Stress Corrosion Cracking of Chemical Reactor

The Flixborough explosion, UK 1974

The Flixborough explosion was the largest-ever peacetime explosion in the UK. There were 28 fatalities as well as the near complete destruction of the NYPRO plant in North Lincolnshire by blast and then fire. The catastrophic explosion at Flixborough in June 1974 has been traced to the failure of a bypass assembly introduced into a train of six cyclohexane oxidation reactors after one of the reactors was removed owing to the development of a leak. The leaking reactor, like the others, was constructed of 12.3 mm mild steel plate with 3 mm stainless steel bonded to it, and it developed a vertical crack in the mild steel outer layer of the reactor from which cyclohexane leaked leading to the removal of the reactor.

One of the factors contributing to the crack was stress corrosion, resulting from the presence of nitrates that had contaminated river water being used to cool a leaking flange. Mild steel exposed to hot nitrate solution and to stresses which in extreme cases may be well below the yield strength, and may remain in the structure from the fabrication procedure or may derive from operating stresses, especially if intensified by a defect, can develop intergranular cracks. Such stress corrosion cracking results from the conjoint action of stress, of an appropriate magnitude, and a corrosive environment, of specific composition, upon steel having a wide range of compositions or structures. Different types of steel are not equally susceptible to cracking as measured by the minimum stress to promote cracking or the concentration of the salt responsible for the corrosion reactions that cause crack propagation.

Other corrosion accidents: Aloha, Bhopal, Carlsbad, Davis-Besse, Guadalajara, EL AL, Erika, F-16, FAC, Flixborough, Gaylord Chemical, Oil pipeline releases, Pitting of aircraft and helicopters, Prudhoe Bay, Silver bridge, Swimming Pool