Usually, when I write an article or post, it is motivated by questions asked by customers or clients. Regrettably, the question of “At what point do I need to re-qualify my welding procedure specification?” is not asked that often, but it should be. So before we get into that, first, let’s answer the question, “what is a welding procedure specification?”
A welding procedure specification (WPS) is a set of instructions that ensure a sound weld is followed to the letter. A welding procedure specification will typically provide ranges rather than single values for variables such as amperage, voltage, and travel speed. Nonetheless, if the values used for making a weld are outside the WPS parameters, it has been violated. A WPS is like a recipe. It tells you what ingredients and quantities you need to create the desired weld.
You can learn more about PMET’s weld procedure services here.
When to Re-qualify a Welding Procedure Specification
After your preliminary welding procedure specification, you will need to re-qualify. The answer is always when the code or specification requires it. You should always reference the code you are working on for guidance when doing code work. Most codes have similar requirements when the re-qualification of a WPS is necessary. In general, any change beyond the limits of the procedure qualification record (PQR) will require requalification. If any of these welding variables change, consult your code or specification to see if you need to re-qualify a WPS.
- Type of base material
- The thickness of the base metal
- Joint design
- Pipe diameter
- Type of current
- Electrode size
- Electrode classification
- Welding current
- Position of welding
- Contact tip to work distance
- Deposition of weld metal
- Preparation of root of weld for second side welding
- Preheat and interpass temperature
- Post heat treatment
How do you prepare welding procedure specifications?
ABC Company is doing work governed by the AWS D1.1, Structural Welding Code – Steel. As a cost reduction and efficiency improvement measure, the company decides to make the following changes:
- Switch to .052” ER70S-6 mig wire from .045” ER70S-6 wire for higher deposition rates in some areas
- Increase amperage from 250 to 265 with .045” ER70S-6 wire to increase deposition rates in remaining areas
- Change from tapered nozzles to ¾” ID and an increase from 40cfh to 45cfh to reduce issues with porosity.
- Switch their shielding gas mixture from 75% argon/25% CO2 to 90% argon/10%CO2 to reduce spatter and decrease grinding
- Some welds will be made vertical up to improve penetration and reduce leaks (using the same parameters)
Considering these changes individually, here is how things would shake out. We reference AWS D1.1, Structural Welding Code – Steel – Table 4.5 – PQR Essential Variable Changes Requiring WPS re-qualification for SMAW, GMAW, FCAW, and GTAW review each change.
- Switch from .045” to .052” – Table 4.5(10) indicates that “any increase” in filler metal diameter shall require requalification.
- Amperage increase from 250 to 265 staying with .045” wire – Table 4.5(12) requires re-qualification if the change in amperage exceeds 10%; therefore, we do not need to re-qualify in this case, a 15 amp increase only represents a 6% change.
- Change in nozzle size and gas flow rate – Table 4.5 does not mention changes in nozzle size as an essential variable. However, go to the engineer or the customer for clarification when in doubt. The change in gas flow rate does not require requalification per Table 4.5(20). A change is only necessary if the flow rate goes up by more than 50% or is reduced by more than 20%.
It is crucial to consider the effects of changes here as well. For example, differences in the nozzles may not be essential welding variables. Still, if the larger nozzle hampers access and requires the welder to run a longer contact tip to work distance, this could decrease the amperage to the point which requires re-qualification.
- Switch from 75/25 to 90/10 argon/CO2 shielding gas – Table 4.5 (19) requires a change when the gas composition is changed, exceeding code limits. In this case, a change of more than 10% of the minor component requires re-qualification.
Also, this change allows ABC Company to go from globular transfer to spray transfer. However, this is a metal transfer change mode that requires re-qualification per Table 4.5 (14).
- The addition of vertical up welds – requires qualification as well per Table 4.5 (30), which states that re-qualification is needed “for any pass from uphill to downhill or vice versa.”
Sound knowledge of welding processes, welding procedures, and understanding the code or specification are critical. If you don’t have this at your company, give Pittsburgh Mineral and Environmental (PMET) a call or email us. We can provide this type of assistance.