Crack analysis of the inner cylinder in a rectangular container

Everyone is welcome to actively analyze and discuss!

Analyzing it literally: (1) Rectangular pressure vessel; structure: inner cylinder – jacket – reinforcing ribs (the vessel’s structure is subject to uneven stress). (2) After years of use, cracks appeared in the arc-shaped area of the inner cylinder (δ=6, S30408). (3) The inner cylinder was formed through cold working (during manufacturing, residual stresses from cold and hot working existed in the vessel). (4) Medium: steam, water. (5) There is alternating loading (what is the cycle of this alternating loading?) Total number of cycles? ) (6) Failure mode: Fatigue cracking? Corrosion fatigue? Stress corrosion cracking? (7) Sampling and analysis of the failed area should be carried out (chemical composition, metallography, fracture analysis, and energy spectrum analysis of fracture corrosion products). (8) Due to the limited amount of material available for analysis, it is possible that water vapor and alkalis in water caused pitting; under repeated heating, concentrations formed at the bottom of these pitting sites, leading to stress concentration. With the combined effects of the working stress on the inner cylinder, thermal stress, restraint stresses from the interaction between the inner cylinder, jacket, and reinforcing ribs, as well as residual stresses resulting from the processing of the inner cylinder (such as those from cold working or welding), the stress reached the threshold value necessary for stress corrosion to occur, resulting in stress corrosion cracking of the inner cylinder. (9) Of course, the possibility of fatigue cracking or corrosion-fatigue cracking cannot be ruled out either, but this would require evidence regarding the cycle period of the alternating load and the total number of cycles applied. (10) The above is for reference only; only by taking samples from the failed areas for analysis can the exact failure mode that caused the cracking be identified, providing solid evidence for improving product design.

First of all, thank you for your answer. I now understand that cracks are caused by various factors. There are a few points I would like to add: 1. Cracks mainly appear on the sides of the arc-shaped area; after each working cycle, the inner cylinder is dry. 2. The operating conditions involve pulsations 3 times, with a negative pressure of -0.08 and a positive pressure of 0.1； Then maintain at 0.23 MPa for 4 minutes, followed by maintaining the inner chamber pressure at -0.1 MPa for 5 minutes; the pressure in the interlayer remains unchanged throughout. This constitutes one cycle, with 5 cycles per day, over a design period of 8 years

Furthermore: (1) After the cracks appeared, was the inner surface of the inner cylinder, especially at the arc-shaped areas, subjected to non-destructive testing (penetrant testing)? (2) Is the location where the cracks appeared in the liquid phase space (or area where liquid accumulates), the gas phase space, or are cracks present along the arc-shaped areas of the inner cylinder? (3) Judging from the total number of cycles of alternating loading, fatigue is unlikely (the total number of cycles is less than 10 to the power of 7).

Furthermore: (1) After the cracks appeared, was the inner surface of the inner cylinder, especially at the arc-shaped areas, subjected to non-destructive testing (penetrant testing)? (2) Is the location where the cracks occurred in the liquid phase space (or area where fluid accumulates), in the gas phase space, or are cracks present throughout the arc-shaped areas of the inner cylinder? (3) Judging from the total number of cycles of alternating loading, fatigue is unlikely (the total number of cycles is less than 10 to the power of 7).

1. The maintenance plan specifies the use of penetrant testing to detect cracks, but the specific procedures are not clear. 2. The cracks appear mainly at the junctions between the arc-shaped areas and the side or bottom surfaces of the cylinder; there are no welds in these areas, nor is there any accumulation of liquid. The cylinder is equipped with valves that facilitate automatic water drainage. 3. Can the effect of fatigue loads be disregarded if the total number of cycles under alternating loads is less than 10 to the power of 7? Is it within analysis and design? Thank you for your answer! ! !

(1) “The maintenance plan states that penetration testing should be used to detect cracks, but the specific procedures are not clear.” I hope you will continue to pay attention to this matter. This will be of great help in clearly understanding the key aspects of the problem. (2) “Cracks mainly appear at the junctions of the arc section with the side or bottom surface of the cylinder; there are no welds in these areas, and no liquid accumulation occurs. The cylinder is equipped with valves that enable automatic water drainage.” The residual alkali in water vapor may become concentrated ； Eliminating welding residual stress can eliminate it ； The location where cracks occur (liquid phase, gas phase) is not clearly stated. (3) In mechanical design, a total number of cycles of alternating loads less than 10 to the power of 7 is used as the criterion for fatigue to occur. Of course, in container design, analytical design specifications are available for selection. (4) Using patch welding is not appropriate; instead, plate replacement (or creating a skylight) should be employed. At the same time, crack samples can be taken for further analysis.

(1) “The maintenance plan states that penetration testing should be used to detect cracks, but the specific procedures are not clear.” I hope you will continue to pay attention to this matter. This will be of great help in clearly understanding the key aspects of the problem. (2) “Cracks mainly appear at the junctions of the arc section with the side or bottom surface of the cylinder; there are no welds in these areas, and no liquid accumulation occurs. The cylinder is equipped with valves that enable automatic water drainage.” The residual alkali in water vapor may become concentrated ； Eliminating welding residual stress can eliminate it ； The location where cracks occur (liquid phase, gas phase) is not clearly stated. (3) In mechanical design, a total number of cycles of alternating loads less than 10 to the power of 7 is used as the criterion for fatigue to occur. Of course, in container design, analytical design specifications are available for selection. (4) Using patch welding is not appropriate; instead, plate replacement (or creating a skylight) should be employed. At the same time, crack samples can be taken for further analysis.