Cracking of stainless steel equipment

Is the second picture the interior one? How many years has the device been in use? The welding stress issue still needs to be considered.

Since it is a steam tube bank, hydrogen embrittlement is not a possibility; only welding stress needs to be considered.

This case is worth discussing. The poster should first complete the parameters, such as the material of the equipment, pressure, temperature, wall thickness, etc. Is it a heat exchanger? It’s still just a kind of steam distribution station. Is there a fatigue condition? The presence of such cracks is certainly due to stress. Since it is steam, it cannot be brittle fracture caused by low temperatures; therefore, the issue should be analyzed from several aspects: 1. Material. Is the head formed by hot forming or cold forming? Was the performance-restoring heat treatment carried out in accordance with the 150 regulations? 2. Welding. Could welding issues be causing excessive residual welding stress? Or should no heat treatment be carried out after welding? Or should it be preheated, without performing pre-welding preheating? 3. If it is a steam distribution panel, is there an issue of an excessively long blind tube? If the blind zone is too long, it may lead to pulse water hammer; in such cases, the pulse force generated by the pulse water hammer is extremely large, and similar accidents occur in steam pipelines.

I just saw that the title is “Stainless Steel Equipment”... But from the pictures, it doesn’t seem to be made of stainless steel at all! Is there anything wrong with this material?

[Repost] Welding defects are the most direct factors affecting welding quality, and welding cracks, as one of the most difficult-to-resolve welding defects, occur from time to time in welded pipe production. Welding cracks come in two types: transverse cracks and longitudinal cracks. Among them, longitudinal cracks exhibit a typical crack fracture surface with a smooth, curved free surface; sometimes oxides are present, and electron probe analysis reveals no other inclusions. Preventive measures include: 1. Metallurgical factors – Controlling the levels of S, P, and C in the weld is an effective way to improve crack resistance and reduce crystalline cracks. In welded pipe production, selecting appropriate welding wires and fluxes, as well as effectively controlling their S, P, and C contents, are effective measures to reduce longitudinal cracks in the welds. 2 Joint groove shape: An appropriate welding groove is an effective measure to reduce welding cracks. When the sheet metal is thick and it is difficult to control its position, the likelihood of crack formation increases; therefore, improving the quality of the joint and minimizing residual stresses in the steel pipe during the forming process can help reduce crystalline cracks. 3 Process factors: Reducing heat input enables the formation of a microstructure with smaller grain sizes in the weld ； Reducing the welding speed allows the ends of the grains to grow side by side and press together, thereby preventing the concentration of segregation ； Furthermore, wide welds can prevent grains from growing and fusing together compared to narrow welds, thus avoiding the concentration of segregation. Transverse welding cracks, whose direction is perpendicular to the weld seam, exhibit intergranular and transgranular characteristics. Preventive measures include: 1. In terms of metallurgy: 1) It is necessary to ensure excellent mechanical properties of the steel sheet, meeting the requirements for strength and toughness, while minimizing impurities in the steel ； 2) Try to use welding materials with low hydrogen content, as well as high strength and toughness; select appropriate welding wires and fluxes, thoroughly clean the welding wires and the area to be welded, and dry the flux. 2. In terms of processing: 1) Excessive welding line energy can cause the grains in the area near the weld seam to become coarse ； If the wire energy is too low, it will cause hardening in the heat-affected zone, which leads to the formation of transverse cracks; therefore, an appropriate welding wire energy should be selected ； 2) Preheating can reduce the cooling rate, effectively preventing the formation of transverse cracks ； 3) Delaying cooling after welding allows hydrogen to escape fully, and it also prevents the formation of transverse cracks in the weld.

There are many reasons for weld cracking; sometimes it is not caused by temperature. For example, in hydrogenation reactors, hydrogen embrittlement occurs, and this is not due to temperature. Different base metal materials require different welding processes, such as welding parameters, preheating before welding, and slow cooling after welding. 1. Cold cracks generally form during the cooling process after welding high-strength steel, and there are also delayed cracks. It occurs mostly in the heat-affected zone and areas where hydrogen accumulates, sometimes by extending along grain boundaries and sometimes by crossing them. It occurs most frequently in the heat-affected zone of welds in high and medium carbon steels, as well as low and medium alloy steels. The direction is not necessarily parallel to the weld; however, leg cracks (at the junction between the weld surface and the base metal) are definitely parallel to the weld ； Cracks beneath the weld bead can be either parallel or perpendicular to the weld bead. 2. All thermal cracks occur along grain boundaries. Low-carbon steel, austenitic stainless steel, and low-alloy steel can all develop thermal cracks. Thermal cracking is mainly crystalline cracks; in addition, there are polygonalization cracks and so on. Crystalline cracks: During the crystallization of the weld, due to the contraction of the solidified metal and a shortage of liquid metal that cannot be supplied in time (one of the reasons being an excessive cooling rate), cracks occur along the grain boundaries under tensile stress. The most common issue is cracking along the center of the continuous weld. Choosing the correct welding sequence under conditions of low stiffness is an important measure to prevent hot cracks. 2. Additionally, the reasons for cracks in welds during or after welding are as follows: stress (stress is generated when the temperature rises or falls too rapidly), restraint forces, rigidity, chemical composition, gaps left in the weld, current, weld bead shape, cleanliness of the base material, etc. These factors can all be causes of weld cracking, and sometimes it is the combined effect of two or more factors. I believe the most important factor affecting the path of weld hot cracks is the distribution of grain boundaries near the initial cracking point; it determines in which direction the crack will propagate, and there is a certain degree of randomness involved. However, the severe toe cracks that occur during cold cracking are not closely related to this; rather, it is the contraction of the welded metal that pulls it away from the base material. The above is for reference only.

It’s very likely that the head has not been solution-treated. . Caused by stress corrosion~~~

Is there insulation on the outside of the cover? Does the equipment operate intermittently or is it left unused for long periods of time? Is your area located near the sea, or does it experience frequent rainfall or high humidity? Could SCC be caused by copper? ?