Impact Test Exemption of Stiffener Ring Material, PQR & Welds 1

[OmarMuz]

We have a mounded storage tank for LPG with capacity of 4000 m3. And the stiffener ring for the tank was welded with unapproved WPS and PQR. Since the PQR failed in charpy impact test at required MDMT of -46°C.
Stiffener rings are impact testing exempted as per §UCS-68 (c) and §UCS-67 of ASME Section VIII division 1.
Moreover, to solve this issue and not damage the Stiffener ring there are a proposal and code interpretation is as follow
According to the codes and standards
1. Impact testing exemption temperature for 26mm thick P No. 1 (SA-537 Cl.2 / stiffener ring) material is -35°C as per Table UCS-66 and figure UCS-66 for Curve D Materials
a. Stiffener Ring Material : SA 537 Cl-2 Q&T
b. Applicable Curve – D as per Figure UCS-66 and Table UCS-66
c. Governing Thickness of Ring Flange and Web – 26mm

2. PWHT requirement/Exemption for Ring Material/Weld.
a. As per Table UCS-56-1, PWHT is not required for 26mm thick P No. 1 (SA-537 Cl.2 / stiffener ring) material

3. Reduction in impact test temperature for weld joints, if PWHT is performed when it is not a code requirement.
a. §UCS-68 (c) gives reduction of 17°C for impact test temperature from vessel MDMT for P No. 1 materials (Note stiffener ring joints are undergoing PWHT even though it is not required as per Code UCS-56 of ASME Section VIII Division 1. See STEP 2).
b. Hence, the new impact test exemption temperature for P No. 1 material (SA-537 Cl.2 / stiffener ring) is -52°C (17°C reduction from -35°C)
c. With Vessel MDMT at -46°C and impact test temperature exemption as per UCS-68(c) at -52°C, the stiffener ring materials (26mm thick SA-537 Cl.2 material curve D) are exempted from impact testing.

4. Impact testing exemption of welding procedure qualifications
a. Further to above UCS-68(c) exemption of impact test temperature of base material, UCS-67 gives the exemption to impact testing of welding procedure qualification

CONCLUSION:
From the above exercise it is concluded that the material [UCS-68(c)] as well as welding procedure qualification [UCS-67] of
Stiffening Ring welds at 26mm thickness are exempted by applicable construction code at Vessel MDMT.

[highlight #4E9A06]My question is – is the above interpretation is correct and you have any comments on the case in hand?

Can we use the stiffener ring for this tank or we have to cut the weld and repair it?[/highlight]

Thank you for your cooperation

 

[DekDee]

Are you the client or the contractor ?
Are you a Welding Engineer ?
There are many on this forum that have much more experience than me on vessels so hopefully they will respond.
One of my past personal experiences was supervising ( 5 months) major repairs on 4 x brand new vertical vessels that had serious cracking on all of the skirt support rings.
Maybe a little bit different to your situation but it was also welding to an unapproved WPS/PQR,
Regards,
Shane

 

[david339933]

Did you use impact tested filler metal as required by UCS-67(a)(3) for Curve D materials?

 

[OmarMuz]

DekDee
I'm not welding engineer, and your case is different as the stiffener ruing have other function

david339933
yes, the impact was done for the filler metal and failed

 

[david339933]

OmarMuz...not what I am asking. Read UCS-67(a)(3), if you do not use filler metals impact tested by the manufacturer, you must impact test your weld procedure. You are only exempt from impacts if you use the same heat/lot of filler metal that was tested by the manufacturer of the filler metal. The MTR you receive will show impact testing along with the lot #.

If the answer is no....then impact testing is required for the WPS....there is no exemption.

 

[OmarMuz]

yes the filler metals was tested by the manufacturer and found accepted

"UCS-67(a)(3) when joining base metals exempt from impact testing by UCS-66(g) when the minimum design metal temperature is colder than −55°F (−48°C)."

the confutation came from that our MDMT are -46°C and the UCS-67(a)(3) mention that is colder that -48°C.

any advice?

 

[david339933]

That is telling you that if you are colder than -55F, you need to impact test...no exemption.

In your case, based on the info given, base materials are exempt, WPS is exempt, therefore impacts are not necessary.