Specification requirements for regular inspection of permanent storage tanks and vent valves

Thread Content

I. Definition of regular inspections: The \"Guidelines for Identifying and Addressing Safety Risks and Hazards in Hazardous Chemical Enterprises\" (Emergency [2019] No. 78) require that \"enterprises should conduct comprehensive inspections of storage tanks on a regular basis.\" Some enterprises fail to fully understand the meaning and significance of such comprehensive inspections. Article 4 of the \"Notice from the State Administration of Work Safety on Further Strengthening the Safety Management of Chemical Storage Areas\" (Work Safety Admin. General Manage. III [2014] No. 68) stipulates that \"it is necessary to strengthen monitoring of corrosion in chemical storage tanks, carry out regular inspections of these tanks, and take timely action whenever signs of corrosion and thinning are detected.\" Routine inspections and annual inspections are typically regular external checks carried out while the tank is in operation; they cannot detect conditions inside the tank, such as corrosion of the bottom plate. Therefore, it is necessary to conduct \"regular tank cleaning inspections\" in order to achieve a \"comprehensive inspection\". Of course, acoustic emission testing can also be used to inspect the bottom plates at present, but overall, tank cleaning inspections remain more comprehensive and effective. AQ3053 provides a comprehensive and clear description of the daily inspections and periodic inspections for storage tanks at atmospheric pressure: The inspections carried out on such tanks include routine inspections, annual inspections, and periodic inspections. 11.1 Inspection methods for storage tanks a) Routine inspections are a method that relies on visual inspection to examine the external condition of the tank up close ； b) The annual inspection is an online inspection carried out to ensure the safety of the storage tank during the regular inspection period ； c) Periodic inspection refers to a more comprehensive examination of storage tanks at regular intervals; depending on the actual circumstances, it can be carried out using online inspection or tank-opening inspection methods ； 11.2.1 Routine inspections: The items checked during routine inspections include the presence of leaks, deformation of the tank walls, signs of settlement, as well as the operational condition of the tank’s insulation system, safety accessories, and related components. 11.2.2 Annual inspections a) Annual inspections mainly involve external visual inspections; in addition to the routine checks, they should also include assessments of the safety management of the storage tank, as well as measurements of the thickness of the wall panels and roof. 11.2.3 Periodic inspections b) The contents of periodic inspections generally include visual inspections, detection of corrosion on the tank body, thickness measurements, non-destructive testing of welds, inspection of safety accessories, and assessments of the safety management of the storage tank ； c) The methods for regular inspection mainly include visual inspection, magnetic flux leakage testing, acoustic emission testing, ultrasonic thickness measurement, and surface non-destructive testing; when necessary, ultrasonic testing, radiographic testing, guided wave testing, ultrasonic C-scan, metallographic examination, material analysis, stability or strength verification, stress measurement, vacuum leak testing, foundation settlement assessment, material brittle fracture assessment, water filling tests, and other methods can be employed ； II. Requirements of relevant specifications regarding regular inspection of atmospheric pressure storage tanks: (I) Requirements for inspection cycles: 1. \"Integrity Management of Atmospheric Pressure Storage Tanks\" (GB/T 37327-2019) (This standard applies to vertical, cylindrical, welded steel atmospheric pressure storage tanks; the integrity management of other atmospheric or low-pressure (operating pressure less than 0.1 MPa) storage tanks can be carried out with reference to this standard.) 8.1.1 Atmospheric pressure storage tanks are generally subjected to their first integrity assessment 3 to 6 years after being put into use, with subsequent assessment times determined by the inspection agency based on the results of those assessments. 2. \"Safety Technical Code for Vertical Cylindrical Welded Steel Storage Tanks\" (AQ3053-2015) (This standard applies to vertically cylindrical welded steel storage tanks that are designed for a pressure of less than 0.1 MPa(G), have a nominal volume of 1000 m3 or more, are installed on the ground, store petroleum, petroleum products, or chemical liquids that are not extremely or highly hazardous in terms of toxicity (see Note 1), and are assembled on-site). For storage tanks with a nominal volume of less than 1000 m3 that store other similar liquid media, this standard may be applied.) 