stainless steel in swimming pools - constructalia pools... · a large number of public swimming...

Stainless steel inswimming pools

couvPiscinesGB 21/04/08 12:33 Page 2

A large number of public swimming pools builtmany years ago are undergoing refurbishmentor renovation; others are being built wherethere was a lack, particularly in rural areas.At the same time, the use of the pools ismoving away from sport in favour of leisureand we are seeing the advent of increasinglylarge – in terms of size and surface area – and increasingly complex facilities.25-metre or, in the Olympic version, 50-metre rectangular pools are being replacedby aquatic complexes incorporating severalpools of varying size and shape with slides,currents and water jets in addition to thediving boards and ladders.Given the dual need to build or rehabilitate andto upgrade these facilities, the use of stainlesssteel offers a genuine alternative to traditionalpool designs. An innovative design solution,technically proven and financially attractive, as borne out by the thousands of examplesbuilt in Germany and Austria over the last 40 years.When one considers that swimming pools areamong the most costly public facilities in localauthorities’ budgets, it is not difficult tounderstand that it is in their interest to reduceoperating and maintenance costs withoutcompromising safety, hygiene and comfortprovisions.

A solution for refurbishment and newbuilds

stainless steel in swimming pools

PiscinesGB 21/04/08 12:34 Page couv2

/1

Choice of material

Even if it is not the only parameter to beconsidered, the pool water chloride contentis determinant in the choice of grade. For reasons of hygiene, the composition of water in public swimming pools isalways officially regulated. In France, the chloride content is restricted to 250 mg/l. However, given installationoperating practices, it can happen thatthese values are exceeded (high pooltemperature, deviation of chemicalparameters …).

Moreover, depending on its location, the stainless steel component will beexposed to an immediate environment of varying corrosiveness:• parts that are permanently or oftenimmersed in the water (pool, overflowgutter) ;• parts that are not immersed butconstantly or regularly exposed to aerosolor splashing (balustrade, jets…).

Immersed partsIn the rare cases in which one can besure that concentrations of chloride ionswill not exceed 200 ppm, grades withoutmolybdenum can be selected (1.4301,1.4306, 1.4307). However, they should be used with extreme care and only for the production of components withsmooth surfaces, without corners orangles. In all other cases, and providedthat the chloride ion content does notexceed 500 ppm, grades with enhancedanticorrosive properties should be used,such as those containing molybdenum:1.4404, 1.4571, 1.4401. In the case of evenhigher concentrations (particularly inhydrotherapy), the choice of material is performed on a case by case basis.

Non-immersed parts, exposed tosplashes: guardrail, balustrade…Even if these parts are not in directcontact with the water, they are exposedto corrosion. The chloride clusters

present in aerosol or formed as a resultof the evaporation of water dropletscan give rise to localised corrosion.Over some years, aquatic complexeshave seen an increase in theirswimming pool hall temperature andhave been equipped with jets, slides,etc., promoting the development of a more corrosive atmosphere than previously. The use of morecorrosion-resistant grades such as1.4401/1.4404 and 1.4571 is thereforerecommended.

Systematic maintenance of thesecomponents remains essential in order to prevent surfacedeterioration. The use of gradesproviding even higher corrosion-resistance may be recommended on a case by case basis.

Stainless steel in swimming poolapplicationsAn alloy with high corrosionresistance

Stainless steel is a steel alloy, containing a minimum of 10.5%chromium, a maximum of 1.2% carbon, and other elements such as nickel andmolybdenum, as a result of which itprovides excellent corrosion resistance.According to its constituent elementsand their relative percentage contents,the stainless steel will be termed ferritic,austenitic, austeno-ferritic (duplex) ormartensitic.

A material that is entirelycompatible with use inswimming pools

Today, the range of stainless steelscovers all requirements relating toswimming pool applications: pools(including pool edge, overflow gutter,partitions…), ladders, diving boards,starting platforms, but also the waterdistribution system… The gradesemployed are principally austenitic.

For certain applications in harsherenvironments, such as thermal spa, one can employ grades with even higher properties, such as duplex andsuper-austenitics.The characteristics and properties ofstainless steels are detailed in Europeanstandard EN 10088.

A durable material

Stainless steel is a durable materialwhose appearance does not deteriorateand that is simple to maintain.

