As an essential part of urban gas pipeline maintenance and cleaning, the safe and stable operation of underground valve wells is crucial. Due to its particularity, it is located at various key points in the city, and various pipelines are intricate and complex. Due to its enclosed space, once a leak occurs, it can explode when exposed to open flames.
In January 2020, a gas valve well in a certain city exploded. The cause of the accident was a child throwing firecrackers into the valve well, causing a natural gas leak inside the well. In February of the same year, another explosion occurred in the valve well. The cause of the explosion was that passersby were smoking on the cover of the well, and then discarded the cigarette butt in the valve well to detonate natural gas.
Cause of leakage
Corrosion
Due to the presence of certain pressure in the pipeline network, long-term use in humid environments can be affected by soil acidic corrosion and vibration, which can easily lead to damage to the anti-corrosion layer of the pipeline or valve flange in the valve well, resulting in corrosion perforation and leakage.
Component aging, damage or unqualified quality
The valve well mainly includes components such as flanges, bolts, valves, pipelines, etc. Improper flange operation or aging or damage of flange gaskets; Unqualified or poorly closed valves, as well as damage to valve stems, threads, etc., can all lead to gas leakage.
human factor
Due to the need for welding between the pipe mouth and flange, there may be welding quality defects (such as porosity, slag inclusion, lack of penetration, lack of fusion, cracks, pits, undercuts, weld nodules, etc.) due to human influence.
Current anti-corrosion status of valve wells
According to the National Statistical Analysis Report on Underground Pipeline Accidents, there were as many as 230 gas pipeline leakage accidents in China in 2021, of which about 30% occurred at underground valve wells, and the relatively common problem was corrosion and perforation inside the valve wells.
Therefore, it is particularly important to effectively ensure the anti-corrosion protection of the valve flange inside the valve well. However, currently there are few ways to deal with valve well corrosion, only two types are available: coating and mineral grease tape, and each has certain shortcomings.
As the most widely used anti-corrosion coating currently, coatings are generally prefabricated in factories. However, during on-site installation, due to their thin coating thickness and poor mechanical resistance, mechanical damage may inevitably occur, leading to anti-corrosion failure and relatively short service life. If coatings are used for maintenance in the future, there are also the following problems:
1. The surface grade requirement is St3, especially for valve wells with limited space and many irregular components, which are difficult to achieve during on-site construction.
2. Due to the fact that the components themselves are irregular parts, it is difficult to apply them evenly, and some coatings are thin or not applied, which can easily cause damage and failure.
3. Frequent subsequent maintenance, high overall cost, and also prone to safety accidents.
Petrolatum tape system
Petrolatum tape tape is a non-woven synthetic fiber woven fabric that is fully immersed in neutral polymers based on saturated mineral resin and inert silicon fillers. It has the following drawbacks:
The entire process is quite cumbersome and requires the use of primer for filling and shaping.
2. The Petrolatum tape itself has poor adhesion and is prone to interface detachment after long-term operation.
3. Petrolatum tapemainly relies on internal anti-corrosion agents, which gradually consume over time, leading to corrosion failure.