UCS-67_the coincident ratio exemption does not apply to weld metal?

[YuJie_PV]

hi, all experts,

it's about UCS-67 in ASME VIII-1.

i read "CASTI Guidebook to ASME VIII-1", and find the following statement:
"When the minimum design temperature is less than -55°F (-48°C) and the parent
materials are exempt from testing because of a low coincident ratio, the weld is still to be tested
because the coincident ratio exemption does not apply to weld metal."
is it correct?

UCS-67(a):
(1) when either base metal is required to be impact tested by the rules of this Division;
(3) when joining base metals exempt from impact testing by UCS-66(g) or Figure UCS-66 (Figure
UCS-66M), Curve C or D and the MDMT is colder than −20°F (−29°C) but not colder than –55°F (–48°C).....

i assume both the case in ucs-67(a)(1)and (a)(3)are not considering the MDMT reduction based on coincident ratio, is it correct?

thanks in advance.

 

[david339933]

I took a CASTI course on Sec. VIII once.....I threw out the book and never took a course from them again.

 

[YuJie_PV]

David,
i usually took CASTI's book as a reference book, and i don't completely trust it, because i've found some errors before, nevertheless some paragraph is still inspiring.

regarding the specific paragraph i am referencing to, i tend to consider it correct.
what do you think?

Thanks

 

[david339933]

Standard Designation:

BPV Section VIII Div 1

Edition/Addenda:

Para./Fig./Table No:

Subject Description:

Section VIII, Division 1 (1998 Edition, 1999 Addenda); UCS-67(a)(1)

Date Issued:

06/05/2001

Record Number:

BC01-192

Interpretation Number :

VIII-1-01-46

Question(s) and Reply(ies):


Question: Are impact tests per UG-84 of welds made with filler metal required for welded components constructed using Fig. UCS-66 Curve A or Curve B base material that have been exempted from impact testing by the rules illustrated in Fig. UCS-66.2 of Section VIII, Division 1?

Reply: No.

 

[YuJie_PV]

thanks David,

if i understand the interpretation correctly, i think that UCS-67(a)(1) accept exemption temperature after applying the temperature reduction per coincident ratio.

i think out a hypothetical question, which is helpful for the understanding of requirements in UCS-67. there are two same vessel except for the MOC:

a）. vessel #1： MOC， SA-36（curve A）; required MDMT， -50C； impact testing exemption temperature is -105C due to coincident ratio less than 0.35. thus, base metal SA-36 is not required to be impact tested.

Conclusion: per UCS-67(a)(1), impact testing is not required for WPS/PQR.

b). vessel #2： MOC， SA-516 70N(curve D); required MDMT， -50C； impact testing exemption temperature is -105C due to coincident ratio less than 0.35. thus, base metal SA-516 70N is not required to be impact tested.

Conclusion: per UCS-67(a)(3), required MDMT(-50C) doesn't fall into the temperature range of -29C~-48C, so impact testing is required for WPS/PQR.

if my understanding to the code is correct, the conclusions seem contradictory to common sense.
where does the problem lie?

Thanks so much.

 

[david339933]

UCS-67(a)(3) is not applicable. You are exempting based on coincident ratio not Curve D. Doesn't matter what group it is.

 

[YuJie_PV]

let me change the required MDMT, and review the examples again:

a）. vessel #1： MOC， SA-36（curve A）; required MDMT， -45C； impact testing exemption temperature is -105C due to coincident ratio less than 0.35. thus, base metal SA-36 is not required to be impact tested.

Conclusion: per UCS-67(a)(1), impact testing is not required for WPS/PQR.

b). vessel #2： MOC， SA-516 70N(curve D); required MDMT， -45C； impact testing exemption temperature is -48C per figure UCS-66 (i assume the governing thickness is 12.7mm), reduced MDMT is -105C due to coincident ratio less than 0.35. thus, base metal SA-516 70N is not required to be impact tested.

