Design and maintenance of pipe networks transporting hydrogen pure or blended with natural gas

Steel is subject to hydrogen embrittlement (HE). This problem is relatively accurate for pipes transporting hydrogen pure or blended with natural gas. Therefore this problem has to be taken into account for the design and maintenance of pipe networks for this kind of transport. Design needs to modify the design factor for computing maximum working pressure in this case. Defect harmfulness needs specific tools for each type of defect which are the same as for pipe transporting natural gas, but the admissibility criterion is modified when transporting hydrogen. For cracking, harmfulness is determined with a failure assessment diagram with steel fracture toughness under HE. For defect correction, the estimated repair factor (ERF) is changing due to modification of the flow stress. For gouging, the Constraint Modified Failure Assessment Diagram (CMFAD) incorporates the actual material failure master curve. For dents, the criterion proposed by Oyane et al take into account the major reduction of elongation at failure. The influence of HE on fatigue endurance is seen through the fatigue assessment diagram(fAD). Discussion is based on recategorisation of defect, assessment tools, embrittlement and fatigue life duration.