11.3 d) The interval for regular inspections should be determined based on the measured corrosion rate and the minimum allowable thickness of the tank body. The actual inspection interval shall be set such that the thickness of the tank body at the time of the next inspection is not less than the minimum thickness required by the standards. When the corrosion rate is unknown, it can be estimated based on experience with tanks operating under similar conditions. If there is no such experience or data available for similar tanks, the interval between regular inspections shall not exceed 6 years; for large atmospheric-pressure tanks, it shall not exceed 4 years. 3. \"Specifications for Operation, Maintenance, and Repair of Vertical Cylindrical Welded Steel Oil Tanks\" SY/T 5921-2017 (This standard applies to vertical cylindrical welded steel oil tanks with a capacity of 15×10^4 m³ or less.) Other storage media and tanks of different capacities may follow similar guidelines.) 5.1.1 The general repair cycle for tanks is 5 to 7 years; for newly built oil tanks, the first repair cycle should not exceed 10 years. 5.1.2 The inspection and evaluation of oil tanks are generally carried out within one year before the end of their repair cycle; for oil tanks whose repair cycle is to be extended, such inspections and evaluations should be conducted annually. 4. \"Inspection, Repair, Modification, and Reconstruction of Oil Tanks\" SY/T 6620-2014: This standard applies to steel storage tanks constructed in accordance with API Std 650 and its predecessor API Std 12C; it specifies the minimum requirements for maintaining their integrity after installation and use, and addresses their inspection, repair, modification, relocation, and reconstruction. 6.4.2.1 The period between the start of operation of a storage tank and its first inspection shall not exceed 10 years. Personal suggestion: It can be seen that there is no unified standard for the periodic inspection intervals for atmospheric pressure storage tanks across various standards and regulations. The guideline provided in GB/T 37327, which states that \"atmospheric pressure storage tanks should generally undergo their first integrity assessment 3 to 6 years after being put into use, with subsequent assessment times determined by the inspection agency based on the results of those assessments,\" is relatively scientific and in line with the principles of pressure vessel management. Chemical companies can determine appropriate dates for the initial inspections by taking into account the type of material stored in the tanks and their volume. (II) Requirements for inspection qualifications 1. The standard \"Integrity Management of Atmospheric Storage Tanks\" (GB/T 37327-2019) does not specify the responsibilities of inspection agencies and personnel. 2. \"Safety Technical Code for Vertical Cylindrical Welded Steel Storage Tanks\" (AQ 3053-2015) 11.5 Inspectors. Inspectors should possess the relevant professional knowledge as well as experience in tank operation or maintenance, and where necessary, hold qualification certificates for the specific inspection and testing tasks. The inspectors are responsible for the accuracy of the periodic inspection conclusions regarding the storage tanks. Various inspections of storage tanks should be carried out by the following personnel: c) Depending on the specific requirements of the regular inspections for storage tanks, such inspections should be entrusted to qualified equipment inspection agencies. 3. \"Specifications for Operation, Maintenance, and Repair of Vertical Cylindrical Welded Steel Oil Tanks\" (SY/T 5921-2017) 5.4.3.1.1 The inspection of oil tanks shall be carried out by departments and technical personnel with the appropriate qualifications and experience in such inspections, and they shall be responsible for the accuracy and reliability of the results obtained from those inspections. 4. \"Inspection, Repair, Modification, and Reconstruction of Oil Tanks\" (SY/T 6620-2014) 6.4.1.2 All oil tanks shall undergo regular internal inspections at the intervals specified in 6.4.2. The authorized inspector responsible for the tank evaluation shall conduct visual inspections and ensure the quality and completeness of the non-destructive testing results. Personal suggestion: It can be seen that there are no clear specifications regarding the required qualifications and authorized inspection personnel. At present, **the relevant institutions have not explicitly authorized the issuance of such inspection qualification certificates; it can be understood that inspections can be carried out by the enterprises themselves or by third-party agencies. However, most enterprises lack the necessary professionals and equipment for regular inspections, so it is recommended to entrust third parties to ensure the accuracy of the test data, such as pressure vessel inspection agencies. II. Requirements regarding the regular inspection of breathing valves 1. In Table 5, the Equipment Management Inspection Form of the \"Detailed Rules for Special Safety Inspections of Enterprises with Major Hazardous Sources of Hazardous Chemicals\" (Letter No. 210 from the Emergency Management Department), item 3 states that \"breathing valves used in atmospheric pressure storage tanks must be inspected at least once a year.