Installation and replacement cycle of blast discs

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This post was last edited by huanghong on 2023-7-26 at 16:18. 4.3.1 Combination forms of blast disc safety devices and safety valves Depending on the way in which the blast disc safety device is connected to the safety valve and their relative positions, three combination forms can be identified: a) The blast disc safety device is connected in series on the inlet side of the safety valve, as shown in Figure 1a)； b) The rupture disc safety device is connected in series on the outlet side of the safety valve, see Figure 1b) ； c) The burst disc safety device is used in parallel with a safety valve, as shown in Figure 1c). 4.3.2 The rupture disc safety device is connected in series on the inlet side of the safety valve. 4.3.2.1 For protected pressure vessels that fall under one of the following conditions, the rupture disc safety device should be connected in series on the inlet side of the safety valve: a) To prevent significant loss of process material or the medium contained within due to the rupture of the rupture disc ； b) Applications where safety valves cannot be used directly (such as when the medium is corrosive or leakage is not permitted, etc.) ； c) Mobile pressure vessels used for transporting media with an extremely high level of toxicity, high hazard, or strong corrosivity. 4.3.2.2 When the burst disc safety device is installed on the inlet side of the safety valve, the following requirements shall be met: a) The discharge capacity of the combination of the burst disc safety device and the safety valve shall be not less than the safe discharge capacity of the pressure-containing equipment being protected ； b) The nominal diameter of the burst disc safety device shall be no smaller than the pipe diameter on the inlet side of the safety valve, and it shall be installed within 5 times the pipe diameter from the inlet side of the safety valve. Additionally, the pressure loss in the pipeline at the inlet of the safety valve (including that caused by the burst disc safety device) shall not exceed 3% of its set pressure ； c) The discharge area after the rupture disc ruptures should be larger than the inlet cross-sectional area of the safety valve ； d) The rupture disc should not produce fragments, detachment, or sparks upon bursting, so as not to interfere with the normal discharge function of the safety valve ； e) The chamber between the burst disc safety device and the safety valve shall be equipped with a pressure indicator, an exhaust port, and appropriate alarm indicators. 4.3.2.3 For the safety valve of the series-connected burst disc safety device on the inlet side, its rated discharge capacity shall be the rated discharge capacity of a single safety valve multiplied by a coefficient of 0.9 to determine the discharge capacity of the combined device. 4.3.3 The rupture disc safety device is connected in series on the outlet side of the safety valve. 4.3.3.1 If the outlet side of the safety valve may be subject to corrosion or affected by external pressure sources, a rupture disc safety device should be installed there to ensure the proper functioning of the safety valve. 4.3.3.2 The rupture disc safety device installed on mobile pressure vessels shall not be located on the outlet side of the safety valve. 4.3.3.3 When the burst disc safety device is installed on the outlet side of the safety valve, the following requirements shall be met: a) The discharge capacity of the combination of the burst disc safety device and the safety valve shall be not less than the safe discharge capacity of the pressure-containing equipment being protected ； b) The chamber between the rupture disc safety device and the safety valve shall be equipped with a pressure indicating device, an exhaust port, and appropriate alarm indicators ； c) At the burst temperature, the sum of the designed burst pressure of the rupture disc and the pressure present in the relief pipe shall not exceed either of the following conditions: —— the set pressure of the safety valve ； ——The design pressure of any piping or fittings between the rupture disc safety device and the safety valve ； ——The design pressure of the protected pressure-bearing equipment. d) The discharge area after the rupture disc bursts should be large enough so that the flow rate is equal to the rated discharge capacity of the safety valve ； e) No pipeline other than the rupture disc should become blocked as a result of the rupture disc bursting. 4.3.4 Use of burst disc safety devices in parallel with safety valves 4.3.4.1 Protected pressure-bearing equipment falling under one of the following conditions may be equipped with one or more burst disc safety devices used in parallel with safety valves: a) To prevent a rapid increase in pressure under abnormal operating conditions ； b) As an auxiliary safety relief device, it is considered appropriate to use it in situations where a fire might occur or where there is a need to increase the relief area due to the presence of unexpected external heat sources. 4.3.4.2 The discharge capacity of each safety valve and burst disc safety device shall be no less than the safe discharge capacity of the pressure-bearing equipment it is designed to protect. 4.3.4.3 The design burst pressure of the rupture disc shall be greater than the set pressure of the safety valve. 