Learning from past incidents: An analysis of the common causes of pressure pipeline accidents and preventive measures!

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　　With the rapid development of China’s national economy, the number of pressure pipelines in petrochemical and other facilities is increasing steadily. In particular, with the construction of key projects such as the \"West-East Gas Transmission\" project, industrial gas pipelines and urban gas supply pipelines will see rapid growth, which inevitably increases the likelihood of accidents. On February 18, 1996, an explosion occurred in an outdoor gas pipeline in Yangzhou, resulting in a catastrophic accident that claimed 19 lives. This incident led to an acceleration in the implementation of safety inspections; that same year, the \"Regulations on the Safety Management and Inspection of Pressure Pipelines\" were issued to ensure the safe inspection and management of such pipelines. Case Analysis of Pressure Pipeline Accidents Pressure pipelines refer to special types of equipment that are widely used in production and daily life and pose significant risks such as fires, explosions, or poisoning. They fall into three categories: industrial pipelines, utility pipelines, and long-distance transmission pipelines. Pressure pipelines in use can experience abnormal failure due to various issues in design, manufacturing, installation, and operation, leading to sudden catastrophic accidents. 　　Due to the late start in the supervision and management of pressure pipelines, the total number of accidents has increased significantly. Based on an incomplete statistics and analysis of 213 accidents across the country, pressure pipeline accidents are mainly caused by five factors. 　　(1) Reasons for design failure: The main reasons include improper material selection, errors in stress analysis (especially the failure to account for thermal stresses in the pipes), accelerated crack propagation due to pipe vibration, which leads to failure. Additionally, the structural design of the pipeline system does not comply with regulatory standards and technical requirements, and the selection of pipeline components and supports is inappropriate. In January 1995, a gas pipeline burst on a street in Jinan, Shandong Province, resulting in a gas leak and explosion that caused varying degrees of damage to 2.2 kilometers of road surface; 12 people died and 49 were injured. In 2000, at a gas company in Qitaihe City, Heilongjiang Province, improper design caused the pipes to break under pressure, leading to a gas leak and the death of 4 people. An explosion occurred at a chemical plant in Laiwu City, Shandong Province, due to the incorrect use of pipeline materials, resulting in direct economic losses of over one million yuan. 　　(2) Causes of failure The main cause of failure is accidents resulting from manufacturing defects in pipeline components. Among these, valves, pipe fittings (tees, elbows), flanges, gaskets, etc., are the sources of accidents. The pipes have uneven thicknesses, and serious defects such as cracks, inclusions, and pores are present in the material; poor sealing performance leads to leaks and explosions. In a company in Jiande City, Zhejiang Province, 4 people died due to the explosion of pipeline valves ； On March 5, 1998, an explosion occurred at a company in Xi’an during emergency repairs to fix a leak in the sealing surface of a spherical tank, resulting in 12 deaths (7 of whom were firefighters). On March 8, 1999, the inlet pipe of a heat exchanger in the synthesis workshop of a nitrogen fertilizer plant in a certain city leaked under normal operating pressure. The plant’s maintenance staff attempted to carry out repairs while the system was still under high pressure, which caused the pipe to break apart; high-pressure hydrogen and nitrogen gas erupted from the pipe, resulting in an explosion that killed 4 people and injured 1 person seriously. The workshops and equipment in the synthesis, compression, and copper washing sections were severely damaged, with direct economic losses exceeding 3 million yuan. The main causes of the accident were illegal repair procedures and poor quality of the pipes and seals. 　　(3) Reasons for installation The reasons for installation are mainly accidents resulting from the loss of control over the quality management system by the installation unit, poor welding quality, illegal and irregular construction practices, improper use of materials, and the failure to carry out quality inspections during installation. In 2000, at a steel plant in Beijing, the welding joint between a valve and a main steam pipeline ruptured, resulting in an explosion that killed 6 people. 　　(4) Poor management Poor management mainly refers to chaotic usage, incomplete management systems, illegal operations, and failure to conduct regular inspections and maintenance as required. In 1991, a factory in Tonghai County, Yunnan Province, experienced a gas leak due to improper operation, resulting in the death of 2 people from poisoning. In January 1998, gas leaks occurred in a residential building in Harbin due to construction work, resulting in 8 deaths and 44 people being poisoned. 　　