Stainless steel withstands unscathed the permitted temperature variations for this application. The risk of platescracking (and therefore of leaks) is virtually non-existent. For example,the first stainless pool built in Austria 40 years ago is still operating. The easewith which it is possible to modify andenlarge a stainless steel pool contributesto its longevity.This material provides a very effectivealternative to the traditional solution. It is possible that the capital costs maybe slightly higher, but operating costsare lower. Over the facility’s full lifespan,the return on investment is attractive.

European Standard EN US / ASTM Standard Category Cl– content

1.4301 / 1.4307, 1.4306 304 / 304L Austenitic < 200 ppm1.4401 / 1.4404 316 / 316L NB : 316L for the highest

temperatures

1.4404 / 1.4571 316L / 316Ti Austenitic 200 ppm < Cl–< 500 ppm

Grade to be determined Super-austenitic Cl–> 500 ppmon a case by case basis Super-duplex Hydrotherapyincluding 1.4462 Duplex 2205 Duplex

NB1: The limit values are indicative values. As well as the water’s chloride content, other factors must be taken into consideration: temperature, water physico-chemical parameters, conditions of use…NB2: For chloride contents in excess of 500 ppm, it is recommended that a specialist be consulted.

PiscinesGB 21/04/08 12:34 Page 1

All the components are delivered to the construction site ready forassembly. Prefabricated panels are usually polishedin the case of the vertical wall andembossed (for reasons of safety) in the case of the pool bottom and all partswhere users tread. Their thicknessvaries between 1.5 mm and 5 mm, or even 8 mm according to the staticstrength requirements: generally 2.5 mmfor the wall, 1.5 mm for the bottom and up to 5 mm in respect of staticparts. These factory-prefabricatedpanels are welded on site.

Assembly is performed in six stages:erection and welding of wall units;erection of the supporting elements for the pool’s water equipment andwater attractions; execution of the baselayer; erection of the steel bottom;joining of the various parts by welding;complementary pool equipment(gratings, signage, attractions, etc.).

Pool fittings, such as steps or ladders, are welded in the same way.The water distribution system up to 50 cm outside the pool is also in stainless steel. The pipes areincorporated in a drainage layer beneaththe stainless steel bottom plates.These bottom plates slide beneath thevertical walls and are welded to them.They generally sit on a layer of gravelcovered with crushed materials or aconcrete screed that ensures flatness.None of these materials should containiron or chloride.

Diagram of a newbuild pool wall in stainlesssteel (source HSB)

An efficient construction systemA stainless steel pool comprises five sub-assemblies: the walls; fixtures such as steps and handrails; waterdistribution pipes; the pool bottom; and pool fittingsincluding in particular the overflow gutter grating.


Welding of stainless steel parts,particularly when they are load-bearing, must be performedby accredited professionalcontractors. The contractor is required to furnishall supporting documents inaccordance with standards EN 729-2 and EN 287 Part 1 (welded joint requiring the use offiller metal – preparation of weldbeads – professional performanceof welds).

The welds are usually performedusing the TIG (Tungsten Inert Gas) or MAG (Metal Active Gas)processes for arc welding underinert atmosphere. In order toensure corrosion resistance similarto that of the non-welded surfaces,the welds are generally cleanedusing suitable products, or evenpolished.

Professional welding


2 /3

Resistance to deformation,flexibility

Stainless steel’s elasticity and flexibilitymake it possible to withstand slightshifting of the foundations that is likelyto occur over time and, more particularly,to satisfy safety requirements in seismiczones. If a heavy object – a diving tank,for example – falls or is dropped, there is no risk of it cracking the plate;at worst, it will deform it slightly withoutimpairing the pool’s watertightness.Lastly, the construction system employedmakes it possible to allow for expansionto which the plates may be subject dueto temperature variations.

Reduced weight and footprint

The weight saving achieved with the stainless steel solution comparedwith a conventional structure enablesinstallation on plots regarded asproblematic. This solution also considerably reducesthe installation’s footprint: waterdistribution being performed via the bottom, by way of a network of visible pipes, service tunnels are no longer necessary: all maintenance

Self-supporting stainless steelstructure

The properties of stainless steel providethe pool’s vertical walls with the staticstrength required to withstand activewater and soil pressure for a pool depthof up to 2.20 m. In this case, the pool is self-supporting. In excess of thisdepth (and/or if the ground slope isgreater than 5%), unreinforced concretefoundations are required, which are then clad with stainless steel panels. In all cases, a static strength calculationmust confirm the stability of thestructure.

