|TWI Ltd has recently launched a new Joint Industry Project to explore and validate detection methods for high temperature hydrogen attack (HTHA). Inspections will be carried out on a carbon steel pressure vessel – operated in a regime calculated to induce accelerated HTHA – and designed to simulate the real world operations and challenges associated with detecting this phenomenon.
Carbon steels are used extensively in oil and gas refinery equipment, and have fallen victim to HTHA, as is evident from the industrial incident in 2010 at the Tesoro Anacortes refinery in the USA. The US Chemical Safety and Hazard Investigation Board (CSB)’s report, published in 2014, recommended the use of a new boundary for carbon steel in API 941 (Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants) which would effectively prohibit the use of carbon steel equipment at process conditions above 400o F and greater than 50psia hydrogen partial pressure. Consequently, this would preclude the use of carbon steel for many vessels currently operating in refineries. In 2016, a new limit line for non-post-weld heat treated welds in carbon steel was introduced into API 941 to take into account several recent incidents affecting such material.
An important aspect of preventing similar industrial incidents is the effectiveness of the inspection process used to assess components at risk. The CSB’s report found that there were severe limitations to inspection practices on refinery plants, such that they were not sufficiently reliable to ensure mechanical integrity and prevent HTHA equipment damage. Hence, the report raised a key technical challenge to develop and implement practical techniques for industry to use in the field that would be sensitive to early-stage HTHA.
The Joint Industry Project led by TWI proposes to assess and validate front running, ultrasonic techniques for the inspection and identification of HTHA damage. There will be a particular focus on welds and their heat affected zones, which are recognised as being preferential sites for HTHA and were strongly implicated in the Tesoro Anacortes refinery incident. The work will be carried out on a representative pressure vessel, incorporating different weld types and configurations, which will be designed to present similar challenges to those found during monitoring and inspection on petrochemical sites. Periodic inspection of the vessel in use will enable practical demonstration and validation of the techniques for early-stage detection of HTHA. If required, the vessel can be operated until failure within TWI’s unique high-pressure test pit facility.
Channa Nageswaran, NDT Team Manager at TWI, said ‘TWI is currently developing cutting-edge ultrasonic techniques for the detection of early-stage creep damage that are also applicable to the problem of high temperature hydrogen attack (HTHA), therefore, the decision to undertake this project was a natural progression of our existing research.’ ‘Furthermore, we can also bring to this challenge an in-depth knowledge of non-destructive testing practice, and expertise in residual stress measurement, modelling, fracture and metallurgy.’
He went on to explain ‘The benefits that companies or organisations can expect to gain from participating in the Joint Industry Project include: access to proprietary, validated ultrasonic techniques that can detect the early stages of microstructural degradation due to HTHA; resultant procedures for inspecting vessels and pipework whilst in service, or during outages using commercially available equipment; improved ability to meet regulatory requirements for the operation of ageing assets; and a reduction in equipment replacement costs.’
For more information about the project and how your company or organisation can become involved, please email: firstname.lastname@example.org or telephone +44 (0) 1223 899000.
Image shows key stages in the analysis and identification process of high temperature hydrogen attack:
- Top – Concept of the welds in a vessel at elevated temperatures containing hydrogen being monitored by ultrasonic systems
- Bottom left – HTHA damage in specimens created by TWI in a proof of concept
- Bottom right – Finite element simulation of the ultrasonic backscattering from the HTHA damage
TWI Ltd (The Welding Institute)