During LNG storage‑tank production, the tube sheet of the heat exchanger is subject to water erosion, cavitation and corrosion by trace chemical media. As a result, leakage frequently occurs at tube‑sheet welds, causing mixing of water and chemical materials. Process temperature then becomes difficult to control, which affects other products, seriously impairs product quality and downgrades product grade.
After leakage occurs at condenser tube‑sheet welds, enterprises usually adopt traditional repair welding. Internal stress is easily generated inside the tube sheet and is difficult to remove, which may lead to leakage in other heat exchangers. Enterprises have to conduct pressure tests, inspect equipment condition, and perform repeated repair welding and testing. It takes 2 to 4 personnel several days to complete the repair. After several months of service, tube‑sheet welds suffer corrosion again, wasting manpower, materials and financial resources and increasing production cost.
A cryogenic storage tank is a high‑vacuum condenser. In the operation of liquid‑nitrogen tanks, how can we extend the service life of cryogenic storage tanks? Measures are as follows:
- Before using a liquid‑nitrogen tank, inject a small amount of liquid nitrogen for pre‑cooling. When the internal temperature reaches liquid‑nitrogen temperature, fill liquid nitrogen until the tank is full. Inspect the neck and neck plug groove at any time, and remove ice on the neck plug promptly. No plastic cloth or similar materials shall be placed on the neck plug, so as to improve sealing performance and protect the function of the liquid‑nitrogen tank.
- Cryogenic storage tanks shall be handled with care to avoid collision and extrusion. During movement, do not drag them on the ground; lift them up. Store them in dry and well‑ventilated rooms to prevent moisture.
Even if leakage occurs after use, it can be repaired in time through technical means to avoid long‑term piling‑up welding that affects production. With such refined management, the probability of heat‑exchanger leakage can be greatly reduced. This not only lowers the procurement cost of heat‑exchanger equipment, but also protects product quality, shortens production time and improves product competitiveness.
Ⅱ. How to Extend the Service Life of Cryogenic Storage Tanks?Liquefied natural‑gas storage tanks are pressure vessels. They are indispensable and important basic equipment for industries such as petroleum, chemical, grain & oil, food, fire protection, transportation, metallurgy, installation and maintenance. Anti‑corrosion storage tanks of various sizes are inseparable from economic life, and their important role in national economic development is irreplaceable.
For many enterprises, normal production is impossible without storage tanks. In particular, national strategic material reserves cannot be separated from cryogenic storage tanks of various capacities and types.
As large‑scale storage equipment, proper use of cryogenic storage tanks has an important impact on their service life. Anti‑corrosion treatment is a very important maintenance technology in the use of cryogenic storage tanks. Good anti‑corrosion work plays a positive role in all aspects of cryogenic storage tanks and oil products.
Steel plates of cryogenic storage tanks shall be pre‑treated first, and then coated with shop primer. Paint the inner surface of the floating tank, leaving the final coat to be applied after installation. For anti‑corrosion coating on floating‑pan side walls and accessories, coating application shall meet design requirements. Before welding of the cryogenic storage tank, primer coating on tank bottom plates (weld edges reserved or weldable primer applied) shall meet design requirements. After the pressure test is completed, anti‑corrosion coating shall be applied to other parts to meet design requirements.
Multiple technical specifications are applicable to LNG storage tanks, including specification‑related, structural and process‑related technologies. Two commonly‑adopted technologies are introduced below.
1. Specification‑Related Technology
Numerous specifications are available for LNG storage‑tank inspection, covering product specifications, process specifications, document specifications, document test specifications, document acceptance specifications, component specifications, process quality‑inspection specifications and more. There are roughly more than 20 relevant specifications in China. These documents clarify technical parameters and criteria for product quality, serving as authoritative documents for quality evaluation. In China, such specifications include national standards (GB), industry standards (JB/YB) and enterprise‑internal standards.
