Need Expert Advice:-
Contract Spec asks for 100% UT & RT on butt joints and to assess in accordance with AWS D1.1
Actual event : UT was carried out on 1" thk butt joint (groove weld) and the result was satisfactory. Thereafter, RT was done on the same joint but the result was unsatisfactory due LOF and porosities.
Note that UT was carried out twice using inhouse NDT technician and by a NDT third party. Both of them gave the same result - Satisfactory.
Question raised by the owner: WHY UT missed out those defects?
If let say you are the Project Engineer in-charge, how you will handle the situation. AND if you are the Third Party Inspector, what will be
your suggestions.
Thank You
Ariel D C
As a tech I would like to know:
1. Grade of material.
2. Actual welding symbol used and was a welding procedure avaiable and USED.
3. Was this a static or cyclically loaded nontubular item?
As far as why you got different results a lot depends on the above items and more.
Like any technology that involves humans, there are good UT operators and those that aren't as good. The same applies to any other disciplines (consider the number of doctors that practice medicine. Not all of them graduated in the top 10% of their class).
As the project engineer, you should review the written practice that describes the training, experience, and examination of those seeking certification for the NDT method. Next, review the certification of the individuals performing the NDT. Last. but not least, consider making up a test sample with known "defects". Have the NDT technician test the sample and compare the test results. This method can usually separate the competent from the less than competent test technicians.
Remember, each NDT method has limitations. However, properly applied, UT should provide the most information if the written procedure provides adequate direction and the technician follows it correctly.
Best regards - Al
Each NDT method has different advantages, disadvantages and limitations. RT and UT are both considered volumetric inspections, as it tests the entire "volume" of the material or weld in your case. But, these two methods are not identical or interchangable. For example: UT may miss scattered porosity, while RT may miss tight lack of fusion or planar flaws. I can't stress the word "may" enough because so much is dependant upon the particular situation, material, and method technique as well as many other variables.
If the spec. calls for both methods of inspection, you may want to check with the EOR to see if this is really the intention. If so, then you will have to deal with the results of each examination independently. Sometimes both methods will accept or reject the item, and sometimes either one or the other will reject the item- that is the way it is and this should be communicated to those involved so there is no misunderstandings along the way. If both of the methods were equal in identifying defects, then you would only have to do one test.
-Chris
Ariel, the sound path of the UT can miss discontinuities due to position of the discontinuity in the weld. If the discontinuity is in a similar angle as the sound path then the discontinuity can be missed, sort of like throwing a ball at the edge of a knife rather the broad side of the blade. The discontinuity may lay in the same direction as the sound path for the A face of the scan, but if scanned from the B face it may cross the sound path showing up easily. The angle of the sound path will also have an affect on results. The weld geometry could also be affection the results.
Regards, Jerry
Thank you guys!
Mr. kipmank (Mankenberg) if you are there,,any comments from you Sir?
-Ariel D C
By -
Date 12-19-2005 14:42
Ariel,
Without further information, I am going to presume that both the UT and the RT were performed in accordance with the specified requirements.
One possible cause of an acceptable UT and subsequent rejectable RT is the overlap in acceptance criteria. If you do a close comparison of Table 6.3 and Figure 6.4 of D1.1, for instance, you'll notice that in some cases a discontinuity indication may be acceptable to one set of criteria and rejectable to another set of criteria. It is a bit like comparing apples to oranges.
There are many other possible factors, as mentioned in the other posts. One thing about D1.1 Section 6 UT is that in some cases only one search angle is required (Table 6.7), and in that scenario it is very possible that a discontinuity may not be detected.
Additionally, the instrument calibration requirements for D1.1 are very complex and a number of studies (e.g. FEMA) have shown that most UT technicians cannot properly calibrate the instrument for a Section 6 UT exam. When a difference of 1 dB can be the difference between acceptance and rejectance, the lack of a proper calibration can lead to further inaccuracies.
In order to try and root out the cause of this, you will want to get together all parties involved (i.e. the RT and UT people) with their original reports. It would be best to do this before the weld is repaired so that the excavation may be witnessed to further confirm the examination results. Then run through all of the various factors that can have a possible bearing on examination results - some of these factors I have mentioned, some have been mentioned in the other posts, and there are others yet that have not been mentioned.
This all needs to be done in a calm environment - everyone needs to realize that there is a potential problem (it is not certain there is a problem - it is possible that both exams were conducted properly) and that the objective is to understand the situation and not to place blame.
If a problem is uncovered (for instance one of the exams was performed improperly), use the new information to improve the process and not to place blame.
Mankenberg
The UT is conducted prior to RT in order to detect unacceptable discontinuities. This is a cost effective tool used throughout the industry. If discontinuities are detected with UT, repairs can be made without the expense of further testing.
Many times UT will detect discontinuities which may not be resolved with RT, and vice versa. Both methods should be utilized for quality purposes.
In conclusion, American Welding Society Standard AWS D1.1 is not a code but a set of recognized standards and procedures which are readily achievable by qualified crafts persons. NDT is merely a recognized method of assuring quality results.
Best Regards,
Vonash
By -
Date 12-20-2005 15:25
Vonash,
I have to disagree with you - AWS D1.1 is indeed a code and it carries the weight of law when its use is required by local building codes.
Mankenberg
KIPMANK,
If you know anything special about the American Welding Societies legal onus, please let us all in on the data.
