Thoughts and opinions on this interpretation

By Kix

Date 07-15-2013 14:40

I ran into a brazing clause in Sec IX that I was wondering if it might have been worded backwards. The clause in question is QB-408.4 for brazing procedure qualification. Keep in mind that when manual torch brazing, it's all about the flow through in lets say a lap or socket type joint. Meaning that when face feeding the brazing rod from the front side of the joint it has to flow and be drawn to the other side of the socket or lap producing a visible indication of flow through. Also keep in mind that the grater the distance of the socket overlap or the greater the distance the braze material has to travel the harder or more technical the joint is right. Hence the reason why it stipulates in clause QB-408.1 for brazing performance qualification that an increase in lap length of 25% or more requires the individual to re-qualify, but a decrease in lap length does not. So back to the question at hand. Why in QB-408.4 does it basically say the same thing as QB-408.1 except for it's totally flip flopped. It basically says that I can increase the overlap length until the cows come home and not have to re-qualify the procedure. That just does not sound right. Any thoughts or opinions on why this may be or am I misinterpreting this?

Thanks,
Kix

By 803056

Date 07-16-2013 14:57

Why are you looking at 408.1?

The only articles listed as essential variables are articles 408.2 and 408.4. Article 408.1 isn't listed as an essential variable for any of the brazing processes.

Al

By ctacker (****)

Date 07-16-2013 18:01

Al, it is for resistance brazing, see QB351 & 351.1

By 803056

Date 07-16-2013 19:26 Edited 07-16-2013 21:41

The stated process in this case is TB, Torch Brazing, so only those essential variables listed in Article XII apply.

Silly me, procedure qualification versus brazer qualification.

OK, when you qualify the brazing procedure you must qualify the longest lap that will be used in production. That makes sense to me. It also makes sense that if the lap isn't as long, it is still qualified because it should be easier to make.

Now you qualify the brazer and the range of the lap length is extended by 25%, but keep in mind, it still cannot exceed the length that was qualified when the procedure was qualified. I guess that's reasonable.

When you qualify a WPS the thickness range is extended to both thinner and thicker base metal. When qualifying the welder the thickness range extends from the thinnest to the thicker, but still it is limited by the range of the WPS.

Al

By Kix

Date 07-17-2013 15:22

So everyone agrees that 408.1 is an essential element for performance qualification of manual torch brazing correct? ;-) Al, so back to my question about 408.4 for procedure qualification. Do you agree that the wording is slightly skewed because there is no limit to how much you can extend your lap length without having to requalify like there is for performance qualification? I guess what I'm trying to say is that I think the wording in 408.4 should be somewhat similar to the wording in 408.1, but it's totally backwards from each other. It doesn't make sense to me. It totally contradicts the fact that the longer your lap length, the harder it is to get braze material to flow to the other side of the lap.

Kix

By 803056

Date 07-17-2013 15:36 Edited 07-17-2013 16:04

I agree it is confusing.

A decrease in lap length is an essential variable per QB-408.4, but within the brackets it says the lap length can be increased without limit. I understand that a decrease in lap length is accompanied by a decrease in joint efficiency, i.e., strength, but it is more difficult to distribute the filler metal as the length of the lap is increased. However, that is only true if you are using the face feed method of introducing the filler metal.

I cannot speak for the committee, but I suppose you could say that the minimum length of lap qualified must develop the required joint efficiency. Any increase in lap length is not going to diminish the joint efficiency even if there is no bond developed in the excess length. To say it a different way, if a procedure using a ½ inch lap length is sufficient to develop the joint strength, it doesn’t matter if the lap is increased to 5 inches as long as at least ½ inch of the lap length is bonded. Even if 4 ½ inches of the 5 inch lap has no bond, the joint efficient is still met by the ½ inch of bond that is present.

Remember in the case of ASME the object of qualifying a WPS or BPS is to verify the mechanical properties, i.e., joint strength, can be met. In the aforementioned example, ½ inch of bond was all that is necessary to develop the joint strength. The purpose of qualifying the procedure has very little to do with assessing the welder or brazer’s skills or whether the procedure can be used in a production setting.

Welcome to ASME. This is no different than a WPS qualified for welding. It is entirely possible to qualify a WPS that cannot be used for production. There is the presumption by ASME that the user is knowledgeable with regards to welding, brazing, design, etc.

I always hang my hat on the fact that the code specifies the minimum requirements that have to be met. It is incumbent on the contractor to take any additional steps necessary to insure the product produced will meet the quality requirements and service requirements.

Best regards - Al

By Kix

Date 07-17-2013 17:32

Al,

This is a very good explanation that I agree with 100% and is the only thing that I would say as to why it's worded the way it's worded. However, when fabricating to Sec VIII Div 1 which is what we work to here, under UB-15, it stipulates basically that the design of the joint shall be such that however you apply the filler metal there shall be visible evidence that the brazing material has flowed to the other side of the joint. That's why 408.4 has to be all about the strength and again to your point, it's only minimum requirements. They're leaving it up to the individual in charge of procedures to be able to write multiple wps's off of the one PQR and still be able to meet the requirements of the fabrication code. Although, I wouldn't go writing a new BPS for a 1" overlap when the PQR was qualified with 1/2" and send it straight into production without proving it ya know. That could end up an expensive mistake. Thanks again for everyone's input.

Regards,
Kix

By 803056

Date 07-17-2013 17:43

Don't forget that the construction code (Section VIII as an example) can and often does invoke additional requirement upon those listed in Section IX.

Al

By ozniek

Date 08-05-2013 14:00

Hi Kix

Brazing is not my forte, but I think the issue here is to see the procedure qualification in terms of joint strength and the performance qualification in terms of skill. So increasing the joint overlap will increase strength, not decrease it, so all good to increase it as much as you want. Increasing the overlap does however require more skill to achieve, so the brazer needs to display the necessary skill, so an increase is restricted. At the end of the day, if the designer decides (for whatever reason) to increase the overlap, the performance qualification needs to show that the brazer will be able to do the job.

This is like not having a minimum diameter restriction on WPS qualifications, but there is one on welder performance qualification. (In ASME IX)

Regards
Niekie