How to repair refining equipment after brittle failure
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Taking into account the previously mentioned factors such as the causes and risks of brittleness in refining equipment, it is necessary to first assess the extent of the damage after brittleness occurs, before carrying out repair work: Damage assessment comes first – all cracks resulting from brittleness are located using techniques such as penetrant testing and magnetic particle testing; the degree of brittleness is determined through impact tests and metallographic examinations, and it is decided based on API 579 standards whether the equipment is worth repairing. For local crack repair, the fracture surface is cleaned and then the parts are welded together; vertical reinforcement plates are used for strengthening, the pipe is covered on the outside and a corundum lining is inserted. Meanwhile, thermal stresses are recalculated to optimize the pipe design and avoid stress concentration. Restoration of material properties: To address the temper embrittlement of chromium-molybdenum steel, this phenomenon can be eliminated and the toughness of the material restored through a process of short-term heating at temperatures above 593°C followed by rapid cooling. Handling of severe damage: If embrittlement has resulted in widespread loss of toughness and the propagation of internal microcracks, the damaged component must be replaced immediately; it is strictly prohibited to continue operating it with defects present. Verification after repair: After the repair is completed, a hydrostatic test and non-destructive inspection are carried out to ensure that there are no residual defects; thereafter, the equipment is gradually put into operation in accordance with the hot-state start-up and shutdown procedures.
After reading the repair process for brittle failure devices shared by the original poster, it was explained in great detail; especially, the idea of conducting a damage assessment first is very crucial. I have encountered similar cases in chemical plants as well; I would like to add two points that are often overlooked in practice: Welding procedure qualification – the brittle zone generally has high hardness and low toughness, so direct welding can lead to further cracking. It is recommended to conduct a welding procedure qualification (WPQ) first, use low-hydrogen welding electrodes, and establish clear parameters for preheating and post-heating processes. It is best to have experienced welders carry out the welding work. Precautions for lining installation: Expansion joints should be left when filling the corundum lining; otherwise, bulging and detachment may occur upon temperature increase. Additionally, if thermal stress needs to be recalculated for the pipeline design, it is recommended to engage a company with qualifications in pressure vessel design to prepare the calculations, rather than relying solely on experience. Safety first; after repairing such equipment, it’s best to conduct another overall pressure test and random hardness checks to avoid any potential risks. The original poster’s experience has been saved; we can discuss similar issues again in the future.