Perfectly watertight

The use of a single material – stainlesssteel – for the manufacture of the pools makes it possible to join all thecomponents by welding and renders the installations perfectly watertight. As this total watertightness dependsprincipally on the quality of the welds(see box page 2), it is essential that they are performed by accreditedprofessional contractors.

operations can be performed from insidethe pool and only a plant room isrequired.In the case of renovation, due to its lowweight, the construction of a stainlesssteel pool has no repercussion on thefoundations. Furthermore, the thinplates used enable insertion of the poolinside the old structure while onlyreducing by a few centimetres theavailable pool surface. In certain cases,removal of the tiles can even offset the thickness of the plates.

Cross-section of one ofthe pool bottom pipes –diagram of the watersystem

Cross-section of astainless steel pool wall

A high-performance material

stainless steel verticalwall

stainless steel poolbottom

Overflow gutter


A smooth slip-resistantmaterial

All wet surfaces on which users tread must be slip-resistant.Therefore, the bottom and the poolentries – steps, ladders, startingplatforms… – and the impact surfaces situated on the pool walls are produced from embossed plate. The manufacturer is required to furnish a certificate, issued by an independent inspection body,attesting to the surface’s slip-resistantproperty.The welds can be ground and the corners are rounded so as not to incorporate any rough areas with the potential to cause injury.

A hygienic material

Stainless steel is a naturally hygienicmaterial; it is inherently inert with regard to the environment and this property is beneficial in the conditions applicable to use in a swimming pool.Whereas in traditional pools the large number of tile joints and the porosity of the materialsemployed multiply the risks of bacterial growth, the surfaceproperties of stainless steel plates and the method of joining the various parts greatly limit this occurrence.

Ease of management of the water function

Furthermore, the range of stainless steel grades is fully compatible with the various existing water treatmentsystems.

Hygiene and safety for the benefit of usersStainless steel is a material that enables an optimum response to the safety and hygiene requirements applicable to public-access buildings.


Insight

M. Bernhard / Cillit

The role of the water treatmentspecialist consists of supplying the pool with water, extracting it,treating it and resupplying it inaccordance with health requirements.From this point of view, the stainlesssteel solution has many merits andconsiderably reduces the cost of this contract (by 20 to 25%):

• stainless steel is totally compatiblewith existing disinfection systemssubject to choosing the gradeappropriate to the operating range in swimming pool water;

• leakage problems (a majordisadvantage of tiled concrete) are resolved at the outset. Particularly in respect of water inletand outlet/backwash systems, which are complicated to produceand require increasingly rarespecialist know-how on the part ofthe tilers (the walls of the stainlesssteel pool already incorporate allthese features);

• scheduling of the work is lesscomplex: the water treatmentspecialist no longer has to be involvedat the very start of the work on site.Indeed, subject to prior collaborationwith the pool manufacturer, he only has to make connections to the installed system at the end of the project;

• the water system provided is more efficient and the stainlesssteel material is less conducive to bacterial growth.


Lighting and surveillance

The stainless steel pool performs equally as well as the tiled solution as regards lifeguarding requirements.For optical reasons, the plate for the vertical walls is usually 240-grain polished, whereas the bottom plate is roller-flattened. On the bottom, coloured stripes that serve as visual references for swimmers and lifeguards are applied either electromechanically or in the form of a layer of paint.

Fire risk and fire resistance

Like all public access buildings, a swimming pool must comply with fire safety requirements.Generally, when exposed to hightemperatures, stainless steel affords better fire resistance andperformance than carbon steels.Moreover, service tunnels are no longer necessary. The principal fire risk to which the pool was exposed, namely the ignition of electrical cables present in these tunnels, is greatlyreduced or even eliminated.

Stainless steel and watertreatment

Today, European regulations require that the water of publicswimming pools be disinfected and disinfecting. Only threeprocesses for this purpose arestatutorily approved: chlorination,bromination and ozonisation. Today, the bromination process has virtually died out, and while use of the ozonisation process is expanding, it is still chlorinationthat remains the most commonlyused method of treatment. The choice of stainless steel for the pool is possible in all cases.

