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Keywords:valve;endoleak;risk;control CLC number:TE973 Document code:A Article ID:1671-2064(2018)04-0168-01
1 Overview Hot work is a common operation in the company's production safety. It can be seen from the various types of hot work accidents that have occurred in the country recently that there are numerous cases of accidents caused by “insulated non-complianceâ€. However, with the development of the process, more and more town gas secondary high pressure pipeline valves are laid with fully-buried ball valves. All-welded ball valve has its own advantages, such as: can be directly buried in the ground without the construction of large valve wells can reduce the project cost, save a lot of material resources such as flanges, screws, gaskets, but also to the valve under the conditions of leakage Pipeline hot work brings the challenge that the system can't be isolated effectively by installing blanking boards or placing grease traps on the butter wall. Therefore, the risk control of pipeline hot work under the conditions of valve inner leakage is safe and smoothly completed. Necessary conditions for hot work.
2 Risk Analysis The entire hot work process involves approval of work permits, tool and equipment preparation, nitrogen injection replacement, gas detection, and pipeline welding. Any problems in any of these steps may lead to the failure of hot work under the conditions of leaks inside the pipeline. There are mainly the following risks in the operation process:
(1) The risk of internal leakage of the valve was not examined during the approval of the operation permit or the approval of the operation permit before the operation. (2) The pre-operational safety analysis did not identify the risk of insulative non-compliance of the system due to leaks in the pipeline. (3) If the nitrogen injection test is unqualified, the hot cut operation will be performed. (4) When the pipeline is cut at the first crossing, manual cold cutting is not used to prevent combustion and explosion caused by residual combustibles in the pipeline. (5) The continuous detection of combustible gas concentration was not performed during the welding operation, and the explosion caused by the leakage of combustible gas in the valve was caused.
3 Risk control By analyzing the risk of hot work under the condition of a valve inside a leak, it can be seen that the main risk control is the “system isolation†control of the hot work area, and the non-stop detection of the hot work part during the work process. The risk control is implemented through measures such as divergence and drainage at the end-leakage valve. The risk control includes the following three aspects:
3.1 Pre-control (1) Strictly implement the hazardous operation approval system. Carefully organize the business backbone to conduct pre-job safety analysis (JSA), identify various risk factors in the operation process, and formulate effective control measures. (2) The operating plan shall be revised in strict accordance with the approval opinions of the superior unit and the pre-operational safety analysis control measures. After the approval of the plan, the relevant operating personnel shall be organized to carry out learning and publicizing so as to be familiar with each operation. (3) According to the pre-operational safety analysis and operation plan, the safety technical disclosure and safety education before construction are carried out to clarify the risk of endoleak leakage and the control measures taken. (4) According to the plan's emergency plan, organize the preparation of emergency rescue materials to ensure timely and effective on-site rescue in the event of an emergency.
3.2 Process Control (1) The natural gas in pipelines is likely to cause fire and explosion. During the operation process, the residual combustible gas in the pipeline must be vented first and then replaced with nitrogen gas. (2) After replacement, in order to prevent helium in the pipeline from being blown into the cutting position, a method of releasing and diverting [1] may be adopted to open the relief valve of the inner leakage valve at the upper and lower parts of the cutting site, and the natural gas is lighter than nitrogen. Divert the natural gas into the air and monitor the combustible gas concentration in real time at the outlet. (3) Prevent burning and explosion caused by residual combustibles in the pipeline. Use manual cold cutting when cutting the first crossing. First cut a small incision and use a high-precision German vertical mini tester to test. Continuing the cutting, in order to prevent the production of sparks during the operation, spray water while cutting, and continuously monitor the combustible gas concentration in real time. (4) An anti-riot shaft fan is used in the pit to conduct uninterrupted forced ventilation to prevent the nozzles from suffocating by collecting nitrogen in the work pit after the nozzle is cut. (5) During the welding operation, due to the presence of an open flame, the concentration of combustible gas at the upstream and downstream discharge pipe should be determined to be within the qualified range, and then the combustible gas concentration at the weld joint should be within the qualified range, and then the welding operation must be performed and the welding process must be performed. Continuous gas detection.
3.3 When the earthwork is backfilled after the completion of later-stage hot work, a permanent buried gas leak detection pipe shall be buried above the pipe joint to effectively monitor the pipeline operation after the hot work. The following standards shall be followed for the setting of the test pipe:[2] ]
(1) The gas leak detection tube shall be installed above the side of the gas pipeline, and the horizontal distance from the outer wall of the gas pipeline shall be 300mm to 500mm. (2) The depth of the gas leak detection tube should be set to a vertical distance of 100mm to 200mm between the lower end of the test tube and the top of the gas pipeline. (3) When gas leak detection pipes are installed on the roadway, galvanized steel pipes should be used as materials, and PP-R pipes should be used for other parts. Galvanized steel pipe body diameter is DN20, wall thickness is 2.8mm; PP-R pipe body diameter is DN20, wall thickness is 2.0mm. A symmetrical air hole with a diameter of 5mm is drilled on the pipe body with an interval of 50mm in the axial direction, and the adjacent two sets of airholes form an included angle of 90° in the radial direction. (4) The gas leak detection tube cap should be painted with yellow identification paint. (5) The location, quantity, type, etc. of the gas leak detection pipe shall be accurately marked in the plan of the gas pipeline, and the coordinate points shall be indicated.
4 Conclusions The internal leakage of the valve after the installation and operation of the gas pipeline is unavoidable. Therefore, the safety risk when carrying out pipeline fired welding, pressure tapping and other hot work is large, but as long as the pre-operation safety analysis is well established. Perfect operation plan, good control of system isolation and good monitoring of flammable gas concentration, ensuring the smooth start of pipeline hot work under the condition of valve inner leakage, and achieving the goal of controllable safety risk can be realized.
References [1] YI Yiwu, LIN Jun, SUN Yeuqiu, et al. How to make a long-lost pipeline in operation in the pipeline? [J]. China Petroleum and Chemical Industry Standards & Quality, 2013(14):218.
Talking about the Risk Control of Pipeline Fire under the Condition of Internal Leakage of Valve
Abstract : Town gas pipelines, as the main transportation vehicles for gas, have been rapidly popularized with the development of the society. In the course of pipeline operation, due to the influence of third-party construction, etc., it is necessary to carry out hot line operations. There is a risk of fire and explosion from changing the line of gas pipelines. Loss of control over risks will cause major losses to people’s lives and property, cause far-reaching adverse effects on society, and will seriously damage the company’s social image. Therefore, it is of great significance to ensure the smooth operation of the company's safe production by doing a good job in the risk control of pipeline hot work.