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Metallurgical Department

OutlineOutline

PrefacePreface

CORROSION ? INDOOR SWIMMING POOL?

Material SpecificationMaterial Specification

Stainless steel has become a popular choice of material in swimming pools; it is an attractive, modern material whilst at the same time being hygienic, easily cleaned, good strength and highly corrosion resistant.

Stainless Steels are iron-base alloys containing at least 10.5% Cr. With increasing chromium content and the presence or absence of some ten to fifteen other elements. Can be applied to the roof, frame, ladder, and gutter.

ApplicationsApplications

CompositionComposition

Stainless steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, and sufficient nickel or manganese to retain an austenitic structure at all temperatures.

Austenite (FCC) is characterized as nonmagnetic, and it is usually relatively low in yield strength with high ductility, rapid work-hardening rates, and excellent toughness. Especially AISI type 304, the most common of the stainless grades.

Form CorrosionForm Corrosion

A damaged film may not easily self-repair including high levels of acidity and high concentrations of chlorides that can occur in swimming pool atmospheres.

AISI 304 stainless steel

Element in 304 stainless steel ceiling hook in internal stresses

Stress Corrosion Cracking Stress Corrosion Cracking (SCC)(SCC) Stress corrosion cracking (SCC)

is a type of localised corrosion characterised by fine cracks which can propagate extremely.

Room temperature SCC of stainless steels can be produced at very low pH and high chloride levels. Image below is a crack in the roof based on inspection.

Stress Corrosion Cracking Stress Corrosion Cracking (SCC)(SCC)

In 1985, the roof of an indoor pool in Switzerland completely collapsed, resulting in 12 deaths. The accident was caused by stress corrosion cracking in AISI 304 stainless steel bars supporting the roof.

Stress Corrosion Cracking Stress Corrosion Cracking (SCC)(SCC)

The mechanisms crack propagation to be possible from chloride content poses the danger of pitting or crevice attack of stainless steels.

SCC of stainless steels can occur at room temperature. This has been a particular problem for indoor swimming pools.

FactorsFactors

These factors increase chlorination and atmospheric moisture, making pool environment much more corrosive for all material.

Cracking caused by the influence of tensile stress and corrosive medium specific.

Causative factors:

•Specific corrosive environments

•Vulnerability of metal alloys

•Tensile stress

PreventionsPreventions

Kind of Better DesignKind of Better Design

When designing with any metal in a pool environment, crevices should be avoided or sealed since they can be sites for accelerated corrosion. Care should also be taken to prevent direct contact between different metal to prevent galvanic corrosion.

Type 316 stainless steel has been used for pool linings

Selection Stainless Steel GradeSelection Stainless Steel Grade

ConclusionsConclusions• Stainless steels remain

good materials to choose for indoor swimming pool. Stress corrosion cracking is a hazard which can be avoided. Appropriate grades of steel must be used, and maintenance and inspection closely controlled.

• Until the mechanism of attack are clarified, use type 304 stainless steel for stressed components exposed to indoor swimming pool cannot be recommended.

ReferencesReferences

Lawrence J. Korb, Rockwell. 1987. ASM Handbook volume 13 of the 9th edition. ASM International Handbook Committee.

Stainless Steel in Swimming Pool Buildings (1995), Nickel Development Institute (NIDI)

http://www.worldstainless.org/NR/rdonlyres/StainlessSteelinIndoorSwimmingPoolsIndustryPositio.pdf

http://resource.npl.co.uk/docs/science_technology/materials/life_management_of_materials/publications/online_guides/pdf/indoor_swimming_pool_buildings.pdf

http://www.imoa.info/_files/stainless_steel/Successful_Stainless_Swimming_Pool_Design.pdf

RevisionRevision

What is material used for the ladder in the indoor swimming pool ?

Answer :

Material used is 304 stainless steel