The majority of chlorides present in the pool water are producedirrespective of the disinfectionmethods selected. Swimming poolwater always tends to alkalise(increase in pH), either simply due to evaporation, or as a result of theuse of bleach as a treatment product.In order to counterbalance thisprocess and retain an appropriatepH range for disinfection, acid additions are required.

This is usually achieved byhydrochloric acid additions into the pool. It is when these additionsare made that chloride ions,potentially detrimental to stainlesssteel, are released.

For reasons of hygiene, the contentof this substance in public swimmingpool water is set by statute andregularly checked by the publichealth authorities. In France, the chloride content is restricted to 250 mg/l. However, given the working of the installations, it can happen that these values areexceeded (high pool temperature,deviation of chemical parameters…).

The choice of an appropriatestainless steel (1.4404 in the pool)and appropriate component andpool design make it possible to limitthe risks of corrosion. The design of the water circulation within the pool, which falls within the remitof the water treatment specialist,also plays a major part.

4 /5


A durable material

Stainless steel is a material that does notage; its appearance does not deteriorate. Its corrosion resistance is based uponthe formation of a self-healing passiveprotective layer on the material’ssurface. Subject to compliance with simple instructions that ensure the conservation of this protective layer, the material offers exceptionalnatural longevity and experience proves that this can be at least 40 years.The observance of simple rules from the project design stage contributesgreatly to its longevity:• the choice of pool and equipmentdesign is critical. It must not under any circumstances promote the creationof deposition or accumulation zones,liable to act as corrosion initiation sites.It is recommended that only closedsections be used, avoiding sharp edgesin favour of rounded corners, and thatjoins/welds be processed accordingly;• it is essential that stainless steel partsexposed to aerosol and water splashesremain easily accessible by techniciansduring maintenance operations.

Regular maintenance

On a day-to-day basis, stainless steelsurfaces are very simple to clean, but it is important that this maintenancebe meticulous and regular. Particularlywith regard to non-immersed parts and those located at the water/airinterface, which may be exposed to a more corrosive environment: as they dry, water splashes from the pool can result in the creation of zones with a high concentration ofchloride ions, often corrosion initiationsites, on the surface of these parts.Daily freshwater rinsing of all theseitems makes it possible to prevent the development of ochre or browndiscolouration.

When localised stains appear on theimmersed metal, they must be removedpromptly. Only products suitable for the maintenance of stainless steelsurfaces should be used (cf. Cleaningand Maintenance of Stainless SteelArchitectural Surfaces, Euro Inox).In particular, the following chlorine-based everyday maintenance productsmust not be used:• cleaning products containinghydrochloric acid;• bleaches.

Annual maintenance

All public swimming pools must beregularly drained and cleaned: at least twice a year in France, once every two years for stainless steelpools in Germany… The cleaning relates to the pools, but also the water distribution pipes; at this time, the walls are inspected, the filters are checked, water inlets and outlets are inspected, etc.This operation must be performed in accordance with the manufacturer’sinstructions, using products that are compatible with stainless steel. In the absence of the possibility of cracking and bacterial growth on the plates and welds, this operation is generally of short duration, thusminimising operational closures.

Simplified winterising of outdoor pools

A stainless steel outdoor pool can be quickly winterised. Apart from pools with a depth of less than 50 cm, which must bedrained and cleaned, it is possible to leave them filled right through the winter without any special measures being necessary.Whereas frost causes damage to tiles, it does not harm stainless steel surfaces. Due to the material’sthermal conductivity, any ice that might form melts on contact with the metal and does not permit the creation of excess pressure likely to damage the pools.

Longevity and reduced maintenanceAs a direct result of the material’s inherent properties,the upkeep and maintenance of a stainless steel pool is simpler and the service life is longer.



6 /7

A pioneer in France

SIM, the intercommunal agency for the communes of Saint Bonnet de Mure and Saint Laurent de Mure,near Lyon, is the first in France to have opted for stainless steel forthe renovation of a 250 m2 pool andthe construction of a 125 m2 pool.

Attracted by the innovative aspect of stainless steel and by forecasts of substantial savings on operatingcosts, SIM confirms, more than a year after the commissioning of the facility, that it has reducedchlorine consumption, as well ascleaning times (which comes down to cleaning of pre-filters and rinsing of the parts above water level). Water consumption has diminished: it is even lower than it was previouslywith a single 250 m2 pool. Gas andelectricity consumption have alsobeen reduced.

