This article delves into an accident case at Dalian West Pacific Petrochemical Co., Ltd., examining how pump bearing damage led to seal leakage and fire. It identifies causes such as bearing quality defects and improper maintenance. The article also analyzes common reasons for pump leakage, including seal structure failure and end face malfunction, and proposes preventive measures like proper material selection and auxiliary system design. Additionally, it discusses measures to mitigate leakage consequences, offering insights for safe pump operation in the petrochemical industry.
Accident cases
On April 10, 2015, the bottom pump of the distillation tower in the hydrocracking unit of Dalian West Pacific Petrochemical Co., Ltd. leaked and caught fire.
The cause of the accident was confirmed through disassembly inspection of the pump: during high-speed operation, the mechanical double seal quickly failed due to severe damage to the bearings, causing severe vibration of the equipment, resulting in medium leakage and high temperature generated by friction with the bearing body, leading to fire.
The reasons for bearing damage
1. Some bearings have quality defects that cause damage during operation;
2. There may be defects in the inspection, maintenance, and installation of bearings, which can cause malfunctions during operation.
This accident case shows that seal leakage is only the ultimate consequence of pump bearing damage. The accident also exposed two other issues worth paying attention to: 1. the inlet and outlet valves of the pump were designed without remote closing function, which could not cut off materials in a timely manner, resulting in prolonged fire duration; 2, there is no fire and gas detection alarm device installed near the pump, and the central control discovered the fire through CCTV.
Pumps are one of the most widely used general equipment in the petrochemical industry, with a wide variety and specifications. During the operation of the device, the vast majority of types of pumps have leakage issues.
The UK HSE Hydrocarbon Leakage Database (HCRD) is a globally recognized high-quality leak statistics database and widely recognized by the industry. It accurately counts the number of devices and records the completeness and details of leakage events. Even small leaks that may often be overlooked are included in the statistics. This database provides information on pump leakage incidents from 1992 to 2006 (see table above). According to statistical calculations, the leakage frequency corresponding to each leakage aperture range is shown in the table below. These data are based on the equipment and management level of offshore installations in the UK. If the equipment and management level of the factory is lower than the database statistical level, the frequency of leaks will be higher.
There has been a statistical analysis of centrifugal pump leakage in a domestic hydrogenation unit (reference 2).
There are a total of 32 centrifugal pumps in the unit.
From 2010 to 2013, the number of pump leaks per year was 32, 27, 29, and 24, respectively, accounting for 61.5%, 56.2%, 53.7%, and 52.2% of the total equipment failure rate.
After treatment from 2014 to 2016, the number of pump leaks was 6, 5, and 5, respectively.
Statistical data shows that the centrifugal pump of this device has a high frequency of leakage and a high proportion of equipment failures.
Reasons for pump leakage
Leakage of pump mechanical seals is common and widespread. There are many reasons for mechanical seal leakage, and different types of mechanical seal leakage have different causes. The direct causes of mechanical seal leakage include seal structure failure (such as bellows cracking), seal end face failure, compensation component failure, and seal failure in other parts. There are many factors that lead to the occurrence of various direct causes, as follows:
Reasons for Pump Leakage (Continued) |
Preventive measures for pump leakage and mitigation of leakage consequences |
* Seal structure failure * Poor sealing production quality and poor material quality * Unreasonable processing technology * Unreasonable design * Poor quality control, etc * Improper selection of materials * Causing corrosion * Material failure caused by unsuitable operating temperature (high temperature, low temperature) * The different thermal expansion coefficients of each component lead to local stress concentration or loosening * Significant wear and tear * Impact and strong vibration caused by pump evacuation * Installation defects |
Leakage prevention measures * Fully consider the working environment of the pump, the properties and operating conditions of the conveying medium, and select the appropriate pump body structure, mechanical seal type, and sealing medium * Select appropriate materials for mechanical seal components based on working conditions, considering factors such as applicable temperature, corrosion resistance, wear resistance, thermal expansion coefficient, etc * Design a reasonable auxiliary system (such as a cooling system) and ensure that the sealing auxiliary system works well * Add automatic alarm equipment and interlock control to the pump to ensure the stability of the mixing process, monitor parameters such as pressure, temperature, flow rate in real time, and use interlock control if necessary. * Ensure the quality and correct installation of the pump * Strictly install mechanical seals according to requirements * Eliminating the vibration source of the pump must be strictly carried out in accordance with the operating specifications to avoid mechanical accidents caused by operational errors. At the same time, the operation of the pump should be checked regularly to select a reasonable flushing plan and flushing solution * Effective daily management and maintenance of pumps and seals Measures to reduce the consequences of leakage * Set up flow, pressure and other detection equipment * Combustible gas and flame probes are installed around the pump to detect pump leaks in a timely manner. * The remote control system of the pump is installed to stop the pump in a timely manner when a leak is detected. * Cut off valves are installed upstream and downstream of the pump to cut off the connection between the pump and the large capacity upstream and downstream customers in a timely manner when a mud leak occurs, reducing the amount of leakage * Control the ignition source around the pump, and calculate and analyze the possible range of areas that combustible materials may reach based on the consequences of leakage and gas diffusion * Reasonably set up fire-fighting facilities on site, optimize the layout through risk analysis such as fire and explosion, reduce the impact of pump leakage on the store country, and develop reasonable emergency response procedures to alleviate the consequences of accidents * Finally, how to ensure that the above protective measures are considered in practical work and maintain their effectiveness? Structured security analysis techniques such as HAZD can be utilized HAZOP Fire and explosion analysis, bow tie diagram analysis, etc., help identify the causes and possible consequences of pump leakage, and propose reasonable prevention, protection, and mitigation measures for each cause and consequence. Establish a safety management concept for the entire life cycle to ensure that these protective measures can be effectively implemented in the design, construction, and operation processes. |
Sealing end face failure * Unreasonable sealing selection and design result in insufficient or excessive pressure on the end face * Improper material selection leads to end face corrosion * Impurities entering the end face cause wear * Excessive temperature at the end face can cause carbonization of the sealing medium, leading to gradual accumulation and leakage failure. * The sealing flushing plan is unreasonable, and under pump operating conditions, it is prone to gasification and product formation, resulting in dry grinding or corrosion of the end face; * Low inlet pressure of the pump causes gasification of the sealing medium, resulting in dry grinding of the end face * Insufficient capacity of auxiliary cooling system leads to gasification of sealing medium * Unreasonable pump structure leads to misalignment and deformation of the end face * End face failure caused by issues such as eccentric coupling installation, bent pump shaft, unbalanced shaft system, and damaged bearings * Pump vibration caused by other reasons, such as pressure fluctuations |
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Compensation component failure * Poor quality of compensation component materials * Unreasonable processing * Unreasonable design * Impurities entering * Scaling of cooling water causes the inability of replenishment components to rebound * The temperature of the conveying medium is too high, exceeding the normal operating temperature of the compensation component, resulting in material failure |
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Sealing failure in other parts * Damaged or corroded gasket * Cover gasket leakage * Improper installation or lack of tightening of the gland nut sealing gasket leads to leakage due to defects or lack of tightening |
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By listing the reasons, it can be found that some are due to the seal itself, while some pump failures or unreasonable process design ultimately manifest in the form of seal leakage, such as the pump leakage event in the accident case. |
