The objective of the recently completed Phase 1 of a joint industry project (JIP) at DNV, the results of which are described in this paper, was to determine if welding onto an in-service pipeline that transports a mixture of methane and hydrogen results in an increased risk of hydrogen cracking and, if so, to develop guidance pertaining to measures that can be taken to mitigate the increased risk. The mechanisms and the extent to which steel line pipe can become charged with hydrogen when transporting methane/hydrogen mixtures were reviewed. An experimental program was undertaken to determine the extent to which elevated weld hydrogen levels can result during welding onto pipe pressurized with blends of hydrogen and methane (Task 2a) and from welding onto steel that has been exposed to high pressure blends for an extended period of time (Task 2b). The results of Task 2a showed various increases in weld hydrogen level, depending on the pipe wall thickness, the weld heat input, and the partial pressure of hydrogen. Reactions between the pipe contents, the line pipe steel base material, and surface oxides were also observed. Task 2b resulted in no significant increase in weld hydrogen level as the result of welding onto steel that had been exposed to a high pressure blend for an extended period of time. Additional work is required to determine threshold conditions beyond which increased weld hydrogen levels do not occur and to quantify increases in weld hydrogen levels for a broader range of conditions, including higher and lower partial pressures of hydrogen.

The material test report (MTR) provides proof of the mechanical properties of a steel product and confirms that the tests required have been performed and are satisfactory. For this purpose, test pieces that are representative of the steel product are destructively tested and the results are given on the MTR. The MTR is essential as one cannot determine the mechanical properties non-destructively. The standard way of linking the MTR and the product is done by a specific mark on the product, usually the batch/heat number which is given in the MTR. But what if there is no confidence the MTR relates to the steel product? The steel product will then have limited value because there is no proof of compliance with the requirements. A chemical composition is usually mentioned on the MTR. This is the chemical composition of the ladle, also called the heat analysis. The chemical composition does not change during the process of manufacturing a steel product. Therefore it can be considered as the “DNA” of the steel. This paper will explain the use of mobile optical emission spectrometry (OES) as a reliable method for measuring the chemical composition of a steel product. The measured chemical composition, the DNA of the steel, is compared with the heat analysis. If the material test report relates to the steel product, the differences between the two chemical compositions will be very small. If differences in the composition are large we can see that the MTR and steel product do not relate to each other. This does not mean that the steel product does not meet the specified mechanical properties. Only the relationship with the associated MTR is no longer there and thus proof that the steel product complies with requirements.

The actual shape of a real defect differs from the simplified shapes that are assumed within an engineering critical assessment. Additionally, the re-characterization of interacting defects into one simplified defect is known to introduce conservatism, which may be undesirably large. Ongoing and expected technological advances of 3D NDE techniques (such as full-matrix capture ultrasonics and X-ray CT) allow to assume that defect simplification will no longer be required in the future, thus bypassing the uncontrolled conservatism resulting from defect simplification. A recently finished EPRG project has shown the feasibility of integrating the information provided by 3D NDE systems into finite element models. Promising results are obtained which, with additional effort, will provide a solid basis for in-the-field application. This paper first reports on the overall procedure of defect assessment by the adopted finite element analysis (both linearelastic and elastic-plastic). Next, the ability to couple FE model construction with non-destructive evaluation results is demonstrated for three scans obtained from different sources (one X-ray CT and two ultrasonic full matrix capture scans). Finally, concrete opportunities to improve the robustness, speed and accuracy of the methodology are addressed, which will be tackled in a follow-up project funded within PRCI.

N.V. Nederlandse Gasunie (Gasunie) has converted an existing gas transmission line from transporting natural gas to transporting a mixture of gaseous hydrogen and 30% to 0% methane. To enable this, an assessment was carried out on technical safety, process safety, work safety and external safety. The pipeline, with two valve stations, was constructed in 1996 according to applicable Dutch regulations and actively managed in accordance with Gasunie company standards. The pipeline was evaluated for hydrogen transportation and, based on the following measures, this was seen as being feasible: - The water dew point of the feed must not exceed −8° C; - The pipeline must be separated from the natural gas transport system; - Blowdown must be performed either at the site of the supplier or the user of the hydrogen; - Gas measurement equipment, personal safety and leak detection must be suitable for hydrogen; - Due to the assignment of hydrogen as a chemical agent, the safety contour was reduced by performing extra measures, such as additional communication to landowners, additional requirements for the pressure-regulating system and verification of additional settlement and stresses. The operational changes consist of a number of maintenance and management issues: • In-service welding and hot tapping are not allowed; • Equipment suitable for use in gas group IIC (ATEX) must be used; • Emergency and maintenance procedures must be updated to those applicable for pipeline and valve stations containing hydrogen.

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