(5) Pipeline corrosion Corrosion is the main cause of pipeline failure. The main reasons are improper material selection, inadequate anti-corrosion measures, and failure to carry out regular inspections. In 1994, a pipe in a factory in Zhangjiakou City ruptured due to corrosion-induced thinning and leakage, resulting in an explosion that caused 8 deaths. (6) Pipeline explosion accidents caused by other reasons: ① At 19:45 on May 29, 2004, a serious pressure pipeline explosion occurred at the Anfu Management Office of Luzhou Natural Gas Company, located on the ground floor of a residential building at No. 15 Bingling Road, Anfu Town, Naxi District, Luzhou City, Sichuan Province. This accident resulted in 5 deaths and 35 people suffering minor injuries. The main cause of the accident was an oval-shaped hole in a natural gas pipeline with a diameter of 108 millimeters, through which natural gas leaked. This gas entered the gap formed between the basement floor of the residential building and the road embankment, where it mixed with air to form an explosive mixture. This mixture spread onto the sidewalk through gaps in the pavement coverings, and an unknown ignition source caused an explosion. 　　②The severe accident in Xi’an on 98.3.5: A massive explosion occurred at the liquefied petroleum gas pipeline facility of Xi’an Gas Company; the fire burned from March 5th until it was finally extinguished on March 7th. Two 400m3 liquefied petroleum gas spherical tanks were destroyed, 4 liquefied petroleum gas horizontal tanks and 7 tank trucks were completely burned down. At the moment of the explosion, nearly 100,000 residents in the vicinity fled in panic, causing great chaos. The explosion caused 12 deaths (7 of them firefighters) and 30 injuries (15 of them severe). 　　Cause of the accident: Local failure of the sealing surface on the upper flange of the drain valve beneath tank No. 11 led to a large leakage of liquefied petroleum gas; the concentration reached the explosive limit, and sparks from the electrical room triggered a massive explosion. The flange seal area is the junction between the pressure pipe and the pressure vessel. 　　③Incident at a Fujian-based oil refining and chemical company on 92.10.22: On that date, a wave compensator in the liquefied petroleum gas loading pipeline of a Fujian-based oil refining and chemical company burst, resulting in a loss of 113 tons of liquefied petroleum gas. Fortunately, no explosion occurred due to the absence of an open flame. 　　Cause of the accident: After the pipeline safety valve activated, the staff failed to accurately determine the pressure and close the manual valves before and after the safety valve in order to reset the pressure. As a result, liquefied petroleum gas remained trapped in the 6500-meter-long pipeline, causing the temperature to rise and immense pressure to build up inside the pipeline, which led to the explosion of the weakest wave compensator in the pipeline. 　　④Incident at a Fujian-based oil refining and chemical company on 96.4.21: On April 21, 1996, an air storage tank at a Fujian-based oil refining and chemical company exploded, which led to the rupture and explosion of oil transport pipelines as well as gas pipelines, resulting in a massive fire. This forced the refinery to shut down urgently, causing economic losses of several million yuan. Fortunately, no casualties were reported as the incident occurred in the early hours of the night. 　　Cause of the accident: The failure of a check valve in the pressure pipeline allowed combustible gas to enter the air storage tank, reaching the explosion limit and triggering a chemical explosion, which in turn led to a large fire. 　　⑤The 95.1.3 accident in Jinan: On 95.1.3, a massive explosion occurred in the gas pipeline and high-voltage cable pipelines on Donggou Street in Yangtouyu, Lixia District, Jinan. This explosion destroyed 3,000 meters of road surface, as well as nearby buildings and cars. It resulted in 12 deaths, 12 serious injuries, and 43 minor injuries. This accident was the largest explosion caused by a gas pipeline leak in China’s history. 　　Cause of the accident: Gas from the gas pipeline leaked into the cable trench, where it came into contact with an open flame, resulting in an explosion. The distance between the gas pipeline and the high-voltage cables did not comply with the regulations. 　　Furthermore, as the supervision and management of pressure pipeline safety in our country are still in the process of development, there is a significant gap compared to economically developed countries in terms of research on safety technologies related to pressure pipelines. Issues such as the classification and grading of pressure pipelines, the assessment of their safety status, the inspection of buried pipelines, and pipeline leak detection systems have not been effectively resolved. Moreover, the inadequacy of relevant regulations and standards also contributes to problems associated with pressure pipelines. 　Countermeasures to Reduce Accidents in Pressure Pipelines Accidents involving pressure pipelines involve seven systems: design, manufacturing, installation, operation, inspection, repair, and renovation. To minimize such accidents and ensure the economic and safe operation of pressure pipelines, it is necessary to consider countermeasures for these seven systems. 　　