QW-407.2

[castle74]

Gentleman, I had submmited a PQR & WPS to a 3rd party surveyor for review; these were in accordance with ASME IX. The PWHT time on the PQR is 2.5 hrs. at 1150 F, I
had stated on the WPS that the minimum and maximum time
at temperature allowed would be 2 to 2.5 hrs.(my interpertation of QW-407.2)

QW-407.2 " A change in the postweld heat treatment temperature and time range.
The procedure qualification test shall be subjected to PWHT essentially equivalent to that encountered in the fabrication of production welds, including at least 80% of the aggregate time(s) at temperature(s). The PWHT total
time(s) at temperature(s) may be applied in one heating cycle."

The surveyor said that my interperation was incorrect, it should be 2 to 3 hrs. 7 min..

I do not understand how the surveyor can add 80% more time
to the 2.5 hrs. max. time on the PQR. What bothers me about
this is that the charpy's are not actually proven at 3 hrs. 7 min. at 1150 F.

Can anyone add some insight to QW-407.2?

 

[metengr]

castle74;
The specific time for a single PWHT cycle recorded on a PQR can be used if this is used in production weldments. If you anticipate having to perform multiple heat treatment cycles at T for x time durations to account for repairs or at lower T for longer “t” duration, the PWHT temperatures and times are added and 80% minimum of the total times and temperatures are used to qualify a PQR. In your case, you chose to be specific for PWHT temperature and time, this is acceptable per QW-407.

T=temperature
t=time

 

[weldtek]

castle74,
Adding just a little to metengr's post,
when it comes to application of a PWHT'd and impact tested procedure, a rule of thumb is less time at temp is ok, more is limited to 20% more.
Eg. if my impact tested PQR on say 1" plate records 2 hours at 1150 F I'm qualified from .625" thickness to 2" thickness.
The .625" thick joint must be PWHT'd for 1 hr per inch minimum and two hours & 30 min. maximum.
The 2" thick joint must be PWHT'd for 1 hr / in and 2.5 hours max.
These limitations are based on ASME Sec IX.

 

[castle74]

Weldtek,

Can you explain where you located or how you came to the conclusion on "more is limited to 20% more"; for my future reference.

 

[weldtek]

castle74,
QW407.2 states that the procedure qualification test plate shall be subjected to at least 80% of the aggregate time at temperature.

 

[castle74]

weldtek,
I'm sorry.......I just don't see the 20% more.

Is it (ex. PQR 2" test plate(P1 G1) was stressed
relieved at 1150 F for 2 hrs.; while production
weld is actually 4" thick needing at least 2.5 hrs
cook time[Sect.VIII div. 1 UCS-56], so would 2 hrs.
be the "at least 80%" of the actual cook time that
should be 2.5 hrs.(100%)). And if so,is that where
the additional 20% can be added?


I like to make a correction on my first post; in
paragraph four the percentage should state 20%.

 

[weldtek]

castle 74,
Yes. You bring up a good point. When we're qualifying a PQR with impacts we have to excercise foresight to determine what PWHT requirements may be encountered on the job because our PQR must demonstrate the mechanical tests with at least 80 % of the PWHT we intend to use. Stated differently, the committee has determined that PWHT degrades impacts, and that the more time at PWHT temperature, the greater the degradation. Having said that, they are allowing us to exceed the time qualified by 20 %. If we qualify a PQR with 2 hours, that PQR will qualify us to PWHT the work for 2.5 hours. 2.5 x .8 = 2.5. We often PWHT test plates for 8 hours or more to get greater coverage with our PQR.

 

[castle74]

Thanks weldtek....I'm still having some trouble fully understanding QW-407.2, it might have to do with
my weakness with word problems (chuckle).

Oh...should the math be 2/.8 = 2.5 hrs.
(2.5 x .8 = 2)

 

[JoeTank]

Weldtek, You state... "Adding just a little to metengr's post,when it comes to application of a PWHT'd and impact tested procedure, a rule of thumb is less time at temp is ok, more is limited to 20% more" I think you meant "25%" more. Going from 80% to 100% is a 25% increase over the 80%.


Joe Tank

 

[chicopee]

Castle74;
I dont have a copy of the code but if your paraphrasing is correct of Par. 407-2 then the math used by your surveyor is 2*(1+80/100)=3.6hr essentially adding 80% to the 2 hr.min time.

 

[VeryPicky]

I love this disecting of every word in the code.
In my understanding meteng's statement is correct that the code is addressing the multiple PWHT cycles.

To confuse the issue more:
How do you ensure with your famous (or infamous) 80% the heating and cooling rates of multiple PWHT are represented in your simulated qualification? According to some research heating and cooling at 50°C/hr to 600°C translates to 1 hour at 600°C for the loss of tensile strength through tempering effect.

Any thoughts on that?

Putting Human Factor Back in Engineering

 

[pvq]

Hello Gentlemen,
After reading all the previous posted comments, I'm still confused. I have 2-1/4" thk. material test plate which will go thru a total of three heats, that totals 6-3/4 hours. How is the 80% applied??

 

[weldtek]

I think this issue is being over complicated. pvq, in your case the PQR has to have been PWHT'd for 5.4 hours minimum.
Note, for this particular situation Code doesn't make us consider heating and cooling (read ramp up and ramp down) times.