how can we measure a welder's rejection rate? 3

[etrobal]

i am not sure if this is the right thread but i haven't come across a quality assurance/control thread as of yet in this forum.

part of our requirements for welder's qualifications, besides being tested and qualified in accordance to ASME IX and the WPS is this section of our in-house mechanical works technical specifications:

A welder's certification shall be revoked on any of the following grounds:

(a) His overall rejection rate computed in linear inch of production weld length exceeds 3%.

(b) In any one production joint, his rejected weld length exceeds 30% of the total pipe circumference or 18 in., whichever is shorter.

(c) If there is a valid reason to question his ability to make welds that meet the specification.

however, under sub section (a), we have included after 3%, the following phrase: "after 15 days of production welding", in effect changing the whole essence of the original sub section (a), which now reads "His overall rejection rate computed in linear inch of production weld length exceeds 3% after 15 days of production welding."

is this correct? or is the original sub section (a) better?

 

[cloa]

The Quality Control Forum

http://www.eng-tips.com/threadminder.cfm?pid=286

Welding Forum

http://www.eng-tips.com/threadminder.cfm?pid=725

You'll probably still get an answer from this forum as most people read this one as well

 

[Ron]

Suppose his production rate is 20 inches per hour, with an 8 hour shift for 15 days....he welds 2400 inches of production weld. He fails 3%. That's 72 inches of weld, failed.

Wouldn't it be better to keep the time frame a bit tighter as in your original, undefined time frame you can vary the time frame as necessary, rather than running that long and finding out you have a real production/quality issue? I understand you'd be testing all along and evaluating, but under your spec. you can't do anything about it until after 15 days.

What's wrong with stating that his daily failure rate shall not exceed 3%?

 

[tomwalz]

Personally the sooner I find a problem the happier everyone is. It costs me less time and money and we can treat it as a fairly casual matter. My employees are trained to address all problems immediately. They have inspection tools and techniques. They also have tools, training and permission to address the problem.

I realize in welding you often have to have third party inspection. I would offer feedback as soon as you could. I would post everybody’s quality performance and shoot for 100%. Make sure you reinforce heavily the 100% good welds.

Maybe it is not realistic but it is what you really want. Second, you’d be surprised what a good staff can do.

In our production operation our goal is perfect. Our minimum is “Best in the World”. Sounds funny but it works. When we have a batch that is less than perfect but still more than good enough nobody really feels good about it. When we have a batch not good enough we address it immediately and correct the situation including replacing material if needed.

The type of welding with which I am most familiar is nuclear and submarine hulls where quality is really strict so the above may be unrealistic but I just hate to see anybody settle.

Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.