(1) DOT Gas Cylinder Bundles
Designed for a pressure of 25 MPa, these units are generally not utilized for stationary ground storage, as DOT lacks the authority to establish standards for such ground-based applications. They are not permitted to feature drain ports. While initial investment costs are low, operational and maintenance expenses are high; specifically, the entire unit must be disassembled every three years to subject each individual cylinder to a hydrostatic pressure test. The required site area exceeds 50 square meters. Characterized by a loose assembly structure, these units lack structural integrity; the presence of numerous individual vessels and connections creates a risk of leakage, while the small diameter of the associated piping results in high flow resistance.
(2) ASME Vessel Units
Designed for a pressure of 27.6 MPa, the wall thickness of these vessels is 39% greater than that of equivalent DOT cylinders, making them typically suitable for stationary ground storage applications. ASME regulations permit the inclusion of drain ports on these vessels. Although initial investment costs are high, operational and maintenance expenses are low; aside from routine visual inspections of the exterior and interior, no further specialized testing is required. The site requirement is a compact 5 to 7 square meters; featuring a robust, integrated structural design, these units are better equipped to withstand impact loads and seismic fluctuations. Furthermore, they involve fewer individual vessels and connections, while the larger diameter of the associated piping results in lower flow resistance.
(3) Underground Gas Storage Wells
Designed for a pressure of 25 MPa, these underground storage wells typically reach a depth of 100 meters. Each well is constructed from a series of 7-inch steel casings-standard components in the petroleum drilling industry-connected end-to-end via flat-tapered threads. Their minimal surface footprint facilitates efficient site layout and planning. Although the initial investment is substantial, data provided by the Sichuan Petroleum Administration indicates that these storage wells have a service life of at least 25 years, offering significant savings on inspection and maintenance costs while demonstrating high levels of safety and reliability. Their primary disadvantages include the inability to fully verify structural strength and leak-tightness through standard pressure testing, which also means that manufacturing defects may not be detected in a timely manner; additionally, the drainage process is often incomplete, creating a susceptibility to stress corrosion within the casing.
