Special Topic : Green Applications
There is a high risk of cracking for materials that are highly susceptible to sulfide stress cracking ( SSC ) and hydrogen stress cracking ( HSC ), such as high nickel steels and martensitic alloys . High-strength steels with yield strength above 140ksi (> 965N / mm 2 ) can also suffer from HSC . Additionally , designs with stress concentrations increase the risk of cracking .
Studies have shown that the fatigue strength of certain steels may be reduced even in low-pressure hydrogen environments . While hydrogen absorption may not necessarily lead to hydrogen-enhanced cracks , it can still cause changes in the mechanical properties of the metal being studied .
According to Sandia ' s Technical Reference for Hydrogen Compatibility of Materials , the presence of hydrogen gas can lower fatigue resistance , even at low pressure , which can be harmful to machinery exposed to cyclic loads . For an example , the large bore gas
Hydrogen source transportation valves are infrequently actuated . Therefore , fatigue-related failures are unlikely to occur in .
Commonly Used Stainless Steel in The Gas Grid
Since transported hydrogen and natural gas are dry and do not possess corrosive properties , alloys such as duplex and super duplex are not preferred to combat internal corrosion for gas transportation purposes . However , components that are sensitive to dimensional tolerances or subject to a corrosive external environment may require the use of corrosion-resistant alloys such as stainless steel .
Stainless steel is a commonly used material in various industries , including construction materials for valves . Type 304 and 316 are low-strength materials that are generally not prone to hydrogen embrittlement , even in high-severity environments like sour service .
CH [ at ppm ]* equivalent hydrogen pressure [ bar ( a )]**
81 bar H2 0,25 ** 81 0,01 bar H2S , 0,25 wt ppm 14 7062
active cathodic protection 1 wt ppm
3 ml H2 / 100 g welding electrode
56 11438
150 14519
1 bar H2S 3,3 wt ppm 185 15493 cathodic charging 11,6 wt ppm 650 19897
* 0,25 ppm H means 1 hydrogen atom per 1 million iron . ** Calculated based on Sieverts ’ law and solubility data given in the report [ 7 ]. Higher solubility data results in lower equivalent pressures .
Table 1 : Hydrogen concentrations ( CH ) in steel from different sources and calculated equivalent hydrogen pressures in a steady state ( at 20 ° C ) [ 6 ]
There may be rare instances of susceptibility to hydrogen embrittlement in some cases , such as centrifugally cast or wrought material in solution-annealed seal rings and gaskets . As the operating temperatures of the gas network are not within the range susceptible to high-temperature hydrogen attack ( HTHA ), grades such as 347 are not typically utilized .
Martensitic grades , like 17-4 PH , can be utilized where better mechanical properties are necessary . Compared to austenitic or martensitic stainless steel , 17-4 PH is relatively cheap , has high strength , and excellent corrosion resistance . As a result , it is widely used in the petrochemical , aviation , and nuclear industries . However , experience and research have shown that 17-4 PH is highly sensitive to hydrogen . Significant increases in crack growth rates in fatigue have been reported at pressures as low as 2 atm hydrogen gas . This trend can be seen in other martensitic grades , such as 410 and 440C , with reduced ductility and notched tensile strength test results at 69 MPa or even below 1 atm hydrogen gas .
Conclusion
Although hydrogen can affect the mechanical properties of metals , even at low pressures , it does not necessarily pose harm to all exposed metals . In the case of hydrogen transportation through gas distribution networks , it is not expected to have detrimental effects . Hence , there is currently no requirement to employ advanced materials specifically for this purpose .
The current standards have limited specifications for material limits regarding hydrogen gas . However , it is expected that the upcoming API 6Z standard will address this issue for valves , although the extent of its coverage is currently unknown . Association for Materials Protection and Performance ( AMPP ) recently initiated new standards projects under SC26 to address hydrogen related topics . In light of this , manufacturers should be aware of the expected stresses for their products subject to hydrogen and assess the associated risks accordingly until adequate guidance is established by a reputable standard organization .
By adopting a proactive approach and implementing appropriate measures to prevent hydrogen-induced damage , the safe and reliable transport of hydrogen can be ensured . The transition to a more sustainable energy system is achievable by minimizing the risks of failure or catastrophic incidents .
About the Author
Tuncay Kurtulan is a highly skilled Metallurgy & Materials Engineer with technical and practical industrial experience . Currently working as a Senior Materials Engineer at OGC Energy Ltd , he specialises in corrosion assessments , materials selection , and resolving challenges in renewable projects . With his expertise and pragmatic approach , Tuncay is a valuable asset in advancing sustainable technologies and ensuring asset integrity in the energy sector .
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