2024-03-11

What materials can be used for hydrogen valves

Q: When specifying a valve for hydrogen, are some material considerations to keep in mind?

Answer: Hydrogen can cause many different adverse effects in metal materials. The specific problems that can occur and the ways to avoid them depend on the conditions of use. Although the topic is too large to be fully covered in this column, the following is a description of the main hydrogen damage mechanisms and some suggestions to avoid problems.

hydrogen embrittlement
Hydrogen embrittlement, also known as hydrogen stress cracking or hydrogen-induced cracking, is a condition in which the ductility of a metal is low due to the absorption of hydrogen. Hydrogen embrittlement is the ultimate tensile strength greaterThe main problem in 90 ksi steel, although many other alloys are also easily affected. Most hydrogen embrittlement failures are caused by the absorption of hydrogen generated during electroplating, pickling or cleaning operations. However, hydrogen may also be charged during use. This typically occurs with hydrogen generation due to corrosion, although it can also occur in high temperature hydrogen applications. Hydrogen embrittlement failure is generally characterized as a single, unbranched crack at near ambient temperature, with stress below the yield strength. However, failures that deviate from these characteristics can and do occur.

Hydrogen embrittlement requires hydrogen ions (H) or monoatomic hydrogen (H) sources. diatomic (molecular) hydrogen (H2) will not cause hydrogen embrittlement becauseH2The molecules are too large to diffuse into the metal crystal structure.

Hydrogen ions are produced during any electrolytic or aqueous corrosion process, including general corrosion, galvanic corrosion, pitting corrosion, electrocleaning, electropolishing, pickling, and electroplating processes.

Monatomic hydrogen (H) is the decomposition of diatomic hydrogen by high temperature (H2) formed. This dissociation is reported to begin at about350°F（175°C) occurs, as the temperature increasesH / H2increase in proportion.

It should be mentioned that although hydrogen embrittlement is most likely to occur at ambient temperature, ambient temperature failures may occur in materials exposed to hydrogen at high temperatures.

Since sulfide stress cracking is essentially hydrogen embrittlement catalyzed by the presence of sulfide ions,NACE MR0175 / ISO 15156, Petroleum and Natural Gas Industries-Oil and gas production containsH2Smaterials used in the environment, and/orNACE MR0103,Corrosion resistance of materials The effect of sulfide stress cracking in petroleum refining environments, Can be used as a guide for general material selection to avoid hydrogen embrittlement. However, the requirements in these standards are somewhat conservative to avoid conventional hydrogen embrittlement. Usually, less35 HRC steel can usually be used in applications where conventional hydrogen embrittlement needs to be considered, andNACEstandards will require steel to meet22 HRCThe maximum hardness required. Austenitic stainless steels, most nickel and copper alloys, and aluminum alloys are generally resistant to hydrogen embrittlement, although some precipitation hardening and/or strain hardening grades may suffer from hydrogen embrittlement.

hydrogen erosion
When carbon and low-alloy steels are exposed to high-pressure, high-temperature hydrogen, monatomic hydrogen diffuses into the steel and combines with carbon in the steel to form methane gas, which is trapped at grain boundaries and other regions. Discontinuities in the material. The resulting internal decarburization and grain boundary cracking reduce the mechanical properties of the material. As the content of chromium and molybdenum increases, the resistance to hydrogen will also increase, because these elements form more stable carbides than iron and do not easily release carbon into hydrogen.API Recommendations941,Steel for hydrogen at high temperatures and pressures in refineries and petrochemical plantsInclude a graph (often called a Nelson curve) that shows the region of acceptable carbon and alloy steel materials as a function of hydrogen partial pressure and temperature.

Hydrogen bubbling
Hydrogen bubbling is the formation of hydrogen-containing blisters in steel. When monoatomic hydrogen (H) Diffuses through the steel and recombines into molecular hydrogen at internal defects (such as voids, laminations, and non-metallic inclusions) (H2), this happens. Molecular hydrogen cannot diffuse back through the steel, so the gradual accumulation of molecular hydrogen will cause the pressure inside the defect cavity to increase, eventually causing the material to bubble. Killed steels are typically specified for high temperature hydrogen applications or applications known to produce ionic hydrogen. Killed steel is steel treated with a strong deoxidizer (such as silicon or aluminum) in order to reduce the oxygen content in the molten ingot, thereby reducing the porosity in the finished steel. Compared to non-killed steels, killed steels are more resistant to hydrogen blistering due to the relative lack of internal voids.“Kill”The term actually refers only to forged products; however, cast steel is also deoxidized with elements such as silicon or aluminum to prevent the formation of pores.

 

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