The bi-annual cleaning is performedin four days, which makes it possibleto keep the pool open for more thanone extra week per year comparedwith a traditional solution.


By virtue of the construction principleemployed – stainless steel panels joined by welding – it is possible to alter a pool by adding new elements,or even to extend it when the plot is suitable. This makes it possible to modify the facility rapidly in time and space, to adapt it to new needs, withoutnecessarily undertaking a more onerous complete renovation.

Stainless steel is smooth and silky

Stainless steel’s ductility is particularlyadvantageous for projects forunconventionally shaped swimmingpools. The plate can easily be curved and countercurved in tune with the imagination and recreationalswimming facility schemes. The water attractions can be designedfreely in the same material. It is verysmooth or even silky to the touch, which affords it an upmarket aspect that appeals to both project owners and users.

Stainless steel is high-tech

At a time of constantly increasing healthand safety requirements, stainless steelprovides the assurance of exceptionalservice life. Furthermore, the fact that itsappearance does not deteriorate and that the service life of such a pool is estimated to be more than 75 years, reinforces this image of a high-performance technicalmaterial.


Outstanding architectural design freedomNot only does stainless steel have the reputation of being hygienic,it also has the image of a high-tech material, offering great freedom of design, two characteristics that attract both elected representativesand architects.

High-tech and hygienic

The Val-d’Allier urban district councilopted for the stainless steel solutionfor the three pools of its aquaticstadium (architect: Jacques Rougerie;pool manufacturer: HSB): two indoorpools – one being 21 x 25 m and the other, a recreational pool, being500 m2 – and an outdoor Olympic pool. It is the first new facility of this type in France.Hicham Aniss, the urban districtcouncil’s director of sports, justifies this choice not only for aesthetic andarchitectural reasons but also on the basis of technical and financialcriteria. This solution had beenenvisaged at the tender stage.

“Stainless steel offered greaterarchitectural freedom while conveyinga high-tech and hygienic image. The absence of cracking, the material’sability to withstand temperaturedifferences and the absence of joinsall represented future maintenancesavings. Lastly, the construction cost for this project was assessed as being between 5% less than and the same cost as the traditionalsolution.”

PiscinesGB 21/04/08 12:35 Page b8

8 /9

Environmental quality For some years, environmental concernshave been taken into account with regard to facilities’ construction and operation.

A recyclable and recycledmaterial

All of ArcelorMittal’s stainless steels are produced through the electric-arcroute and come entirely from recycledscrap.Stainless steel is a material that is totally recyclable at the end of its life and, in the construction sector, its effective reclamation rate amounts to 90%. Furthermore,ArcelorMittal Stainless Europe’sproduction plants all operate understandard ISO 14001.

A clean construction site

All of the stainless steel components are factory prefabricated for assemblyand welding on site. This dry construction process enablessite nuisance to be reduced: less dust,less waste, less noise, less heavy vehicle traffic, etc.Generally, less concrete is required forthe foundations. For the workforce,factory work is safer and less arduousthan sitework.

Reduced consumption

Water consumption is reduced due to the absence of leaks.Consumption of maintenance products is also reduced and disinfection andrecycling of the water are facilitated.Overall, management of the waterfunction is optimised.

PiscinesGB 21/04/08 12:35 Page b9

Savings on foundations

Compared with traditional construction,the low dead weight of a stainless steelpool offers the advantage of being able to reduce the foundations in the case of a newbuild or of notapplying additional loads to existingfoundations in the case of renovation.Reduced weight and footprint enablecost reduction.

Reduced build time

Very little time is required for the erectionof prefabricated stainless steel pools. Stainless steel as a material enablesswimming pools to be assembled at low temperatures, during the wintermonths. The construction or renovationof a pool can therefore take placebetween two swimming seasons. This is all extra operating time fromwhich to benefit.

Operating savings

Compulsory annual shutdowns areconsiderably curtailed and operationextended accordingly.Purchases of cleaning products anddisinfectants are reduced, as are waterand gas bills.

Total cost of ownership under controlNewbuild or refurbishment : longer service life and reduced maintenance for a comparableconstruction cost.


