5 Essential Factors to Consider when Choosing an NDT ...

Non-Destructive Testing (NDT) plays a crucial role in ensuring the integrity and reliability of various materials and structures. When selecting an NDT method, it’s important to evaluate several key factors to ensure its effectiveness and practicality. In this blog post, we will discuss the five vital elements to consider when choosing an NDT method: accuracy and precision, speed, quantitativeness/objectivity, automation, and affordability.

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Accuracy and Precision

The primary purpose of NDT is to provide accurate and precise inspection results. If an inspection method lacks accuracy (does it get the right answer?) and/or precision (does it get consistent answers?), it becomes unreliable and loses its value. Therefore, it’s crucial to select an NDT method that:

1. Offers sufficient resolution and reliability to detect the defects of interest in your application.
2. Demonstrates excellent Gauge Repeatability and Reproducibility (Gage R&R) to ensure consistent and dependable results.
3. Has had its accuracy and reliability assessed and validated via methods like destructive cutups, referee NDT, or statistical evaluations like Probability of Detection (POD).

Speed and Efficiency

Speed and efficiency are key considerations when choosing an NDT method. If the inspection process is excessively slow, it can hinder productivity and delay critical operations. What is a good inspection speed? It depends on the required throughput for an inspection. For high-volume component production, inspection times measured in single-digit seconds per part may be required. For low-volume production of high-value components, a slower inspection with testing times measured in minutes may be acceptable, especially if that inspection yields higher accuracy and/or precision needed for critical applications. The time needed for part preparation for the inspection and part restoration post-inspection must also be considered when evaluating inspection speed. The removal of paint prior to inspection and restoration of paint after inspection is one example. Automated inspections that minimize operator touch time offer efficiency benefits.

To ensure timely and effective testing, opt for an NDT method that:

1. Provides high-speed testing capabilities to meet your throughput requirements.
2. Enables swift inspection without compromising accuracy or reliability.
3. Minimizes the operations and time needed for part preparation and restoration
4. Minimizes operator touch time

Quantitativeness/Objectivity

Objective and quantitative inspection methods are essential to minimize uncertainty in results. By eliminating operator interpretation of indications, you can enhance the reliability and repeatability of the inspection process. Look for an NDT method that:

1. Offers an objective approach, reducing the reliance on subjective operator judgment.
2. Provides quantitative inspections that yield precise data, reducing uncertainty in results.
3. Supports automation, as it further enhances objectivity and eliminates human error in inspections.

Automation

Streamlining the inspection process through automation can significantly improve efficiency and reduce human error. When evaluating NDT methods, consider the benefits of automation and what level of automation optimizes the efficiency and value of your processes:

1. Reduces operator touch time, making inspections faster and more efficient.
2. Minimizes operator training requirements, making it easier to implement and maintain.
3. Enhances objectivity by eliminating human error as a factor in inspection results.

Affordability

The cost-effectiveness of an NDT method is an important aspect to consider, especially for long-term and widespread use. Consider carefully the value of the part relative to the cost of inspection. Cheap parts that are not safety critical may not merit expensive inspections, but expensive and/or safety critical parts often do. The cost of equipment is important, but there are many other factors to consider. To ensure an ideal NDT cost scenario, look for a method that:

1. Utilizes affordable equipment, minimizing upfront and ongoing expenses.
2. Requires minimal operator touch time, reducing labor costs.
3. Has minimal operator training requirements, lowering training-related expenses.
4. Minimizes the operations needed to prepare a part for inspection, such as cleaning or paint stripping, reducing non-value adding operations, equipment expenses, and hazardous materials handling.

When selecting an NDT method, it’s crucial to consider multiple factors to ensure its suitability and effectiveness. By prioritizing accuracy and precision, speed, quantitativeness/objectivity, automation, and affordability, you can make an informed decision that meets your specific inspection requirements. Remember, each of these factors contributes to the overall success and reliability of your NDT process.

About Vibrant

Vibrant Corporation provides revolutionary PCRT technology that is changing how aerospace, automotive and power generation markets conduct nondestructive testing (NDT). PCRT is an economical standalone addition to, or replacement for, NDT that enhances safety and operating economics by detecting process variation and structural defects undetectable by other methods. Learn more about PCRT here or about our testing services here.

 

Percentages of NDT for weld Inspection in different services

Percentages of NDT for weld Inspection in different services

babajamali

(Petroleum)

(OP)

13 Sep 11 15:56

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,
 

RE: Percentages of NDT for weld Inspection in different services

stanweld

(Materials)

13 Sep 11 16:32

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

RE: Percentages of NDT for weld Inspection in different services

Kiwi2671

(Structural)

13 Sep 11 18:53

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

RE: Percentages of NDT for weld Inspection in different services

Duwe6

(Industrial)

14 Sep 11 14:12

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.

RE: Percentages of NDT for weld Inspection in different services

babajamali

(Petroleum)

(OP)

14 Sep 11 14:26

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  

RE: Percentages of NDT for weld Inspection in different services

metengr

(Materials)

Related links:
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AJR Product Page

14 Sep 11 21:41

Quote:

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.

Quote:

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.
 

Quote:

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

Yes.

Quote:

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.
 

Yes, regardless of material, a minimum of 5% of fabrication welds. Make sure the selected welds are representative of all welders or welding operators.I would use the same percentage of fillet welds for either wet MT or PT, using the same reason as stated above.Yes.This is a material suitability issue. In other words, materials should be selected for low temperature service.

RE: Percentages of NDT for weld Inspection in different services

Duwe6

(Industrial)

15 Sep 11 13:20

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.

RE: Percentages of NDT for weld Inspection in different services

babajamali

(Petroleum)

(OP)

20 Sep 11 16:45

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

RE: Percentages of NDT for weld Inspection in different services

Duwe6

(Industrial)

21 Sep 11 08:43

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.

RE: Percentages of NDT for weld Inspection in different services

babajamali

(Petroleum)

(OP)

21 Sep 11 08:47

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

RE: Percentages of NDT for weld Inspection in different services

Duwe6

(Industrial)

21 Sep 11 08:53

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

RE: Percentages of NDT for weld Inspection in different services

moltenmetal

(Chemical)

21 Sep 11 14:05

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.

RE: Percentages of NDT for weld Inspection in different services

stanweld

(Materials)

21 Sep 11 16:09

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.   

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.

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