Industrial Code vs the so-called advanced tools

Date 08-24-2019 01:03

Dear all,

A thought came across my mind during this weekend for a disscussion.

With years of experience for manufacturing of boilers and pressure vessels, I believe many practitioners like me have to work dailly with the govening Codes at the same time if in a BIG company you are also introduced to various advanced tools for "process improvement" and it is not a surprise that there has been contradictory concepts in various aspects.

One example is that the ASME Code recoganizes education, experience, and the use of engineering judgments made by knowledgeable engineers experienced in the application of the Code.

You will see Code wording such as Section I, PW-11 saying

"Experience has demonstrated that welded butt joints not requiring volumetric examination by these rules have
given safe and reliable service even if they contain imperfections that may be disclosed upon further examination.
Any examination and acceptance standards beyond the requirements of this Section are beyond the scope of this
Code and shall be a matter of agreement between the Manufacturer and the User."

For welded joints, I have never seen any Code or manufacturers establishing acceptance critieria by accurate measurement/analysis for each combination of joint configuration, restraint level, service condition, base material, welding process, filler metal, heat treatment parameter, etc.

An NDE criteria generally established to accept or reject a discontinuity regardless of the specific conditions of an individual joint is more of an industry-wide, well-recoganized, experience-based workmanship control, simply becuase Code commitees established it via a consensus process with enough number of people who believe its necessity and not many bored enough like me now for this weekend to disscuss it.

With this fact we are living with, the concept of tools such as 6-sigma with the term coming from the notion that "if one has six standard deviations between the process mean and the nearest specification limit", and with over-reliance on statistical tools will draw you into endless time dealing with charts, figures far away from the undercut, lack of fusion, porosity, root opening, etc. encountered on the shop floor or constraction site.

I really wonder if there is any one on this forum who can take a stand saying he is holding industrial recoganized certtificate such as AWS CWI and at the same time certified as a 6-sigma green/black belt. :twisted:

How you aligned this two in your head?

Any comment or throughts are welcome :wink:

By 803056

Date 08-24-2019 13:11 Edited 08-25-2019 14:34

There are several codes that recognize the use of finite element analysis as a means to deviate from the prescriptive acceptance criteria included in our construction codes and standards.

The slippery slope is the analysis has to include accurate information regarding the location, orientation, size, and character of the discontinuity and how to properly use the analytical tools the determine whether the connection is usable as-is or not. There is the danger of garbage in, garbage out.

I think many of us can rationalize that approach if the weld joint is in a region of low stress where a discontinuity may have little influence on the longevity of the structure. On the other hand, the same discontinuity located in a highly stressed region could result in a failure. The prescriptive approach for sizing and characterizing a discontinuity side steps the need to perform a time-consuming analysis of the influence of every detectable discontinuity. So, the owner has to make a decision based on economics, is it more cost effective to use the prescriptive acceptance criteria included in the governing code or whether the cost perform an engineering analysis can be justified?

Just saying.

Al

By Jovi Zhu (**)

Date 08-25-2019 08:09

Hi Al, it’s been a while. Thx for the points, good as always :grin: