What About The Cryosphere Valve Leak? Common Glitches And Solutions

Once the a cryogenic ball valve leaks, from production shutdowns maintenance to serious leak accidents may occur. Cryosphere cryogenic ball valves the last line of defense in extreme operating conditions such as LNG reception terminals, air separation units and ethylene plants. If this line fails, the consequences will be far more serious than simply replacing one component. Understanding the root cause of leaks is key to effective treatment.
First, distinguish between internal and external leaks.
Leaks from cryogenic ball valves fall into two main categories-internal and external leaks. Their causes are completely different and their solutions are different.
When the valve is closed, an internal leak occurs, but the medium still seeps out of the sealing surface. The root cause is that the sealing surface deforms at low temperature. When the temperature of the medium drops to a critical point, the material changes phase and volume suddenly, causing the originally highly precision-ground sealing surface to warp, causing the seal to collapse instantly. It's not wear and tear, the material itself has "warped" in the cold.
There are two main problems with external leaks. The first problem is the flange connection-when the valve is connected to the pipe, flanges, gaskets, bolts and fittings contract asynchronously at low temperatures, causing loosening and allowing media to leak through the gap. The second problem is stem packing --aging fillings, loose glands and scratches on the valve stem surface cause cryogenic media to seep out along the gap. The loss of cold air can also cause moisture in the air to freeze on the stuffing, freezing valve stem directly.
How to fix the leak? Take it in three steps and don't disassemble at random. ball valves have a soft sealing structure, so the logic of dealing with cryosphere valves is very mature.
Step 1: Try tightening it. When there is a slight internal leak in a soft seal, the problem can usually be solved temporarily by tightening the seal properly with a wrench. This is the least costly method and applies to emergency situations.
Step 2: the gasket. If leakage persists after tightening, the PTFE gasket are generally considered to be aging or damaged. Replacing it with a new PTFE gasket will solve most internal leak problems in this step. Note that the gasket specifications must match the valve model exactly; even a slight mismatch will not work. Step 3: Replace the seat or even the entire valve. If the leak persists after the the gasket is replaced, the problem lies with the seat-the sealing surface is damaged by impurities or deformed beyond repair due to low temperatures. In this case, simply replacing the gasket is useless, the valve seat must be replaced and, in severe cases, the entire valve must be replaced. Don't skimp on the cost, internal leakage at low temperatures is a safety hazard.
How to fix leaks? Packaging and flanking are two separate battlegrounds. Stem packing leakage is the most common type of external leakage. The core of repair is to replace the packaging and adjust the sealing. First, cut off the media source, close the valve before and after, before running decompression cooling. Loosen cover bolts, remove old packing, clean stuffing box and stem surface. For new packaging, a combination of PTFE and graphite is recommended as it protects against cold temperatures and wear and tear. During installation, each packing ring shall be tightly compressed with a staggered incision of 90 or 180°. Tighten the cover bolts evenly in diagonal sequence. After installation, open and close the valve several times, and if valve stem rotates smoothly without leakage, the repair is complete. Remember not to tighten it at the same time; use a torque wrench to gradually tighten it to the specified value.
The most fundamental solution to flange connection leaks is to replace the flange connection with welded structure, which eliminates the problem of asynchronous material shrinkage of the material at low temperature. If welding is not possible, tighten the bolts evenly, check the gaskets complete, and ensure the bolt material is cold resistant. Common carbon steel bolts are susceptible to brittle fracture below -100°C.
Prevention is more valuable than repair. More than 80% of leaks from cryogenic ball valves are avoidable. Check the sealing of the packing cover regularly and do not wait for a leak to occur. Keep valve unused for a long time to prevent packaging aging and stem rust. When operating, once the valve is fully open, stop tightening and don't push too hard-if the thread is damaged, the valve can only be opened and not closed, which is a real problem.
At cryogenic conditions, a leak is a ticking time bomb. Don't procrastinate. Solving problems early in the day can reduce risk.