Which pipes require static grounding/bonding?

Thread Content

There are not many standard specifications or industry standards regarding the electrostatic grounding of pipelines; the main ones include GB12158-2006 General Guidelines for Preventing Electrostatic Accidents, HG/T20675-1990 Design Code for Electrostatic Grounding in Chemical Enterprises, and SH3097-2017 Design Specifications for Electrostatic Grounding in Petrochemical Industries. GB50235-2010 Code for Construction of Industrial Metal Piping Projects also contains specific sections that address the implementation of electrostatic grounding for pipelines. Some large-scale process industry manufacturing companies and engineering design and construction firms have corporate-level regulations regarding the design of pipeline static grounding, such as the SDEP-SPT-PD2206-2008 Regulations on Pipeline Static Grounding Design ； These enterprise-level regulations are often quite specific and can serve as a reference for defining the scope of pipeline static grounding. The following pipelines shall be electrically grounded: 1) Pipelines located in areas at risk of explosion and fire shall be electrically grounded. In areas at risk of explosion and fire, flammable gases and combustible dusts may accumulate, and the presence of electric sparks could lead to fires or explosions. Electrical and electronic equipment in areas prone to explosions and fires must be of explosion-proof type, in order to prevent the generation of sparks during their operation, which could ignite or explode flammable gases or dusts. If the pipes in areas prone to explosions and fires are not properly grounded, static electricity can accumulate to such an extent that it generates electrical sparks, which may lead to fire or explosion accidents. 2) The oxygen pipeline should have wires bridged at the flanges to ensure reliable grounding. Oxygen is a special medium that does not burn on its own, but it is a strong oxidizing agent; in an environment with pure oxygen, steel pipes can be ignited. Therefore, although oxygen is not a flammable medium, pure oxygen pipelines must be properly grounded. 3) The pipelines for pneumatic transport of solid particles should have wires bridged at the flanges to ensure reliable grounding. Gas-solid pipelines generate a large amount of static electricity during operation; it is essential to ensure that the pipelines are properly grounded so as to quickly transfer the charge and prevent the accumulation of excessive static electricity. 4) For pipes laid parallel to each other with a clear distance of less than 100, static bonding straps should be installed every 20 meters. For pipe galleries laid parallel at close distances, to ensure that the two pipelines are at the same potential, bonding straps need to be installed every 20 meters. 5) Static grounding should be provided at the boundary between the pipeline inlet and outlet devices to prevent the transfer of charge between pipelines outside the boundary and those inside the devices. Explanation on static grounding: The static grounding of pipelines is divided into direct grounding and indirect grounding. Direct grounding means that the pipeline’s static electricity grounding system is directly connected to the main grounding network of the device ； Indirect grounding refers to the situation where the pipeline itself is connected via bolts or flanges, and thereby linked to grounded equipment or steel structures, thus being indirectly connected to the main grounding network of the installation. All equipment is equipped with static grounding, and all pipelines are connected to the equipment; the vast majority of these pipelines are indirectly grounded. One of the common questions is that, during the implementation of engineering projects, many people believe that only flammable media require static grounding, while non-flammable media such as instrument air, plant air, and nitrogen do not need it. We know that three conditions are required for a fire or explosion to occur: first, the presence of a combustible material; second, contact between the combustible material and oxygen; third, the presence of a spark sufficient to ignite the mixture of the combustible material and oxygen. All three conditions are essential. Fire or explosion accidents caused by static electricity occur as a result of electric sparks generated by static discharge igniting or detonating mixtures of flammable gases or flammable dusts in contact with oxygen that have leaked outside the pipes or equipment. Wherever there are areas where flammable gases or dusts accumulate, there is a risk of fire or explosion caused by static discharge. Therefore, the criterion for determining whether a general pipeline needs to be grounded is not whether the medium inside it is flammable, but rather whether it is located in an area at risk of fire and explosion. October 27-29, Hangzhou – 2023 Training Course on Automation Transformation in Fine Chemicals, Engineering Design for Pharmaceutical and Chemical Projects, Batch Control, and Intelligent Factory Construction. HG20675 provides clear guidelines regarding the need for static electricity grounding of pipelines in areas prone to explosions and fires; its section 2.1.1 states that “industrial static electricity grounding measures should be taken for objects in environments prone to explosions and fires that may pose a risk due to static electricity.” Some argue that water is conductive, so water pipes and steam pipes do not need to be grounded. In fact, steam is not a good conductor of electricity ； Water itself does not conduct electricity; it is water containing conductive ions that does. Many types of water used in the process industry, such as boiler water, deoxygenated water, and steam condensate, have most of their conductive ions removed, resulting in poor electrical conductivity. Even for circulating water, it is softened to remove most of the calcium and magnesium ions in order to reduce scaling in heat exchange equipment. Unless experiments prove that the water used in the process equipment has good electrical conductivity within the pipes, water cannot be considered conductive, and the requirements for static grounding of steam and water pipes in areas at risk of explosion and fire cannot be waived. Common Question 2: Some people believe that flanges connected using metal bolts do not require electrostatic grounding, on the grounds that Section 4.3.3 of SH3097 states that \"when metal flanges are fastened with metal bolts or clamps, it is generally not necessary to install additional electrostatic connection wires, but it is essential to ensure that there is good electrical contact between at least two bolts or clamps.\" ”This understanding is incorrect. This specification states that, under certain conditions, it is not necessary to provide additional wire bonds for the flanges; it does not mean that the requirement for static grounding of the pipes can be waived. The requirement for static grounding of pipelines does not mean that static bonding must be installed. The static grounding of pipelines is divided into direct grounding and indirect grounding. Direct grounding means that the pipeline’s static electricity grounding system is directly connected to the main grounding grid ； Indirect grounding refers to the situation where a pipeline is connected, indirectly, to the main grounding network of the installation through connection with devices that are already grounded or with steel structures. All equipment is equipped with static grounding, and all pipelines are connected to the equipment; the vast majority of these pipelines are indirectly grounded. Whether to set a wire bypass depends not only on the design requirements but also on the measured resistance between the connections. There are two necessary conditions for setting up wire bridging: first, the design requires electrostatic bridging. Secondly, for most media (except pure oxygen, gas-solid mixtures, and hydrogen), wire bypassing is required only when the measured resistance on both sides of the junction is greater than 0.03 ohms. It should be noted that for applications requiring static grounding, resistance testing is an essential procedure, regardless of whether a physical jumper wire is used or not. Additionally, for some special media, an electrostatic bonding should be provided regardless of whether the measured resistance between the connectors is less than or equal to 0.03 ohms. These media include pure oxygen, gas-solid mixtures, and hydrogen. The reasons for requiring bonding in the first two cases have been explained earlier; as for hydrogen, its low molecular weight makes it highly prone to leakage, and it has a wide explosive range along with a low ignition current. For safety reasons, advanced static electricity grounding measures must be implemented. Statement