Pump leakage

Thread Content

Leakage is a very common occurrence during the operation of our devices. Generally speaking, the causes of leakage include corrosion, abnormal fluctuations in the manufacturing process, incorrect material selection, and so on. In production facilities, pumps, which are the most commonly used conveying machinery, also experience frequent leakage incidents. As is well known, when a device operates continuously, the pump also runs for long periods of time. During this time, leaks occur within the device due to wear and tear, erosion by the material being handled, corrosion, and other factors. However, it is often such minor incidents that lead to safety accidents, or even serious disasters. For pumps, we can also use the HAZOP analysis method to conduct risk discussions. On April 10, 2015, a leak and fire occurred in the bottom pump of the stripping tower in the hydrocracking unit of Dalian West Pacific Petrochemical Co., Ltd. A pipeline (with a diameter of 200 mm) above the bottom pump cracked, and the oil and gas inside the pipeline ignited at the site of the crack. As a result of this incident, 3 pumps, the framework above them, some instruments, and power cables were damaged by fire; one pipeline cracked, but no other equipment was damaged, and there were no casualties. The cause of the accident was: failure of the seal on the bottom pump of the stripper, resulting in a leak and fire. Through disassembly and inspection of the pump, it was found that bearing damage is the main cause of the rapid seal failure. During high-speed operation of the pump, severe damage to the bearings causes intense vibrations in the equipment, which leads to the rapid and simultaneous failure of the mechanical double seals and results in fluid leakage. The high temperatures generated by friction with the bearing housings can then trigger a fire. At 22:57 on April 10, 2015, the operator in the control room detected a fire in the pump area near the stripper of the hydrocracking unit through video surveillance. It was confirmed that the fire was caused by a leak in the pump at the bottom of the stripper. Xitai Company’s facility initiated an emergency pressure release, shutting off the valves for the inlet and outlet pipelines of the stripper, thereby bringing the operation of the facility back to a stable state and preventing further expansion of the accident. At 23:00, the company’s fire trucks arrived at the scene to extinguish the fire and cool down the area. By 23:30, the fire had diminished. Due to the damage to the cables, it was necessary to manually close all isolation valves. To ensure the safety of personnel and prevent further disasters, the open flame associated with the bottom pump was extinguished at 1:35 on the 11th, after the stripping tower and the bottom pump had been completely isolated to guarantee safety. To prevent the accumulation of flammable gases that could lead to secondary accidents, fire suppression and cooling measures were employed to control the combustion at the cracked sections of the pipelines. Once the oil and gas inside the pipelines and their connected devices had been largely burned up, the remaining embers were completely extinguished at 4:50, and the residual oil and gas within the pipelines and devices was successfully sealed off. The occurrence of the above accidents could actually have had its related risks identified through a HAZOP analysis: Cause: Damage to the pump bearings, with vibrations leading to seal failure. Consequence: Medium leakage, combined with the high temperatures generated by friction against the bearing housing, can lead to a fire. In severe cases, it can lead to fires and explosions. Protection measures: 1. Flammable gas alarm ； 2. On-site fire protection facilities ； 3. Video surveillance ； 4. Conduct regular inspections according to the operating procedures, and perform periodic checks on the equipment. It was precisely because of the proper protective measures that the on-site operators were able to respond quickly when the accident occurred, preventing it from spreading any further. Regarding the risks associated with pumps, we discuss them in detail here and list the protective measures that may be necessary: Reason: Improper selection of the sealing material ； Vacuum, cavitation, or prolonged pressure retention lead to seal failure ； ； Lubrication failure leads to bearing damage, which in turn causes seal damage ； Frequent changes or adjustments in operating conditions lead to seal damage ； Consequences: Pump damage, material leakage, environmental pollution. In severe cases, a large amount of material leaks, and the leaked material can cause fires and explosions. Protection measures: 1. The pump is equipped with a reliable seal (such as a double-end face seal) ； 2. Add emergency pump shutdown facilities to the DCS ； 3. Install an emergency shut-off valve on the equipment upstream of the pump ； 4. Video surveillance ； 5. Flammable gas alarm (or smoke detector, flame detector, etc.) ； 6. On-site fire protection facilities ； 7. The operating procedures require regular inspections and periodic checks. Of course, with all the above protective measures in place, the safety factor is very high. However, the investment in such cases is also very high. In fact, in actual plant design, to prevent accidents caused by pump leaks and taking into account the investment required for the plant as well as the hazard level of the medium being transported, these protective measures are applied selectively. For example, in 1997, a petrochemical company experienced a sudden failure of the seals, resulting in a large leak of liquefied gas. In 2011, the mechanical seal of an propylene feed pump at a certain company failed suddenly, resulting in a propylene leak. Similar accidents have occurred in the same company, all due to the use of a single-end face multi-spring design for the pump seals. Later, for pumps with a high risk level, the company adopted double mechanical seals to enhance the stability and reliability of the sealing system. Additionally, emergency shut-off valves were installed at the inlets and outlets of existing high-risk equipment and flammable/explosive pumps. An emergency pump shutdown button was also added in the control room to enable remote control ； At the same time, the operating procedures specify the key steps for emergency operations, outline the priority order of such actions in case of an accident, and enhance the efficiency of responding to accidents. In device design, the protective measures against pump leaks essentially involve preventive measures and mitigation measures: additional preventive measures are implemented on the pump itself, while mitigation measures are put in place around it. The activation of these safety measures can protect the device to the greatest extent possible. Think about it: if a pump leaks, just dripping may not lead to any serious accidents ； During continuous operation, if it is not detected early and a large amount of flammable material leaks out, once ignition occurs, it becomes much harder to bring the situation under control. If the facilities and equipment near the pump catch fire, it is very likely to lead to more severe fire and explosion accidents. Since we can identify these risks through HAZOP analysis, then why can’t these safety measures be adopted? Don’t wait until an accident occurs to try to fix things; by then it will be too late to regret it. Risks exist objectively; the key is whether you have truly enhanced your awareness of risk prevention and whether you genuinely want to ensure the safety of your equipment. Be careful of leaks and ensure the device is safe!