Design service life and actual service life
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What is the design service life specified by the standards? The standard recommends 25 years. During actual operation, I posted a survey a couple of days ago; some owners are still using spherical tanks built in the 1980s. However, as time goes by, the inspection standards set by the regulatory authorities become stricter, and inspections have to be carried out more frequently. Has the design life specified in the drawings been reached, meaning the spherical tank must be scrapped? Theoretically, as long as it passes the inspections conducted by the special inspection agency, it can be used continuously within the specified annual inspection period. However, over time, it becomes necessary to consider whether its use is cost-effective and safe; if the usage costs are too high, then replacing it with a new one should be considered. In fact, this is to prevent safety issues arising from the operation of pressure vessels beyond their designed service life; therefore, the design agency should generally indicate the designed service life of the pressure vessel on the design drawings. The design service life of pressure vessels is not necessarily equal to their actual useful life. Indicating the design service life is merely a reminder to users that once a spherical tank exceeds this design service life, its safety margin decreases, as does its safety rating. At this point, necessary guardianship measures should be put in place and the inspection cycle shortened.
To run into them here by the sea is amazing. . .
Let’s discuss some viewpoints: 1. First, it is necessary to understand the selection of time-related parameters within the design lifespan – parameters such as corrosion allowance, number of fatigue cycles, and those defined by the LARSON-MILLER curve for high-temperature materials. These are parameters that are closely related to the lifespan of a device. If the operating conditions are very similar to those designed for, then the actual service life will be close to the design lifespan. Operating beyond the design lifespan means making use of a safety margin, which in turn implies sacrificing safety in order to extend the lifespan. 2. For devices that operate in less demanding environmental conditions, if time-related parameters are not taken into account during the design process, there can be a significant difference between the actual service life and the design lifespan. As an extreme example, containers used for storing lubricants at room temperature experience little corrosion from the medium, and this results in a long service life. We have even seen some equipment from World War II still in use at an established European oil refinery. 3. When the environmental conditions are very harsh, especially in cases of stress corrosion, the device may fail after a short period of time. 4. Therefore, conducting regular tests based on specific circumstances is an effective measure
Thank you for sharing; it’s really comprehensive. Have you learned it? . .
1. Once the equipment has exceeded its service life, the design and manufacturing units assume no responsibility for its quality； 2. If the inspection agency gives its approval for use, then in case of any problems, the inspection agency is responsible. As a result, all inspection agencies are quite cautious and apply strict inspection standards. 3. The operating environment and the medium in which the equipment is used have a significant impact on its durability. Take liquefied petroleum gas cylinders as an example: the level of H2S in the medium has a considerable effect on the operating conditions of such equipment; therefore, inspection agencies generally shorten the inspection intervals when dealing with equipment that has exceeded its designed service life.
Most design agencies do not specify a design service life; in the absence of such a specification, the code assumes a default value of 20 years. After the issuance of TSG21, most agencies began to include this parameter, as otherwise the inspection and drawing review would not be approved. Of course, there are also very rare cases where it isn’t added, and even if it leaves the factory, it will be sent back. As for lifespan, it is usually set to be relatively short; 8 or 10 years is common, while cases of a lifespan of 15 years or more are very rare. As for critical equipment, the lifespan is generally 15 years or more. Equipment that has exceeded its designed service life is generally required to be scrapped. Of course, some companies consider factors such as cost and time before applying for inspections or conducting RBIs, but these services are quite expensive. The main reason is that the design and manufacturing parties are no longer liable for such equipment; since those two parties refuse to take responsibility, the regulatory and inspection agencies are also unwilling to assume that responsibility.
Users generally request a relatively long design life, 15 years or more; for critical equipment, it is usually over 30 years.
Most small projects in the domestic market pursue short-term profits; it’s already good if they can operate for 10 years； There are probably few devices that have been in service for over 30 years
Expert, which source does the first photo come from?
I would like to discuss whether there is any legal basis for shortening the inspection interval, in the case where a testing agency conducts a comprehensive inspection near the end of the device’s design lifespan, and if the inspection results indicate a safety rating of level 1