2. Structural‑Related Technology
Major loads for LNG storage tanks include internal gas pressure, wind load and seismic load. Wind vibration coefficient shall be taken into consideration for wind‑load calculation. For high‑pressure spherical tanks, the wind‑load shape coefficient is generally 0.30‑0.35. For wet‑type tanks, horizontal seismic effects cover seismic force generated by self‑weight of the water tank and each tower section, as well as hydrodynamic pressure induced by water oscillation inside the water tank. For dry‑type tanks, horizontal seismic effects come from seismic force generated by shell self‑weight and piston components. Snow load calculation shall consider eccentric moment caused by partial snow accumulation on tank top.
LNG storage tanks carry inherent risks and require regular maintenance to improve operating efficiency, extend service life and ensure safe operation. Key safety‑protection points are listed below:
(1) Apply anti‑corrosion coating
Anti‑corrosion coating shall remain intact. Operating media may erode tank material, so painting, spraying, electroplating or lining shall be adopted to prevent medium‑induced corrosion. If anti‑corrosion coating is damaged, process media will directly contact tank shell and trigger corrosion. The coating shall be regularly inspected for peeling, scratches or impact damage during equipment assembly. Check for surface cracks and weld‑joint leakage. Carry out timely repair before re‑operation once coating damage is detected.
(2) Remove chemical‑corrosion triggers
Chemical corrosion on LNG tank base material only occurs under specific conditions. Corrosion‑inducing factors shall be eliminated as far as possible.
For oxygen‑filled LNG tanks, excessive moisture tends to accumulate at tank bottom and creates severe corrosion at the water‑oxygen interface. To avoid such localized corrosion, oxygen shall be dried, or accumulated water inside tanks shall be drained regularly during operation.
Brittle failure of steel pressure vessels mostly arises from abnormal equipment and process conditions, which cause concentration and enrichment of dilute alkali solution. For pressure vessels exposed to dilute alkali media, eliminate conditions that may trigger alkali concentration, such as pipeline leakage, rough tank surfaces or iron‑rust‑containing porous substances.
During pressure‑vessel operation, overflow and dripping shall be eliminated. Overflow not only wastes raw materials and energy and pollutes working environment, but also leads to equipment corrosion and even catastrophic tank failure in severe cases.
Ⅱ. Measures to Avoid Problems During Cryogenic‑Storage‑Tank OperationLNG storage tanks are mainly applied for gas storage. To avoid malfunctions in operation, follow the requirements below:
- Periodically analyze acetylene concentration in liquid oxygen, keep it below 0.1×10⁻⁶; drain liquid oxygen if exceeding the limit.
- Assign operators to monitor pressure for closed storage of liquid oxygen inside LNG tanks to prevent over‑pressure.
- Prevent liquid oxygen from splashing onto unprotected skin to avoid severe injury.
- When the storage tank is fully drained and immediate heating is unavailable, close all valves. Low internal temperature may draw moist air through connected pipelines and result in ice blockage.
- LNG storage tanks adopt internal thermal‑insulation structure design, delivering superior thermal‑insulation performance compared with conventional structures. With self‑developed vacuum‑pumping technology and helium‑mass‑spectrometer leak‑detection, long‑term vacuum performance is guaranteed, and static evaporation rate outperforms industry‑standard requirements.
- Adopt innovative modular piping design for LNG storage tanks: compact layout, centralized control and user‑friendly operation.
- Reliable one‑to‑one lateral supports and lifting lugs are equipped for transportation, enabling safe hoisting and shipment of storage tanks.
Hongruixiangtong LNG cryogenic tanks are widely used in petrochemical, gas stations, metallurgy, food, new‑energy and other industries. They store cryogenic media such as LNG, liquid oxygen and liquid nitrogen. Custom‑built solutions are available.
Yes. We can customize volume, pressure rating, nozzle configuration and piping layout according to site conditions and deliver complete design documentation.
Every tank undergoes pressure test, tightness inspection, weld nondestructive testing and vacuum performance test, complying with pressure‑vessel standards.