Condition assessment and integrity of pipelines

Picture: pixabay

Pipeline networks with a length of more than three million kilometers cover our globe. They ensure the safe, efficient and cost-effective transportation of energy resources – such as crude oil, natural gas or water – across continents and make a significant contribution to a stable supply situation. According to the Global Energy Monitor, around 69,700 km of new gas transmission pipelines were under construction worldwide at the end of 2023 alone, an increase of 18 % compared to the previous year. Any damage that occurs, such as leaks, can not only jeopardize security of supply, but also pose – often considerable – risks to the environment. As the expansion of critical infrastructure increases, so do the requirements for its safe operation.

A microscopic view of hydrogen embrittlement in Inconel. Image from Iannuzzi, Mariano & Barnoush, Afrooz & Johnsen, Roy. (2017): Materials and Corrosion Trends In Offshore and Subsea Oil and Gas Production.
Image: © General Electric

1. Condition assessment with inspection pigs

Corrosion is the main cause of pipeline damage worldwide. Regular inspections can identify potential problems at an early stage and avoid costly repairs with longer downtimes. They also contribute to compliance with legal regulations and minimise potential environmental risks that can arise from leaks. Large leaks can usually be detected quickly, whereas small (slow) leaks are more difficult to detect and can sometimes remain undetected for years. Effective pipeline integrity management therefore protects both the environment and the economic interests of the operators.

Image: Rosen Group
Preparation of an inspection pig

Inspection pigs are used in pipelines as part of inline inspections (ILI). Based on different technologies, they can localise and identify specific damage such as cracks, leaks or corrosion. In some inspections, AI technologies such as ‘data fusion’ are used to analyse the data obtained, which process the sensor signals using so-called ‘neural networks’. This makes it possible to derive specific corrosion or crack patterns from large amounts of data and improve integrity management.

Use of intelligent measuring techniques: two examples
With magnetic flux leakage technology (MFL), a magnetic field is generated in ferritic steel pipes using a strong permanent magnet. The MFL sensors detect existing leaks by using measurements to identify the location where the magnetic flux is „disturbed“ (magnetic flux leak) and store this information in the electronic module. This technology can be used in pipelines that transport gases, liquids or multiphase products.

Ultrasonic testing (UT) is particularly suitable for locating and identifying cracks or other structural deviations. With this technology, an ultrasonic sensor transmits ultra-high frequency sound pulses through the medium into the pipe wall in order to gain insights into existing damage, other anomalies or the wall thickness by means of the reflection behaviour.

2. Inspection of non-piggable pipelines and culvert sounding

Inline inspections (ILI) with pigs to assess pipeline integrity are not suitable for all piping systems or pipelines. For example, changes in diameter, sharp bends (e.g. in culverts) or protruding components can prevent the free passage of a pig. In this case, other inspection methods are required to check the pipeline integrity or damage.

New CMI-based process enables overhead inspection
Last year, the Deutsche Verein des Gas- und Wasserfaches e.V. (DVGW) launched the „Korrosionsschutz neu“ research project together with several co-operation partners. The technology developed in Germany, which is based on Current Magnetometry Inspection (CMI), is currently being used to investigate a suitable alternative to the costly exposure of non-piggable pipelines.

The methodology is intended to „enable the detection of defects and their corrosion status in a single defects and their corrosion condition in a single measurement run“, says the DVGW, describing the aim of the project. „In addition, the conversion to hydrogen transport raises further questions, such as the condition assessment of the pipeline, which can be answered efficiently with CMI.“

Magnetic surveying to locate corrosion or leaks can be carried out remotely from the surface, down to great depths, and during operation. CMI uses an artificially applied alternating current to enable precise magnetic field measurements regardless of ambient conditions. The alternating currents are applied to the pipework as a so-called multi-frequency signal.

Picture: Electromagnetic Pipeline Testing GmbH
Defects identified with CMI

According to project partner EMPIT, the technology „in principle offers the possibility of recording the relevant parameters that are required for the evaluation of effective corrosion protection at each coating defect. The process therefore harbours the potential for a comprehensive description of the corrosion-relevant properties of a defect“.

Precise culvert positioning with CMI
Conventional methods (such as ground penetrating radar/GPR and conventional magnetometry) reach their limits in terms of accuracy and reliability when it comes to precise positioning and determining the coverage of pipelines that pass under watercourses or other infrastructures – so-called culverts – due to soil properties and external influences. For example, damp substrates such as riverbeds, which severely limit the signal range, are considered particularly problematic.

Picture: Electromagnetic Pipeline Testing GmbH
The CMI inspection boat „Yellow-Fin“ on a shore shortly before deployment

CMI has proven to be particularly advantageous for use under complex conditions, such as in flowing waters or areas with intensive shipping traffic. Practical examples show that the method can be used to carry out precise inspections even at great water depths and with challenging geometries. The results provide crucial information for effective risk management and help to minimise environmental and infrastructure risks.

The method, which can therefore determine both the position of the pipeline and its cover very precisely in a single inspection run, has now established itself as the standard for German network operators and is being continuously developed to enable inspections at depths of up to 3000 metres in the future.