.
After interruption and prior to recommencement the temperature is 140 degrees C - minimum preheat is still 100 degrees C and interpass temp is 140 degrees C.
Maximum interpass recorded during welding PQR was 220 degrees C.
WPS could show minimum preheat of 45 degrees C and maximum interpass of 275 degrees C based on QW 406.1 and 406.3.

 

[ethan18]

Dekdee, respectfully, I disagree with you again.
Maybe this will change your mind. See the attachment. This is from CASTI handbook, written by one Michael Houle, who was on Section IX committee for 40 years.

If you have qualified a PQR with preheat of 100°C, you cannot specify 45°C on the WPS.

 

[SJones]

It would appear that reference to a terms and definitions, or vocabulary, standard is required to confirm the specific difference between 'preheat temperature', and 'interpass temperature.' Try AWS A3.0, or ISO TR 25901-1.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[ethan18]

Good point. Sec IX defines preheat temperature as follows:

'The minimum temperature in the weld joint preparation immediately prior to the welding; or in the case of multiple pass welds, the minimum temperature in the section of the previously deposited weld metal, immediately prior to welding.'

So, @DekDee, refer your quote: 'All other temperature readings are interpass temperatures unless welding is interrupted.' - is not quite correct, I think, at least in the context of Sec IX. IMHO, interpass is a supplementary essential variable, and comes into play only when toughness is a consideration. One can forget about interpass temp. otherwise.

In ordinary multipass welding, the preheat temperature is not just the temp. before deposition of the first pass, but is in fact the temp. before any pass is deposited. Correct me if you disagree, please.

 

[SJones]

How does that gel against the definition of interpass temperature, also in ASME IX?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[DekDee]

Ethan,
I agree 100% with Steve on this.
When was Mr Houles CASTI book published ?
My library only goes back to 2004 but it is quite clear preheating is related to minimum temperatures - preheat cannot "rise", it can only decrease.

2004

preheat temperature - the minimum temperature in the
weld joint preparation immediately prior to the welding;
or in the case of multiple pass welds, the minimum temperature
in the section of the previously deposited weld
metal, immediately prior to welding

2021
preheat temperature: the minimum temperature in the
weld joint preparation immediately prior to the welding;
or in the case of multiple pass welds, the minimum temperature
in the section of the previously deposited weld
metal, immediately prior to welding.

If you preheat to 100 degrees and after the first pass but before the second pass you measure 150 degrees your minimum preheat is still 100 degrees and your interpass is then 150 max.
Interpass can increase with subsequent runs but your minimum preheat will never change unless you interrupt welding and start again with a temperature less than your previously recorded minimum preheat.
As I noted in a previous post.
I am just about done on this, you are entitled to your opinion and I am entitled to mine,
Cheers,
Shane

 

[ethan18]

Shane, I don't think you want to see the point i am trying to make. I am gonna try one more time:

1. CASTI book was published around 1995. But i don't see how that affects anything. The definition of preheat temperature has stayed same since before that.

2. Interpass temp def under QG-109 is: 'for multiple-pass welds, the temperature in the previously deposited weld metal or adjacent base metal [typically within 1 in. (25 mm) of the weld deposit] immediately before the next pass is started.' So it would seem that both definitions point to the same thing. However, like i said - inter pass temp is only a supplementary essential variable, & can be ignored when toughness is not a consideration.

3. You are right that among all temperatures observed on the base metal during coupon welding, the minimum temperature - which is typically the starting temperature recorded before first pass is laid - should be recorded on the PQR. No problem on this. This is a fine position, although in my opinion, not the best one. The best way, IMHO, would be to record the range observed. For example: 150° to 200°C. Subsequently, the WPS should specify 150°C as the minimum temp. that must be observed all the time.

The objection is with the 55°C rule. You state that 95°C can be specified on a WPS supported by a PQR that shows 150°C as the preheat recorded during coupon welding. I say that that is not how the rule is intended to be used; the correct way, in fact, would be to specify 150°C on the WPS. The 55°C is only to take into account the inevitable rise in preheat observed during coupon welding (assuming the rise is within 55°C). The discussion by Michael Houle clearly demonstrates this.

