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INTERVIEWS FOR NDT ROLES

Here are some tips and sample technical interview questions relating to NDT jobs in the integrity industry. The Matthews Integrity Hub: HEAD OFFICE website contains a series of these, relevant to different jobs in the industry. Before you read the individual sets, first have a read through our short introductory articles Technical interviews in the world of asset integrity  and Integrity job technical interviews; some facts to help put them in context.

What NDT jobs are we talking about?

In this category, it’s straightforward NDT-technician type jobs. This is at the edge of the scope of the Matthews Integrity Hub: HEAD OFFICE website but still a valid part of the asset integrity industry, and hence relevant to many candidates and employers.

Let’s look at a few facts about NDT-technician-type jobs (you are allowed to disagree if you wish)

  • NDT knowledge is not particularly scarce. There are thousands of people holding the relevant qualifications and certifications.
  • NDT skills are easily transferrable between employers
  • Certifications are split into 3 well-recognised levels run by ASNT, CSWIP and others
  • NDT technicians mainly follow instructions and procedures that help determine the integrity of a component
  • NDT is part of the integrity story, but a long way from being the full story

Although some NDT technicians may be interested in climbing the integrity ladder to higher positions, many are not. Also, transferring to higher inspection or integrity roles in some parts of the industry is not as easy as it sounds. The higher the technology level of the industry, the greater the skills gap between NDT and integrity positions; aerospace, nuclear and rotating machinery are good examples where the skills gap is high. In other industries; offshore, small plant, process plant etc, the gap is less. That still doesn’t mean that NDT people can move up easily though.

The result of this is that technical interviews for purely NDT positions are some of the easiest to handle, whether you are an employer or a candidate. They are likely to be made up of questions on easily assessible NDT subjects, so both sides can expect fewer surprises.

NDT job interview questions; what to expect

In our Integrity job technical interviews; some facts article, questions used in technical interviews were considered to be made up of categories or ‘quadrants’, as shown below;

For NDT jobs the situation is simplified as the top two quadrants are the most relevant ones. The bottom two are only really relevant if it is a position that moves outside the traditional NDT-only role.This could be jobs entailing assessing defects, rather than just finding them, knowledge of post-construction or fitness-for-purpose codes or similar. You can think of this type of extended role as ‘NDT-Plus’, and they are not too common.

 Let’s look at some good technical interview questions covering the top two subjects in the quadrant. They are not intended to be easy questions (or everyone would get them correct), or unfeasibly difficult ones, but they are meant to be searching questions. Here they are, with commentary for both candidates and employers;

First, code knowledge

Question 1. NDT codes

How would you say the general NDT principles of ASME V differ from those of EN harmonised standards?

Look at what’s happening here. The question is about code comparisons. There is so much more to be gained from discussing the comparison of codes than discussing a single one. Anyone can have poor knowledge of a particular code so unsolicited single-code questions are a poor test of knowledge, and a bit unfair. To answer this question well needs some knowledge of both sets of codes, but not a full knowledge, which would be impractical. There are many ways to answer this question; answers could go down the routes of NDT personnel certification, scopes of the various codes, or technical details about any of the NDT techniques covered. The scope is left completely open, giving candidates the chance to choose what area they wish to discuss. If you are a job candidate, this is good news.

Question 2. NDT codes

Choose any NDT code with which you are familiar. How would you summarise its content and objectives to someone who wasn’t familiar with NDT codes?

This is a good one for finding out whether someone really knows about NDT codes. Most NDT codes, irrespective of their origin, contain a very similar breakdown of content, so the individual code chosen doesn’t matter. Knowing the overall layout and content of a code shows much better knowledge of the subject than knowing the content of a code table or two by virtue of having worked to its requirements.

To assess the answers a candidate gives to this question, just compare their answer about code content with the contents pages of a code such as ASME V, which sets out the content in a logical fashion, and you will soon find out how much they know.

Now look more carefully at the question. It’s actually asking two questions in one, first about content, which most people will spot and also about objectives, which many people won’t. This second part is harder to answer because it gets to the heart of what a NDT code is actually for, and how it compares with an application code (ASME VIII for vessels etc) or one covering personnel qualifications (ASME IX or equivalent).

As an interview candidate, you need to be able to live off questions like this. As well as an effective way to test you, they also give you your greatest opportunity to impress, if you do have the knowledge to offer. If you don’t know the answers to this question, then perhaps now is the time to pick up ASME V or an equivalent EN code and find out.

Question 3. Technical breadth

Remember the definition of ‘technical breadth’ questions; they test for a breadth of knowledge that can be applied in wider, unexpected contexts on the edge of your existing knowledge. The more someone in an NDT job has this, the more suitable they will be in contributing to the bigger picture of assessing the integrity of a piece of equipment. Without it, they will remain fixed in the NDT-only role.

Here’s the question.

Question: All NDT techniques have an inherent Probability of Detection (POD) associated with them? Can you explain why this is so, and how this affects the evaluation of the integrity of a corroded pressure systems component?

This is the dreaded double-barrelled question; the first about the existence of POD and the second about its effects. As before, the more important bit of the question is the second part. POD is a good topic for discussion for NDT/integrity positions; it has a real effect on the validity of the results of any integrity evaluation. Strangely, it is often ignored, with everyone assuming that the NDT techniques used are 100% effective and drawing integrity conclusions based on that.

If NDT technicians can discuss POD it is a good indicator of both technical breadth and technical curiosity. If you are a candidate charged with answering it, here is a checklist of subjects that could be included in your answer. It’s not the only approach, but it’s a good start.

The first part of the question; Why do NDT techniques have a POD associated with them?

Answer: NDT techniques have restrictions placed on them by:

  • Material surface condition (front and back wall)
  • The metal’s grain structure
  • Geometry of the component
  • Sensitivity of the equipment used
  • Human error

POD is not just a function of the NDT technique itself; there are other factors involved such as decisions as to what actually constitutes a flaw (i.e. minimum size)

Here’s the second (more important) part of the question; How would this affect the evaluation of the integrity of a corroded pressure systems component?

  • The existence of POD means that any test result is probabilistic; that means that any integrity conclusions drawn from them will be probabilistic also. There will always be some risk of the conclusions being wrong, and the item failing. It’s therefore wise to consider the consequence of any failure, not just its probability. Risk-based Inspection (RBI) does this.
  • POD curves are used, relating the probability of detection of a characteristic parameter of the flaw, usually its size. Achieving a 90-95% confidence limit in flaw identification/sizing is a good target to aim for. To help the situation where empirical POD data is not available, statistical software can be used for estimating of PODs
  • Confidence in NDT results can be increased by using multiple NDT techniques rather than just one.

Questions for other Integrity job roles

Interview questions for other job roles can be very different to those for NDT-only positions. They are generally more wide-ranging and may actually include some NDT-type topics. Have a look at them in the Small plant inspection , In-service Inspection, and Integrity Evaluation question sets.

For more general discussion of NDT matters, see our NDE OFFICE webpage

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