Safety measures for gas pressure regulator design City gas is generally regulated by a pressure regulator to be used by end users. The gas pressure regulating device is generally composed of several functional modules, such as a pressure regulator to realize the pressure regulating function; the filter realizes a clean filtering function; the heat exchanger can avoid the ice blocking caused by the sudden drop of the gas due to the large decompression of the gas. Phenomenon; the flow meter realizes the metering function of gas. These modules are assembled together by welding and flange connection to achieve the function of the gas pressure regulator. The gas pressure regulating device should pay attention to the following problems when designing due to the particularity of its use.
1 device classification
In current industry standards, gas pressure regulators are neither pressure vessels nor difficult to classify and monitor by pressure vessels, nor are they any of the pressure pipelines. There are some misunderstandings in the design and manufacture of related companies, such as mistakenly treating them as non-standard equipment, neither subject to the Pressure Vessel Safety Technology Supervision Regulations (National Quality Technology)
The supervision and supervision bureau promulgated the 1999 edition) and did not design and manufacture according to the relevant regulations and standards of the pressure pipeline. This will inevitably lead to insufficient supervision and cause hidden dangers. The device should be managed by the “component combination device†in the special equipment catalogue. For details of the special equipment catalogue, please refer to the national quality inspection pot [2004] No. 31 document on the publication of special equipment.
Directory of notifications. For the combined device, in accordance with the Regulations of the Special Equipment Safety Supervision Regulations (promulgated by the State Council in 2003), the manufacturing unit must apply to the AQSIQ for a manufacturing license for special equipment (specifically, pressure pipe components) before manufacturing. ,installation. Pressure vessels attached to the unit, such as heat exchangers, filters, buffer tanks
Etc., should be made by the unit that obtained the corresponding category of pressure vessel manufacturing license.
2 According to the pressure, the design, manufacturing and inspection requirements are respectively proposed.
The pressure regulating device generally has one or more stages of pressure regulation. The pressure regulating device can propose different design, manufacturing and inspection requirements according to different pressures before and after pressure regulation. Specifically, the flanges, steel pipes and valves of each pressure section can be manufactured and selected according to different pressure levels to reduce weight and reduce costs. Non-destructive testing of welded joints is also proposed accordingly
Different testing requirements. The strength test can be carried out separately according to each pressure section, and the airtightness test is performed once after each section is assembled.
3 safety measures to be considered in the design;
Gas is a flammable and explosive gas. The safety of using a pressure regulating device cannot be ignored. It is necessary to take corresponding safety measures, as follows.
1Set emergency shut-off valve and safety relief valve
The emergency shut-off valve is generally located upstream of the pressure regulator, and is automatically shut off (ie, overpressure cut) when the gas pressure exceeds the set pressure of the emergency shut-off valve during the gas delivery process to protect the downstream pipeline and the pressure regulator. At the same time, if there is an accident in the downstream pipeline, the pipeline may be cut off (ie, low-pressure cut-off) when a large amount of gas leaks, causing a more serious accident.
The safety relief valve is arranged downstream of each stage of the pressure regulator. When the pipeline pressure exceeds the opening pressure, the safety relief valve is automatically opened to release part of the gas to protect the downstream pipeline from pressure.
The set pressure of the emergency shut-off valve and the safety release valve can be determined according to the need. It can be set to cut off the pipeline first when overpressure, and then release the gas (usually used for high pressure pipe section with design pressure >1.6 MPa), and vice versa. The set pressure of the two should have a certain difference to ensure the continuous and stable export gas.
2 set the static conduction device
Due to the flange and thread connection in the pressure regulating device, the presence of non-metal gaskets, thread sealant and raw material belts increases the local resistance in the pipeline, and the static charge generated by the gas is accumulated, which is prone to spark accidents. . Therefore, when the resistance between each pair of flanges or threaded joints is >0.03 ohms, a copper stranded wire or a copper plate with good electrical conductivity should be placed across the flange or the threaded joint to discharge the static electricity in the pipeline in time. The conductive contact surface must be rust-proof and tightly connected, and should not be painted to avoid affecting the conductive effect.
The voltage regulator should also be considered for reliable grounding during installation. If the pipe system has a ground resistance of >100 ohms, two grounding leads should be provided.
3 set the odor
Liquefied petroleum gas has a special smell and is easily detected by people when it leaks. However, natural gas itself is colorless and odorless. If a leak is difficult to find, it is easy to form an accident. According to the requirements of GB 50028--2006 "Code for Design of Urban Gases", non-toxic city gas should be detectable when it reaches 20% of the lower explosion limit in the air. When toxic gas leaks into the air and reaches harmful levels permitted by the human body, it should be noticeable. Therefore, for gas that does not have obvious odor, it is necessary to add a special substance that has no influence on the combustion characteristics of the gas and is non-corrosive to the pipeline, and is also easily perceived by people to eliminate hidden dangers. At present, tetrahydrothiophene THT (C4H8S) and ethanethiol (C2H5SH) are often used, and the amount is small, and the effect is good. Generally, an odorizing port is provided at the exit section of the pressure regulating device.
4 set pressure measuring, temperature measuring instrument
After each stage of pressure regulation, a pressure measuring and temperature measuring instrument shall be set to indicate whether the working condition is normal. If conditions permit, when the remote display instrument is added, the operation of the remote monitoring pressure regulating device can be realized in the control room.
4 Conclusion
In recent years, gas pressure regulators have also been more widely used due to the promotion of clean energy such as natural gas. Since the relevant design and manufacturing have not yet been determined by specific standards, the defects in the design will inevitably cause problems in use, and there will be considerable security risks. Therefore, relevant departments should strengthen the supervision of the design, manufacture, installation and use of such devices, and strictly control the design, manufacturing and inspection, so that the product quality can be further guaranteed and improved.
(Source: Hebei Zhenxing Gas Pressure Regulator Co., Ltd. gas pressure regulator)
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