Non Intrusive Inspection for Corrosion Under Insulation

Kellas Logo Header Net Zero

tlb-landscape-icon OVERVIEW

Led by Kellas Midstream the objective of this ISP programme is to deliver readily accessible, low cost field trials of Non Intrusive Inspection technology for structural integrity inspection and monitoring applicable to onshore and offshore processing facilities.

The programme aims to harness opportunities to trial technologies for detection of Corrosion Under Insulation during planned inspection and maintenance shut downs at the CATS and other onshore facilities. Avoiding the need for additional operational disruption to trial developing solutions, aligning the trials with scheduled visual CUI inspections provides direct comparison of the ability of the solutions to detect and monitor corrosion.

It is intended that the approach will facilitate qualification of the successful solutions and promote acceptance by facilities operators and regulators. This has potential to accelerate the deployment of promising new technologies helping to reduce the significant cost incurred by industry to conduct conventional visual inspection that requires removal and replacement of insulation.

The Challenge

Corrosion Under Insulation (CUI) continues to pose a significant operational, safety and economic challenge to the upstream and downstream oil and gas industry in offshore and onshore locations. It is estimated CUI accounts for circa 20 % of pipework leaks and 40 – 60% of plant pipework maintenance costs is associated with inspection and mitigation of CUI.

In a mature basin such as the UKCS with increasingly mature assets, dealing with CUI can directly impact on Production Efficiency through plant inefficiency or downtime while remediating leaks or lengthy maintenance outages required for inspection programmes.

The Solution

Inspection and monitoring for CUI itself is an inherently inefficient process with access costs and stripping/replacing insulation accounting for up to 80% of the inspection programme costs.

Conventional visual CUI inspection is time consuming, labour intensive and not suited to difficult to reach locations. Short of removing extensive lengths of insulation, even with risk-based inspection the potential to miss emerging sites of corrosion is likely while the burden of monitoring developing corrosion sites adds to the overall inspection burden. There is a clear opportunity for new technologies that can allow rapid screening of pipework without the need to remove insulation that allows early detection of CUI to facilitate monitoring over time to enable intervention programmes to be scheduled and targeted where needed.

CATS Terminal

The CATS terminal on Teeside provides hydrocarbon gas reception and processing facilities across a 72 acre site delivering gas from the Central North Sea directly into the National Gas Transmission System. Reception capacity of 48 scm3 per day and two processing trains each with with 17 scm3 per day capacity results in a significant length of insulated pipework on site operating under a range of temperature and pressure conditions. Inspection programmes to identify and remediate corrosion under inspection is a key element of the facilities asset integrity management to ensure safe operation and the ability to deliver plant availability in excess of 99.5%.

Image courtesy of Kellas Midstream

The Industry Lead Sponsor

Kellas Midstream is a leading UK energy infrastructure business which owns and operates the Central Area Transmission System (CATS) transferring gas from the Central North Sea to the CATS terminal on Teesside, the Humber Gathering System serving the Tolmount gas development and the Esmond Gathering System serving the Cygnus gas field.

Conventional visual inspection for CUI

Conventional visual inspection for CUI requires time consuming and costly removal and replacement of layers of insulation and metal cladding. Image courtesy of Oceaneering

Potential NII technologies for CUI applications

  • Focused Stress Concentration Tomography
  • Capacitance – moisture monitoring
  • Magnetic Imaging – advanced Hall Effect sensors
  • Electrical Impedance Spectroscopy
  • Terahertz sensing
  • Quantum magnetometer

The Programme

In 2020, Kellas accepted an invitation from the to lead a TLB Industry Sponsor Programme to contribute to accelerating the development and commercialisation of new technologies applicable to NII of CUI with potential to improve management of CUI, reduce the cost to industry and address current industry blind spots. The means identified to support these goals was by providing access to pipework around the CATS terminal which would allow technology developers to test deployment methods and acquire physical and spatial data in the field to enhance analysis and interpretation techniques. The approach would also provide successful technologies with a suite of data points for product qualification to support adoption of the technology by other onshore and offshore operators.

Field trials are arranged to coincide with planned CUI inspection programmes during plant turnarounds which allows direct comparison between NII results and conventional direct inspection with the insulation removed. While technologies being tested will hopefully find application offshore, testing onshore significantly reduces the cost of field trials and simplified logistics. This allows more test to be supported with available funding support and a wider range of conditions to be tested.

Industry Collaboration

For this first suite of field trials Kellas worked closely with the Net Zero Technology Centre who provided funding to support development of the technology. The Net Zero Technology Centre also secured field trials for the developer at the Flotta Terminal operated by Repsol Sinopec UK providing a further opportunity to test the deployment of the technology and acquire data to help refine interpretation of the tool responses.

Net Zero Technology Centre


The first season of NII trials at CATS was completed in June 2021 during the planned CUI inspection programme with Oceaneering/Speir Hunter given access to survey sections to acquire data using their Focussed Stress Corrosion Tomography. This method works on the principal that the magnetic field will be distorted around localised corrosive metal loss due to CUI. Magnetometers in hand held sensor arrays arranged around pipework detects the change in magnetic field. The initial results were promising with low to moderate levels of CUI identified at locations which were confirmed by conventional visual inspection with the insulation removed. Based on these initial results, Kellas remobilised the technology developers to test the technology on further sections of pipework where CUI was identified during the course of the inspection programme. During the surveys, information on the response of the magnetic field to operating conditions were identified that will contribute to further development of the technology to improve sensitivity. Based on the successful demonstration of the technology further trials on pipework at other locations are now being planned to coincide with the annual CUI inspection programme.

Trials of a second technology based on different measurement principles are being organised for 2022 having been delayed due to travel restrictions related to the global pandemic. The iSensPro Electrical Capacitance Measurement system uses changes in dielectric properties to detect the presence of moisture under insulation with could lead to development of corrosion. The fixed sensors allow the condition of the insulation to be monitored over time to identify locations where CUI may develop in addition to detecting degraded paint coating on pipework under the insulation.

Non Instrusive

Focussed Stress Corrosion Tomography inspection using a hand held sensor array on CATS pipework Image courtesy of Oceaneering

Non Intrusive

FMonitoring moisture content of insulation using Electrical Capacitance Measurement to identify potential site of CUI Image courtesy of iSensPro


The 2021 programme has successfully demonstrated the benefits of conducting field trials at onshore facilities. The basis for effective collaboration between asset operators, technology developers and funding partners has also been established. However, to sustain the programme at the required pace to ensure that promising technologies can be supported between development and commercial deployment requires expansion of the available facilities for field trials and additional funding support.

Operators of midstream and downstream facilities who wish to benefit from the operational and economic potential for NII for CUI are invited to participate the next phase to expand the programme.

tlb-landscape-icon GET INVOLVED

  • Operators interested in participating in programme
  • Technology developers with deployment ready solutions seeking field trials
  • General questions and feedback