4. The definition of preheat under QG-109 is clear enough in communicating that preheat is not just the starting temp; in fact for multipass welds it is the temp on previously deposited weld metal.

Cheers

 

[DekDee]

Section IX, QW-406.1
Date Issued:
01/19/1978
Record Number:
BC-77-118
Interpretation Number :
IX-78-02
Question(s) and Reply(ies):
Question: QW-406.1 reads "A decrease of 100°F or more in the minimum specified preheating or interpass temperature." Does the word "specified" refer to the preheating temperature on the WPS or as recorded on the PQR?

Reply: The word "specified" in QW-406.1 refers to the temperature specified on the WPS. However, the minimum specified temperature cannot be more than 100°F lower than that stated on the PQR.



Section IX, Procedure Qualification Variables
Date Issued:
05/13/1981
Record Number:
BC-80-749
Interpretation Number :
IX-81-20
Question (3): On the WPS and PQR, is it necessary to specify or record the minimum preheat, maximum interpass, and preheat maintenance temperatures for materials not requiring heat treatment?

Reply (3): The Code requires all variables listed in QW-250 (by process) be listed on the WPS, and, therefore, preheat (not less than 100F below the PQR) shall be listed on the WPS, the preheat maintenance shall be described (or "none" if not required) on the WPS, and the interpass temperature (not more than 100F above the PQR) shall be

 

[ethan18]

Cool. This brings us to the reason why i started the thread in the first place.

I am familiar with both interpretations. To a layman, QW-406.1 can mean nothing else other than the understanding you have espoused in above posts, as well as the understanding that seemingly flows from these two interpretations, to the naked eye.

However, the discussion done by Mr Michael Houle, who was on the Sec IX committee for 40 years, and who would have surely had a hand in framing QW-406.1, leaves no room for doubt. Who better than the guy who made the rule, to tell us about what it means.

According to Houle, if the highest preheat temp. during coupon welding is not more than 55°C above the starting temperature, then that highest temperature is the qualified preheat temperature. And one is free to specify in WPS a temp. not more than 55° below the qualified temp. For eg. if the observed preheat on the coupon was in the range 150°C-205°C, the 205°C is the qualified preheat, and a minimum of 150°C is what you can specify on wps. If one sees this point, it is possible to reconcile both these interpretations with this thinking too.

To me, the position taken by Mr Houle appears more logical, although - a plain reading of QW-406.1 certainly gives off the meaning you have been repeating, @DekDee. Which is why QW-406.1 needs a rewording, in my opinion.

All this is, of course, only my understanding, and i would love to be proven wrong. But currently, there is no interpretation that can dispel this understanding.

With all due respect @DekDee.

 

[SJones]

If it was your plan all along to go with Houle, why ask the question? Just because the gentleman was on the committee doesn’t mean that he definitely had a hand in the formulation of the text that, as you rightly point out, requires a reword because the definitions of preheat and interpass temperature are conflicting. In my 35 years of reviewing and approving WPSs, I have never seen the temperatures interpreted and recorded in the manner described by Houle. This is probably because welding and inspection personnel are familiar with other definitions such as from AWS, or ISO that are more akin to what happens in practice.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[ethan18]

Mr Jones, thanks for reply. Well, it is clear that this thinking meets opposition frequently, like it did here. And one wants validation of one's thinking. I came here seeking to know opinion of learned people on the subjects that are controversial at my office.

And sure, i think a rewording might be in order, for the definitions of both preheat & interpass, as well as QW-406.1. In ISO standards, preheat is not measured ON the bead, like it does as per Sec IX.

If i recall correctly, it is to be measured at a distance not greater than the joint thickness or 75 mm, whichever is smaller. The differences between ISO and Sec IX on the subject of welding qualifications keep shrinking with each new edition. So it is odd that they are so different on the subject of preheat. But that is besides the point for this thread, i think.

 

[DekDee]

Ethan,
I am willing to learn even at my advanced age but I cannot reconcile Mr Houles statements (with all due respect).
Preheat is exactly what it says - something you do "pre".
Anything after that is interpass.
Preheat rising after subsequent passes ???

