Limitation of Prequalified WPS-AWS D1.1-2010-Clause 3

Date 06-11-2012 02:47

Review the requirements of Clause 4, Part D for CVN requirements. The Engineer has to provide direction regarding what to test, weld, HAZ, base metal, minimum absorbed energy, and test temperature.

The range of base metal qualified, i.e., specifications, are severely limited.

A prequalified WPS includes a wide range of base metal specifications, that isn't the case when CVN is required.

Best regards - Al

By Nalla

Date 06-12-2012 00:51

Dear Al
That's waht i told Workshop Fab. Engineer.
Hi argument is Table 3.1- Include Group II & III Mat.( for example - EH36- CVN with -40 deg. celcius based on Mill Cert.)as well.

Pls guide me to where in the code it has been prohibited.
Thanks

By 803056

Date 06-12-2012 02:39

Hello Nalla;

I am using AWS D1.1-2010 as my reference.

Start with clause 4.36.3. Paraphrased: The WPS must be qualified, i.e., it must be supported with a PQR. If the PQR does not include CVN, a sample large enough to provide the necessary samples can be welded using the same parameters used when the original PQR was welded.

Since a prequalified WPS has no supporting PQR on which the welding parameters used are available, how can a sample be welded replicating the welding parameters originally used? It is a chicken and egg argument. A dog chasing its own tail.

Also, check table 4.6 for the ranges that the "new" WPS will include.

It is presupposed the base metal is already CVN tested.

Best regards - Al

By Nalla

Date 06-12-2012 12:40

Dear AL

Pls explain
Believe all Pre-qualified WPSs shown in AWS D1.1-2010- AWS must have done and documented all the required Mechanical Tests except for CVN testing as it is contractual requirement between Fabricator x Client.
So if it is the case, can i qualify based PWPS ( following AWS pre-qualified WPSs) and only carry out CVN Testing at -40 deg. celcius?
Porposed to qualify :
1 - Base material - Group II( EH36 ) x 25.4mm-thk
2 - Process - 1 coupon- SMAW & 1 more - FCAW
3 - Test Position - both - 3G-Vert-Up.

Thanks

By heritage06 (*)

Date 06-21-2012 02:29

Nalla,

Going through the post tonite and see you were still looking for an answer. Here goes. Al's logic string looks correct to me as concerns how CVN testing is performed to qualify an existing PQR. In a prequalified there is no existing PQR paperwork laying around with parameters and such to reference and reproduce. A prequalified is allowed by code based upon years of experience using process, material, joint design and good engineering judgement. Take the logic and use it. Anyone that would accept a prequalified procedure with a paper including CVN results attached doesn't understand how or what prequalified is.
Also I am not sure that if you use the material you are proposing which looks like an A-36 you are going to get any acceptable CVN results. Typically a Group II material such as A-516-Gr. 70 normalized and a weld that is post weld heat treated is needed to get any decent charpys. although you didn't state a ft-lb value to meet.
Hope that helped.

By Shane Feder (****)

Date 06-21-2012 05:53

Nalla,

Annex III
Requirements for CVN Testing

III3.3 When CVN testing is a requirement and a qualified WPS exists which satisfies all requirements except
for CVN testing, it shall be necessary only to prepare an
additional test weldment with sufficient material to provide
the required CVN test specimens. The test plate
shall be welded using that WPS, which conforms to the
limits of Tables 4.1, 4.2, and 4.5, plus those supplementary
essential variables applicable only to CVN testing
(Table 4.6). A new or revised PQR shall be prepared and
a new or revised WPS written to accommodate the qualification
variables for CVN testing.

See above - you can do what you are suggesting if you have a QUALIFIED WPS.
You cannot do what you are suggesting with a PRE-QUALIFIED WPS

Regards,
Shane

By js55

Date 06-21-2012 12:09 Edited 06-21-2012 12:11

A-36 is actually capable of quite good CVN's. The reasoning is that A-36 is a large grained material but as soon as you weld it the HAZ is essentially a normalized microstructure(unless you weld it with really high heat input). The only other issue of concern would be any dilution of the base metal into the weld metal, but since, as stated, the primary issue with A-36 and CVN's is grain size, in that it is hot rolled, this is not a problem for the weld metal either.
The only time you would have a problem theoretically is if you had a fairly low test temp and had to do unnaffected base metal. And even then, todays A-36 is not your grandfathers A-36.
I used to use A/SA-36 for nuclear CVN quals in that I knew the HAZ would exceed the UBM, simply because it normalizes the large grain, i.e., turns it into a finer grain.