dehydrogenation treatment

This is a great question! Before, I only knew why hydrogen removal was necessary; it was only by chance that I learned about the source of hydrogen. Hydrogen comes from water, and that’s why removing moisture is one of the steps in pre-welding preparation. Welding flux also needs to be dried before use. Now everything makes sense. Hehe, I’m a little proud of myself

The moisture content in the welding electrodes and wires is above the specified limit； The relative humidity in the welding environment is high ； The hydrogen content in the welding electrodes and wires is above the acceptable level. For these reasons, hydrogen does not have enough time to escape during welding. For steel materials that are highly susceptible to hydrogen-induced stress corrosion, it is necessary to remove hydrogen after welding, and this should be done immediately following welding.

There is also a significant amount of moisture in the air; if not managed properly, hydrogen corrosion can occur, and this type of corrosion is irreversible, so hydrogen removal treatment is necessary； For the same reason, the environmental humidity during welding should not be too high.

Hydrogen, in other words, refers to hydrogen atoms that are generated from water at the high temperatures produced during welding. Hydrogen atoms have a tendency to gather together; when they accumulate, it leads to localized high pressure (some say it causes localized internal stress buildup), which in turn results in the formation of cracks； Post-weld hydrogen removal: It involves releasing the internal hydrogen atoms (i.e., internal stress) to prevent the formation of cracks ； I hope you can give me a few more points ；

I would like to add another reason for carrying out dehydrogenation treatment: since hydrogen, once it enters the metal, causes damage to its mechanical properties, hydrogen dissolved in the metal’s crystal lattice significantly reduces plasticity and toughness, and can even lead to cracks, resulting in brittle failure. Before this brittle failure occurs, the container shows no visible deformation; such failure is not only sudden and tends to generate metal fragments, but it can also happen at relatively low stress levels. Cracking of welded joints caused by hydrogen usually occurs within a few hours to days after welding, which makes it particularly hazardous. The sources of hydrogen have been comprehensively discussed by everyone here: some comes from absorption during the equipment manufacturing process, and some results from absorption when materials are used for extended periods in high-temperature environments with hydrogen present. However, for containers that require degassing treatment after welding, this step can be omitted if post-weld heat treatment is carried out immediately thereafter.

The welding rod coating contains water； During welding, the hydrogen generated by decomposition enters the weld. Hydrogen corrosion will occur.

Hydrogen in welds mainly comes from moisture in the welding materials, hydrogen-containing substances (such as organic materials like grease around the weld), and water vapor in the air surrounding the arc. Hydrogen is harmful during the welding of many metals and alloys. Its harmful effects are mainly manifested in the following four aspects: 1. Hydrogen embrittlement (the phenomenon in which hydrogen causes a significant reduction in the plasticity of steel at room temperature is known as hydrogen embrittlement). 2. White spots (when carbon steel and low-alloy steels contain high levels of hydrogen, silver-white circular areas of localized brittle fracture often appear on their tensile or bending surfaces; these are called white spots). 3. Formation of pores. 4. Occurrence of cold cracks (with delayed cracking being the most severe form). To prevent the adverse effects of hydrogen on steel, it is necessary to strictly control the hydrogen content in welds; the so-called hydrogen removal treatment is an important method to prevent this content from exceeding acceptable levels. The process involves heating the welded parts to 350°C and then holding them at that temperature for about 1 hour, which allows any hydrogen that might be released suddenly during welding to diffuse outward sufficiently. Materials commonly used such as 15CrMo and 12Cr1MoV require degassing treatment after welding.

The 9th floor’s view is extreme. Not all pressure vessels made of certain materials require hydrogen removal treatment; this treatment is mainly necessary for high-strength steels, such as Cr-Mo steel!

Only low-alloy steels with higher strength levels are prone to delayed cracking and thus require dehydrogenation treatment. Hydrogen may originate from the hydrogen absorbed by metals when the material is stored in a hydrogen-rich environment, or it may come from the moisture absorbed by welding materials during welding.

Hydrogen embrittlement can occur; the hydrogen comes from the welding materials, air, and the steel itself. Heat treatment is required, at a temperature of around 300 degrees.