Thickness Qualified 1

[jwhit]

This is probably a good question for GTAW. In order to qualify a WPS to cover the range of potential thicknesses to be welded per ASME IX, I need to qualify a ¼” plate and a 1-1/2” plate. What I’m trying to accomplish is casting repairs for wall thicknesses from 1/8” to at least 3” using 2 PQR’s to generate a single weld procedure. Our production thicknesses have been creeping upwards which is the reason for 3” minimum qualified. Process is Tig (currently the only process we have fully in place) and impact tests are involved bringing in QW403.6 and the 5/8” minimum thickness restriction on the 1-1/2” plate. A ¼” plate will cover 1/8” to ½” T and the 1-1/2” plate will cover 5/8” to 8”. What happens to the 1/8” in between the ½” maximum and 5/8”minimum qualified thickness? Following the code to the letter, it seems an additional plate would be required to cover that sliver of material that isn’t included, but logic says that it is ridiculous to have to do it, since it could be argued that the uncovered T is actually 1/16”. How much leeway on T qualified is actually given? I haven’t been able to find an answer in Sec. IX.

 

[metengr]

jwhit;
Regarding thickness qualification for impact testing, the guidance given in QW-403.6 is minimum only and does not cover a maximum thickness for qualification. So, if you qualify on base material 5/8" or greater you are good to go from 5/8" to the maximum thickness permitted by the WPS for impact qualification.

If you qualify on a coupon thickness below 5/8", the minimum thickness is the thickness of the coupon with a maximum as supported by the WPS.

For material 1/4" or less, the minimum is 1/2T to the maximum as stated in your WPS.

So you need to select your minimum thickness for impact qualification wisely for overlap.


The minimum base metal thickness
qualified is the thickness of the test coupon T or 5/8 in.
(16 mm), whichever is less. However, where T is less than
1/4 in. (6 mm), the minimum thickness qualified is 1/2T.
This variable does not apply when a WPS is qualified with
a PWHT above the upper transformation temperature or
when an austenitic or P-No. 10H material is solution annealed
after welding.

 

[jwhit]

metengr,
I understand all of that and the concept of 2d and 3d cooling, the issue is the material between the 1/2" maximum qualified by the 1/4" plate and the 5/8" minimum that isn't qualified by either PQR. The 1/4" plate covers 1/8" to 1/2" and the 1-1/2" plate will cover from 5/8" to 8". The problem is what to do with the "no mans land of 1/2" thick to 5/8" thick" that isn't covered between the two PQR's. If I use a 3/8" plate I leave T<3/8" uncovered in the procedure but will cover 3/8 to 3/4". Base metal thickness down to 1/8" isn't uncommon, so also needs to be covered by the WPS. I'm trying to avoid having to do a third PQR to cover all possibilities. It's difficult enough to get some of the people around me to understand that base metal thickness matters at all.

 

[weldstan]

You cannot weld all thicknesses in your stated range with two inpact test specimens. You will need at least three. You will need more if your design Code is B31.3. Please note the operative wording of QW-403.6, "where T is less than 1/4", the minimum thickness qualified is 1/2 T."

 

[weldtek]

jwhit,
No offense intended, you say you understand but from your response it appears that you're not grasping the concept.
Per Sec IX rules, for impact testing, you're not qualifying impacts for maximum thickness - you're qualifying for minimum thickness. Metengr has clearly laid out the rules in his post.

That's why per those rules, when one qualifies a PQR on material 5/8" or thicker the qualified range for that PQR bottoms out at 5/8". To extend the qualification range for thinner materials one may weld a thinner coupon and perform impact tests only. The bends and tensiles performed on the thicker plate need not be repeated on the thinner plate.
Eg. First plate 1.5" thick tested with bends and tensiles. The second plate 3/8" thick impact tested only. The two PQR's will now support a range of 3/8" through 8" with impact tests. This assumes all other essential variables are unchanged.

 

[jwhit]

I actually do grasp the concept, and the plates (1/4" and 1-1/2") that I proposed using would cover 1/8" to 1/2" and 5/8"-8". My issue is with that 1/8" between the two qualifications. I've pulled teeth trying to get it understood here that we can't just weld a single plate and declare it good for all thicknesses. Been made an arse of more than once about it. It looks like I have to throw in a third plate to cover what is essentially +1/16" on the max. T qualified by the 1/4" plate and -1/16" on the min T qualified by the 1-1/2" plate. It's the gap between that is the issue and there seems to be no good way around it short of qualifying a plate at 3/8" or even 1/2" to cover it.
If I was doing an above transformation PWHT after welding as Metengr mentioned earlier there would be no question about needing to do three plates, but because the uncovered gap is miniscule I was hoping for somebody having a workaround. You ought to hear the reaction when I try to explain the 1.1T rule for above upper transformation and duplex
materials. You would then understand the reason for my looking for an out on this one.

 

[weldtek]

jw,
I see three possibilities;
a) You did not read my post
b) You read it but did not comprehend it
c) You understand but choose to ignore it

If it's b) you can be helped but if it's one of the other two - you'll have to figure it out by yourself.

 

[DekDee]

jwhit,
I am sorry but you are not understanding what has been explained - read weldstans response.
If you use a 1/4" coupon your minimum thickness is 1/4", not 1/8".
So based on your initial tests you have 1 x PQR for 1/4" to 1/2" and 1 x PQR for 5/8" to unlimited.
There is no way you can get the coverage you require with 2 x PQRs, 3 x PQRs are required.
Regards,
DD

 

[jwhit]

I see what I missed, it states less than 1/4". My mind insisted on reading it as less than or equal to. Shouldn't do this stuff on days when I'm out of sorts, woke up with diuretic induced gout yesterday. Spent the end of the day at the Dr. I apologize for sounding like a stubborn Dutchman.
Looks like I will have to explain 3 plates to people who insist one will do it, and have even less reading comprehension than me. That is if they will even look at the code. But, that's my problem as is trying to make sure we are compliant.