In industrial production and all types of pressure‑bearing systems, safety valves act as critical safety accessories to protect piping against over‑pressure, preventing equipment damage and safety incidents. Not every piping line requires a safety valve; installation shall be determined by evaluating the risk of abnormal pressure rise, in compliance with safety codes and process requirements.
Combined with practical service conditions and relevant technical standards, safety valves shall be installed on the following categories of piping. Core installation principles and precautions are also specified for on‑site technical reference.
- Pressure‑bearing fluid transport piping, especially for flammable, explosive and toxic media This represents the most common application scenario for safety valves against over‑pressure.
Where valves are accidentally closed, thermal expansion of trapped fluid occurs or process upset takes place, line pressure may rise rapidly and exceed the design pressure rating of piping, potentially resulting in leakage, explosion and other hazardous events.
For example, for liquefied hydrocarbon and flammable liquid piping: when isolation valves at both ends are closed, trapped fluid will experience pressure build‑up due to ambient‑temperature thermal expansion. Safety valves shall be provided for pressure relief, supplemented by venting provisions to enhance safety. For corrosive‑service piping, corrosion may impair valve function and restrict flow, indirectly triggering over‑pressure. Safety valves shall be selected where required, with materials compatible with process media to prevent safety‑valve component failure. - Piping directly connected to pressure‑boosting equipment
Safety valves shall be fitted on discharge piping of each stage of reciprocating compressors and positive‑displacement pumps. Blocked discharge or back‑flow may cause instantaneous over‑pressure. Even if safety valves are fitted on the equipment itself, additional line‑mounted safety valves are still required if isolating valves exist between equipment and piping.
For discharge lines of centrifugal compressors and centrifugal pumps: where downstream equipment cannot withstand the maximum discharge pressure of the rotating equipment, safety valves shall be installed on discharge piping to protect downstream hardware from high‑pressure impact damage. - Piping subject to pressure fluctuation and medium phase‑change
Safety valves shall be considered for steam and high‑temperature hot‑water piping. Heat accumulation and flow transients can produce pressure surges; steam exhibits high volumetric expansion and elevated over‑pressure risk. Full‑lift safety valves shall be adopted for fast pressure relief.
Per Safety Technical Supervision Regulation for Safety Valves (TSG ZF001), the set pressure of safety valves shall be calibrated and shall not exceed the piping design pressure. For downstream piping of pressure‑reducing valves: if downstream systems cannot tolerate upstream full pressure, safety valves shall be installed on the low‑pressure side to guard against pressure‑reducing‑valve failure, which could expose downstream piping to high‑pressure fluid and potential rupture.
Safety valves are not to be over‑specified The guiding principle:
within one common pressure system, if safety valves are already installed at the pressure source and no isolating valves separate the source from other parts of the system, additional safety valves on downstream equipment and piping are not mandatory. This avoids redundant hardware, unnecessary cost and excessive maintenance workload. According to Code for Construction of Industrial Metallic Piping Engineering (GB 50235‑2010), safety valves shall be mounted vertically. Inlet and outlet nozzles and connected piping shall be kept short and straight to minimize pressure loss.
Engineering data indicates roughly 75 % of safety‑valve functional problems originate from improper installation. Pressure‑drop control across inlet and outlet connections is therefore vital:
- Inlet piping pressure drop shall generally not exceed 3 % of the safety‑valve set pressure.
- Built‑up back‑pressure on the outlet side shall not exceed allowable limits; for conventional safety‑valve designs, this value is typically limited to 10 % of set pressure.
- Where stop valves are fitted on safety‑valve inlet or outlet lines, such stop valves shall be sealed by lead seals and locked in the fully‑open position.
Periodic calibration and maintenance are essential for reliable safety‑valve performance
In accordance with relevant codes, safety valves shall undergo calibration at least every 12 months, either on‑line or off‑line. For severe‑service conditions including high temperature, high pressure and strong corrosion, intensified routine inspection is required; corrosion and leakage shall be addressed promptly. Calibrated safety valves shall be lead‑sealed with complete records to prevent inadvertent mal‑operation.
To conclude:
safety‑valve installation is driven by over‑pressure hazard assessment. Selection and arrangement shall integrate medium properties, process conditions and existing equipment safeguards. Focus shall be placed on pressure‑bearing service, connections to pressure‑boosting equipment and locations with pressure fluctuation. Strict adherence to technical codes ensures safety‑valve functionality and reliable operation of the overall piping system.
