Stainless steels for swimming pool building applications - selection, use and avoidance of stress corrosion cracking (SCC)

Stainless steels for swimming pool building applications - selection, use and avoidance of stress corrosion cracking (SCC)

Stainless steels are widely used for pool ladders, wave machine grilles, handrails and diving board structures as well as in environmental engineering plant. When correctly selected, designed, fabricated and operated, they give generally good performance. However, there have been some instances of corrosion as a result of the particular atmospheric circumstances which can arise in indoor swimming pool buildings.

Grade selection
For the following items:

  • fully immersed or drenched every session - e.g. pool ladders, pool-side rails, some diving board structures;
  • only splashed with pool water but neither safety-critical nor load-bearing - e.g. changing room fittings, lockers etc;
  • in the pool hall atmosphere but neither safety-critical nor load-bearing - e.g. decorative panelling;
  • remote from the influence of the pool hall atmosphere - e.g. café and entrance lobby fittings;
types 304 and 316 are widely used and have given excellent service when properly maintained. Type 316 is strongly preferred for its greater resistance to staining, pitting and crevice corrosion in the majority of pool conditions

 

Components which are in the pool hall atmosphere, which are safety-critical and load-bearing but which are not washed or cleaned frequently, are potentially vulnerable to stress corrosion cracking (SCC). Examples are:

  • brackets for suspended light fittings, loudspeakers, pipework etc;
  • supports for suspended ceilings;
  • supports for ventilation trunking, water slides etc;
  • wire rope supports for water slides etc;
  • fasteners.

Types 304 and 316 have been found to be susceptible to SCC in laboratory tests and in some swimming pool atmospheres, and must not be used for components vulnerable to SCC if failure could result in personal injury. More highly alloyed grades of austenitic stainless steel have a much greater degree of SCC resistance. The currently recommended grades for these applications include:

  • 1.4547 (254SMO)
  • 1.4529 (1925hMo)
  • 1.4565 (Nirosta 4565S)

Alternative high alloy stainless steels are under review.

Highly aggressive conditions can be found in some areas of the ventilation and water treatment plant. Specific advice on material selection should be sought.

Design
The following guidelines should be followed to achieve good performance:

  • choose an appropriate grade, as described above;
  • choose an appropriate surface finish;
  • use smooth, flowing lines which avoid crevices;
  • allow for the lower corrosion resistance of some free machining grades when specifying fasteners;
  • design any safety-critical, load-bearing structure to be fail-safe so that progressive collapse will not follow SCC and there is some built-in indication of failure;
  • use correct welding and post-weld cleaning procedures;
  • allow access for inspection and maintenance.

 

Maintenance and inspection
Good design will minimise the burden of maintenance. All stainless steel items around the pool should be washed down daily. Other stainless items should be cleaned by wiping once a week where practicable. Brown staining of stainless steel items is an indication of either an inadequate cleaning regime or an aggressive pool hall atmosphere. Carbon steel brushes or carbon steel wire wool should never be used on stainless steel. Chemical cleaners must be compatible with stainless steel.

The inspection procedures should be such that the safety can be guaranteed of structures which rely on stainless steel items subject to corrosion. Guidelines are given in the reference.

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