If I make a test coupon of 25mm, in wich, every actual pass is 10% greater in current than previous pass. Starting from 160amp to 300 amp. Can i write a WPS with thickness 3mm to unlimited and a current from 160 to 300 amp? or i must to do one coupon for every range of current?

thanks in advance.

Hello Gaston;

You didn't specify which D1 you are using and you didn't specify which welding process you are using. That can complicate the matter of providing you with a reasonable response, especially if you are trying to qualify a WPS that includes notch toughness testing.

In general, a welder is going to vary both voltage as well as welding amperage during the welding of a test coupon. To add to the "problem", travel speed is often varied unless the welding process is mechanized or automatic. What you propose is acceptable provided the welds deposited are acceptable. Your PQR would list the range of the parameters used, i.e., voltage, amperage, and travel speed.

Best regards - Al

There are a number of issues that must be addressed when qualifying a WPS that meets toughness requirements. AWS D1.1-2010, Table 4.6 lists the supplementary essential variables (in addition to the essential variables listed in Table 4.5). Right off the bat there is thickness limitations when notch toughness is a concern that is more restrictive than a "regular" WPS. For instance; Table 4.6, item 2 limits the minimum thickness to T or 5/8 inch, whichever is less. There goes the one test or unlimited thickness idea. 

My question regarding how the heat input will be calculation is simple. If the welding parameters are intentionally increased from one bead to the next, how is the heat input for the completed assembly going to be calculated? Is the heat input based on the average voltage and current used once the plate is welded? Is the heat input based on the average heat input calculated for each weld bead? Is the travel speed held constant or is it also a variable? Is the "average" representative of the heat input of the location where the CVN specimens are removed from the plate? My response would be that is does not when the root is intentionally deposited at low heat input and where the final weld beads are at high heat input (by design). In this case, there will be no correlation between heat input and the absorbed energy because the heat input of every weld bead, hence every layer will be different depending on which thickness the specimens are taken from. The values of absorbed energy would only represent the toughness of that specific location.

There will be some spread measured for the values of voltage, amperage, and travel speed when the welded assembly is welded manually. However, the spread is assumed to be within a relatively tight window because the welder should not be changing the parameters while welding the assembly. If the welder changes the welding parameters, the heat input is a variable that isn't controlled and nothing is "proven" by testing one specific location in the welded assembly.

The usual goal is to weld the assembly using the highest heat input anticipated in production to verify the welded assembly meets the toughness requirements of the project. There is no standard toughness requirement in AWS. The Engineer must specify what absorbed energy and what test temperature is required for that specific project. The design parameters can, and usually do, from one job to the next. If the test fails, the heat input or other variable is modified to produce the required values.

Let's consider Forest Gump making his trek across the USA. He starts out at a walk when he leaves the east coast and slowly increases his speed to the point he is running at the speed of light by the time he reaches the opposite shore. If his speed is clocked in Rhode Island, he is walking at a leisurely pace. By the time he is at the New York / Ohio border he is running at 1000 miles an hour, by the time he reaches Omaha he is going at 5/8 the speed of light and finally he is clocked doing the speed of light in San Diego just as he hits the water line. Poof, he disappears in a cloud of steam. Do we assume he is in a different dimension? That’s a different question for another time. Now you need to figure out if his running shoes were robust enough to withstand the rigors of high speed running. Where do you measure his speed? It varies from one location to the next. When and where did they fail? You only have one opportunity to check his feet to see if his shoes are still intact. You check him when he reaches Memphis. They are still on his feet. Good results. However, just because the shoes were intact when he passed through Memphis, does that mean they were still intact when he got to Kansas City, Denver, or San Diego? That is essential what the poster is trying to do. He is varying the heat input, continually increasing it, until at some point it may no longer meet the toughness requirement, but where did the heat input reach the point where toughness dropped below the acceptable value? Gaston is only testing his sample at one location. The code tells you where that location must be; in this case the shoes are check when Forest reaches .........  

Best regards - Al

They are called jokes here in the US. An attempt to lighten the mood. Sorry if you found no humor in them. Everyone's sense of humor is a little different. What is considered funny in one country isn't so funny in another.

The Forest Gump example was an analogy, an exaggeration, to make a point.

Since my way with words offended you, I will not make the mistake a second time.

I looked at the photos of some of the projects your employer has been involved with. Very nice.

Contractors/fabricators have many different ideas of what the purpose of a WPS is. They develop their WPSs to address the problems encountered in their respective shops. One shop may be welding on material types and thicknesses that are limited. Other shops are welding a variety of base metals and many different thicknesses. A company that has a large production run of one type of base metal and one widget will have a WPS that is specific to that one widget or just one particular weld. Other companies use a very general WPS that can be used for a range of material thicknesses.

In a similar manner, different codes have different requirements regarding how the WPS is to be qualified and documented. They may limit the thickness range as does ASME when qualifying GMAW using short circuiting transfer. The code may make the thickness range qualified more restrictive when notch toughness is required. Our job, whether it is as an engineer, inspector, or line supervisors is to ensure the welds made by the welders are sound and meet the requirements of the applicable code. The one working document we use to provide information to the welder is the WPS. It must be detailed sufficiently to provide them with the level of detail needed to make a code compliant weld.

For general structural fabrication of most structural steel composed of low carbon and high strength low alloy steels a general WPS with generous ranges for voltage, amperage, wire feed speed, travel speed, etc. is sufficient. However, when toughness is an additional requirement it is usually specified because the operating/service conditions involve impact loads and/or low temperature applications. Since different steels behave differently at low temperatures or because different rolling practices may be involved the codes are usually more restrictive on the thickness ranges qualified and the welding parameters used. Once again, the contractor depends on the welding engineer and the inspector knowing when to be generous with the ranges and when to be more restrictive with the ranges of welding parameters. We in turn, depend on the welding standards and codes to provide a certain level of direction. We cannot be all knowing, but the welding standards and codes cannot anticipate every conceivable situation. Engineering judgment and experience comes into play for the unusual situations we encounter. We are human, mistakes will be made. Once in a while a major tragedy will shake us from our complacency and hopefully we learn from our mistakes.

By the way, your English is fine. Much better than my Spanish.

Best regards - Al