Welding inspection 3

[Cuyanausul]

Please tell me where to find the % of radiographic samples to take from a project, I have my AWS D1.1 but couldn´t find it. I also remember and always used 15%+15%+100% for every project, but I need to show it writen to a contractor.-
Thank you

 

[metengr]

Cuyanausul;
You won't find this in the Code, this is a technical specification that is issued by the Owner or Owner's Engineer on a case-by-case basis.

I like to specify a 10% sampling of butt welds, per weld crew, for starters. If rejectable defects are found, we typically expand the percentage sampling to 25% or higher until we are satisfied that the weld quality issue has been addressed.

 

[Cuyanausul]

So very thank you!
I spent a lot of time looking in my codes...AISC, AWS, ASME.-

But for some reason and for some time, many of my old clients and myself have been using 15% to start. Maybe in ASME B31.1 for pipe and preassure vessels? And how do you decide when clients ask for 15%, specially when this specification is not in the initial contract.-

 

[metengr]

Cuyanausul;
You can look at ASME B31.3 for guidance, there is a section on Examination Normally Required. In this section, under other examination, there is a minimum sampling of 5% of the total welds for radiography.

 

[Cuyanausul]

Ok, and acording to AISC and AWS 5% would also be the minimum?

 

[henri2]

Appendix Q, Section Q5.2 of AISC Provisions for Structural Buildings, has some criteria you might want to consider. It's based on the findings of the FEMA/SAC program

http://www.aisc.org/Content/ContentGroups/Documents/2005_seismic_provisions/SeismicProv_web.pdf

 

[Cuyanausul]

Thank you Henri:
Acording to this I could use 5% as a good start with each welder right?

 

[henri2]

If you will be specifiying UT, then Q5.2(2)(g) deals with reduction in testing. Essentially the rate of testing is 100%, but can be reduced to 25%, if the reject rate is 5% or less. This provision is similar to UBC Section 1702.

 

[Cuyanausul]

Ups...
We are actually using RT, and we always used 15% on the first group of weld for each welder, is this accepatble or could it be 5%??

 

[henri2]

In UBC Section 1702(1),exception, the reduction of percentage testing rate for UT is the same as that for RT. And since the reduction of percentage rate for UT in AISC 341-05 is essentially th same as the UBC, then I'd use that same reduction for RT.

BTW, the reduced of testing kicks in after evaluating 40 welds....and it's 25% not 15% testing rate. The 5% is the reject rate which must not be exceeded in this evaluation.

BTW, why are you specifying RT and not UT? What type of joints are you dealing with...what type of construction?

 

[Cuyanausul]

Our contractor did 5% PT, and for me that is too litle, what would yo guys say if we as main contractors make 5% RT for QA? and increase to 25% for rejected welders...

 

[Cuyanausul]

We have an industrial building one single deck.

And as far as I understand not much was writen in the contract, our contractor offered only 5% PT.

I am not at that project ( I haven´t seen the drawings), but usually we have plate to columns, single grove welds on trusses and stiffeners mainly.-

So I understand what the Codes ask is 100% UT and if in the first 40 welds we have less than 5% rejections we can go to 25%?

RT is the usual but it could be UT, is cheaper right?

 

[henri2]

So as not to mislead you, I want to make one thing clear. The AISC provision I provided was just a guide, and not necessarily code, as it will depend on which edition of the IBC applies in your area, the SDC category, R factor etc. Here in California, NDT testing (rates, reduction etc) is a code requirement for certain joints.

For commentary on UT and RT, as it applies to structural steel construction, please refer to pages 8-6 and 8-7 of the 13th edition of the AISC manual. You might then decide to switch methods.

 

[Cuyanausul]

Well thank you very much, we were also adviced to ask the recomendation of from the designer, who I believe should recomend the method and is the main responsible for this desition...

 

[ndeguy]

Cuyanansul

I dont want to teach granny how to suck eggs but just a brief note to say in these environmentally-conscious times (esp, CA under the Terminator!) every attempt should be made to limit the use of RT due to its inherent safety issues. Where a suitable other method exists, it should be used. In the case of structural steel work UT should be practical and preferential. It is better-suited to detecting fatigue-prone planar defects as opposed to the volumetric detection capabilities of RT. Previously the big advantage of RT over UT was seen as the permanent record provided by the radiographic film - plus the world and his uncle thought they were radiograph interpretation experts. Now with the low cost of computer processing power and memory permanent records of UT scans are possible, if required.

Second, on structural steel I do not understand why PT in place of MT. The latter is much quicker, equally if not more sensitive to surface-breaking defects and less susceptible to poor technique. I would only specify PT on non-ferromagnetic materials.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[Cuyanausul]

Good point ndeguy
PT was offered by our subcontractor and I believe they use it due to a lower cost and not needing to buy equipment.
And your opinion on RT is very welcome, we´ve been using it almost exclusively because no one has specified anything else.
And in my country there is only one company doing NDT. Maybe is time I do more research on UT, we´ve done it before but only where RT wasn´t feasible.
Thanks.