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Technical Discussions
Michael
Michael
23:49 Mar-09-2010
ASTM A578 clarification of Level B

The acceptance criteria for 7.1 (Level A) and 8.1 (First half of Level B) are identical. The issue that has been coming up more and more with our clients and other inspectors is what role 8.2 plays in rejecting a plate. The use of the words, "in addition" confuses many. Is this to imply that a plate would have to fail 8.1 and also 8.2 in order to fail Level B? Or can it pass 8.1 but fail 8.2 and therefore fail Level B? It boils down to whether "in addition" means a plate has to fail both criteria or just one.

I have had a Level III tell me he had no idea, and another one tell me that for decades he has believed a plate has to fail 8.1 and 8.2 in the same spot without moving the transducer in order to fail Level B. I can't imagine a plate in the world being so terrible it would fail both at the same time, but the "in addition" words lead many to believe this is what it means.

Secondly, 8.2 speaks of "two or more discontinuities smaller than described in 8.1." To clarify, does this mean that while scanning at your back-reflection calibration decibel level, that any indication you see whatsoever is subject to evaluation and failure? It seems like a huge contrast between Levels A, C, and Level B regarding how strict the quality level is. I have never rejected a plate on Level A or C because there would basically have to be a golf ball lodged in the plate for it to lose 100% BR for 1-3 inches. However, I reject plates on Level B all the time due to the 8.2 clause. I see lots of plate that has numerous adjacent clusters of midwall indications going on for more than a 3 inch circle.

Also, when clients request ASTM A578 Level II, what do most other inspectors use as their rejection criteria? Level II is an outdated, obsolete reference that I know does not equal Level B.

    
 
 
Derek
Derek
12:57 Mar-10-2010
Re: ASTM A578 clarification of Level B
In Reply to Michael at 23:49 Mar-09-2010 (Opening).

You are right when you say that 7.1 and 8.1 are Identical but paragaph 8 is seperate acceptance criteria than that of Level A. 8.2 is additional acceptance criteria for Para. 8 Acceptance Standards-Level B. What is being said is that if you have indications that do not exceed the requrements of 8.1 then you must evaluate it to 8.2. multiple indications must be measured for size(-6 dB method would suffice) and then measured for distance from eachother. The distance from eachother must be greater than that of the largest indication to be acceptable. The last statement can be difficult to interperate, but i think it is best explained with an example.

Ex: 2 indications in steel plate.

Discontinuity 1: 100% LOB 1.5" approx. diameter
Discontinuity 2: 100% LOB 1.0" approx. diameter
Discontinuity 1 and Indication 2 are seperated by .75"

Discontinuity 1 and Discontinuity 2 are not seperated by the minimum distance required "(8.2) shall be unacceptable unless seperated by a minimum distance equal to the greatest diameter of the largest discontinuity(1.5") or unless they may be collectively encompassed by the circle described in 8.1 (3" diameter).

If you measure the the diameter of the discontinuities with the addition of the .75" seperation it is 3.25" The discontinuities must be seperated by 1.5" or fully encompassed in the 3" diameter circle as described in 8.1. The total diameter of the discontinuities is 3.25" which cannot be contained in the 3" circle.

These discontinuities would be rejected to paragraph 8.2.

I hope this helps with your question. It is pretty generic but it gives you the basic principal.

    
 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
13:38 Mar-10-2010
Re: ASTM A578 clarification of Level B
In Reply to Derek at 12:57 Mar-10-2010 .

Good well thought-out answer, Derek!

Michael, it reads to me as if you have been doing it right all along. What particularly charms me about your post is the insouciance of the Level III who replied "Nah, not a clue mate" when you asked for clarification! The 2nd Level III's response that you can (have to) evaluate the acceptance/rejection of a lamination without moving the probe also raised a laugh!

    
 
 
Michael
Michael
15:29 Mar-10-2010
Re: ASTM A578 clarification of Level B
In Reply to Derek at 12:57 Mar-10-2010 .

Per Derek's response:

I agree that 8.1 and 8.2 should be used separately and that a plate can fail either one not necessarily both. Another point of clarification, however, is regarding the definition of "smaller than described in 8.1." Your example uses two indications that lose 100% BR. What if they were indications that did not affect the back reflection? What if they only produced 50% LOB? They would technically be "smaller than described in 8.1." This is a recurring issue, as I scan plate that has dozens of small indications midwall adjacent to each other, but they do not produce any loss of BR. Once they go on for more than a 3 inch path, they technically are "smaller than described in 8.1" and exceed the "encompassed in a circle as in 8.1."

While this interpretation makes sense to me, it seems like a huge gap in quality level between total loss of back reflection for 1-3 inches and any relevant indications for more than 3" It appears there is no middle ground with this interpretation, but 8.2 does not say you still need to lose any back reflection.

    
 
 
Derek
Derek
13:06 Mar-11-2010
Re: ASTM A578 clarification of Level B
In Reply to Michael at 15:29 Mar-10-2010 .

Michael,

I would still interperate the indications at requiring the 100% loss of back reflection due to the "In addition" statement at the beginning of 8.2. To me that means that you would still need to meet the requirements of 8.1 except as described as smaller indications which is elaborted in 8.2.

In your example of the indications with only 50% LOB appear to be acceptable as long as they do noe exceed the 3" circle requirement. If we were to say that the indications that i described earlier each had 50% LOB would still be rejectable because they cannot be encompassed in 3" diameter circle. If the indicatins were able to be encompassed they would be acceptable.

This is only my interpretation of this spec. I have never had to work to it at all, but i would also be asking the same questions if i were to find similar indications as we described. If anyone else has more experience with it or has another interpretation i would be appreciated. The more the merrier. I wouldnt rely on only my response.

Derek

    
 
 

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