QG-109.2 DEFINITIONS
preheating: the application of heat to the base metal immediately
before a welding or cutting operation to
achieve a specified minimum preheat temperature.

I think that is pretty clear preheat is applied by means other than welding.

I think this clause is confusing (especially when we look at interpass)
I have added in the bold

preheat temperature: the minimum temperature in the
weld joint preparation immediately prior to the welding;
or in the case of multiple pass welds, where welding has been interrupted the minimum temperature
in the section of the previously deposited weld
metal, immediately prior to welding.

Cheers,
Shane

 

[weldstan]

The minimum preheat temp should be specified on the WPS to assure a sound weld and/or be in accordance with Code or contract requirements. I once reviewed a manufacturer's WPS for welding Mn-Mo alloy steel pressure vessels with 4" wall thickness. I recommended that a 300 F preheat be employed and the manuacture stated that all the Code required was 200F minimum and that is what they did. The first circ seams welded cracked all the way around after allowing to sit over night. They amended their WPS to my recommendation and thanked me for the insight. They never had another cracking incident on those vessels.

 

[ethan18]

weldstan, true, one must always be awake to other considerations such as metallurgical, mechanical etc. (and not rely on code alone) when deciding upon the preheat. Here, though, we are only grappling with how to read QW-406.1 correctly.

Dekdee, you might be right. But i am inclined to give more weightage to Mr Houle's discussion in his book, seeing that we are only code users, and the gentleman sat on the committee that made the rule, and that too for four decades. We stand in confusion till an interpretation can set the matter right. I have asked one; waiting for the reply. Will post the reply here if/when i receive it.

I know one should refrain from logic in code matters, but i will venture to say this - it isn't very logical to specify 95°C in a WPS that is supported by a PQR that was welded fully with a preheat of 150°C, (if we take at QW-406.1 at its' face value, that is).

Regarding the thinking that preheat is temp. before the 1st bead is laid (seeing the 'pre' in the term), isn't the minimum preheat temp. expected to be on the base metal before every pass? It won't be correct if the welder ensured 150°C before the 1st pass, but allowed it to drop it to 100°C after a couple of passes, right?

Also, sometimes - the welder completely switches off the burner once welding is started, aiming to keep up the preheat through the heat generated by weld deposition itself. So we can see that it isn't always the case that preheat is applied by means other than welding (like you said); sometimes it can be kept up by welding itself too.

Be that as it may, only one thinking can be correct. I would only like to know the real stand of asme - one way or the other. If we have to subscribe to the Houle's reasoning, QW-406.1 may to be reworded as follows:

“The range of preheat temperature observed across all passes of test coupon welding shall be recorded. If this range is not more than 100°F, the preheat specified on production WPS shall not be less than the minimum preheat temperature recorded on PQR. If the range exceeds 100°F, the preheat specified on production WPS shall not be more than 100°F below the highest preheat temperature recorded on the PQR.”

 

[r6155]

@ ethan18
What edition of ASME IX are you working on?

Regards

 

[SJones]

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[DekDee]

Sorry Ethan - I give up.
You are fixated on something I totally disagree with (and Mr Houles statement does not help).
Let us look at my reasoning.
Hypothetically we have 25 mm (1") coupon used in the PQR qualification with 100 degrees C preheat.
That PQR enables you to write a WPS for 5 mm to 50 mm.
Now, again hypothetically we want to weld 6, 8, 10 mm etc thickness with this WPS.
Do we want to weld 6 mm thick material with 100 degrees Celcius preheat ? - of course not. (unless it is some exotic material that requires it but that is not what this post is about).
So, we have 6 mm material, and 100 degrees C minimum preheat seems way over the top.
So, what do we do - we go to QW 406.1 which allows us to reduce minimum preheat up to 55 degrees celcius without requalifying the PQR.
Welding 6 mm thickness with 45 or 100 degrees celcius preheat - which makes more sense ? (45 degrees still seems too high but this is only an example)
Best we call it quits here - getting sick of bashing my head against the wall,
Cheers,
Shane