How is the service life of pressure vessels specified, and how often do they need to be inspected?

During use, qualified professionals conduct non-destructive testing (per standards) to determine the service life of pressure vessels. For boilers, external inspections are generally carried out once a year. Internal inspections every two years, and hydrostatic tests every six years. Other pressure vessels also have relatively detailed regulations based on the medium, operating conditions, etc.

For implementation, refer to the pressure vessel regulations and the rules for periodic inspection of pressure vessels

The regular inspections of pressure vessels are divided into: 1. External inspection: This refers to the regular on-line inspections carried out while the pressure vessel is in use, at least once a year. External inspections can be carried out by qualified pressure vessel inspectors from inspection agencies, or by specialized pressure vessel personnel from the using units who have been approved by safety supervision authorities. 2. Internal and external inspections: refer to the inspections carried out when a pressure vessel in use is shut down. Internal and external inspections shall be carried out by qualified pressure vessel inspectors from the inspection agency. Its inspection cycle is as follows: (1) For those with a safety status rating of 1 or 2, inspections must be carried out at least once every 6 years ； (2) For those with a safety status level of 3, it shall be conducted at least once every 3 years. The first internal and external inspection cycle after commissioning is generally 3 years. The subsequent internal and external inspection schedules shall be determined by the inspection agency in consultation with the user unit, based on the results of previous internal and external inspections, and then submitted to the local safety supervision authority for record-keeping. For pressure vessels in any of the following situations, the internal and external inspection intervals should be shortened appropriately: 1. When the degree of corrosion of the pressure vessel material by the medium is unknown, or when the corrosion rate of the material caused by the medium is greater than 0.25 mm/year, or when the corrosion data determined by the designer do not match the actual conditions. 2. Poor surface quality of the material or internal defects, poor weldability of the material, or multiple revisions during manufacturing. 3. In conditions of harsh operation or when the hydrogen sulfide and sulfur content in the medium is high (generally referring to levels above 100 mg/L). 4. Those that have been in use for over 20 years, and which, after technical assessment, or as confirmed by inspectors, cannot be used safely within a normal inspection cycle. 5. Those that have been out of use for more than two years. 6. Continue to be used after passing the defect safety assessment. 7. Those that frequently change the medium used (such as printing and dyeing machines). 8. Linered glass equipment. 9. Spherical storage tanks (manufactured from material with 6b ≥ 540 MPa; inspection inside the tank should be carried out one year after commissioning). 10. When the medium is liquefied petroleum gas and there is a tendency for stress corrosion such as hydrogen blistering, internal and external inspections shall be carried out annually or as needed. 11. When using the “immonium process” for paper production, and in the absence of anti-corrosion measures, internal and external inspections should be carried out at least once a year, or more frequently as required by actual conditions.

