Preventing hydrogen cracking

To prevent hydrogen cracking, at least one of the three conditions necessary for its occurrence must be eliminated or reduced to below a threshold level. A significant amount of residual tensile stress acting on the weld cannot be avoided and must always be assumed. The first step taken by many companies toward avoiding hydrogen 

Rehabilitation of Kpelines Using Fiber-reinforced Polymer (FRP) Composites 

For in-service welding applications, operators should specify electrodes with the H4R designator (e.g., E7018-H4R). These are becoming more common and, while there may be a price premium, this is negligible compared to the cost for remedial action that would be required following the discovery or failure of an in-service weld with hydrogen cracks. 

For in-service welding applications, the use of electrodes that are packaged in hermetically sealed cans (i.e., appropriate for use in the as-received condition) should 

Low-hydrogen electrodes with the H4R supplemental designator (e.g., E7018-H4R), packaged in small quantities hermetically sealed cans are ideally suited for in-service welding. 

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Embrittlement occurs when the metal absorbs hydrogen which can cause the metal to crack. If you make your own tanks, to prevent hydrogen from getting into the metal, do not use water while welding. Also, preheat the metal before welding and allow the weld to cool slowly. Embrittlement proceeds faster at high pressures and higher temperatures. 

It follows from the work of Darling and others that formation of the beta phase palladium hydride must be avoided to prevent embrittlement, cracking and delamination of thin catalytic films of unalloyed palladium used on composite membranes of Nb, Ta, Ti, V, and Zr. This also holds true for alloys of palladium susceptible to hydrogen embrittlement. Likewise, transformation of Nb, Ta, Ti, V and Zr substrates into brittle hydrides at low temperatures or at high hydrogen partial pressures must also be avoided. 

Electrochemical and mechanical factors both contribute to failure by SCC. The electrochemical nature of SCC is easily illustrated by the fact that an impressed cathodic current prevents the metal from cracking. Removing the impressed current allows the cracking to progress. Although cathodic protection is effective to mitigate the SCC, excessive polarization must be avoided to prevent hydrogen embrittlement. 

By increasing cathodic polarization, SCC is prevented but hydrogen cracking is accelerated. 

Several researchers have revealed a marked effect of rare earths on improving the thicknesswise ductility of steels resistant to lamellar tear, reducing the anisotropy of steels, and preventing hydrogen-induced cracking, etc. Basically, all these seem to be attributable to the following four principal functions achieved by rare earths and Ca addition to the molten steels ... 

Arosolvan process A process for the extraction of benzene and toluene from a mixture of aromatic and saturated hydrocarbons using a mixture of water and N-methylpyrrolidone. The process is used when naphtha is cracked to produce alkenes. To prevent extraction of alkenes these are saturated by hydrogenation prior to extraction. 

Hydrogen at elevated temperatures can also attack the carbon in steel, forming methane bubbles that can link to form cracks. Alloying materials such as molybdenum and chromium combine with the carbon in steel to prevent decarburization by hydrogen (132). 

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