Cost control

The stainless steel solution is a financiallycompetitive solution and particularly so over the long term. It enables better control of theswimming pool’s construction costs –due in particular to the prefabricationprocess – but also substantial reductions in routine operating costssuch as repairs and maintenance: factors that are assuming increasingimportance for the local authorities and management companies thatoperate pools.


Economy and durability

Longlasting

Stainless steel’s immutable propertiesafford stainless steel pools a significantlylonger service life than that of traditionalfacilities. In Austria and Germany, pools have been operating for almost 40 years without any deterioration intheir appearance and without requiringany major refurbishment.

Adaptable

Stainless steel pools are easier to upgrade and extend – provided that land is available – by welding in new panels or a new section of poolto an existing pool. An operation thatalso contributes to a facility’s lifeexpectancy.

Ecological

Stainless steel is a recyclable andrecycled material. Today, environmentalconsiderations must be taken intoaccount in all new construction projects.During the build, working conditions are easier and more comfortable. Water consumption is reduced,particularly due to the elimination of leak-engendered waste that canoccur in traditional facilities.

A negligible additional outlay for substantial maintenancesavings

According to Thierry Silbert – jointmanaging director of the SPRINTconsultancy, which specialises in assistance to project owners, putting together projects for localauthorities, and for whom publicswimming pools represent threequarters of their business – thestainless steel solution is bound to become established, as it has in Germany and Austria.

He reckons that in France today, the additional construction cost can amount to 2% of overall project costs, which is negligible given the subsequent savings in upkeep and maintenance; moreover, thisadditional cost should come down oreven disappear. There are numerousadvantages: from sitework, which is more easily managed due to the preparatory work in the factory, to upkeep, which now constitutes only a residual cost, without takingaccount of savings in energy andwater consumption.

10 /11



ArcelorMittal’s offerContactSteel Solutions and ServicesBuilding & Construction Support5, rue Luigi-CherubiniF-93212 La Plaine-Saint-Denis, FranceTel.: +33 (0)1 71 92 16 86www.arcelormittal.comwww.constructalia.com

Technical informationStainless EuropeAutomotive & IndustrySwinnenwijerweg 5Genk-Zuid, zone AB-3600 Genk, BelgiumTel.: +32 89 30 19 59 e-mail: inge.houben@arcelormittal.comwww.ugine-alz.comwww.ugine-alz-construction.com

Stainless Tubes Europe1, rue de la PrêleF-55170 Ancerville, FranceTel.: +33 (0)3 29 79 90 25 e-mail: [email protected]

A partner: HSBManufacture and erection of indoor and outdoor stainless steelsports and Olympic pools, recreational,leisure and fitness pools.

HSBHinke Schwimmbad Österreich GmbHDr.-Scheiber-Strasse 284870 VöcklamarktAustriaTel.: + 43 76 82 28 31Fax.: + 43 76 82 28 31-16e-mail: [email protected]

Publications

• Euro InoxStainless Steel for Outdoor SwimmingPoolsCleaning and Maintenance of StainlessSteel Architectural Surfaces

• Stahl Applications for Stainless Steel in theWater industry, Water industry information& guidance note IG N 4-25-02Schwimmbecken aus Edelstahl Rostfrei für die Ausschreibung des Beckens unddie unmittelbaren Zubehörteile

Websites

www.idinox.comwww.euro-inox.orgwww.worldstainless.orgwww.nidi.orgwww.otua.org

For further information


12 /

Photo credits Inside back cover: HSB; p 2: DR; SIM; HSB; p 3-5: HSB; p 6: HSB, Martina Helzel (circa drei, Munich); p 7: DR; p 8: Jacques Rougerie, architect, HSB; p 9: HSB, DR; p 10-inside back cover: HSB.

Publication Building and Construction Support with theassistance of Eve Jouannais for copywriting and editing.Translation Tom Bishop.Graphic design Bärbel Müllbacher.Printing Qatena.


Steel Solutions and ServicesBuilding & Construction Support5, rue Luigi-CherubiniF-93212 La Plaine-Saint-Denis, FranceTel.: 33 (0)1 71 92 16 86www.arcelormittal.comwww.constructalia.com

couvPiscinesGB 21/04/08 12:32 Page 1

stainless steel in swimming pools - constructalia pools... · a large number of public swimming...

Documents