Base Metal Thickness in Section IX

[Fizza453]

Today I was reviewing WPS and PQR submitted by our subcontractor.
PQR was made on a pipe NPS 18 with 11.13 nominal wall thickness, this info comes from MTR. But on PQR base metal thickness is recorded to be 9.6 mm. What I guess, he deducted 12.5% allowance on the wall thickness.
In my opinion base metal thickness should be nominal thickness, am I correct?
Secondly if 9.6 mm is the thickness of coupon, PQR shows 4 side bend tests while QW-451 permits 4 side bends if thickness is 10 mm and over. May the difference of just 0.4 mm (10-9.6 = 0.4 mm) be tolerated and side bends be accepted? in lieu of two root, two face bends?

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

Fizza453;
No, the 12.5% was not subtracted. Base metal thickness was probably measured when the material was received and should be measured to ensure proper weld deposit thickness range. The PQR is a record of what welding was done, welding process parameters, material and dimensions.

No. The requirements and Notes in QW-451.1 state absolute values.

 

[Kiwi2671]

metengr,
Agree with your first response but with all due respect have to query your second response.
QW 451 states 3/8" (10 mm)and over.
3/8" is not 10 mm, it is actually 9.525 mm so the 9.6 mm thick coupon is greater than 3/8".
As ASME IX is an American code one would assume the imperial measurement (3/8")would take precedence over the metric measurement (10 mm).
I have had issues in the past with the rounding out of metric measurements - as an example 3/4" is rounded out to 20 mm (B31.3 Table 331.1.1)when 3/4" is actually 19.05 mm.
Hypothetically,if we had a 14" Sched 60 pipe with actual Wall thickness of 19.5 mm (nominal is 19.05 mm)would it require PWHT ?
It is less than 20 mm but greater than 3/4"
Your thoughts greatly appreciated,
Regards,
Kiwi

 

[metengr]

ASME Code committee is a consensus comittee and uses hard/soft conversions as applicable to make the units more rational or to comply with metric grids where the material is originally purchased. There is an ASME document ASME Guide SI-1 that provides this information. One has to draw the line. In this instance if the Code text lists 10mm as a thickness this is what the Committee selected and agreed upon.

 

[Kiwi2671]

metengr,
How can you tell me that 3/8" equals 10 mm - irrespective of what your code committee has decided ?
3/8" is/was the requirement which used to appear in most American codes as 9.6 mm, now it has suddenly become 10 mm and 3/4" has suddenly become 20 mm ????
The text may list 10 mm but I (as the clients representative) have to enforce the code.
If I cannot understand the reasoning behind "rounding off" of metric measurements how can I possibly enforce it on the contractor ?
Cheers,
Kiwi

 

[metengr]

Kiwi;
Review information on soft and hard metric conversions. I had to do this so that I can understand the methodology when I forst became invovled with Coders and Standards. For example, standard plate thickness that is purchased using SI units , not being converted to SI units from standard units, may not be standard as 3/8" plate conversion, so 10mm plate is the nearest standard plate thickness and this is part of the reason for using hard conversions, when necessary. Agree or disagree this is the rationale and how the committee decided.

 

[Fizza453]

Thanks a lot for both Metengr and Kiwi.
I think code users would feel more easy if the definition of "Thickness of the test coupon" is added in QW/QB-492, my opinion only.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN