What is the risk of a stuck pressure relief valve? How often is the manual test done?

What is the risk of pressure relief valve sticking? How often is it manually tested? Answer: The pressure relief valve is the key mechanical protection of the storage tank, and the sticking means that the two lines of defense fail at the same time-the pressure in the tank is too high to be discharged, and the risk of overpressure is conducted along the pipeline and the tank; when the oil is pumped or the temperature drops too fast, the intake cannot be replenished, and the negative pressure of the tank is unstable. The passing caliber is to do manual testing at least once a month, check once a year, and keep the test records on file. Sites with poor exposure environment encrypt manual testing on a quarterly basis. Valve long-term static, sealing surface corrosion, spring rust, oil and gas condensate stuck to the valve disc, are common causes of stuck. This article clariates the risk of sticking, testing practices and daily inspection points.

The role of the pressure relief valve and the performance of sticking

The gas phase space of the storage tank is exchanged with the atmosphere through a pressure relief valve: when the pressure exceeds the set upper limit, the valve disc opens for exhaust, when the pressure is lower than the set lower limit, the suction is opened, and the tank pressure is restricted within a safe range once in and out. It is a supporting relationship with the oil and gas recovery system-the recovery device operates according to the tank pressure, and the pressure relief valve covers the bottom, both of which jointly maintain the stability of the gas phase. The performance of sticking is hidden in the details: the valve disc is slow to open, the back seat is not tight after opening, the condensate sticks to the valve disc in winter, the valve is in place on the surface, and the function has been discounted. The judgment of sticking depends on manual test and visual inspection: the manual lifting rod is smooth and the return position is simply normal, and the astringent, stuck and not in place are all treated as faults.

Three Types of Risk of Stagnation

The first risk is the failure of the overpressure side: when the tank pressure rises, the valve will not be discharged, the pressure will continue to be high, the breathing line and flange will leak, and the tank body will deform. This kind of accident is the most dangerous at the site where the recovery device is disabled and the pressure relief valve is ignored. The second risk is the failure of the negative pressure side: the tank is vacuumed during oil unloading or temperature drop, the valve cannot be sucked open, the tank body is concave, the stress concentration in the welding area and the connecting pipe is concentrated, and the buried tank is also accompanied by the risk of groundwater infiltration. The third risk is that the emission is out of control: the valve disc is stuck in the half-open position, the tank pressure continues to be discharged when the tank pressure is normal, the oil and gas loss and emission concentration both rise, and the data is not good-looking in environmental protection testing. Three types of risks correspond to different trigger conditions. The common premise is the sticking itself. Daily testing is to nip the sticking in the bud.

How to do manual testing

Manual testing is done during the period when there is no operation in the tank farm: one person operates and one person monitors, the lifting force is uniform, the opening smoothness and seat return state of the valve disc are felt, and the opening height is observed according to product requirements or full opening. Stations with test platforms use blowing or vacuuming equipment to check the set values. Three points should be paid attention to in the test: when the wind speed is high, the reading on the leeward side is unstable, and when the wind is small; Two people cooperate in the operation, the tank area is a fire prevention area, and the tools and clothing shall be in accordance with the site regulations. After the test, make sure that the valve plate is back in place, and don't leave the valve in a half-open state. Test records write date, results, exceptions and disposal, monthly summary, valve status trends at a glance.

Risk vs. Test

Test Maintenance Procedure

1. Carry out manual test on a monthly basis as planned;
2. Lift the rod to feel the smoothness and observe the seat return;
3. Record the deviation between the opening height and the set value;
4. Appearance inspection: corrosion of valve body and accumulation of condensate;
5. Clean up condensate and sundries according to safety regulations;
6. Annual delivery and filing of records throughout the year.

Frequently Asked Questions

Will the manual test damage the valve?

Standard operation will not: the lifting force of the rod is uniform, the stroke is according to the product requirements, and the test itself is to keep the sealing surface and moving parts active; For fear of long-term accidents, the consequences of rust and sticking are far greater than the test risk.

Do test records need to be retained?

It is suggested to keep it for a long time: the record is a continuous chain of evidence for valve status, which can be used for annual verification, accident traceability and third-party inspection. Electronic ledgers are backed up on a monthly basis, not just in paper books.

What is the relationship between the pressure relief valve and the vacuum pump of the recovery device?

Different division of labor: vacuum pump active pumping recovery, pressure relief valve passive bottom protection; The pumping capacity of the pump is designed according to normal working conditions. Abnormal pressure suppression and negative pressure are bottomed by valves. The two are complementary in parallel. Do not replace the recovery device with normally open valves. Loss and discharge cannot be collected.

This article is organized by Luoyang wohong petrochemical equipment co., ltd. the company provides design, manufacture, installation, commissioning and operation and maintenance services for oil and gas recovery equipment, solvent recovery devices and buried composite pipe networks at gas stations, oil depots and chemical enterprises. if you need scheme configuration or on-site investigation, please contact and exchange.