The following is the original text of the regulations: Chapter 7 Regular Inspections, Article 114: The entities that use pressure vessels must arrange for their regular inspections in a proper manner, and shall submit the annual inspection plan for those vessels to the competent authorities as well as to the local labor department’s boiler and pressure vessel safety supervision agency. The competent authorities are responsible for ensuring implementation, while the safety inspection agencies for boilers and pressure vessels under the labor department are in charge of supervision and inspection. Article 115: The regular inspections of pressure vessels are divided into: 1. External inspection: This refers to the regular on-site inspections carried out by professionals while the pressure vessel is in operation, at least once a year. 2. Internal and external inspections: These refer to inspections carried out by qualified inspectors when the pressure vessel is shut down. The frequency of such inspections is as follows: for vessels with a safety rating of 1 to 3, inspections must be conducted at least once every 6 years ； For those with a safety status level of 3–4, it should be conducted at least once every 3 years. 3. Pressure test: This refers to the hydraulic or pneumatic test carried out during the shutdown inspection of pressure vessels, at a pressure higher than the maximum operating pressure, and it must be conducted at least once every 10 years. The provisions regarding external inspections, internal and external testing contents, and safety condition grades are outlined in the \"Inspection Regulations for In-service Pressure Vessels\". Article 116: For pressure vessels under any of the following circumstances, the internal and external inspection intervals shall be appropriately shortened: 1. When the degree of corrosion of the pressure vessel material by the medium is unknown, when the corrosion rate of the medium on the material is greater than 0.25 millimeters per year, or when the corrosion data determined by the designer are significantly inaccurate ； 2. The material has poor weldability and required multiple revisions during manufacturing ； 3. First inspection ； 4. Poor operating conditions and low management level ； 5. Those with a service life of over 15 years, which have been assessed by technical experts as unable to be used according to the regular inspection schedule ； 6. What the inspector believes should be shortened. Article 117: For pressure vessels under any of the following circumstances, the internal and external inspection intervals may be appropriately extended: 1. Where the non-metallic lining is in good condition, its inspection cycle shall not exceed 9 years. 2. For pressure vessels in which the corrosion rate of the medium on the material is below 0.1 millimeters per year, or those equipped with a reliable corrosion-resistant metal lining, if they pass one or two internal and external inspections and it is confirmed that they still meet the original requirements, the service life shall not exceed 10 years. 3. The periodic inspection intervals for reaction vessels equipped with catalysts, as well as large pressure vessels containing fillers, are determined by the user based on the design drawings and actual usage conditions. Article 118 Pressure vessels under any of the following circumstances must undergo a pressure test after passing internal and external inspections: 1. Those in which the main pressure-bearing components have been repaired or replaced by welding ； 2. Changing the operating conditions beyond the original design parameters ； 3. Replacing the lining Before re-lining ； 4. Restarted after being out of use for two years ； 5. Newly installed or relocated ； 6. Unable to conduct internal inspection ； 7. The user entity has doubts regarding the safety performance of the pressure vessel. Article 119: In cases where it is not possible to carry out internal, external inspections or pressure tests on schedule due to special circumstances, the user entity must provide a justification, submit an application three months in advance. After approval by the technical supervisor of the entity, the original inspection agency shall submit its recommendations; upon approval by the provincial competent authority and registration with the boiler and pressure vessel safety supervision agency of the labor department that issues the ‘Pressure Vessel Use Certificate’, the deadline can be extended, but generally it should not exceed 12 months. Articles 12 and 13: For large, critical pressure vessels that are in use and for which it is necessary to conduct defect assessments, the following procedures shall be followed: 1. The entity using the pressure vessel shall submit a written request explaining the reasons; only after obtaining approval from the competent authority in charge of that entity as well as from the boiler and pressure vessel safety supervision agency of the provincial labor department can it entrust a qualified unit specialized in pressure vessel defect assessment to carry out such assessments. The qualification accreditation for defect assessment units of pressure vessels shall be handled in accordance with the relevant regulations of the Ministry of Labor. 2. The unit responsible for defect assessment must be accountable for the inspection results of the defects, the conclusions drawn regarding those defects, and the safety performance of the pressure vessel. The final evaluation report and conclusions must be reviewed and approved by the technical supervisor of the unit responsible for the evaluation. After being sent to the client organization, they shall also be submitted to the enterprise’s competent authorities, as well as to the boiler and pressure vessel safety supervision agencies at the provincial, municipal, and district levels where the client organization is located, for record-keeping.

The service life of pressure vessels is generally 10 years; this period can be extended appropriately depending on the safety condition of the equipment

The design life of pressure vessels is generally 15 years, with some equipment having a lifespan of around 10 years. However, the design life is not the same as the actual service life of the vessel. The former Ministry of Chemical Industry stipulated that vessels whose service life exceeded their design life should undergo safety assessments; but now, the **Quality and Technical Supervision Bureau adopts a system of submitting applications for such assessments on a case-by-case basis, which incurs costs for enterprises and results in limited practicality. Pressure vessels that have been in use for more than 20 years should undergo more frequent regular inspections. The normal service life should be indicated on the drawings, but many drawings do not include this information. New regulations have been introduced in this regard; since the replacement of currently in-use pressure vessels relies mainly on regular inspections, they are replaced only when serious defects are detected. These new regulations aim to increase the frequency of inspections for pressure vessels that have exceeded their designated service life. In China, the service life of containers is determined based on the corrosion allowance. Due to specific conditions in the country, many containers continue to be in use beyond their designed service life. Containers abroad must be phased out once their useful life is reached! Because it’s no longer safe. As a result, many containers that have reached the end of their useful life abroad are purchased in China and continue to be used there. Of course, inspection and evaluation are required before use! There are also many discarded containers that continue to be used in China for decades! ! ! ! ! ! ! The most crucial factor in a container’s lifespan is whether the costs of repair, inspection, and maintenance exceed what is economically viable; otherwise, it can continue to be used!

A test report is provided after each test, and the appropriate date for the next inspection is indicated based on the assessed safety level. Although I haven’t checked the relevant standards, I think pressure vessels and similar devices don’t have a limited service life; what’s important is the level of maintenance of such equipment. Of course, companies will assign an asset value to these devices, specifying a service life of 10 years or 20 years, for example

Passing by, just asking – I’ve learned *!

A lot has already been mentioned above; in our factory, whenever maintenance work is carried out, non-destructive testing of the containers is performed, and based on the results of those tests, appropriate actions are taken on the relevant parts of the containers!

Additional note: Pressure vessels with a service life exceeding their designed lifespan must be inspected annually.