【Discussion Thread 22】Is dehydrogenation treatment considered a heat treatment?
Thread Content
This post was last edited by kareale88 on 2019-3-6 17:17: bg4.png【Discussion Thread 22】Is dehydrogenation considered a type of heat treatment? It is not explicitly stated in GB150-2011. GB150-1988 states as follows: In 10.4 Heat Treatment, under 10.4.3: For vessels that require hydrogen removal treatment after welding, if post-weld heat treatment is carried out immediately thereafter, the hydrogen removal treatment can be omitted.
Dehydrogenation treatment is a method of heat treatment; it is not clear whether dehydrogenation treatment can be omitted when post-weld heat treatment is carried out immediately after welding.
The new GB150 does not specify this in detail; can it be understood that this is covered under stress corrosion?
I found some information related to hydrogen removal treatment for bg4.png: Hydrogen removal treatment refers to the elimination of the \"hydrogen\" absorbed by the weld joint during welding (usually coming from moisture in the welding environment). Hydrogen dissolved in the metal lattice significantly reduces the plasticity and toughness of the weld joint, and can even cause cracks, leading to brittle fracture – what is commonly known as delayed cracking. The method to remove hydrogen is to carry out heat treatment immediately after welding; this helps to eliminate excessive welding stress and allows the diffused hydrogen in the welded joint to escape. For containers that do not require post-welding heat treatment, hydrogen removal can be carried out separately. The treatment temperature depends on the type of steel, but it is generally between 200°C and 350°C. If the temperature is too low, the effect of hydrogen removal is not significant; if it is too high, and exceeds the martensite transformation temperature, martensite structure may remain in the welded joint. Not all metal materials develop delayed cracking during welding; this phenomenon is related to the material’s strength grade and chemical composition, and it only occurs in low-alloy steels with higher strength grades. Generally, Cr-Mo steel vessels have thick walls and high rigidity, and their manufacturing cycle is long; heat treatment cannot be carried out promptly after welding. To prevent cracking and stabilize the dimensions of the welded parts, an intermediate heat treatment at a temperature lower than that of the final heat treatment is performed after the completion of the main welds (or the main welds and the welds connecting the shell fittings). The longitudinal ring welds of the shell should be thoroughly and evenly preheated before welding. During welding (including the welding of temporary attachments, etc.), the temperature of the base metal within a range of not less than 150 mm on each side of the weld seam, as well as the interpass temperature, must always remain above the preheating temperature; hydrogen removal treatment should be carried out immediately after welding.
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Dehydrogenation treatment can actually be carried out in conjunction with post-weld heat treatment; it simply involves keeping the welded joint above the temperature at which hydrogen escapes. It is generally 200-300°C, which is fundamentally different from post-weld heat treatment.
I think the same, and in GB/T30583, the thermal activity of carbon steel and low-alloy steel below 490°C is not considered to be heat treatment (that’s roughly what it means)
Post-weld dehydrogenation is also known as post-heating; the temperature is maintained at two to three hundred degrees after welding for a certain period of time to facilitate the escape of diffused hydrogen.
Hydrogen removal treatment should be a form of heat treatment, involving heating after welding to 200–350 degrees and maintaining that temperature for a certain period of time; the purpose of this is to prevent brittle failure.