Regarding the safety accessories of gas cylinders

I know that liquid chlorine cylinders are equipped with changeable plugs

This post was last edited by Yang Jiulang on 2010-12-13 at 10:55. This is the information I found regarding fusible plugs; please take a look and see if it’s useful to you :) http://wenku.baidu.com/view/8c4c06d376a20029bd642dcb.html GB 8337-87: Fusible Plug for Gas Cylinders 1. Terms and Definitions 1.1 Fusible plug (hereinafter referred to as fusible plug): A safety pressure-relief device in which a fusible alloy is filled inside the plug hole; it is a removable component. Under normal conditions, the plug hole is closed ； Under the action of the predetermined temperature, the fusible alloy melts, releasing gas to relieve pressure in the gas cylinder. 1.2 Plug hole: The central channel in the body of a fusible plug. 1.3 The flow temperature of the fusible alloy refers to the temperature of the glycerin bath at the time when the fusible alloy sample melts during the test specified in clause 3.1. 1.4 The operating temperature of the fusible plug refers to the temperature of the glycerin bath at which the fusible alloy melts and gas is released, when testing in accordance with the provisions of 3.2.4. 1.5 Flow rate: The volume of free air discharged at the required rated pressure, as measured at a pressure of 0.1013 MPa (1.033 kgf/cm2) and a temperature of 15°C. 1.6 Batch: The number of fusible plugs that can be continuously poured from the same furnace of fusible alloy, as determined by the fusible plug itself. 1.7 Compressed gases: Various gases with a critical temperature below -10°C. 1.8 Liquefied gases: Various gases with a critical temperature of -10°C or higher. 2 Technical Requirements 2.1 Basic Structure of the Fuse Link The basic structure of the fuse link is shown in Figure 1. 2.2 Operating temperature of the fusible plug: The operating temperatures for the fusible plug are 100+5°C and 70°C; the former is used for acetylene gas cylinders, while the latter is used for other types of gas cylinders. 2.3 Fusible Alloys 2.3.1 Fusible alloys are composed of bismuth (Bi), lead (Pb), tin (Sn), and cadmium (Cd) in various weight ratios; eutectic alloys should be used, with a bismuth content of not less than 48%. The formulation details can be found in Appendix A (reference). 2.3.2 Purity of alloy raw materials: Bismuth: It should be not lower than the specification for Bi-2 in GB915 (Bismuth Ingots) ； Lead: It should be not lower than the specified value of Pb-2 in GB469 (Lead Ingots) ； Tin: Should not be lower than the specified value for Sn-2 in GB728 (Tin Ingots) ； Cadmium: It shall be not lower than the specified value of Cd-3 in GB914 (Cadmium Ingots). 2.3.3 After the formula is determined, weigh the components according to the formula, and melt them in the order specified in 2.3.1. 2.3.4 During the mixing process of bismuth and lead, the temperature should not exceed 371°C. When adding tin and cadmium, the temperature should not exceed 260°C. 2.3.5 After the raw materials are melted, they should be continuously stirred before and during casting. 2.3.6 For the melted raw material, the casting temperature should be slightly higher than the flow temperature of the fusible alloy. Each time casting, the slag, dirt, and metal oxides must be removed first. 2.3.7 The casting of fusible alloy per furnace should be carried out continuously within the same shift, and it can be cast into rods or other shapes. 2.3.8 Each cast rod or other shaped fusible alloy shall have a distinct furnace number mark. 2.4 Plug body 2.4.1 The material of the plug body shall have sufficient whiteness, corrosion resistance, and mechanical properties, and shall not react in any way with the gas contained within the cylinder. Brass (when used for acetylene cylinders, the copper content should not exceed 70%), steel, or other suitable metals should be selected; their chemical composition and mechanical properties must meet the relevant technical requirements as well as the demands of manufacturing. 2.4.2 The basic forms of the plug are recommended as follows (see Figure 2). Its structure must ensure sufficient strength so that it does not deform during use. 2.4.3 The external thread of the plug must be a tapered thread. The profile, dimensions, and tolerances of its threads shall comply with the provisions of GB8335 \"Threads for Gas Cylinders\". 2.5 Fusible plugs for dissolved acetylene cylinders: The plug hole area and installation requirements for the fusible plugs used in dissolved acetylene cylinders shall be determined based on the surrounding heating tests specified in relevant standards. 2.6 Pouring of fusible alloys 2.6.1 The plug should be thoroughly cleaned with an appropriate solution before coating and pouring, in order to remove oil and rust from within the plug holes. 2.6.2 After cleaning the plug holes, it is advisable to apply a coating layer first; tin or a tin-lead alloy is recommended as the material for this coating. 2.6.3 Place the plug body on a clean flat surface, coat the plug hole with an appropriate solvent, and then pour the fusible alloy using one of the following methods. 2.6.3.1 Heat the plug to a certain temperature, which is slightly higher than the flow temperature of the fusible alloy, and then pour the melted fusible alloy into the plug. 2.6.3.2 Place the fusible alloy strip in the plug hole heated to a certain temperature, so that the fusible alloy strip melts inside the plug hole. 2.6.3.3 Insert fusing alloys of predetermined length or size into the plug holes, and then place them in an induction furnace to be heated, causing the fusing alloys to melt. However, this method requires careful control of temperature to avoid overheating. 