Why Is "Position" An Essential Variable ? 5

[tc7]

This question is in reference to the AWS D1.1 requirements, but I suppose is applicable to all other industry Codes & Mil standards.

I am trying to understand why "position" is considered an essential variable on WPS's. From a metallurgical point of view, will a WPS read any different if a weld is horizontal or vertical? or overhead? I don't see how it would. It seems to me that a WPS is basically a recipe to create a succesful joint and should only address variables that can affect the result. Certainly I understand why the welders need to be tested & qualified to peform those welds in all the anticipated positions.

Please don't interpret my question as being defiant or challanging the Codes, I really want to understand the why's and hows of them.

Thanks for any advice you can offer.

 

[metengr]

tc7;
I will give you my 2 cents worth of advice (based on my knowledge of Codes and Standards), and my colleagues that participate on Codes and Standards bodies. First off, in ASME B&PV Code space, position is not always considered as an essential welding variable for a WPS (review QW-250).

There are two aspects for welding; skill and knowledge. The skill of the welder is evaluated by welder performance qualification. This is an important demonstration of the welder's ability to deposit a quality weld. So, things like position, backing, uphill and downhill, etc., are very important.

The WPS provides the technical requirements to the welder after they have demonstrated their ability to deposit a quality weld.

 

[MintJulep]

Because management of the melt puddle is important. In a downhand weld, you can pour a bunch of current into a weld and the puddle may get larger, but it will pretty much stay in place.

The same weld vertical or overhead, the puddle may want to run, or fall out entirely.

For thick base material, what you could do in a single pass downhand may require multiple passes overhead.

 

[emrekop]

position is just an essential variable for the welds which require impact toughness.

 

[gtaw]

In general, position is a nonessential variable when qualifying a welding procedure per ASME Section IX. It is a supplementary essential variable when qualifying for impact toughness.

The essential variables of one welding code or standard are not always the same as another due to differences in the organization’s philosophy. In my opinion, ASME concentrates on the mechanical properties of the weld, not whether the WPS will result in a weld that can be made. Again, in my opinion, AWS considers the mechanical properties and whether or not the weld can be successfully made. I’m sure the philosophy followed by ASME is influenced as a result of being sued in the “early years” by a boiler manufacturer that based their case on their view that ASME was setting themselves up as a monopoly and telling manufactures how to build boilers. ASME’s defense was that they do not tell manufacturers how to build boiler (or anything else).

ASME doesn't tell you how to design or build a boiler, pressure vessel, or piping system. They don't tell you how to make a weld or what filler metal is compatible with which base metals. ASME takes the position that you are competent to do what you are attempting to do. In other words, if you are tasked with writing a WPS based on the PQR, you are expected to know enough about welding to provide reasonable ranges for the voltage, amperage, travel speed, etc. for use by the welder. ASME Section IX or the construction codes are not going to provide much in the way of guidance about writing a usable WPS. It is possible to write a WPS that meets ASME Section IX that will not work in production. For example: Joint design is a nonessential variable per Section IX, therefore you can change the groove angle with a simple edit of the existing WPS. Change the groove angle from 75 degrees to 10 degrees and change the root opening (root gap in some circles) from 1/16 inch to zero with a few strokes of the pen. There is a good chance the welder will no longer be able to achieve complete joint penetration if the base metal is relatively thick. The mechanical properties of the weld deposit may not change, but the joint penetration may well be affected.

AWS welding codes are like cookbooks. They tell you how to make a weld and consider the WPS to be prequalified if you follow their "rules". If you decide you want to do something different, they will allow you to do so if you prove it will produce the required mechanical properties. The AWS has different essential variables because they impose limits on the acceptable ranges of voltage, amperage, groove details, etc. (base on the values used and recorded when qualifying the PQR). The welding parameters of voltage, amps, wire feed speed, etc. are needed by the welder to properly set the welding parameters and to produce welds with predictable mechanical properties (which are influenced by the microstructure, grain size, etc.). If you follow the "direction" provided by the AWS welding codes, you should have a WPS that is reasonable and should produce welds with predictable results.


Best regards - Al

 

[metengr]

gtaw;
I do respect your opinion, and I don't want to get into AWS versus ASME discussion. However, I must take exception to the following statements;

In my opinion, ASME concentrates on the mechanical properties of the weld, not whether the WPS will result in a weld that can be made.

I respectfully disagree. The purpose of a WPS under ASME Boiler and Pressure vessel Code rules is to provide technical requirements to a welder to demonstrate that a production weld will have adequate strength and ductility in service. Having a welder follow the intended weld procedure using a coupon completes the validation process for the procedure (qualification) and also indicates successful or unsuccessful demonstration of the welder's performance. Yes, there is flexibility in writing a WPS, because the Code assumes some level of technical competency. As you have heard many times, the ASME Boiler and Pressure Vessel Code is not an engineering handbook or cook book.