Conclusion: per UCS-67(a)(3), required MDMT(-45C) fall into the temperature range of -29C~-48C, so impact testing is required for WPS/PQR.

The conclusion still seems too odd.

 

[GD2]

Op,
There are two aspects - impact test exemption of base metals and impact test exemption of welding procedure.
Your question is on impact test exemption on welding. The rule is given in UCS-67.
As per the rule of UCS-67(3), welding impact test is required for exempted materials when MDMT is colder than -29C but not colder than -48C.
Anything colder than -48C MDMT, impact testing is required regardless of exempted or not exempted materials.

GDD
Canada

 

[david339933]

If your ratio is .35 or less brittle fracture will not occur. See UCS-66(b)(3).

 

[YuJie_PV]

GDD, and Divid, thank you both.

both your comments have basis,and seemingly correct, but conflicting with each other.


as implied in interpretation VIII-1-01-46, at least UCS-67(a)(1)seems accept coincident ratio in checking if base material (at least for curve A&B material) is required to perform impact testing when determining impact testing requirement for WPS/PQR.


@GDD， regarding UCS-67(a)(3), to make issue less complex, let's temporarily ignore the impact testing of filler metals in UCS-67(a)(3).
you may have noticed that UCS-67 never explicitly address the material exempted from impact test while MDMT <48C. what's the reason? i guess, maybe it's because such situation never exist. to be specific, there is no base material(curve C&D, no to mention curve A&B) obtaining exemption from impact testing while required MDMT<48C, if coincident ratio is forbidden, which explains why UCS-67 paragraphs are formulated such way.
conclusively, i assume at least UCS-67(a)(3) don't apply coincident ratio.


finally, i conclude that UCS-67(a)(1) accept coincident ratio, but UCS-67(a)(3) not.
so inconsistent philosophy comes out. under such provisions, a more tough MOC(SA-516 70N) may require impact testing of WPS/PQR, while a less one(sa-36) may be exempted even under a same design conditions.

so confusing, there must be something wrong.

 

[david339933]

UCS-67(a)(3) has nothing to do with coincident ratio. This is only for exempting per Curve D. If you are exempting per Curve D, you need to use impacted tested filler metals, and this can only be exempted to -55F. If it is colder than -55F you cannot exempt with Curve D.
If the coincident ratio is less than .35 you can exempt down to -155F. This is two separate ways of exempting.

For your examples both SA-36 and SA-516-70 have a coincident ratio less than .35 and therefore are exempt from impact testing. You are not concerned with UCS-67(a)(3) as it is not used in this instance.

 

[GD2]

Op,
For both UCS-67(a)(1) and UCS-67(a)(3), temperature reduction by coincident ratio is not permitted. Read the text under Para 67.
Note that exemption of welding procedure qualification for exempted materials by the rule of UCS-67(a)(3) is only conditional up to -48C. It's not a blanket exemption. Conditions are explained in the para. One of the requirements is the filler metals and the flux has been classified as impact tested by the manufacturer at or below the specified MDMT. The other condition is the limitation to individual weld pass thickness to 1/4 in.
Now you can see the logic. We have exempted materials,impact tested filler wire and flux and also limited weld pass deposit thickness limiting the heat input and ultimate residual stresses.
Going back to the CASTI statement, I would argue that the MDMT exemption don't apply the temperature reduction by the Coincident ratio.
GDD
Canada

 

[YuJie_PV]

@GDD, and David,
1 appreciate both your help. thanks so much.

@GDD, i tend to agree with you.
i've noticed the statement in UCS-67 that "The minimum design metal temperature (MDMT) used below shall be either the MDMT stamped on the nameplate or the exemption temperature of the welded component before applying the temperature reduction permitted by UCS-66(b) or UCS-68(c)."

