I love these types of threads. They start small and grow from the seed that was planted.
First point that should be clarified is who typically writes a code, a standard, and specification?
Anyone can write a specification. A specification can be written to describe and define purchasing requirements of an item such as a pencil. It can describe the particulars of a welding process, i.e., a welding procedure specification. It can be written by an individual, a company, or a professional organization. An example of a specification would be a filler metal specification developed by a committee under the auspices of the American Welding Society or a base metal specification developed by ASTM. A specification may only have standing within the organization that writes it or it can have national or international standing when it is developed by an organization that has national or international recognition.
A code is a special category of standards that is developed by an organization with the intention of being incorporated as a legal requirement once it is adopted by a government body. They are consensus documents where the committee membership votes on the proposed requirements or any proposed changes. Codes are organized for easy reference and can be adopted by government bodies and incorporated into legal statues, at which point they become law. Think of the building codes that reference the electrical codes, plumbing codes, welding codes, codes of standard practice, etc. Technically, the code is a standard that has legal standing. The codes also include various specifications by reference, in which case, they too become legal requirements. AWS D1.1 is an example often given as an example of a code that has legal standing once it is adopted by a governmental body such as the federal government, state government, or a municipality. Another example is the ASME Boiler and Pressure Vessel Code. Until the consensus code is adopted by a government body, it is no different in a practical sense than any other standard, that is, it has no legal standing.
A standard is an umbrella term that includes any document, i.e., codes, specifications, recommended practices, etc., that has national recognition. The committee tasked with developing the standard has to have a diverse membership and there are formal rules for the voting process. A standard has industry recognition, but may or may not become a legal requirement. AWS D1.1 is an example of a standard that is also a code. The “Statement of Use of AWS Standards” contained in AWS D1.1 describes the process and is well worth reading.
A National Standard has specific rules of how the document is developed and approved for publication. ANSI has been adopted as the organization that defines how nationally recognized documents are developed by organizations such as AWS or ASME. The committees charged with developing codes have a membership that represents fabricators, owners, suppliers, and interested parties. Even the general public has an opportunity to input and comment on the contents of the code. Examples of standards that are not codes, i.e., they are not intended to be incorporated in to legal statues include welding standards for machinery such as the D14.X welding standards, AWS B2.1 Specification for Welding Procedure and Performance Qualification, AWS B4.0 Standard Methods for Mechanical Testing or Welds, and of course AWS A3.0 Standard Welding Terms and Definitions.
Guides can be included under the banner of a standard. Two examples I like are AWS B1.10 Guide for the Nondestructive Examination of Welds and AWS B1.11 Guide for the Visual Examination of Welds. All the AWS documents cited are examples of American National Standards that comply with the requirements of ANSI.
I hope this helps answer your inquiry.
Best regards - Al
Once again a very well written answer to a question Al.
I was wondering how to state some of those differences myself while looking through some of the various referenced documents. I think you stated and clarified the issue very well.
Have a Great Day, Brent
Knew you were sandbagging Al..
Putting this response on the "return to when somebody asks me this" box.
Edit: My students asked me this same question a few weeks ago and I took about an hour to answer it, with copies of codes and copies of specifications.. But I diddn't really do it the justice you did even though I blathered on for a long time..
Thank you for the vote of confidence gentlemen.
I probably didn't do the question the justice it deserves, but the person that posted the question can go to his dictionary for the precise technical definition.
I hope everyone is well prepared for the weekend festivities. By that I mean well rested for the evening of frivolities.
My wife has the evening all planned out well in advance. I just go along for the ride. When asked, "What is the secret to a long marriage?"
The response is simple, "Learn to say 'Yes Dear'."
Happy New Year!
Best regards - Al
By 803056
Date 12-29-2010 19:00
Edited 12-29-2010 19:04
I did miss the most important part of Milles' question. The part I missed was relating to the ultrasonic acceptance criteria.
Different welding standards (remember the term standard is an umbrella covering codes, specifications, guides, etc.) have different requirements for visual acceptance criteria, ultrasonic acceptance criteria, radiographic acceptance criteria, etc. Unfortunately the standard does not typically offer a historical perspective of the “hows and why's” the criteria was developed.
Ultrasonic examination is a comparative type test. That is, the test instrument must be calibrated using a calibration standard so that the accept/reject levels can be established. Essentially, any reflector that produces a response on the display of the test instrument is compared to the response produced by the calibration standard. It is for that reason that the calibration standard must be constructed of the same material as that being tested. Different standards require the ultrasonic technician to use different calibration standards, i.e., a standard used for inspection rough aluminum forgings is not the same material or construct as the calibration standard used for inspecting welds joining carbon steel.
The ultrasonic acceptance criteria used for a rotating component subjected to cyclic loading where the load range is small relative to the load range of a dynamically loaded structure such as a bridge crane are considerably different. However, the number of cycles experienced by the rotating component is most like to be much greater than that experienced by the bridge crane. I would expect the rotating component would be much more sensitive to small stress risers such deep scratches, inclusions, undercut, etc. in comparison to the bridge crane due to the increases number of cycles the rotating component experiences over its useful life.
The decision to adopt the criteria of AWS D1.1 or AWS D14.4 is judgment call engineering should be involved with. Perhaps the non-rotating components can be welded using AWS D1.1 as the criteria and D14.4 for the rotating elements. A simplified means of comparing the two criteria is to compare the amplitude of the signal produced by the two holes. The amplitude of the 3/32 inch diameter hole will be greater than the 1/16 inch diameter hole because more of the sound energy is reflected off the large diameter hole. However, it is not a simple ratio of one hole diameter to another. You are comparing the reflective area of two round surfaces, which involves exponential relationships. In other words if you compare the area of a 1 inch x 1 inch surface to that of a 2 inch x 2 inch surface the ratio of the linear dimensions is 1/2, but the ratio of one area to the other is 1/4.
I suggest you retain the services of a UT technician that is a qualified Level III. I would recommend that you insist on the individual be qualified in accordance to ASNT's ACCP program meaning that the individual has passed the ASNT standardized test rather than someone that is qualified to in-house requirements that permits the employer to write their own examinations and allows the employer to modify the recommendations of SNT-TC-1A. You can easily confirm whether or not the individual has passed ASNT's ACCP or ASNT's Level III by going to the ASNT's website and looking under the section "Certification". You do need to know the name of the individual and the state where he or she lives. You can also look at the site to see who in your area is certified through ASNT as a Level III.
Best regards - Al
Are you talking about Amateur drinking night Al? Btw, I'm long retired from being a professional drinker, so I'm allowed to call it "Amateur Night." ;)
A SAFE AND HAPPY NEW YEAR TO YOU AL, AND EVERYONE ELSE IN HERE ALONG WITH ALL OF YOUR FAMILIES TOO!!! :) :) :)Respectfully,
Henry