in various forms and is often depicted by colour . Each variation of hydrogen is produced in different ways but contains little to no carbon emissions . As the use of hydrogen in pipelines continue to gain the attention of industry professionals , it is important to consider the tribulations that might be present with steel applications and hydrogen . |
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There are a few standard codes that the industry currently uses when working with equipment made of steel in hydrogen services . These codes are to ensure proper handling and functioning of the equipment while hydrogen is being pumped through the applications . The two most relevant codes are API RP 941 and ASME B31.12 . They detail the following : |
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API RP 941 |
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API RP 941 applies to any equipment in refineries , petrochemical facilities , or hydrogenation plants that operate in environments where hydrogen-containing fluids are processed at elevated temperatures and pressures . |
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The API RP 941 is a recommended practice developed and published by the American Petroleum Institute ( API ). The RP is intended to help identify and manage equipment potentially subject to high temperature hydrogen attack by putting into place practical operating limits for carbon and low alloy steels in hydrogen service at elevated temperatures and pressures . This RP also discusses how the resistance of steels to hydrogen damage can be affected by high stress , heat treating , chemical composition , and cladding . A summary of inspection methods to evaluate equipment for the presence of HTHA is also included . API RP 941 was originally published in 1997 , and the most recent 8th Edition was published in February of 2016 . API RP 941 only covers equipment that runs at high temperatures and does not cover any equipment that runs at below 400 ° F ( 204 ° C ). At those lower temperatures , hydrogen enters the steel with the assistance of an electrochemical mechanism , operating under different principles . |
4 . ANSI FCI 70-2 , Control Valve Seat Leakage
5 . MSS SP61 , Hydrostatic Testing of Steel Valves
6 . ISA-S75 , Hydrostatic Testing of Control Valves
The primary test conducted on valve assemblies to be used in hydrogen applications are external test , such as a hydrostatic shell test . The shell test confirms the soundness and strength of the valve body . It also pre-stresses the valve body , which aids in avoiding fatigue with cyclic pressure . It is done with water at 1.5x the valve body pressure rating . The shell test is typically done with valve in the partially open position . As the body of the valve should be externally leak resistance , it is preferred to use fully welded body design for this application .
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amples of steels that have been proven for hydrogen gas service include : ASTM A106 Grade B as well as API 5L Grade X42 , and API 5L Grade X52.5,6 .
The API 5L steels contain small amounts of niobium , vanadium , and titanium and are referred to as ‘ microalloyed ’ steels . Microalloyed X52 steel has been used extensively in hydrogen gas pipelines .
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Material Selection and The Carbon Equivalent .
Material strength is an important variable that affects hydrogen embrittlement of pipeline steels . One of the principal criteria to consider when selecting steel grades and processing procedures is the limit strength . The maximum tensile strength , recommended for hydrogen
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Additionally , this RP only covers HTHA resistance for steels operating within the recommended guidelines . The guidelines in this RP can also be applied to hydrogenation plants such as those that manufacture ammonia , methanol , edible oils , or higher alcohols .
ASME B31.12
ASME B31.12 is a standard on Hydrogen Piping and Pipelines containing requirements for piping in gaseous and liquid hydrogen service .
These standards will aid with the transition to implementing the use of hydrogen on a more regular basis .
Valves in the Hydrogen Industry
Valves used in hydrogen industry have several requirements that extend above and beyond general application testing standards . These standards define leak testing requirements for external or internal leaks . Common standards include :
1 . API 598 , Valve Inspection and Test
2 . ASME B16.34 , Valves – Flanged , Threaded and Welding End
3 . ISO 5208 , Industrial Valves , Pressure Testing of Valves
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Transporting Hydrogen
The transportation of high-pressure hydrogen in steel structures presents challenges . Hydrogen gas can adsorb and dissociate on the steel surface to produce atomic hydrogen . Dissolution and diffusion of atomic hydrogen into steels can degrade mechanical properties , creating hydrogen embrittlement , thus making the application susceptible to fractures . Hydrogen reduces typical measures of fracture resistance such as tensile strength , ductility , and fracture toughness , accelerates fatigue crack propagation , and introduces additional material failure . Steel structures that do not fail under static loads at ambient temperature are susceptible to time-dependent crack propagation in hydrogen .
Carbon and low-alloy steels are therefore common structural materials for high-pressure hydrogen gas vessels and pipelines . The materials used in hydrogen application , such as steel pipelines , have been operated safely with hydrogen gas when specific limits have been placed on properties of the steels . Relatively low strength carbon steels are specified for hydrogen gas pipelines . Ex-
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