Welding issues in hydrogenation reactors
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During inspections of the hydrogenation reactor while it was in use, cracks were found on its inner wall. After discussion, it was agreed that this was caused by uneven distribution of elements in the welding material. Could Expert Haiyou suggest ways to ensure a uniform distribution of trace elements in the welding metal during surfacing?
This post was last edited by Shutong on 2019-12-24 at 16:43. First, let’s discuss the reasons for the formation of cracks: Hydrogenation reactors operate under high temperature and pressure conditions, with hydrocarbons, hydrogen, and hydrogen sulfide as the working media; thus, the operating conditions are quite severe. Corrosion by high-temperature hydrogen – surface decarburization and internal decarburization (Hydrogen corrosion: High-temperature, high-pressure hydrogen diffuses into the steel and reacts with unstable carbides to produce methane gas). Corrosion by high-temperature hydrogen and hydrogen sulfide (The form of corrosion is chemical degradation of the steel by hydrogen sulfide; in a hydrogen-rich environment, 90%–98% of organic sulfur is converted into hydrogen sulfide, which accelerates the corrosion of the steel under the influence of hydrogen). This is the actual cause: hydrogen-induced cracks in the surfacing layer, not uneven distribution of electrode elements!
Should the elements in the welding rod be adjusted evenly during surfacing? Never heard of it!
It should be considered from the design stage: this issue is addressed by selecting appropriate materials – chromium-molybdenum steel as the base material, and stainless steel cladding for the lining.
The measures taken in manufacturing are as follows: depending on the severity of the operating conditions, either a double-layer cladding weld (309+347) or a single-layer cladding weld (347) can be used. The double-layer configuration offers better resistance to delamination than the single-layer one; if a single-layer weld with shallow penetration (PZ method) is used, the dilution rate of the weld metal must be increased appropriately to enhance its resistance to delamination. Our company uses a high-speed, high-current surfacing method with excellent anti-peel performance. To prevent welding thermal cracks in the surfacing layer and the formation of σ-phase during operation, the ferrite content in the surfacing layer after welding should be kept within the range of 3–10%. The ferrite content in the surfacing layer can be estimated using the SCHÄFFLER diagram, or it can be measured directly on the surfacing layer using a ferrite meter. Under normal circumstances, the latter measurement is on the high side, especially in the case of single-layer surfacing. It has been in use for 10 years, with only minor cracks.
From an operational perspective as well, it is necessary to avoid sudden changes in temperature; otherwise, the lifespan will not exceed 10 years
Cladding? For manufacturing or repair. Cladding and welding should be different
If we consider this question alone, it is theoretically explainable. It’s like making formula milk: substances that haven’t dissolved and remain at the bottom can be mixed evenly by stirring. Similarly, the metals in welding materials can also be made to flow during the surfacing process using electromagnetic methods, and perhaps this could achieve the same result.
Are you using electrode cladding or electroslag welding? How wide is the solder ribbon? In the image, we used 75mm welding rods, and surfacing was carried out using electroslag welding combined with magnetron control; the results were quite good. Are the minor cracks you mentioned caused by hydrogen?