{"id":19324,"date":"2023-10-06T08:53:00","date_gmt":"2023-10-06T06:53:00","guid":{"rendered":"https:\/\/www.ntnu.no\/blogger\/cius\/?p=19324"},"modified":"2023-08-11T14:25:47","modified_gmt":"2023-08-11T12:25:47","slug":"crack-detecting-waves","status":"publish","type":"post","link":"https:\/\/www.ntnu.no\/blogger\/cius\/2023\/crack-detecting-waves\/","title":{"rendered":"Crack-detecting waves"},"content":{"rendered":"\n

Whether they transport oil, gas, water, or other substances \u2013 you do not want them to leak. But if a pipe is in an inaccessible area, how do you then check for cracks? And if there are any \u2013 are they critical, or not?<\/p>\n\n\n\n

These are important questions for health and safety, and for the environment \u2013 especially in the oil and gas industry. Simen Hammervold Midtb\u00f8 is now finalising his PhD on crack detection and assessment using Lamb waves and has already been employed by CIUS partner NDT Global, which specialises in ultrasonic and non-ultrasonic inspection of, amongst other things, pipelines.<\/p>\n\n\n\n

How deep is the crack?<\/h2>\n\n\n
\n
\"Portrait
Simen Hammervold Midtb\u00f8, PhD-Candidate, NTNU and NDT Global Photo: Karl J\u00f8rgen Marthinsen\/NTNU<\/figcaption><\/figure>\n<\/div>\n\n\n

\u201cThe overall goal of crack detection technologies in pipelines is to find cracks of certain sizes and notify the pipeline operators of critical cracks. Critical cracks are defined by their shape and depth,\u201d Midtb\u00f8 explains. \u201cA crack that is going through the entire pipe wall is very critical to detect, whereas a crack that is only 1% of the wall thickness is non-critical \u2013 though it would still be necessary to monitor that crack and its potential development.\u201d<\/p>\n\n\n\n

This is why crack depth is one of the more important variables that have to be accurately identified. Midtb\u00f8 has chosen to use Lamb waves for this:<\/p>\n\n\n\n

\u201cThe measurement of a Lamb wave that travels in a pipe wall will change if there is a crack in its path, and the change will vary with crack depth. However, this change can be subtle, depending on the measurement system and method, which can be modelled. This is where my work comes in, as I am working with a model that can be used for optimisation for such a measurement system to detect as much change as possible.\u201d<\/p>\n\n\n\n

Lamb waves modelling<\/h2>\n\n\n\n

To create Lamb waves one can set a transmitter to radiate sound waves towards, for example, a metal plate \u2013 like a loudspeaker facing a wall. The sound waves will generate a Lamb wave inside the plate, and it travels along it. The wave energy can be measured using a receiver at a certain distance from the transmitter \u2013 a bit like placing a microphone along the plate a certain distance away from the loudspeaker.<\/p>\n\n\n\n

\"Graphic
Illustration of the measurement principle in a pipewall. The tool is inside the pipe as it is moving along the pipe and radiating sound towards the wall. The transmitted sound generates Lamb waves in the pipe wall, which will change and be distorted if there is a crack. Illustration: Simen Hammervold Midtb\u00f8\/ NTNU and NDT Global.<\/figcaption><\/figure>\n\n\n\n

If there is a crack between the transmitter and the receiver, the wave energy will change and can thereby be measured \u2013 in theory\u2026<\/p>\n\n\n\n

The size of the transmitter, the thickness of the plate, the distance between the transmitter and the receiver \u2013 they all affect the outcome. The proposed solution is therefore to use modelling:<\/p>\n\n\n\n

\u201cThe first step of such a model is to develop a description that can account for a transmitter and plate, without cracks. This is described in my first PhD article “ASM and finite beam description of the excited leaky Lamb waves in a fluid-immersed plate” (Ultrasonics, 2022).<\/p>\n\n\n\n

The second step is to perform measurements of cracks and use the model to analyse how the measurement-response is related to the different parameters, and how one can exploit that information to optimise the measurement system,\u201d Midtb\u00f8 says.<\/p>\n\n\n\n

It may sound straight forward, but theories do not always correspond with the \u2018real world\u2019:<\/p>\n\n\n\n

\u201cThe biggest challenge is perhaps being able to compare theory with measurements \u2013 or vice versa. Theory in physics\/ acoustics are often limited by assumptions, so to understand what those assumptions mean for an actual, physical, real setup can sometimes be challenging,\u201d he explains.<\/p>\n\n\n\n

Already a fulltime employee<\/h2>\n\n\n\n

Midtb\u00f8 is now in the process of finishing his second PhD article but has already started fulltime work for NDT Global. They are currently developing a crack detection tool, for which Midtb\u00f8\u2019s expertise comes in useful.<\/p>\n\n\n\n

Doing a PhD with an industrial partner has been a positive experience \u2013 also academically:<\/p>\n\n\n\n

\u201cAs a researcher, I had access to tools and laboratory equipment necessary to do my studies. I was also fortunate enough to be stationed at NDT Global\u2019s location in Bergen, so that I had an office and close contact with the technology, people, and challenges.<\/p>\n\n\n\n

\u201cObviously this also put me in a good position when ending my time at CIUS and was offered a position within the research & development department at NDT Global,\u201d Midtb\u00f8 concludes.<\/p>\n\n\n\n

\n

Lamb waves<\/h3>\n\n\n\n

Lamb waves are waves generated within a thin layer of solid material such as a metal plate or pipe wall. They exhibit different properties depending on the material, but also depending on changes within that material \u2013 like cracks. The trick is to interpret the changing properties correctly \u2013 to correctly identify and measure cracks.<\/p>\n<\/div><\/div>\n\n\n\n

This article first appeared in the 2022 CIUS Annual Report.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Whether they transport oil, gas, water, or other substances \u2013 you do not want them to leak. But if a pipe is in an inaccessible area, how do you then check for cracks? And if there are any \u2013 are they critical, or not?<\/p>\n","protected":false},"author":433,"featured_media":19332,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[197,215,45,199],"class_list":["post-19324","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oilgas","tag-crack-detection","tag-ndt-global","tag-oilgas","tag-pipeline"],"_links":{"self":[{"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/posts\/19324","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/users\/433"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/comments?post=19324"}],"version-history":[{"count":6,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/posts\/19324\/revisions"}],"predecessor-version":[{"id":19333,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/posts\/19324\/revisions\/19333"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/media\/19332"}],"wp:attachment":[{"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/media?parent=19324"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/categories?post=19324"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ntnu.no\/blogger\/cius\/wp-json\/wp\/v2\/tags?post=19324"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}