SLC is a metallurgical phenomenon that occasionally develops in cylinders made of 6351 aluminum alloy, as well as in other types of pressure vessels and structural components under stress for sustained periods of time. SLC has occurred in cylinders manufactured by various companies, including Luxfer. Very slowly, as extensive research by Luxfer and outside laboratories has shown.
Cracks typically take six or more years to grow large enough to cause a cylinder leak.
Because SLC growth is so slow, properly trained inspectors have adequate opportunity to detect cracks during the normal requalification process. Any type of cylinder manufactured from 6351 alloy could conceivably develop a sustained-load crack over time if subjected to certain conditions. However, a cylinder is more likely to rupture in applications where pressure is higher and where overfilling and abuse occur more often. Of these ruptures, eight have been scuba cylinders. Four occurred in the United States, and the remainder occurred elsewhere in the world.