Pre-protection technology for pipeline leaks to prevent leakage accidents (illustrated cases)

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Abstract: Leakage problems occurred at the welds of 32% sodium hydroxide pipelines in a chlor-alkali plant, with severe damage as a result. A forward-looking solution involving the use of polymer composite materials for the pre-protection of undamaged, leaking pipelines was proposed for this issue. This paper introduces the scheme for using such polymer composite materials for the pre-protection of pipeline leaks, and analyzes the importance of pipeline pre-protection techniques for safety management and equipment management in the chemical industry. Keywords: chlor-alkali plant, sodium hydroxide pipeline, leakage, weld protection, corrosion, on-site repair techniques, pre-protection. I. Background on equipment problems Pipelines are special types of equipment commonly used for transporting fluid substances, and they are widely utilized in the chemical and petroleum industries. According to statistics, the investment in the construction of pipelines for chemical plants accounts for over 30% of the total investment in such plants. Pipelines used in the fertilizer, chemical, and petroleum refining industries are primarily used for transporting, separating, mixing, discharging, measuring, and controlling or stopping the flow of fluids. Due to the continuous nature of chemical production, many processes take place under conditions of high temperature, high pressure, low temperature, or vacuum, in addition to normal temperature and pressure. Moreover, many of the working fluids are flammable, explosive, corrosive, or toxic, which poses certain threats to the safe operation of pipelines. Additionally, compared to other industries, petrochemical plants have a large number of pipelines with various sizes and shapes, and these pipelines are highly complex, thereby increasing the likelihood and severity of safety accidents. II. Analysis of equipment issues: In a certain chlor-alkali plant, alkali leakage occurred at the welds and heat-affected zones of some bends in the 32% caustic soda delivery pipelines, posing a significant safety hazard. After analyzing and summarizing the pipeline leakage problems in various industries, the main causes of such problems are as follows: 1) Improper pipeline design. Weld cracks caused by insufficient flexibility, or pipe ruptures resulting from fatigue or support deformation. Defects in the process design result in no space for the pipes to expand due to heat, leading to pipe rupture. 2) Material defects or manufacturing quality defects. During the processing and fabrication of pipes, defects in the pipe material itself, or poor welding quality (such as weld cracks, misalignment, burn-through, incomplete welding, weld beads, undercuts, etc.) can all lead to sand holes in the pipes or within the welds, resulting in leaks. 3) Human damage. Collisions that occur during operation, inadequate maintenance, or pipe leaks resulting from improper operations. The above three points are the main causes of pipeline leakage. While the two issues of unreasonable pipeline design and human-induced damage can be controlled through measures such as improving equipment management, the most difficult to control is defects in the pipeline materials or welds. Therefore, selecting an appropriate strategy to provide pre-protection for the areas of new pipelines where problems are likely to occur (usually the welds) is crucial to preventing leakage in the future. III. Pipeline pre-protection technology and processes: To address this issue, companies have developed welding pre-protection methods for new pipelines, in order to prevent leaks and thus avoid the possibility of safety accidents resulting from such leaks. The Fushi Blue restoration technique was selected, which offers the following advantages: 1) Good corrosion resistance ； 2) It causes minimal damage to the substrate and does not weaken the overall strength of the pipe; applying sandpaper during surface treatment is sufficient to meet the requirements for use. 3) It offers good metal repair capabilities – using this material to repair weak areas of the pipe (such as welds) can enhance the pipe’s strength. The main properties of the materials used were analyzed, along with the repair techniques as follows: Polymer composite materials possess advantages over metal materials in terms of resistance to medium corrosion; through surface treatment and the application of appropriate materials, heat stress can be avoided, thereby extending the service life of the equipment. For the pipes affected by corrosion and leakage, EE-101 anti-corrosion material was first used to repair the leaks, followed by the use of a 901 reinforcement strip combined with 2211F metal repair material for enhanced protection (see Figure 1). EE-101 anti-corrosion material is a substance that provides protection against high temperatures and severe chemical corrosion in immersion environments, and it is primarily used in situations with strong chemicals and high temperatures. It exhibits excellent corrosion resistance to nitrogen, hydrochloric acid, glacial acetic acid, and methanol ； Used in high-temperature, highly corrosive environments where ordinary coatings cannot function ； It can repair and protect various enamel tanks, metal tanks, pipes, and valves, preventing corrosion ； Specifically used for the repair and overall protection of enamel reaction kettles exposed to high temperatures and severe chemical corrosion in soaking environments. It has the following main properties: 1) It can adhere well to various materials such as metals, rubber, concrete, and plastics. 2) It exhibits excellent high-temperature resistance in a fully immersed environment. 