Best regards,
Vonash
By -
Date 12-30-2005 18:50
Vonash,
I'm sure that I don't know any more about it than you do. All I really know is what is stated in AWS D1.1 in the "Statement on Use of AWS American National Standards". The second sentence here states "when AWS standards are either incorporated in, or made part of, documents that are included in federal or state laws and regulations, or the regulations of other governmental bodies, their provisions carry the full legal authority of the statute".
In the past I have worked on numerous projects where the state and local building codes required the use of D1.1 for structural welding. Currently, I am involved in a number of US military projects that also require the use of D1.1 for structural welding. In both instances, I am aware of cases where individuals and/or organizations either maliciously or negligently did not adhere to the requirements of D1.1 and were subsequently legally prosecuted or otherwise penalized. That sounds like a code to me.
Best regards,
Mankenberg
Thank you Mr. Kip
Thank you guys for sharing your knowledge.
Regards
Ariel
Kipmank,
Your post appears to be semantics.
By -
Date 12-31-2005 18:31
Vonash,
Semantics could be our problem. I take it then that we are in agreement on the legal status of D1.1?
Mankenberg
Greetings everyone and Happy New Year,
Kipmank,
I am a Welding Inspector based in Australia and I have posted quite a few cries for help from my fellow inspectors on this forum regarding AWS D1.1.
I am involved frequently as the clients representative on the construction of heavy earthmoving machinery valued in the $80 - 100 million mark and the OEM's are very large American companies.
I am constantly confronted with the clause (I haven't got my code with me at the moment) that allows the OEM to assume some or all of the duties of the " Engineer".
Then when you go to the clause describing the role of the Engineer it states that they can change or modify the code as required. ( As long as it is reflected in the contract documents)
Everytime I query something that appears to be not quite right I get the response that we are the OEM so can change it as required.Sometimes the contract is still being finalised well after the job has started so these changes may be added to the contract documents after the welding has commenced.
Now I find out that these three very large American companies are only using AWS D1.1 as a guideline and their internal welding standards only comply with AWS D14.3 as a minimum.They clearly state in these standards that they do not and are not meant to fully comply with AWS D1.1.
How can they use the OEM clause from AWS D1.1 if they are only using the code for a guideline.?
I consider a specified code/standard to be my bible and it will clearly tell me what is acceptable and what is not acceptable and it is pretty black and white.
How can you call it a code if it can be chopped and changed to suit ?
Your thoughts / clarification on these queries would be greatly appreciated,
Regards,
Shane Feder
I have to step in and put my 2 cent in here. The codes including AWS D.1.1 are not guidelines but minimum requirements.
However, most codes including AWS and ASME have provisions that allow parties to deviate from the requirements as long as they are incorporated into the contract documents and all parties are in agreement or as in the case of ASME the "inspector" is satisfied.
That is not to say an "Engineer" or an "Inspector" can do whatever he/she wants. They must be able to justify it.
The contract is the legal document unless in a case where local Federal and/or State laws have jurisdiction and states a code is mandatory, the code must be followed.
By -
Date 01-04-2006 18:50
Shane,
The OEM provision was added in the 2002 D1.1. The definition of "OEM" at paragraph 1.3.4 does not make the code writers' intentions very clear. However, they did include some excellent commentary at paragraph C1.3.4 on this issue. In effect, the commentary here says that the relationships and responsibilities of the Owner, Engineer, and OEM need to be defined in the contract documents. It sounds like in your situation this has not been done, and based on my experience (see below) this will inevitably lead to the sort of practices of which you speak.
I am currently working for a company that manufactures mining equipment in addition to our US military work, and since I've been on board I have been pushing this exact same issue with our company's top management. Some of our engineers had been of the belief that because we are an OEM they are able to make any and all changes that they see fit. I did not have any contention with the nature of the deviations to the code that they were proposing/accepting - I believe that they were using good engineering practice in all cases.
My problem with our situation was that because we are selling this equipment as being "welded in accordance with AWS D1.1", any time there was a deviation to the code that was not agreed to by the client and that was accepted by we the OEM, we were in effect misrepresenting our product to our client (i.e. the Owner). Essentially we were not adhering to paragraph 1.1 of the D1.1 code (see also C1.1). What we are currently doing to address this is to:
--either switch to AWS D14.3 (which is more applicable to the equipment that we fabricate anyway) or,
--for equipment manufactured to D1.1 ensure that the wording in the purchase documents reflects exactly "how the various responsibilities are handled", as is stated in D1.1 C1.3.4.
Mankenberg
Kipmank,
Thank you for your response.
One of numerous discrepancies that I have encountered was posted on this forum earlier regarding welder qualification.
The machine was supposedly "welded in accordance with AWS D1.1" but welder quals were radiographed ( short-circuiting arc) instead of having bend tests which if I am interpreting the code correctly is not allowed under AWS D1.1.
I am strongly pushing to have repair / maintenance work done on these machines using the Australian structural steel code which does not have the OEM clause.(AS/NZS 1554 Part 1 is very similar to AWS D1.1)
It is my personal opinion that once a machine has been paid for and it is well out of its warranty period then engineering decisions should be made by the owner (with technical advice/input from the OEM).
Regards,
Shane Feder
Ariel DC,
Your question was best answered by jfwi, gerold, and 803056.
All of these make sense.
Best regards,
Vonash
