A series of accidents has recently been affecting swimming pools all over Europe, with lampposts, air conditioners, ceilings and other suspended objects falling. In one incident in The Netherlands a whole ceiling collapsed into the swimming pool. The cause of these accidents appears to be stress corrosion cracking of stainless steel threaded bars used for attaching air conditioner units and air-channels. The units, weighing hundreds of kilograms, fell on the ceiling, causing it to collapse into the swimming pool. Luckily this happened while the swimming pool was closed. Stress corrosion cracking at 30º C, the temperature in the swimming pool, is in contradiction with general corrosion literature. According to this literature, this phenomenon only occurs at temperatures over 50–60º C. The reason for this accident was a combination of the presence of aerosols with the very strong oxidator sodium-hypochlorite and high internal stress in the fasteners and threaded bars. CorrOcean BV is involved in materials selections and has set up an inspection programme for swimming pools where materials of critical components (wires, cables, fasteners) can be checked. If they are fabricated out of stainless steel A2, A4, 303, 304, 316, immediate replacement will be advised. Materials that can be used in this situation are hot-dipped steel, galvanised steel, coated steel or duplex stainless steel.
