Hydrogen attack

Types of Damage. Hydrogen attaek is eharaeterized by three types of damage, as follows  

Compounds such as hydrogen sulfide and cyanides are the most common metal surface poisoners occurring in process units subject to aqueous-phase hydrogen attack. In many process units, these compounds can be effectively eliminated and hydrogen diffusion stopped by adding ammonium polysulfides and oxygen to the process streams which converts the compounds to polysulfides and thiocyanates, provided the pH is kept on the alkaline side. 

To avoid decarburization and fissuring of the carbon and low-alloy steels, which is cumulative with time and, for all practical purposes irreversible, the limitations of the Nelson Curves should be followed religiously, as a minimum. Suitable low-alloy plate materials include ASTM-A204-A, B, and C and A387-A, B, C, D, and E, and similarly alloyed materials for pipe, tubes, and castings, depending upon stream temperatures and hydrogen partial pressures, as indicated by the Nelson Curves. 

Skei and Wachttr, Hydrogen Blistering of Steel in Hydrogen Sulfide Solutions, Corrosion, May 1953. 

Boimer, W. A., et al Prevention of Hydrogen Attack on Steel in Refinery Equipment, paper presented at API Div. of Refining 18th Mid-year Meeting, May 1953. 

High-temperature hydrogen attack refers to a reaction between hydrogen and a component of the alloy. For example, in steels, hydrogen reacts with iron carbide at high temperatures to form methane gas according to the 

Schematic of hydrogen damage for low-alloy steels in hydrogen service. Decarburization and hydrogen attack above alloy lines. 

In several steps of the ammonia production process, especially in the synthesis section, the pressure shells of reaction vessels as well as the connecting pipes are in contact with hydrogen at elevated pressure and temperature with a potential risk of material deterioration [1211]-[1213], [1484]. 

Physical Hydrogen Attack. A related phenomenon is physical hydrogen attack, which may happen simultaneously with chemical attack. It occurs when adsorbed 

At higher temperature and partial pressure, hydrogen is always soluble to a minor extent in construction steels. For this reason it is advisable not to cool vessels too rapidly when taking them out of service, and to hold them at atmospheric pressure for some hours at 300 °C so that the hydrogen can largely diffuse out (soaking). In contrast to the hydrogen attack described above this phenomenon is reversible. 

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Hydrogen attack at a. Ambient to boiling a. Numerous a. Gas plants, acidic a. Rimmed, capped, a. Diffusion of a. Eliminate water... 

For hot wall vessels, the increased strength may be such that the use of chromium and molybdenum alloy steels will be cheaper. Also, these steels may be required to prevent hydrogen attack and to reduce oxidation and sulfidation. 

Carbon steel, where not limited by sulfur corrosion or hydrogen attack, can be the most economical material... 

Hydroprocesses Hydrogen is chemically stable and relatively unreactive at ordinary temperatures most processes utilizing it require a catalyst. Above 500°C it reacts readily with oxygen and confined flammable mixtures explode violently if ignited Main hazards fire, explosion, metallurgical problems arising from hydrogen attack... 

The most spectacular failure of this sort occurred when the exit pipe from a high-pressure ammonia converter was constructed from carbon steel instead of l A% Cr, 0.5% Mo. Hydrogen attack occurred, and a hole appeared at a bend. The hydrogen leaked out, and the reaction forces pushed the converter over. 

Material of construction The materials of fabrication for this type of packing are more critical to long life due to pad size, wall thickness of metal or plastic components, and actual selection based on the system corrosion, hydrogen attack, and oxygen attack in the column environment. 

Main hazards fire, explosion, metallurgical problems arising from hydrogen attack... 

B. A. R. Ciuffreda and W. D. Rowland, Hydrogen Attack of Steel in Reformer Service, Proceedings, 1957, Vol. 37, American Petroleum Institute, New York, pp. 116-128. 

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