UCS-67(a)(1) doesn't directly mention MDMT, which causes my confusion.
thanks for clarify my question, please allow me to raise one more question.

what do you think of interpretation VIII-1-01-46? is it wrong or my understanding is wrong?
is there any chance that an interpretation is wrong?
according to my experience that even though some interpretation to previous edition of ASME may be outdated and inapplicable, they always follow a consistent logic, seldom make mistakes.

Thanks.

 

[david339933]

Standard Designation:

BPV Section VIII Div 1

Edition/Addenda:

Para./Fig./Table No:

Subject Description:

Section VIII, Division 1 (1995 Edition, 1996 Addenda); UCS-66 and UCS-67

Date Issued:

05/30/1997

Record Number:

BC97-254

Interpretation Number :

VIII-1-95-158

Question(s) and Reply(ies):

Question (1): If the design of a pressure vessel satisfies the requirements of UCS-66(b)(3) in Section VIII, Division 1 such that no base material impact tests are required, are WPS and PQR impact tests required per UCS-67?

Reply (1): No.

Question (2): If the design of a pressure vessel satisfies the requirements of UCS-66(b)(3) in Section VIII, Division 1 such that no base material or WPS impact tests are required, are production impact tests required?

Reply (2): No.

 

[YuJie_PV]

@david, thanks for a new ASME interpretation. i also noticed them.

i am listening to something of Darwin recently. i find, to me, these interpretations are alike the peacock's tail to Charles Darwin.
how to account for them, i am frustrated again.

Sorry, please allow me to offer another example so as to make clear my concern which seems causing more confusion in above example:

another two hypothetical vessels, which are identical except for MOC under same design conditions:

a). vessel 3#: Required MDMT -48C; MOC, SA-516 70 (not normalized), Figure UCS-66 Curve B, governing thickness=12.7mm，look up table UCS-66, and get basic MDMT:-22C, reduced MDMT:-48C;

required MDMT=REDUCED MDMT; therefore, base material is exempted from impact testing.

follow such flow to determine impact testing of WPS/PQR:
covered by UCS-67(a)(1)? no >> covered by UCS-67(a)(2)? no >>covered by UCS-67(a)(3)? no >>covered by UCS-67(a)(4)? no
conclusion: impact testing of WPS/PQR is not required.

b) vessel 4#: Required MDMT -48C; MOC, SA-516 70 (normalized), Figure UCS-66 Curve D, governing thickness=12.7mm，look up table UCS-66, and get basic MDMT:-48C, reduced MDMT:-48C （per UCS-66(b)(2)）;

required MDMT=REDUCED MDMT; therefore, base material is exempted from impact testing.

follow such flow to determine impact testing of WPS/PQR:
covered by UCS-67(a)(1)? no >> covered by UCS-67(a)(2)? no >>covered by UCS-67(a)(3)? YES

conclusion: impact testing of WPS/PQR is required.

if my understanding to the ASME code is correct, it's odd that SA-516 70N is required to perform impact testing to WPS/PQR , while SA-516 70 (as-rolled)is not, under same design conditions.

@David, and GDD, any thought? am i missing something about the Code? thanks.

 

[david339933]

The reason is because you are abnormally thick in the first instance (relative to the thickness needed for pressure) and not in the second.
Of course if you used an impacted tested filler metal in the second, you would also be exempt.

 

[GD2]

OP,
My thoughts are following:
1. Temperature Reductions by UCS-66.1 are not allowed for qualifying welding procedures. The MDMT will be as stamped on the vessel nameplate or exemption temperature before applying the temperature reduction. Read UCS-67.
2. Are the old interpretations still valid when the Code gets revised every two years? The above interpretation of 1997 is an example.
3. UCS-67(a)(1) doesn't directly mention MDMT, which causes my confusion - In this case, vessel MDMT (stamped MDMT) or MDMT before temperature reduction will be the MDMT.

GDD
Canada

 

[YuJie_PV]

David, GDD.
Thanks for your help.
the topic could be closed even though no agreement reached.
maybe i should raise a request to the CODE Committee for a interpretation to the latest edition of ASME.
thanks