The safety of pressure pipelines is a systematic engineering task; implementing comprehensive, all-round, and systematic supervision and management of such pipelines is necessary as part of China’s efforts to join the WTO and integrate with the international community ； It is necessary to effectively prevent accidents and safeguard people's lives and **property safety. Therefore, one cannot focus solely on individual systems; the seven systems are interdependent and inseparable from one another. The use of pressure pipelines is the core; all other systems revolve around this central use. Designing, manufacturing, and installing the system are prerequisites for ensuring the \"optimal quality\" of pressure pipelines, with installation being the most crucial part of this process. Issues related to the design and manufacturing phases can be identified and corrected during the installation phase ； Inspection, repair, and renovation are essential guarantees for the proper operation of pressure pipelines, thereby establishing a scientific, comprehensive, and internationally standardized safety supervision and management system for such pipelines. 　　(1) A qualification licensing system is implemented for units responsible for the design, manufacturing, installation, and inspection of pressure pipelines; this is a prerequisite for ensuring the quality of such pipelines. Qualification licensing is a mandatory measure imposed on these units in accordance with **laws and regulations. It involves a comprehensive evaluation of their quality management systems, compliance with relevant laws and standards, allocation of resources, and overall quality. It differs from ordinary voluntary system certifications, and therefore cannot be replaced by certification processes. 　　(2) Type testing of pressure pipeline components shall be carried out in accordance with the law. Type testing is used to determine whether these components meet the product standards, and it represents the most direct measure for controlling the quality of such components. Accident analysis shows that 27.2% of accidents are caused by poor quality of pipeline components; therefore, users and installation parties must choose pipeline components that are **safely registered and bear the AZ mark** in order to eliminate the root causes of such accidents. The Jiangsu Province Quality and Technical Supervision Pressure Pipeline Components Type Test Center is an **authorized type test institution. 　　(3) Legal supervision and inspection of the installation quality of newly built, expanded, or renovated pressure pipelines. The installation of pressure pipelines is a crucial stage, and the supervision and inspection of its installation quality serves as a comprehensive verification of the quality control in the design and manufacturing processes of these pipelines. It involves not only monitoring the operation of the quality management systems used by the installation companies but also conducting thorough inspections at various stages, including design, pipeline components and materials, welding process evaluation and welding quality, non-destructive testing, and pressure testing. This approach is essential for ensuring high installation quality. 　　(4) Ensure the safety supervision and management of system usage. The user units shall strictly comply with the requirements of the Regulations by assigning full-time or part-time personnel and establishing organizations responsible for the safety of pressure pipelines, implementing safety management systems including inspection protocols and various operating procedures, establishing plans for regular inspections and maintenance. Operators must undergo training, pass assessments, and hold valid certificates before taking up their duties, while pressure pipelines should be registered step by step. For pipelines prone to corrosion, appropriate materials should be selected, proper design should be employed, and effective protective coatings must be used; in special cases, corrosion-resistant non-metallic materials should be chosen, and cathodic protection should be applied to buried pipelines as well. 　　(5) Strictly enforce the regular inspection system for in-use pressure pipelines in accordance with the law. Regular inspections are the main measures for promptly identifying and eliminating potential accident hazards and ensuring the safe operation of pressure pipelines. At present, regular inspections of industrial pipelines were initiated early on; inspection regulations and standards have become increasingly comprehensive, and the rate of such inspections is constantly rising. Due to reasons such as being buried underground, installed overhead, or passing through rivers and mountains, as well as incomplete inspection regulations and outdated testing methods, the inspection rate for utility pipelines and long-distance pipelines is low, which also creates many potential hazards for accidents. Therefore, future inspections of in-service pressure pipelines should focus on making progress in the areas of buried pipeline inspection, online monitoring, life prediction, safety assessment, remote monitoring, and protection research, in order to make pipeline inspections more scientific and reliable. 　　(6) Establish a regulatory and standardization system for pressure pipelines featuring orderly supervision and scientific management. Promptly issue regulations on the inspection of existing pressure pipelines, so as to gradually bring the safety supervision and management of such pipelines onto a legal and standardized track.