Pipelines are used across the world to transport a whole range of materials, from gas to liquids such as oil, slurry, and water. In Australia alone, there are more than 39,000 kilometres of high-pressure pipelines. These pipes provide a range of unique inspection challenges to asset owners and managers. This is often due to the vast areas that require inspecting for relatively small defects.
As pipes transport abrasive materials, internal wear and tear is commonplace. This leads to issues in the form of erosion and corrosion resulting in a loss in sectional thickness. Other defects include cracking, manufacturing flaws and other third-party damage.
This blog covers why Non-Destructive Testing (NDT) is important in pipeline inspections, some NDT techniques that can be used to investigate pipes, and an example of an inspection we completed for a client to show how these methods are used in the real world.
Why is Non-Destructive Testing Important in Pipeline Inspections?
With pipes continuing to age and environmental concerns rising as the result of failures, it is more important than ever before to complete accurate pipeline inspections. The failure of these assets can be costly due to the expense of replacement, the downtime to fix or replace, and the potential associated fines.
At Revo Group, our pipe inspection services aim to test the asset and produce results that will efficiently and accurately inform asset managers regarding accident prevention, condition monitoring, product integrity, quality assurance (QA), safety concerns and maintenance. It should go without saying, but it is vital to ensure that all results are measured against all safety and compliance standards.
NDT Pipeline Inspection Techniques
There are new advancements made in pipe inspection every year, and there are a wide range of techniques available, each with their own pros and cons. The most common NDT techniques can be broadly grouped into the following seven most common:
- Ultrasonic (UT)
- Eddy Current
- Magnetic Particle
- Acoustic Emission
- Laser Profiling.
Some conventional methods are slow, some look for very specific defects, some only inspect one surface or the other, some require highly specialised and expensive equipment and/or personnel, and they all have their own accuracy thresholds. Many require the pipeline to be shut down during inspection.
There is plenty of information on the other methods available if desired, so this article focusses on one of the newer techniques that can solve many issues related to the incumbent methods.
Guided Wave Ultrasonic Testing (UT) using Electro Magnetic Acoustic Transducer (EMAT) technologies can solve many inspection-related problems. EMAT generates ultrasonic wave forms within a metallic material (rather than generating outside and directing them inwards through couplant). The waves are guided by the inner and outer walls of the pipe under inspection. This Non-Destructive Testing (NDT) technique allows for the detection of flaws in materials up to 50m away from the search unit (coil) per inspection, without the use of any couplant, and at elevated temperatures.
There are three main EMAT Ultrasonic Testing techniques that can be used in the inspection of pipes. These are Long-Range UT (LRUT), Medium-Range UT Axial (MRUT-A), and Medium-Range UT Circumferential (MRUT-C).
Long-Range Ultrasonic Testing
The LRUT package available from Innerspec Technologies allows for inspecting up to 100 metres of pipeline in a single shot. Long-range capabilities allow for a fast and easy to set up inspection that can be employed as a rapid screening test for integrity assessments.
Using guided waves, LRUT enables the inspection of 100% of pipe circumference and thickness from a single location. The shot takes mere seconds to capture, then the operator can annotate all the welded pipe joint indications on the A Scan followed by any other known features evident (valves, welded brackets etc.). Any A Scan signals that are not attributable to welds or features can be annotated as defects.
Medium-Range Ultrasonic Testing Axial
MRUT-A inspections are designed to inspect pipes that are hard to access with traditional inspection methods due to lack of access. Axial scanning is a through transmission technique that achieves 100% volumetric pipe inspection through rapid ultrasonic sampling of the pipe circumference. The method uses one (Pitch Catch) or two (Pulse Echo) search units on wheeled, handheld trolleys.
The search units only need the top surface of the pipeline (or any longitudinal surface) to inspect the full circumference, making it ideal for pipes ganged together, causing limited access to the full circumference. This inspection is especially suited to detecting Corrosion Under Pipe Supports (CUPS). It works particularly well to detect erosion and corrosion in slurry pipes, even with caked on material.
The axial position of any defect is immediately evident, then by twisting the search units 90 degrees and scanning circumferentially, the circumferential position of the defect can be quickly pinpointed and recorded. Defects, such as cracks, pits and wall loss, provide observable attenuation of the sound or phase shift due to time-of-flight change.
Medium-Range Ultrasonic Testing Circumferential
MRUT-C inspections are performed by permanently or temporarily adhering a 50mm wide strip of metallic tape circumferentially around a pipe. Circumferential scanning achieves 100% volumetric pipe inspection as the sensor is moved around the pipe’s circumference. Pulse-echo sensors are configured to measure the ultrasonic reflections down the length of the pipe to a distance of up to 3m in each direction.
The shear waves travel axially along the pipe and reflect signals back to the search coil from any changes in wall thickness, whether that be welds, defects, or holes in the pipe. This inspection provides excellent axial and circumferential resolution to pinpoint areas of concern. The MRUT-C should not be used as a defect sizing tool; however, defects can be roughly sized according to their signal amplitude.
This method is designed to detect flaws under insulation and lagging, underneath pipe supports, underground (up to 3m) or in any other inaccessible place. The Volta reporting software records all defects along with their amplitude, positions, and any notes the inspector wishes to make.
Real-Life Example of Pipe Inspection
We have experienced many cases over the years where EMAT technology has been vital in the inspection of pipelines, including slurry pipes, oil and gas pipes and water pipes. One such case was the use of MRUT-A in the inspection of 6km of slurry pipeline in Western Australia. Due to the abrasive nature of the slurry, the pipes were assumed to have been worn down over time.
The standard thickness readings at regular (~6m intervals) that were in use were not effectively detecting the issues in the pipes and proved to be extremely time consuming, rendering them uneconomical and inaccurate. Upon consultation, it was determined that the solution was to use the Innerspec gear and complete a full-length, full circumference, full wall thickness scan of the pipe using MRUT-A.
The scan was conducted in a matter of weeks and detected several areas to be monitored, and at least one area where the above-mentioned defect had reached a point where it required repair. These areas would not have been detected using other methods, especially with the same timeframe and budget.
With over 80 years of experience, our inspection team is always happy to discuss NDT tools and technology. While we are the Australian, New Zealand and South-East Asian agents for Innerspec Technologies, you will find our advice and consultancy, tool agnostic.
Revo Group provides on-site training and support in the use of EMAT technology to many of the largest Industrial NDT contractors in Australia and Asia. We work alongside many of these companies providing relief manning and professional consultancy services on a variety of challenging projects.
Give our specialists a call to discuss how we can help you.