Non-destructive testing (NDT), sometimes referred to as non-destructive evaluation (NDE), is used in overhead line inspections to test for and analyse defects in a structure or asset. Without an effective NDT inspection strategy in place, overhead line networks are at a greater susceptibility to:
- Safety issues.
- Unexpected asset failure.
- Power outages.
- Incorrect assessment of product life, i.e. condemned earlier than necessary.
- Regulator pressure for more efficient/safe systems.
Over the past 20-30 years utilities have been testing a range of NDT technologies for use in their wood pole network. The utilities that have obtained positive results from their testing and then implemented a new NDT system are seeing huge cost savings and an increase in inspector confidence and inspection accuracy.
As asset age profiles continue to rise, it is vital that the best NDT techniques are used. This blog will look at how to properly assess NDT techniques for use in your overhead line inspections.
Why Use NDT in Overhead Line Inspections?
The goal of NDT (read more here) is to gather information regarding the condition of an asset without causing any adverse effects. For wood poles in overhead line networks, this specifically means assessing the quality and life span without affecting the future effectiveness or usefulness of the pole being tested.
Regular testing using NDT can provide inspectors with the data required to make decisions that protect the asset, environment, personnel, and the public from higher risks of failure.
The current methods of testing used for poles are rudimentary and rely heavily on either:
- Subjective assessment techniques, i.e. hammer sounding.
- Limited destructive tests, i.e. drilling, which only assesses a very small proportion of the pole cross section.
Some NDT techniques show promise in assessing the whole-of-pole condition which would provide a considerable benefit compared to the existing methods above.
Why is it Important to Assess NDT Techniques?
As technology continues to evolve and improve, new NDT tools become available that can improve your asset inspections. New technology can:
- Increase the accuracy of results.
- Reduce the time taken to complete a pole inspection.
- Reduce the inspection cost per pole.
- Improve the confidence of inspectors.
- Increase field practicality of your systems.
Every method of NDT has its own advantages and disadvantages which means there is not a “one method fits all” solution. To properly assess NDT techniques for your company, weighing up the advantages and disadvantages of each tool for your specific situation is paramount.
Requirements of the New System that You Should Assess for?
The first step in assessing NDT techniques is developing a list of requirements. These requirements will ensure a measurable and clear result based on quantifiable baselines while minimising the cost associated with the assessment process. As a minimum, these requirements should include:
- Speed of inspection.
- Repeatability – how consistently one inspector achieves results with the technique.
- Reproducibility – how consistent are results between inspectors.
- Cost per pole.
- Competency/education (training) requirements.
- Market ready or is refinement required?
- Local support.
- Calibration requirements.
- Quality Assurance (QA)/Quality Control (QC) requirements.
- Calculation standards compliance.
- Amount of equipment that is added.
- Data capture requirements.
- What is the current problem?
To find out more about these requirements, download our whitepaper at the bottom of the blog.
Setting the Baseline of Your Current Systems
If you plan to complete an objective test that gives you accurate results justifying or refuting change, you need to baseline the performance of the current system. By establishing the status-quo, you create a base to compare the NDT methods that you test. Without it, your evaluation of the new tools will be inaccurate or misinform you of the right decision.
If you have not already completed a baseline analysis, don’t worry. The accuracy, repeatability and reproducibility testing of your current systems can be done alongside the testing of the new devices. In setting the baseline, try to select a larger testing base of assets, both in number of poles and other factors including age groups, species, sizes, environments, etc.
Performing an Accurate Cost Evaluation
There is no point testing a range of NDT techniques for your overhead lines without a cost evaluation. An accurate cost evaluation can assist in making the decision to stick with your current techniques or to implement a new NDT tool to your inspection process.
For a strong cost evaluation, three main calculations need to be considered: cost per pole, over-condemning cost savings (false positives), and failure cost savings (false negatives).
- Cost per pole is a simple calculation employing the established personnel time rates, time taken per pole in the trials, and standard on-costs. This is then compared to the cost per pole of the traditional inspection methods.
- Over-condemning cost savings determines the value of false positives. This is calculated by comparing traditional inspection methods with the new methods on a per-pole average replacement cost by analysing the number of serviceable poles that were condemned by the methods.
- Finally the failure cost saving should be analysed if the data is available. The data should consider the current or predicted failure rate, and the typical cost of failure for the different pole types (both in emergency replacement, community/environment costs and fines/compensation). You can even look at environment specific failure costs (e.g. bushfire risk).
Our 4 Tips for Assessing New NDT Techniques
Complete a Full Assessment
Full scale destructive testing is the ONLY WAY to properly test and assess the performance of the NDT techniques. Small scale tests of section properties and other smaller tests can hide significant downsides of different technologies. This can skew your assessment and potentially lead to the implementation of an NDT method not appropriate for you.
Look at Both Big Picture and Individual Results
To accurately assess which NDT method provides the most benefit to your testing system, you should consider the results of the entire inspection system as the main acceptability criteria. However, an in-depth look at the accuracy of the specific results of the NDT devices needs to be considered to assess where the strengths and weaknesses of each tool lies. This will assist in determining if a specific NDT method could be calibrated to your network/inspection systems.
Do not assume that the supplier has thoroughly tested the devices. Due to the high variability in poles, proper assessments require a lot of full-scale testing and are very expensive. As a result, suppliers often rely on industry studies, many of which have been poorly scoped and executed in the past. Following the above guidelines and having someone with a good breadth of experience doing the testing will prevent you from repeating previous mistakes.
Keep it Simple, Keep it Clear
Benchmarking is a very important part of making an accurate assessment. However, knowing what parts of your existing systems needs improvement is just as vital. By taking the time to work out where you want to improve, you keep it simple as to what it is you are calculating. Be clear on what you are looking for.
If you would like any assistance with your NDT assessments, our engineering team are always happy to discuss your ideas/requirements. Despite us having the PortaSCAN devices, you will find our advice and consultancy agnostic. At Revo Group, we want to see the assessment of NDT methods done properly. We have seen too many utilities spend millions of dollars on implementing techniques that are scrapped within months of use due to incomplete assessment processes.