Accurate, fast and highly quantitative – why laser measurement is a powerful technique for inspecting internal welds

Safe and long-lasting pipelines depend on strong girth welds. And not just the weld, but also the surrounding heat-affected zone (HAZ) and any internal corrosion protection. For CRA, CLAD or internally epoxy-coated pipelines, the weld and surrounding HAZ is critical to ensure longevity of the corrosion resistant layer. As operators at the top of the energy industry demand even higher safety standards, and longer lasting assets, the need to monitor and improve weld quality is critical.

There are many NDT (non-destructive testing) methods specified for inspection of a pipeline girth weld. Internal laser inspection, coupled with a high-definition camera and well managed lighting, is often considered the best for getting crystal clear information on the condition of the internal weld surface. This type of inspection, usually called Intermediate Visual Testing (IVT), is typically carried out after the first internal weld pass, or root pass, as an intermediate check of the weld – before the remaining weld passes are carried out.

As such, this type of inspection is particularly helpful when it identifies a weld that is destined to fail later during the final inspection process.

What type of laser-based weld inspection does OMS offer?

OMS’s robotic inspection machines primarily use laser triangulation, which is a non-contact technique that can provide extremely high data acquisition speed (millions of data points collected and saved in a 30-second 360-degree scan) and high accuracy (+/- 0.02 mm). The scan fully digitises the internal surface of the pipe (in this case the weld and the HAZ) into a 3D surface map. This provides the objective data necessary to make a judgment on whether to accept the weld and continue with the remaining fills. Furthermore, OMS’s WeldAnalysis software automates the calculation of the acceptance criteria parameters outlined in DNVGL-ST-F101 – including but not limited to undercut, concavity (including permissible lengths), root penetration, HiLo, and several others. Automating scanning and feature detection removes the human element and helps with repeatability. OMS’s robotic system provides all of this data instantly in real-time up to 1km down a pipeline, or just a few metres inside a pipe - depending on the project.

What are some of the benefits of laser-based internal weld inspection?

One of the key benefits of this type of intermediate laser inspection is the early detection of defects, which can be identified before spending unnecessary time completing a weld that is destined to fail during final inspection – thus saving time and costs.

Laser and camera data can also be collected and viewed using the same coordinate frame of reference as the AUT and RT. Combining these elements means all NDT data can be viewed holistically – which can bring huge advantages. OMS has been involved in numerous projects like this where laser and camera data has been used to avoid an unnecessary weld reject by providing quantitative and objective results where AUT and/or RT were showing a potential issue. In this instance, having the high-resolution surface data (3D map and images) meant the QC/QA engineer did not need to take the conservative approach, which would have led to needless weld rejection.  

OMS’s robotic inspection is also now deployed in the nuclear sector. Our surface mapping is now being specified for welds that will be internally ground – a process carried out to mitigate against stress corrosion cracking in the HAZ. The robotic inspection system acquires a fully calibrated 360-degree weld and HAZ surface map in extremely hard to reach locations (through non-return valves, through up to nine (9) 1.5D elbows, long vertical sections, and diameter changes). Our software then generates a 3D surface model before and after grinding. This overlays before/after data to ensure the specification is being met, and that no steep slopes remain.

A second order laser inspection benefit has been used by OMS’s software engineers during the development of our SmartGrind weld repair robot. The team knew that they could acquire the full 3D surface map of the weld, and they also knew the weld that the customer wanted to achieve. This enabled the team to develop a weld repair algorithm that uses the laser data as part of its input and then conducts automated repair operation of the weld root to bring it within specifications. The user can then conduct a secondary laser scan to check the weld and confirm it has been repaired. Aspects of this process are patent pending.

Some other examples where our customers are finding further value-add with laser inspection are:

Minimising HiLo risk

Some of our customers are using our internal scanning system for pre-weld HiLo checks. This means that they are conducting a 360-degree scan with the pipes butted together – but before the weld has been started. This gives a very good indication of what the HiLo will be like after welding – and therefore if any adjustments need to be made.

Optimal pipe end buttering

OMS WeldAnalysis software has a feature to advise the customer on areas that would benefit from ‘buttering’ – i.e., adding additional CRA material in specific locations to minimise the HiLo at fit-up. When done in a targeted manner it enables customers to carry out this step quickly and efficiently – with a high degree of confidence that the resultant weld with be acceptable. This is particularly useful when fitting up with pipe bends and in cases where pipe rotation is not an option.

Absolute internal dimensioning

Our laser mapping system can take absolute dimension measurements, allowing us to calibrate the system so to provide absolute minimum ID, maximum ID, average ID and ovality. This is useful if pigging is planned and there are concerns that the pig may get stuck on any pipeline locations – particularly if excess CRA material has been added in certain regions during the buttering process.

Corrosion mapping and remaining wall thickness estimation

OMS has recently (in Q1 2026) developed new software to estimate the amount of wall thickness loss without taking a direct measurement using a conventional NDT technique like UT. The software works by taking an extra wide laser scan and then generating the nominal surface of the pipe. It then automatically analyses localised deviations from this surface and focuses on deviations that were unlikely to be present when the pipeline was fabricated. This process and algorithm have recently been proven to be an extremely good estimator of remaining WT when localised internal corrosion is present. It is particularly useful when traditional UT or other direct WT measurement isn’t possible because the outside of the pipe is not easily accessible. Because OMS are doing this robotically from the inside of the pipe with an extra-wide laser, it means the data acquisition is non-contact, requires no couplant, and can cover large areas very quickly.

Alex Felce, OMS CEO, said, ‘We find that most of our customers take full advantage of having a laser based IVT system on their project. They leverage all the possible benefits to be had from the data – which means they meet the required standards – while also increasing their efficiency and saving construction costs over the duration of their project. We are really excited to begin offering more to our customers in oil and gas, nuclear, offshore wind, and hydroelectric – such as the introduction of our new robotic weld repair system for these industries. I am also very interested in our new software to infer remaining wall thickness when localised corrosion is present on the inside of the pipe. For many decades, the industry has relied purely on conventional UT, and our new approach is able to cover large sections of piping at high speed, providing remaining WT results to asset owners.”

If you are interested in our weld inspection, weld repair and/or corrosion mapping technology please contact our team for more information on info@omsmeasure.com.