In industrial fields such as petroleum, chemical engineering, and manufacturing, pressure vessels are core pressure-bearing equipment and are widely used in special production conditions involving toxic, flammable, and explosive media, placing extremely high requirements on equipment sealing performance, safety, and stability. Pressure vessels connect to various supporting equipment through inlet flanges. As the core sealing part, the flange end face is highly susceptible to corrosion, wear, scratches, and other damage under the long-term effects of operating conditions, medium erosion, and operation and maintenance factors.
Damage to the flange face not only destroys equipment sealing performance, causing medium leakage and production shutdowns, but in severe cases can also induce safety production accidents, directly affecting product quality and production efficiency. Therefore, the design, manufacturing, and later repair and maintenance of pressure vessel flanges are key aspects of industrial equipment operation and maintenance. This article focuses on analyzing the causes of surface damage to pressure vessel flange joints, the drawbacks of traditional repair processes, and the current application status of online repair processes using polymer materials.
I. Analysis of Surface Damage to Pressure Vessel Flanges
Damage to the sealing surface of pressure vessel flanges is not caused by a single factor. It is mainly divided into five categories: mechanical damage, medium erosion, chemical corrosion, improper installation and maintenance, and processing quality defects. These types of damage often overlap and accelerate sealing surface failure.
1. Mechanical Damage
During opening and closing, operation, and connection of pressure vessels, the flange sealing surface is prone to mechanical damage such as scratches, abrasions, and extrusion deformation. At the same time, under long-term high-temperature and high-pressure operating conditions, the metal atoms of the two mating sealing surfaces may undergo mutual diffusion and adhesion. When vibration and displacement generated during equipment operation cause relative movement of the sealing surfaces, the adhered metal areas are torn, further aggravating sealing surface damage and destroying sealing precision.
2. Medium Scouring and Erosion
High-speed flow of process media causes continuous scouring wear on the flange sealing surface and is the main cause of physical damage. Suspended particles contained in the medium continuously rub against the sealing surface, causing local wear and pit defects. High-speed flowing media directly impacting the sealing surface aggravates surface loss. In addition, mixed flow and local vaporization of the medium generate large numbers of bubbles. The instantaneous collapse of bubbles creates impact pressure that repeatedly strikes the sealing surface, causing cavitation damage. The alternating action of physical scouring and chemical corrosion greatly accelerates the failure rate of the flange sealing surface.
3. Chemical Corrosion by Media
Under operating conditions without an external current, acids, alkalis, and corrosive media inside the pressure vessel directly undergo chemical reactions with the metal of the flange sealing surface, continuously corroding the metal surface layer and causing defects such as oxidation, rust, and pitting on the sealing surface. This leads to reduced flatness of the sealing surface and sealing failure.
4. Improper Installation and Maintenance
Insufficient equipment installation precision, flange misalignment, uneven bolt tightening torque, and inadequate routine inspection and maintenance can cause the flange sealing surface to remain under abnormal stress and in an improper sealing state for extended periods, resulting in faulty operation and premature wear, deformation, and damage of the sealing surface.
5. Defects in Sealing Surface Machining Quality
During factory machining or subsequent repair welding of flanges, improper selection of surfacing welding processes and heat treatment specifications, or non-standard operating procedures can cause primary defects such as cracks, porosity, slag inclusion, and compression deformation on the sealing surface. These defects continue to expand under high-temperature and high-pressure conditions, ultimately causing sealing failure.
II. Traditional Repair Methods for Pressure Vessel Flange Faces and Their Drawbacks
For varying degrees of damage to pressure vessel flange faces, traditional treatment methods in the industry are mainly divided into three types: local grinding repair, disassembly and machining repair, and flange replacement. Each process has significant shortcomings and is difficult to adapt to efficient, low-cost industrial operation and maintenance needs.
1. Minor Damage: Local Surfacing Welding + Manual Grinding Repair
For small-scale, minor damage such as scratches and slight pitting on the flange face, the conventional treatment method is local repair welding followed by manual on-site lapping and grinding for leveling. The advantage of this process is that it requires no disassembly and is easy to operate, but the core drawback is extremely low repair precision. Manual grinding cannot guarantee the flatness and surface finish tolerance standards of the flange end face, and the repaired surface is difficult to meet the requirements of high-pressure sealing conditions, making the equipment prone to leakage again after operation.
2. Severe Damage: Disassembly and Outsourced Machining Repair
When the flange face has a large damaged area, deep pits, and severe deformation, the entire pressure vessel must be disassembled and transported to a machining workshop for precision turning and grinding repair. After completion, it is transported back to the site for reassembly, leveling, and alignment.
The entire process flow is cumbersome, consisting of the following steps in sequence: equipment disassembly → equipment transport → workshop machining repair → transport back to the plant → secondary installation → precise leveling and alignment. For large pressure vessel flanges, the equipment is large in size and heavy in weight, making the entire process of disassembly, transportation, and installation time-consuming and labor-intensive, resulting inlong-term shutdown and production stoppagesignificantly increasing labor, logistics, and schedule costs, and seriously affecting continuous operation of the production line. Therefore, it is generally not recommended.
3. Overall Flange Replacement
The process of directly replacing with a brand-new flange is relatively simple, and the repair efficiency is superior to disassembly and machining repair, making it an emergency option for some enterprises. However, this process has inherent shortcomings: petrochemical pressure vessels mostly operate under flammable, explosive, and high-risk conditions, and open-flame operations are strictly prohibited on site. Flange replacement requires welding and fixation, and a large number of high-risk site conditions cannot meet the requirements for hot work construction, resulting in severely limited application scenarios.
III. Online Repair Process for Flanges Using Polymer Materials (Preferred Solution)
To address the pain points of traditional repair processes, such as low precision, long turnaround time, high cost, and limited working conditions, the online overlap repair process using polymer materials has become a mainstream new technology for repairing pressure vessel flange faces. This process can achieveonline repair without shutdown, without disassembly, and without hot workperfectly adapting to high-risk petrochemical working conditions.
The core repair process is simple and efficient: first, thoroughly grind and level the damaged flange end face, remove surface rust, oil stains, and impurities, and complete the substrate surface cleaning and purification treatment; then, evenly apply the dedicated polymer repair material to the damaged sealing face of the flange, and through material curing and molding, fill pits, scratches, and corrosion defects on the sealing face, ultimately forming a flat, wear-resistant, and corrosion-resistant new sealing layer.
This process requires no hot work welding and no disassembly of large equipment, completely avoiding the problems of traditional processes such as long turnaround time, high cost, insufficient precision, and limited working conditions. It greatly shortens equipment downtime and reduces operation and maintenance costs. At the same time, the repair layer has excellent resistance to medium corrosion, high pressure, and erosion, and can meet the sealing operation requirements of pressure vessels over the long term, making it suitable for flange repair needs under various high-risk working conditions in petroleum, chemical, energy, and other industries.