5.6 Determination of the replacement cycle for rupture discs 5.6.1 When selecting a rupture disc safety device, the replacement cycle of the rupture disc must be taken into consideration. This cycle depends on factors such as the category, model, and material used, as well as the operating conditions. The determination of the rupture disc replacement cycle can be referred to the provisions in Appendix D. 5.6.2 The burst disc shall be replaced in any of the following situations: a) A burst disc that has not ruptured despite exceeding the minimum burst pressure shall be replaced immediately ； b) The blast discs that have been removed for equipment maintenance should be replaced ； c) Blown films used under harsh conditions or in critical applications should be replaced regularly on an annual basis. Appendix D D.1 Purpose of determining the replacement cycle for pressure relief valves D.1.1 To ensure the safety of pressure-bearing equipment, pressure relief devices that can prevent overpressure conditions should be installed. Common pressure relief devices include safety valves, rupture disks, and fusible plugs. Due to its advantages such as rapid response, good sealing performance, high precision, and large discharge area, the rupture disc safety device is widely used for safe pressure relief. D.1.2 Under operational conditions, pressure relief devices can be affected by various factors such as corrosion, dirt, and significant fluctuations in temperature or pressure. This can cause them to lose their original performance, and in some cases it may even lead to premature release of pressure under normal operating conditions, thereby compromising the safety of the equipment and disrupting normal production processes. Therefore, it is very important to determine the interval between two consecutive inspections or the replacement cycle for the pressure relief device. D.1.3 After manufacturing a batch of rupture discs, the manufacturer shall randomly select a specified number of them for sampling burst tests in order to verify that the burst pressure meets the requirements of standards or safety technical specifications; however, this can only ensure the burst performance of the rupture discs at the time of shipment. D.1.4 After being used in practice and subjected to certain operating pressures, the bursting performance of a rupture disc may change due to factors such as temperature and pressure. After a certain period of time, its performance will no longer meet the requirements specified at the time of manufacture, and it may burst even under normal operating pressures. To avoid such a situation, it is necessary to identify the possible time periods when it may occur and determine the replacement cycle to ensure the normal and safe operation of pressure-bearing equipment. D.2 Factors affecting the replacement cycle of blast discs D.2.1 The replacement cycle of blast discs should not exceed a certain predetermined period; after that period, the performance of the blast discs will no longer meet the specified requirements. Once the replacement cycle has been determined, the bursting disc should not be replaced before the end of that cycle, unless further research and analysis of past experience and all operating conditions are conducted. D.2.2 The appropriate replacement cycle for the shrapnel should be determined before it is put into use. This period can be extended based on reliable work experience or shortened in cases where reliability has been proven lacking. D.2.3 When determining the replacement cycle for rupture discs, the influence of the following factors must be taken into account: a) the fatigue resistance of the rupture disc (related to its structural design) ； b) The corrosion resistance of the disc material to the corresponding medium and environmental conditions, the creep properties of the disc material under high-temperature conditions, as well as changes in the density and corrosion resistance of the sealing and protective film materials, along with any aging that may occur ； c) Actual operating pressure ratio ； d) Actual operating temperature of the rupture disc, temperature fluctuations, etc ； e) The actual pressure exerted on the rupture disc, pressure fluctuations, etc. D.2.4 The user shall determine the operating temperature, operating pressure, working medium, and other foreseeable operating conditions (including pressure and temperature cycles) under which the burst disc will be used, and provide them to the manufacturer so that the manufacturer can determine the replacement cycle for the selected type of burst disc. D.2.5 Incorrect installation, wrong torque (where applicable), and mechanical damage can have a direct impact on the burst pressure of the rupture disc, thereby shortening its replacement cycle. D.3 Methods for determining the replacement cycle of rupture discs D.3.1 The replacement cycle is determined by the manufacturer a) Since the manufacturer is familiar with the most appropriate mechanical loading methods, stress levels, and operating pressure ratios for rupture discs of each design type under different working conditions, and may possess analytical test (fatigue, corrosion) data, historical records, and results from similar engineering tests on various types of rupture discs for reference. Therefore, for rupture disks under normal operating conditions, the replacement cycle can be determined by the manufacturer. b) To verify whether the determined replacement cycle for the rupture disc is appropriate, the rupture disc can be carefully removed after one working period, packaged as required, and returned to the manufacturer for inspection and testing. The manufacturing unit shall record the dimensional changes, signs of corrosion, sealing performance (where appropriate), burst pressure, and any other relevant details of the returned disc valves. By comparing these with the original records from the time of manufacture, the replacement cycle can be adjusted. c) On some particularly important occasions, blast discs that are identical in terms of the type, model, specifications, material, and required blasting parameters to those actually used can be tested under conditions simulating the expected operating conditions. Blast discs that have been in use for a certain period of time are then blown up by the manufacturer, and the replacement cycle is determined based on the blasting data. D.3.2 The replacement cycle is determined by the user unit. Under certain special working conditions, since the user unit is familiar with the effects on the material of the blast disc or its blasting performance under similar working conditions, it may have records available for reference (operation, inspection, monitoring, and historical records). Therefore, the replacement cycle for the blast disc can be determined by the user based on experience.