PQR Essential Variable Changes Requiring WPS

[78500902]

Hello,

I am quiet new to this world of welding and I need help to develop a WPS with AWS D1.1.

I need to develop a PQR that qualifies me all the positions possible for a butt weld on a plate, for production welding, and this procedure will have impact requirements. I go to table 4.1 and the recommendable position will be 6G in pipe. My question comes when I see table 4.6, for PQR Supplementary Essential Variable Changes for CVN Testing Applications Requiring WPS Requalification for SMAW, SAW, GMAW, FCAW, and GTAW, which states "A change in position to vertical up. A 3G vertical up test qualifies for all positions and vertical down".

Therefore, does a 3G up qualify all plates when impact testing is required?

Thanks in advance!

 

[gtaw]

As I read the code, specifically Table 4.5, item 30, I see that a change in vertical progression is an essential variable. As such, a WPS qualified, by testing in accordance with clause 4, in the vertical uphill direction is not qualified for vertical downhill progression. Likewise, a WPS qualified for downhill progression is not qualified for uphill progression.

Table 4.6 lists additional requirements that supplement the essential variables included in table 4.5. With regards to table 4.6, item 6, the table indicates that a WPS that is qualified for vertical uphill progression is also qualified with regards to notch toughness for downhill progression. That does not mean that the WPS qualified for uphill progression is also qualified for downhill progression (table 4.5 item 30). It means that the contractor would be required to qualify two procedures, one using vertical uphill progression and a second coupon welded using vertical downhill progression. Only the procedure qualified using uphill progression would have to pass the notch toughness testing. Since the heat input affects the grain size, thus the notch toughness, a WPS successfully qualified for uphill progression using high heat input would have lower heat input using downhill progression. The lower heat input would typically provide notch toughness on par or better than the WPS qualified with higher heat input.

Clause 4.36.3 states that the WPS must meet the requirements of table 4.1, 4.5, and the supplemental requirements of table 4.6. Position limitation is listed in table 4.1, the essential variables that have to be addressed by the WPS (and PQR) are listed in table 4.5, plus the additional (supplementary variable) are listed in table 4.6. Table 4.6 is not a standalone list of the variables that must be considered when qualifying the WPS for notch toughness.



Best regards - Al

 

[Fizza453]

gtaw(structural),

I agree with you regarding the above interpretations.
I believe case is not like this in ASME Section IX. Uphill or downhill is not essential variables for procedure qualification when impact testing is not a requirement.
In case of toughness requirements, QW-405.2 is invoked for some welding processes, that says PQR made with vert up qualifies for all welding positions, so just one PQR would be required to qualify all positions. Do you agree?

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[gtaw]

ASME does not generally consider position to be an essential variable. They include position provisions as a supplementary essential variable when notch toughness is a requirement because the position and direction of progression can have an effect on heat input.

Vertical uphill progression typically employs slow travel speeds and may use a wide weave bead technique. In comparison, downhill progression typically employs stringer beads and high travel speeds to stay ahead of the molten weld pool and slag (if a welding process that utilizes flux as a shielding medium). The slower travel speed, assuming all other variables are held constant, produces the highest heat input and larger grain size. The heat input influences the cooling rate, thus the grain size. There is a correlation between grain size and toughness. In general the correlation is the smaller grain size typically exhibits better toughness when compared to larger grain size.

There are other considerations that have an effect on cooling rate and grain size: such as the use of preheat, ambient conditions, etc. However, those conditions are held constant when comparing heat input and comparing the resultant grain size and toughness.

Codes such as AWS and ASME utilize the knowledge that the high heat input associated with vertical uphill progression will produce the largest grain size and lowest impact test results when compared to other test positions. It stands to reason that if the test results of the coupon welded in the vertical position using uphill progression meets the minimum toughness requirements of the design or code, any weld made in a different test position will meet the minimum toughness requirements as well. Therefore, why test each test position for toughness if the worst case has already proven to be acceptable?

In cases where the test position is considered to be an essential variable, such as AWS D1.X structural welding codes, NAVSEA welding standards, etc., the contractor still has to weld test coupons in the required test positions. However, some welding standards simply allow the contractor to forego the notch toughness testing if the coupon welded in the vertical position using the uphill progression passes the notch toughness testing requirements. It saves the contractor and customer time and money by eliminating the need to do additional notch toughness testing for each test position.


Best regards - Al

 

[78500902]

Thank you very much guys, so if I interpret correctly, for production team the best qualification to cover all positions will be:
- 6G or 5G if pipe is available
- 2G, 3Gup and 4G to cover as many positions
?

Is this correct or how would you qualify a procedure?

Thanks!!

 

[gtaw]

If you are testing for impact toughness and you are using an "open root" joint, you do have to qualify the WPS.


Best regards - Al

 

[78500902]

gtaw I understand your idea, but my question is:

I need to qualify a WPS, which positions I use?

 

[gtaw]

What positions will be used in production?

If vertical is one of the positions used in production, I would qualify it as well as the other required to comply with D1.1, but I would include notch toughness testing when I qualified the vertical (uphill progression) position.



Best regards - Al

 

[78500902]

Al, in production we want to be sure there will be no problem, so as you say I think I will do 2G (qualifies F, H), 3G up (qualifies V up) and 4G (qualifies OH), and to comply with CVN I will do impact testing only on 3G up (according to table 4.6 qualifies all). Like this I imagine I cover all/most positions on plate. Do you agree?

Thanks for your time, you have been of great help!

Regards,

 

[gtaw]

That sound about right.

Al

Best regards - Al