Hydrogen blending in existing natural gas transmission pipelines: a review of hydrogen embrittlement, governing codes, and life prediction methods

Abstract

Existing natural gas pipelines provide an economic alternative for the transport of hydrogen (H2) in an envisioned hydrogen economy. Hydrogen can dissolve in the steel and cause hydrogen embrittlement (HE), compromising pipeline structural integrity. HE causes subcritical cracking, decreases ductility and fracture toughness, and increases the fatigue crack growth rate (FCGR). This work analyzes the testing standards in gaseous hydrogen used to quantify those effects. Design code ASME B31.12 applicable to hydrogen pipelines has more stringent requirements than ASME B31.8 code commonly used for constructing natural gas pipelines. Differences in materials requirements specified by those codes are summarized. ASME B31.12 pipeline code applies for H2 at a concentration greater than 10% molar. However, recent testing programs acknowledge that H2 degrades steel mechanical properties regardless of its percentage in the blend. This paper discusses how the hydrogen degraded mechanical properties affect pipeline integrity. Decreased mechanical properties cause a drop in the failure pressure of a flawed pipeline, calculated following a fitness for service methodology. There is an increasing risk of subcritical crack growth in H2 as the hardness of base metal and welds increases. This paper analyzes where zones with high hardness and susceptible microstructures are expected in existing pipelines.

Hydrogen Embrittlement as a Conspicuous Material Challenge─Comprehensive Review and Future Directions

“…Another aspect gaining attention is the effect of H blended in natural gas. 27,28,804 FCG is still accelerated with a blend of the gases, while the degree of acceleration is manageable by regulating gas pressure and H content in the blend. Hence, the assessment and optimization of these factors in blended gas usage are important subjects of H-related fatigue research.…”

“…Hence, improving the critical tensile strength for the transition from cycle- to frequency-dependent crack growth can be the next trend for development of H-compatible materials. Another aspect gaining attention is the effect of H blended in natural gas. ,, FCG is still accelerated with a blend of the gases, while the degree of acceleration is manageable by regulating gas pressure and H content in the blend. Hence, the assessment and optimization of these factors in blended gas usage are important subjects of H-related fatigue research.…”

“…A large number of review articles on HE have been published in the last five years. These review articles zoomed into some specific aspects of HE, being theory-specific, − method-specific, ,− or material-specific. ,,, Due to its long history, diverse compelling theories, and evolving nature, there is a need for a comprehensive review that not only summarizes the existing knowledge but also identifies the knowledge gaps, unresolved issues, and future research directions.…”

Purifying Hydrogen from Dilute Hydrogen–Natural Gas Mixtures Using HT-PEM Electrochemical Hydrogen Pumps

“…The biggest concerns are hydrogen leakage from the pipeline and embrittlement of natural gas pipeline materials. 11 Coating the pipeline with polyethylene has been proposed to ameliorate the embrittlement problem; 12 however, the effect of hydrogen on polyethylene is not fully understood at high pressures and exposure over a long time. 13 Diluting the hydrogen to less than 30 vol % can mitigate embrittlement, 13 but end users of the transported hydrogen require high purity for their operations.…”

“…There are several challenges in storing and transporting hydrogen in a natural gas pipeline. The biggest concerns are hydrogen leakage from the pipeline and embrittlement of natural gas pipeline materials . Coating the pipeline with polyethylene has been proposed to ameliorate the embrittlement problem; however, the effect of hydrogen on polyethylene is not fully understood at high pressures and exposure over a long time .…”