Safety issues during sealing under pressure

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In recent years, pressure-sealing technology has been widely applied in thermoelectric systems and the petrochemical industry, and has been well received by users. However, two perspectives on safety issues in pressurized sealing are worth noting: one is that pressurized sealing is unsafe ； Another view is that there’s nothing special about it; anyone can carry out the construction work. These two views are actually based on a lack of understanding of the basic principles and characteristics of pressure-sealing technology. This article discusses the characteristics of safety issues related to sealing under pressure, the fundamentals of safe operations for such sealing, as well as associated risks, and proposes safety measures to ensure that leaks can be resolved smoothly while maintaining construction safety. In the early stages of promoting the pressure-based leak sealing technology in our country, its construction methods were considered to be inconsistent with certain provisions of the \"Regulations on the Safety Supervision of Pressure Vessels,\" and it was suspected of violating those regulations; its safety was called into question, particularly with regard to the safety of the bolts. Tests on the stress conditions of the bolts during on-site pressure-sealing showed that the stress on the bolts increased, but it remained within acceptable limits; thus, the operating condition of the bolts ensured safety. This provides an important scientific basis for the safety of pressure-sealing operations. Of course, this conclusion is conditional. First, the original bolts were not damaged; they were all in good condition ； Second, the injection pressure that the bolt can withstand meets the sealing specific pressure requirement for eliminating leaks through pressurized sealing. Another issue of concern is the impact of pressure sealing performed when there are leaks in the equipment and pipeline walls on the safety performance of the leaking areas. We know that under external pressure, circumferential compressive stresses are generated within the walls of pipes and vessels. When the external pressure increases to a certain level, the walls of these pipes and vessels gradually deform and get crushed; this phenomenon is known as the instability of pipes and vessels. The external pressure that causes instability is called the critical pressure. The allowable external pressure for equipment and pipelines (i.e., the difference between external and internal pressure) must not exceed or approach the critical pressure. Pressurized sealing to eliminate leaks in equipment pipelines is achieved by using injection pressure (external pressure) to generate a sufficient sealing pressure ratio. At this point, does the sealing pressure ratio exceed or approach the critical pressure? Experiments show that the critical pressure is related to the elastic modulus (E) of the equipment pipeline material and the wall thickness to outer diameter ratio. The greater the elastic modulus, the higher the critical pressure. Steel has a higher elastic modulus than aluminum and plastics, so the critical pressure for equipment pipes made of steel is higher than that for those made of aluminum or plastics. For the same outer diameter, the greater the wall thickness, the higher the critical pressure ； For the same wall thickness, the larger the outer diameter, the lower the critical pressure. Theoretical calculations and practical tests have shown that sealing the leak under pressure is a safe approach, as long as the equipment pipes are undamaged and there is no significant thinning of their wall thickness. These two important conclusions undoubtedly form a crucial foundation for ensuring the safety of pressure-sealing construction operations. However, the locations of leaks and the extent of damage involved are quite complex; therefore, we employ different methods and measures depending on the specific circumstances of each leak. (1) Most of the leakage sites meet the requirements for safe construction using pressure-sealing techniques, and the leaks can be eliminated through conventional construction methods. (II) In the case of leakage in flange seals with conical sealing surfaces, corresponding methods must be used for pressure-bearing sealing based on the specific conditions of the flange in question; otherwise, safe pressure-bearing sealing cannot be ensured. (III) If there is thinning and leakage in the walls of the equipment pipes, it is necessary to accurately determine the extent of the thinning so that measures can be taken to ensure the safety of pressure-sealing operations. However, if it is not possible to detect it clearly for some reason, the leak cannot be eliminated using pressure-sealing methods. (IV) Cracks in equipment and pipelines are the most dangerous type of defect, as many blasting accidents originate from such cracks. According to foreign reports, accidents caused by cracks account for 89.4% of all accidents; therefore, leaks resulting from cracks require special attention. There are many complex reasons for the formation of cracks, but they generally continue to spread. Different measures can be taken depending on the situation in order to eliminate them or prevent further expansion. Then, the leak is eliminated using a pressure-sealing method. It should be specifically noted that without crack prevention measures, leakage cannot be eliminated using pressure-sealing methods. The construction procedures for pressure-sealing are key to ensuring safety. Because, even at leakage sites where the safety basics for construction operations are in place, if safety procedures are not strictly followed and safety measures are not implemented, the safety of sealing under pressure cannot be guaranteed. Not to mention other specific leakage points. When performing pressure-sealing operations, it is necessary to ensure not only the safety of the leaking area and the system, but also the safety of the operators themselves. Due to the operator’s direct contact with the leaking medium, they are highly susceptible to various harms caused by it, as well as various accidents resulting from it (including fires and explosions, fatal poisoning incidents, etc.). Therefore, the protection of personnel, as well as the protection and management of the operation site, are of great importance; such protections are implemented in accordance with the relevant regulations regarding ** and work under pressure. Ultimately, the safety of pressure-sealing construction operations depends on the technical competence and management skills of the construction team and workers, as well as on the technical abilities, operational proficiency, and safety awareness of those involved in the work. It is hard to imagine that a construction company that has not received specialized training in pressure-sealing techniques, that only has a superficial understanding of these techniques, or that lacks the resources to train its workers and staff, can carry out safe construction operations, even if it manages to complete a few projects using pressure-sealing methods. Due to their lack of understanding of pressure-sealing technology, they inevitably fall into operational blindness, which is extremely dangerous. Over the more than twenty years that Jiangda Yangsheng Enterprise has been engaged in the development and research of pressure-sealing technology, it has always regarded safety as an essential aspect and component of this technology. It can be said that without safety, there can be no pressure-sealing technology; it is understood that without safety, there is no possibility of project success. We conduct our research with a scientific approach, acknowledging the risks associated with construction operations while also carefully examining the possibilities and feasible methods for eliminating those risks. By drawing on experience and lessons learned from practice, we have developed a set of scientific and effective safety operation techniques as well as measures to ensure construction quality and safety. These are used to train construction workers so as to guarantee quality and safety during pressure-sealing operations, making significant contributions to the safe production of numerous enterprises.