3) Resistance to severe chemical corrosion. It can resist corrosion from almost all inorganic strong acids and organic acids, as well as salts, all organic solvents, fuel oil, aviation kerosene, and gasoline. Its main physical properties are as follows: The 2211F metal repair material is a metal repair and protection composite material that is resistant to high temperatures and severe corrosion, and can be machined; it is primarily used to repair various types of worn shafts, bushings, bearing housings, keyways, and threads ； It can also be used for minor scratches on hydraulic arms and track surfaces. By utilizing the material’s resistance to high-temperature corrosion, various enamel tanks, metal tanks, pipes, valves, and other components can be repaired and protected. It has the following main properties: 1) It adheres well to various materials such as metals, rubber, concrete, and plastics. 2) It possesses excellent resistance to high temperatures and corrosion. It can resist corrosion from most inorganic acids, organic acids, and the like. 3) It possesses good machinability and wear resistance. Its physical properties are shown in the table below: IV. Experimental Procedure for the Proposed Solution The experimental steps involved manufacturing test pieces to simulate the actual operating conditions of pipelines, including temperature, pressure, and the type of fluid used, as well as scenarios involving sand holes, thereby verifying the feasibility of this solution. The main experimental steps are as follows: 1) Manufacturing test pieces. The test piece was fabricated by welding a DN50 elbow, straight pipe, and flange together; the material used was 304 with a thickness of 4 mm. One Φ4 through-hole was drilled in each of the elbow and the elbow weld ； 2) Repair the 2 through-holes using the Fushilan repair process ； 3) The repaired specimen was subjected to a hydrostatic test at 1.75 MPa, with the pressure maintained for 20 minutes; no leakage was observed ； 4) The specimen is placed in 32% sodium hydroxide solution for corrosion resistance testing. After 10 days of testing, no defects such as corrosion or cracks were observed ； 5) The specimen was subjected to another hydrostatic test at 1.65 MPa, with the pressure maintained for 20 minutes; no leakage was observed ； 6) Cut the specimen open for macroscopic inspection. No obvious signs of corrosion were observed on the inner wall and the repair layer ； The repair layer is hard in texture, with a thickness of about 4 mm, and adheres well to the substrate. Experimental images and test conclusions: Based on the above experiments, the following conclusions can be drawn: 1) The test specimen exhibits good pressure resistance, capable of meeting the pipeline’s requirement of a pressure tolerance of 1.2 MPa. 2) The test specimen exhibits good corrosion resistance, and it can meet the corrosion resistance requirements of 32% caustic soda at room temperature. 3) This repair technology can be used to fix leaks in 32% caustic soda pipelines of the company. It has been proven that pipes repaired using the Fushilan pipeline pre-protection technology possess excellent corrosion resistance, compressive strength, safety in operation, and simple processing procedures; therefore, this approach is highly feasible. V. On-site construction process 1) Surface treatment: Use wire wheels to grind the weld areas that need to be protected ； 2) Immediately clean and wash the polished surface with acetone or 99.7% anhydrous ethanol; the surface after treatment should be clean, dry, firm, and rough ； 3) Mix an appropriate amount of EE-101 material in proportion to achieve a uniform color without any differences ； 4) Apply the material evenly to the area to be protected. 5) After the EE-101 material has cured, the elbow weld area is reinforced and protected as a whole using a 901 reinforcement strip combined with 2211F metal repair material (see Figure 2) ； 6) Repair completed; wait for the material to cure. Construction image information: Compared to various chemical processing equipment, pipes have a relatively low added value. Although they do not receive as much attention, the damage incidents caused by pipe leaks cannot be ignored. In particular, safety accidents caused by pipeline leaks. As **safety and environmental management requirements continue to evolve, along with increasingly strict new policies and regulations, a development model based on high energy consumption, high pollution, and high risks will become unsustainable. Effectively assessing and controlling potential risks in the early stages when equipment begins to show problems is the current trend in the management of industrial equipment. For a long time, how chemical enterprises can address pipeline leaks quickly and effectively has been a top priority for those responsible for equipment safety. We believe that repeated plugging of leaking pipelines while they are still in use is an outdated maintenance method; it leads to serious problems such as increased energy consumption, reduced equipment efficiency, frequent safety accidents, and severe pollution emissions. Therefore, pipes that are prone to leakage issues, as well as those used for transporting hazardous materials, should be given preventive protection measures; this can effectively prevent a range of problems resulting from pipe leakage. Moreover, the cost of such preventive measures is far lower than the cost of shutting down operations to replace the pipes in case of leakage, or of attempting to seal the leaks while the pipes are still in use. It not only ensures the proper, safe, and efficient operation of the company’s equipment, but also realizes the corporate management philosophy of low energy consumption, low emissions, and low costs in the chemical industry.