I’m sure the philosophy followed by ASME is influenced as a result of being sued in the “early years” by a boiler manufacturer that based their case on their view that ASME was setting themselves up as a monopoly and telling manufactures how to build boilers. ASME’s defense was that they do not tell manufacturers how to build boiler (or anything else).

Is this only your perception? Do you have proof of this? I have never heard of this since the inception of the ASME Boiler and Pressure Vessel Code.

The ASME B&PV Code is not to be used as an engineering handbook (never was and will never be), and is not to be used as to how to fabricate a boiler or pressure vessel. The intent of the ASME Boiler and Pressure Vessel Code is to provide design rules to be used for fabricating a boiler or pressure vessel to assure personnel safety and reasonably long life.

 

[gtaw]

I don't claim to be an expert and don't disagree with what you say. My comments are my perceptions of ASME Section IX, ASME construction code sections, and AWS welding codes. For the most part, I believe you and I are saying the same thing, but with different words.

Don't get me wrong, I think ASME has withstood the test of time and has been successful in accomplishing what they set out to do. A good portion of my work involves clients involved with ASME codes. However, I do perceive a major difference between AWS welding codes and ASME B&PV code sections relative to the qualification of welding procedures and how the WPSs are developed for use by production personnel. I believe it goes back to the basic premise or differences in philosophy of the two code bodies. It is not my intent to say one code is better than the other or justify the differences between them. They are what they are and I reap the benefit of those differences.

Your second question relates to the early years of ASME. The case is known as the "Parker Case". It lasted from "1915 until well into the 1930's". I found it in "The Code" (An Authorized History of the ASME Boiler and Pressure Vessel Code) purchased from ASME a number of years back. I tried to summarize a couple of pages from the book into a sentence and probably didn't do it the justice it deserves.


Best regards - Al

 

[tc7]

Thanks for all thoughtful responses and the time taken to reply. The above shows there is no such thing as a simple Code question, or at least no such thing as a simple answer to a simple Code question. But MintJulep's answer about puddle management was very interesting to me and I think came closer to my mark. So I'd like to rephrase my original question:

"If a WPS is applicable to all positions (including overhead) should the WPS specifically distinguish between the current setting, rate of progression, type of electrode, number of passes, etc. if these parameters are different than required for flat or vertical?" Or shall an entirely separate WPS be prepared only for overhead welds?

Thank you again for your generosities.

 

[gtaw]

Many companies develop one WPS supported by one or more PQRs (when required by the applicable code)for all positions.

Some companies address the variations in welding parameters needed for each welding position by developing a table listing the position, voltage, amperage (wire feed speed), travel speed, direction of progression, etc.

Your approach to the problem should be based on how the welding is performed in your company. Is the welding and fabrication done in a shop or in the field? Are you using a manufacturing "cell" where all the welding and fabrication is performed in a "cell" that entails welding in several positions? Are you moving the parts and components from one cell to the next where a specific part or component is welded in one cell and then moved to the next cell for the next operation? Each set of circumstances may use a different WPS, instead of a general all encompassing WPS, a specific WPS for the work being performed in each cell.

Best regards - Al

 

[MintJulep]

I would say, if any parameters are different, perpare a new WPS.

My reason:

With a separate WPS for each, Joe welder first needs to select a WPS based on joint configuration, material and material thickness, and position. Once he has made that decision, everything else is clearly written down for him on the WPS.

With a WPS that lists multiple parameters, Joe needs to make many more decisions. He still needs to select the WPS based on joint configuration, material and material thickness. Then he needs to made additional decisions about current, progression, number of passes and such, based on position.

Fewer decisions = less likely to make a mistake.

 

[gtaw]

I don't disagree with your advice "MintJulep". However, too many WPSs leads to more paperwork to track and control. Document control is often the weak link in many organizations.

When there are many WPSs in the system you can minimize the difficulty faced by the welder by considering how to "name" the WPSs. How do you identify and differentiate one WPS from the other. You can number them starting with 001 through 999, use Sally, Bob, Jim, or any other system you like. However, consider the individual that has to select the proper WPS. Does the individual have to start with the first one, read it to see if it applies to the work at hand, then proceed to the next until the correct one is located. If that is the scenario I can predict the WPSs will be ignored.

I use a system where the process is listed, the base metal joined to the base metal, and the filler metal used. As an example: SMA-1/8/5 is shielded metal arc welding used to join a P1 to a P8 base metal with a F5 filler metal. Likewise, GTA-1/8/6 is gas tungsten arc welding used to join a P1 to P8 base metal with a F6 filler metal.

In contrast to this system, I have one client (a refinery) that has over three hundred WPSs (for maintenance work)identified as 1 through 352 in two three ring binders. You have to read each one to see what it is for until you find the right one, a laborious task for anyone. In the best of instances, the appropriate WPS is listed on the work order.

Unfortunately, many people charged with developing WPSs have to deal with a system that is already in place, i.e., a legacy system that is cumbersome to use.

I guess we're straying from the original question about welding positions at this point and a new thread may be in order.


Best regards - Al