\" The reference here is to Clause 8.6.1 of \"Integrity Management of Atmospheric Storage Tanks\" (GB/T 37327-2019). Since the issuance of the detailed guidelines for this special inspection in 2021, various regions across the country have made it a mandatory requirement to regularly inspect the breather valves of atmospheric pressure storage tanks in enterprises that handle major hazards, which has prompted chemical companies in these areas to pay attention to the inspection of such breather valves. 2. \"Integrity Management of Atmospheric Storage Tanks\" (GB/T 37327-2019) 8.6.1 Breather valves used in atmospheric storage tanks shall be inspected at least once a year. 8.6.4 The inspection items for the breathing valve include visual inspection, opening pressure test, air flow rate test, and leakage test. This standard requires annual inspections of breathing valves, with inspection items including visual checks, opening pressure tests, ventilation volume tests, and leakage tests; it also does not specify the qualifications required of the inspection agencies. Looking at the implementation in various places, although tests were carried out, the test reports provided only examined the appearance and opening pressure; almost no testing facility checked the air volume and leakage rate. Furthermore, the testing standards cited by most testing institutions are \"Attachments for Oil Storage Tanks – Part 1: Breather Valves\" (SYT 0511.1-2010). 3. “Attachments for Oil Storage Tanks – Part 1: Breather Valves” (SYT 0511.1-2010) 8.1.2 Factory testing: Before leaving the factory, breather valves shall be inspected individually in accordance with the requirements of 6.4 and 8.5.2, and sampled for inspection in accordance with the requirements of 6.3 (excluding the test for opening pressure at low temperatures), 8.4, 8.5.3, and 8.6. Breather valves of the same specification are grouped into batches of 100 units each; no less than two units from each batch shall be inspected randomly. If one unit fails the inspection during the sampling process, the number of units to be inspected should be doubled. If there are still failures, individual inspection of all units is required. 6.4 The valve disc of the breathing valve should move smoothly when opening and closing; once the operation is complete and it is in the closed position, it should provide effective sealing. 8.4 Hydrostatic test of the valve body 8.5.2 Opening pressure test 8.5.3 Air leakage test 8.6 Leakage rate test It can be seen from this standard that requirements such as opening pressure, air leakage, and leakage rate tests are part of the \"factory inspection\" procedures; SYT 0511.1 also does not require annual inspections of breathing valves. Personal advice: Enterprises with major hazard sources should conduct annual inspections of the breathing valves on their atmospheric pressure storage tanks in accordance with the requirements of the Ministry of Emergency Management. Enterprises without such major hazard sources should follow these guidelines as well, carrying out at least one disassembly inspection of the breathing valves each year to check for rust or damage to the valve disc. Since the opening pressure of atmospheric pressure storage tank breathing valves is determined by the weight of the valve disc itself, any signs of rust or damage must be promptly investigated to determine whether the opening pressure has changed, and the breathing valves should be updated accordingly. III. Local standards issued by some provinces must be complied with by local enterprises. DB11/T 1400-2017 Safety Management Specifications for Atmospheric Pressure Storage Tanks of Hazardous Chemicals (Beijing); DB32/T 4484-2023 Rules for Periodic Inspection of Atmospheric Pressure Storage Tanks (Jiangsu); DB12/T 581-2015 Specifications for Periodic Inspection of Fixed Atmospheric Pressure Vessels for Hazardous Chemicals (Tianjin); DB61/T 526-2011 Rules for Periodic Inspection of Vertical Cylindrical Welded Steel Storage Tanks (Shaanxi); DB43/T 2513-2022 Inspection Specifications for Fixed Steel Atmospheric Pressure Storage Tanks of Hazardous Chemicals (Hunan); DB41/T 1460-2017 Inspection Specifications for Metal Atmospheric Pressure Storage Tanks (Henan). We hope that the release of the “Safety Management Specifications for Atmospheric Pressure Storage Tank Areas of Chemical Enterprises” (AQXXXX-202X) will bring us some solutions to the current challenges.