Does UCS-68(c) apply to SA 516-70N?

[MechEMain]

Hi,

I am trying to determine a MDMT for a vessel which is made of SA 516-70N. My question is:

1. Is SA 516-70N still P1 material?
2. If this vessel is post weld heat treated? Can I apply UCS-68(c) to this vessel?
3. How will PWHT affect a normalized material?

Thanks,

 

[Tomtation]

1) SA516 Gr.70 is P1 group 2 whether normalized or not. When normalized it is a Fig. UCS-66 Curve D material instead of a Curve B material.

2) Yes, you can apply UCS-68(c).

3) Read through UCS-56 completely. Take note, you must use weld procedures which have been qualified with PWHT.

 

[SnTMan]

MechEMain, you may only use the UCS-68(c) exemption if PWHT is NOT a Code requirement, such as based on thickness, lethal service etc.

Regards,

Mike

 

[MechEMain]

Thanks for all your help.

I read UCS-56 table for P1 material. In note 2a, it says PWHT is required for welded joints over 1/5" nominal thickness. Is this nominal thickness the maximum thickness of the plates or the weld size? In my condition, two plates are welded together with a groove weld. One of the plate (tube sheet) has a thickness of 1.625". The other plate is 1.125" thick. Is PWHT required for this weld per UCS-56?

 

[eliebl]

A tubesheet is typically given a nominal thickness per UCS-66 (and UCS-56) based on nominal thickness divided by 4. The attached shell or channel would typically govern because the thickness of the weld joint is the governing thickness. In this case 1.125". At a nominal thickness of 1.125" PWHT is not required due to thickness. If it is not required due to service (i.e. lethal) then you can PWHT and use the 30 degree reduction in MDMT.

Side note: If you exempt PWHT due to weld preheat (1.25" thru 1.5") you cannot use the MDMT reduction from UCS-68(c). There is an interpretation to this effect but I do not have the number handy.

EJL

 

[CodeRef]

eliebl,
FYI, Here is the interpretation and it states the opposite.

Interpretation: VIII-1-01-19

Subject: Section VIII, Division 1 (1998 Edition, 1999 Addenda); Table UCS-56 and UCS-68(c)

Date Issued: January 3, 2001

Question: A P-No. 1, Gr. No. 1 or 2 material with a thickness of t = 1.375 in. is welded. A 200°F preheat is applied as permitted by Note (2)(b) of Table UCS-56 in Section VIII, Division 1. Is it then permissible to apply a 30°F reduction in impact testing exemption temperature, as permitted by UCS-68(c), if the vessel is also subjected to PWHT per Table UCS-56?

Reply: Yes


I had to look this up because it just did not make any sense that the code did not allow the reduction if PWHT was exempted, yet performed.



There are three kinds of people in this world; those who can count and those who can't.

 

[eliebl]

I stand corrected.

The interpretation states something that is not acceptable to the jurisdiction where I was reviewing submissions.

The reasoning of the jurisdiction is that if PWHT is exempted due to preheat (reduced residual stress upon welding) then you cannot reduce the stress further by PWHT and lower the MDMT.

Sorry for the misinformation.

EJL

 

[CodeRef]

Yes, I see! Here is the link to the paper:

http://www.absa.ca/Forms/AB-511 Impact Testing Enigma.pdf

I suppose knowing the jurisdiction of installation can be quite impoprtant for Owner's/User's/etc...


There are three kinds of people in this world; those who can count and those who can't.

 

[metengr]

Jurisdictions in the US and Canada always have the final say unless they do not regulate pressure vessels.