2.6.4 The heating amount during casting should be uniform, and overheating should be avoided. 2.6.5 The poured fusible alloy should fill the entire plug hole, and any excess material should be removed after the pouring is complete. 3 Test Methods and Acceptance Criteria 3.1 Melting Alloy Flow Temperature Test 3.1.1 Two specimens are selected at random from each batch of melting alloy for testing; the diameter of the specimens is 6 mm and their length is 50 mm. 3.1.2 The specimen is horizontally supported on cutting edges spaced 25 mm apart, with its ends extending 12.5 mm outside the cutting edges, and then immersed in an inner glycerin tank whose temperature is controlled by an outer glycerin tank; the test setup is shown in Figure 3. 3.1.3 The two specimens shall be tested simultaneously. A thermometer for temperature measurement shall be inserted into the glycerin and placed between the two specimens, ensuring that the bulb of the thermometer is at the same level as the specimens. The temperature rise in the glycerin bath shall not exceed 2°C per minute; the glycerin shall be stirred during the test to maintain uniform temperature. 3.1.4 The temperature at which the second fused end among the four ends of the two specimens fuses is the flow temperature of the fusible alloy. 3.1.5 The acceptance rules shall comply with the provisions of relevant technical requirements. 3.2 Fuse Plug Test 3.2.1 A batch of cast fuse plugs shall consist of no more than 300 pieces. 3.2.2 Select two specimens at random from each batch of fusible plugs, and conduct the tests in sequence in accordance with the provisions of 3.2.3 and 3.2.4. 3.2.3 Fusible plug extrusion resistance test: A compressive air pressure of 3.4 MPa (35 kgf/cm2) is applied to the end of the sample that comes into contact with the medium inside the gas cylinder, and this condition is maintained at temperatures above 55°C for 24 hours. Subsequently, an inspection is carried out on the other end; no leakage and no visible extrusion of the fusible alloy indicate successful compliance. 3.2.4 Test for determining the operating temperature of the fuse link; the test setup is shown in Figure 4. Two specimens that have passed the tests in accordance with 3.2.3 shall be tightened to the support, with the end in contact with the medium inside the gas cylinder facing downward; compressed air shall be supplied to this end at a pressure of not less than 0.02 MPa (0.2 kgf/cm2). At the same time, the sample should be immersed in a glycerin bath, the thermometer should be as close as possible to the fusible plug, and the temperature of the glycerin bath should be within 3°C below the specified minimum temperature. Maintained at this pressure and temperature for 10 minutes, no air should seep out or burst out. Then, increase the temperature of the glycerin at a rate of no more than 2°C per minute, while simultaneously raising the pressure, although this pressure should not exceed 0.4 MPa (4 kgf/cm2). When the easy-to-melt alloy in the sample is extruded, causing gas leakage, the temperature of the glycerin bath at that moment is recorded as the operating temperature of the easy-to-melt plug; this temperature must comply with the requirements of clause 2.2. When conducting the above tests, it is allowed to stir the glycerol to ensure uniform temperature. 3.2.5 Acceptance criteria: Both specimens must meet the requirements specified in sections 3.2.3 and 3.2.4; in such case, the batch is considered acceptable ； Otherwise, four additional samples should be selected from the same batch for testing; if even one of these four samples fails to meet the requirements, the entire batch is deemed defective. 3.3 Fusible plug flow test 3.3.1 Fusible plugs that are newly designed or have had their design modified shall undergo a flow test. 3.3.2 For the fusible plugs manufactured according to the same design, three additional samples shall be taken for testing, so that the fusible plugs operate at their respective temperatures; the testing methods and operating temperatures shall comply with the provisions of 3.2.3 and 3.2.4. 3.3.3 Then, without any cleaning, actual flow tests are conducted on them one by one. Air was used in the experiment; air was supplied to the fusible plug through a tube equipped with a pressure gauge and a thermometer. Once stable conditions were established, observations and recordings were made to determine the amount of air released. Record the flow rates of the three samples as the measured flow rates. The test conditions need not be exactly the same as the operating conditions, but the air inlet pressure should not be less than 0.7 MPa (7 kgf/cm2). 3.3.4 Acceptance criteria: For the flow rate values of the three samples, the difference between the highest value and the lowest value shall not exceed 10% of the highest value to be considered acceptable. 3.4 Gas-tightness test of fusible plugs: The already cast fusible plugs shall be subjected to a gas-tightness test one by one. The test pressure should be one-third of the hydrostatic test pressure (for acetylene cylinders, the test pressure is one-half of the hydrostatic test pressure). The holding time should be no less than that required for the gas-tightness test of cylinders; no leakage indicates success. 4 Marking 4.1 Each fusible plug shall be marked on the outside; the marking shall be clear and durable. 4.2 Marking content: a. Fuse plug temperature: 70°C or 100℃ ； b. Manufacturing date ； c. Manufacturer code. 5 Other 5.1 Ventilation measures should be taken during the preparation and pouring of fusible alloys. 5.2 Safety protection measures should be employed during the fuse plug test.