Effect of PWHT on Sharpy Value of SA 516 GR 70 Plate

By Utpal Ghosh Date 03-31-2007 04:37

Our company is trying to register a PQR for Shell. The plate is 1 1/2" thickness.
The drawing calls for welding Material category P1 Group 1 to material categoryP1 Group 2. Customer specifies hardness as well as impact at -50 Deg F.
First, we made three coupons, namely for Stick P1 Group 1 ( Plate), Sub Arc P1 Group 1(Plate) and Tig P1 Group 2(Pipe). All coupons have PWHT of 1 1/2 hr at 1125 Deg F. Coupons for Tig and Sub Arc process passed.
Coupon for Stick P1Group 1 failed in hardness. Two V-notch sharpy value reading in HAZ came as 12 ft lbs. Customer did not specify any cut off limit for sharpy valye. They have specified max hardness value.
My first question is:
Q1: Had the stick coupon passed in hardness could we have used it in welding P1 Group 1 to P1 Group 2 with Stick process? ASME code does not specify PQR to indicate Group#. We intended to prepare one WPS showing P1 Group1 & 2 for stick process using Stick Procedure. Customer's inspector raised objection.
We decided to do another combination PQR to circumvent P1 Group1 to P1 Group 2 welding issue. We used SA 516 Gr 70 ( P1 Group1)and SA 516 Gr 65( P1 Group 2)as our test coupon and did tig root, mid pass stick and cap with sub arc. PWHT is done at 6hrs which customer wanted to cover at least two reapirs. Well! hardness improved, tensile passed, bend passed but sharpy value is only around 10-15 Ft Lbs as opposed to base metal's sharpy value of 170-200 ft lbs per MTR at - 50 Deg F. Customer did not specify any minimum for sharpy value.
My next series of questions are:
Q2. Does ASME Code have any minimun sharpy value for weld metal aand HAZ for SA 516 Gr 65 and Gr 70? What is the value?
Q3.What is the relationship between Sharpy value and Hardness? If Hardness goes down, can we not expect that sharpy value increases? Whay is this decrease in sharpy value?
Q 4 Does PWHT requiring minimum soaking for 6 hrs at 1125 Deg F have compared to first coupon where PWHT soaking was 1 1/2 hr at same temp have any impact on lowering sharpy value? If yes, what are the reasons?
Q5 What we need to do for WPS and accompanying PQR to qualify to weld P1 Group 1to P1 Group 2 with stick process? In short, nozzle to shell in pressure vessel
Thanks in advance
Utpal
ughosh1@hotmail.com

We decided to make new PQR with combination of processes, namely

By 803056

Date 03-31-2007 16:59

You have to read the applicable construction code to find the requirements for the Charpy V-Notch test. The preparation of the samples are critical. Not all SMAW electrodes are created equal. Make sure you select the specific electrode that is intended to be post weld heat treated.

When impact testing is required, you have to include the supplemental essential variable in ASME Section IX, Article 2, tables QW-252 thru QW265 (for the applcable welding process(es). As such, the electrode classification and the base metal P-number and Group numbers become essential variables that have to be addressed.

The post weld heat treatment variables include whether the PWHT is done at all, or if the temperature is below the lower transformation temperature, above the upper transformation temperature, or in between the lower and upper TT. The time at temperature has to be at least 80% of the aggregate time at temperature of the production work. The time at temperature is a function of the material thickness. Unless you are doing very thick sections, six hours sounds like a very long PWHT. As for the repairs, I would expect you would perform some NDT and subsequent repairs before performing the PWHT on P-1 base metal. Then once the PWHT is completed, follow up with your final NDT to verify nothing happend during the PWHT.

With the number of questions you ask, you may want to consider bring in a consultant that is well versed in welding and ASME requirements.

Good luck - Al

By js55

Date 04-02-2007 14:41

It sounds to me, frist of all, like your customer has you sorta sittin on the fence. Unless I misread. They are requiring impacts with no minimum values? Seems to me this could imply that the supplementaries do not kick in. I mean, how do you determine pass or fail? What criteria would you use to impliment the Supplementaries?
On the other hand, if you did not use SMAW against the bevel a Group 2 you could not use SMAW for Group 2.
Check Section 9, If memory serves there is a paragraph with words to the effect that you can weld Group dissimilars to qual both Groups. You can also use dual Classification base materials. Which would have been the way to go since you were using 1 1/2" material.
As for a relationship between hardness and impacts there isn't one directly. However, if you are doing impact strnegth as measured though hammer recoil then strength will definately influence your results. If you are doing lateral expansion it may be detrimental. Sounds like your doing impact strength so increases in strength will "generally", and I emphasize generally, increase you recoil. Though this is certainly not an absolute. It also depends on test temperture and ductile to brittle transitions. I think yield to tensile ratios also have an effect. Thats why the Charpy is an entirely different test and results cannot be equated with strength, or hardness. They are different tests that are asking different things of the material.

By js55

Date 04-02-2007 15:00

"If Hardness goes down, can we not expect that sharpy value increases?"
Sometimes yes. But not necessarily. It depends on where you are as far as the ductile to brittle relationship of your weld material. And you can really only determine this with a series of impact tests.
Since there is a close but not exact relationship between hardness and strength, it is conceivable that a reduced hardness could actually be detrimental to your impacts. Especially since you are testing by impact strength, i.e. ft/lbs.

Does PWHT requiring minimum soaking for 6 hrs at 1125 Deg F have compared to first coupon where PWHT soaking was 1 1/2 hr at same temp have any impact on lowering sharpy value? If yes, what are the reasons?
Most of the gains in Charpies will take place rather soon. By 1 1/2 hrs you have probably realized maybe 90% of your gain. After that, if you continue to lose tensile strength (although also diminishing in effect through time though at a different rate) its possible that you could end up losing impact strength, though had you tested using lateral expansion you may see a gain.

In the end, you are experiencing the very reason that tests have to be run. There are just too many variables for cookbook weld engineering in these cases.