Percentages of NDT for weld Inspection in different services

[babajamali]

Hello All,
I am Piping Engineer and working in a Project and trying to classify the services we have.
We want to find out (according to ASME B31.3) how many of our services are Category D, M or Normal fluid service, then consider a Non destructive testing for weld inspection of each one.
As I know, the code only tells us that, do we need NDT or not but about the percentages I couldn’t find anything.
I want to see if we have a Normal fluid service what kind of NDT (RT, MP and LP) with what percentages we should consider for inspecting the welds.
As I found out, we consider RT only for butt weld and MP, LP for fillet welds and I believe that Visual Exam. Should be considered 100% for all welds (butt welds and fillet welds), please correct me if I am wrong.
Thanks,

 

[stanweld]

Please review 341.4 again in total and M341.4 (b)(1).

 

[Kiwi2671]

babajamali,
B31.3 only gives you minimum requirements.
It is up to you as the designer to stipulate via project specifications the required amount of NDT.
For example,some specs require RT of branch welds, some specs require RT of socket weld gaps, some specs require 20% RT of Normal Fluid Service welds, some specs require 5% of Cat D welds etc, etc - all these examples are not listed in B31.3 - they have been imposed by the designer or owner.
Regards,
Kiwi

 

[Duwe6]

The three biggest problems in compliance are:

1) Estimater failed to note that 100% of Category M welds is required, and thus you are over-budget 1/4th of the way through the project.

2) The Normal Fluid Service 5% means 5% of the total number of buttwelds [obviously], but must also include welds from every welder to ever make a buttweld on the project. This makes a tracking each welder and putting the data on a Weld Map essential.

3) The person who drafts the contract for RT leaves out that the Owner is not required to pay for any Repair RT. Remember that B31.3 has mandatory 'tracer' shots engendered by each RT Reject/Repair. One Reject causes 2 welds by that welder to be immediatly RT's, and those are to be similar to the failed one in material, size, and timeframe. If either of those tracers is Rejected, 2 *more* tracers are mandated. If either of the second set of tracers fails, 100% of that welder's work shall be RT's [or cut out]. Since field RT [gamma-ray source] costs more than the weld, the Welding Contractor always elects to cut out all of that failed welder's work.

Scenario #3 is brutally expensive, and those costs need to fall on the Welding Contractor -- he hired and certified that failed welder. Ensure that your contract reads that way.

 

[babajamali]

Thanks all for your replies:

So according to ASME B31.3 as a minimum, should we consider 5% RT for all welds regardless of the Material, means for Carbon steel, SS and Alloy are the same (percentages)?
Another question is if we are going to consider RT for butt-welds is it correct to consider MP and LP for Fillet welds?
Any Idea about the percentages for MP and LP?
Are these percentages for all Materials (CS, SS, AS)?
Do we have any additional consideration for a Normal Fluid service which is at low temperature (around minus 50 centigrade)?
Thanks

 

[metengr]

So according to ASME B31.3 as a minimum, should we consider 5% RT for all welds regardless of the Material, means for Carbon steel, SS and Alloy are the same (percentages)?

Yes, regardless of material, a minimum of 5% of fabrication welds. Make sure the selected welds are representative of all welders or welding operators.

Another question is if we are going to consider RT for butt-welds is it correct to consider MP and LP for Fillet welds?
Any Idea about the percentages for MP and LP?

I would use the same percentage of fillet welds for either wet MT or PT, using the same reason as stated above.

Are these percentages for all Materials (CS, SS, AS)?

Yes.

Do we have any additional consideration for a Normal Fluid service which is at low temperature (around minus 50 centigrade)?

This is a material suitability issue. In other words, materials should be selected for low temperature service.

 

[Duwe6]

5% is the minimum ammount of RT. A prudent engineer is expected to focus extra attention on anything he/she deems to have a higher potential for catastrophic failure, like 'loosing' a process unit due to a line break. If the unit procuces $200,000 per day [not unusual], I RT unit-critical lines at 10-20%. Cheap insurance to increase unit reliability.

 

[babajamali]

Thanks all for replying to the question.
My last question (I hope so),
Is about Visual Examination in Normal Fluid Service,
Should we consider Visual Examination 100% for all welds regardless of Material? or less than that?
Thanks again

 

[Duwe6]

I try for 100% VT -- visual exam -- of the Normal Fluid Service welds. I feel that the B31.3 5% is much, much too small a sample. If you are performing In-Process checks of the welding, you will have inspected about half of the welds by the time of hydrostatic testing. Now, just look at all the welds during the hydro. Bring a flashlight and mirror for the marginally accessible ones.

 

[babajamali]

Thanks Duwe6
What do you think about Visual Exam in Category D fluid?
We don't consider any other NDT for this services but the question is what about VT in these services?
Thanks

 

[Duwe6]

Category D I go more than 5%, but do not try for 100%.

 

[moltenmetal]

Unless I'm mistaken, the owner may elect to do no radiography in Category D, and to service test those lines (i.e. no hydrotest). 5% is the minimum for normal fluid service.

It's the owner's call.

 

[stanweld]

It's the Owner's decision (in addition to OSHA in USA or similar regulations in other Jurisdictions) as to what systems are in Category M and what additional NDE is required.

The same is true for those systems in Normal Service, Category D Service, Severe Cyclic Service and Elevated Temperature Fluid Service.

These decisions are based on safe operation of the systems and the probability of service induced failures (corrosion, stress corrosion cracking, fatigue cracking, brittle fracture, etc. and the consequences of having a failure.