STAINLESS STEELS - APPLICATIONS, GRADES AND HUMAN EXPOSURE

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STAINLESS STEELS - APPLICATIONS, GRADES AND HUMAN EXPOSURE

Tony Newson

AvestaPolarit Oyj Abp

October 2001

New edition, February 2002

Updated 8/2/2002

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Stainless Steels – Applications, Grades and Human Exposure

IntroductionThe following information has been prepared by Tony Newson (Avesta Polarit, UK), on behalf of the Eurofer Stainless Steel Producers Group. It is provided at the request of the Danish EPA to assist their work on the Risk Assessment of metallic nickel, nickel sulphate, nickel chloride, nickel dinitrate and nickel carbonate.

This information is presented in broad categories of use (eg transport, consumer goods, etc), which each provide details of applications, the stainless steel grades used for those applications and an assessment of human exposure encountered in each specific application. Each individual broad category is introduced by general background information designed to provide an overview of the use of stainless steels in that particular sector.

The Stainless Steel FamilyStainless steel is the term used to describe an extremely versatile family of engineering materials, which are selected primarily for their corrosion and heat resistant properties.

All stainless steels contain principally iron and a minimum of 10.5% chromium. At this level, chromium reacts with oxygen and moisture in the environment to form a protective, adherent and coherent, oxide film that envelops the entire surface of the material. This oxide film (known as the passive or boundary layer) is very thin (2-3 namometres). [1nanometre = 10-9 m].

The passive layer on stainless steels exhibits a truly remarkable property: when damaged (e.g. abraded), it self-repairs as chromium in the steel reacts rapidly with oxygen and moisture in the environment to reform the oxide layer.

Increasing the chromium content beyond the minimum of 10.5% confers still greater corrosion resistance. Corrosion resistance may be further improved, and a wide range of properties provided, by the addition of 8% or more nickel. The addition of molybdenum further increases corrosion resistance (in particular, resistance to pitting corrosion), while nitrogen increases mechanical strength and enhances resistance to pitting.

Categories of Stainless SteelsThe stainless steel family tree has several branches, which may be differentiated in a variety of ways e.g. in terms of their areas of application, by the alloying elements used in their production, or, perhaps the most accurate way, by the metallurgical phases present in their microscopic structures:

- Ferritic- Martensitic (including precipitation hardening steels)- Austenitic- Duplex steels, consisting of mixture of ferrite and austenite

Within each of these groups, there are several “grades” of stainless steel defined according to their compositional ranges. These compositional ranges are defined in European (and other e.g. USA) standards, and within the specified range, the stainless steel grade will exhibit all of the desired properties (e.g. corrosion resistance and/or heat resistance and/or machineability). More detail on standards and grades is given below.

Ferritic stainless steels (e.g. grades 1.4512 and 1.4016) consist of chromium (typically 12.5% or 17%) and iron. Ferritic stainless steels are essentially nickel-free. These materials contain very little carbon and are non-heat treatable, but exhibit superior corrosion resistance to martensitic stainless steels and possess good resistance to oxidation. They are ferromagnetic and, although subject to an impact transition (i.e. become brittle) at low temperatures, possess adequate formability. Their thermal expansion and other thermal properties are similar to conventional steels. Ferritic stainless steels are readily welded in thin sections, but suffer grain growth with consequential loss of properties when welded in thicker sections.

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Martensitic stainless steels (e.g. grades 1.4006, 1.4028 and 1.4112) consist of carbon (0.2-1.0%), chromium (10.5-18%) and iron. These materials may be heat treated, in a similar manner to conventional steels, to provide a range of mechanical properties, but offer higher hardenability and have different heat treatment temperatures. Their corrosion resistance may be described as moderate (i.e. their corrosion performance is poorer than other stainless steels of the same chromium and alloy content). They are ferromagnetic, subject to an impact transition at low temperatures and possess poor formability. Their thermal expansion and other thermal properties are similar to conventional steels. They may be welded with caution, but cracking can be a feature when matching filler metals are used.

Austenitic stainless steels (e.g. grades 1.4301 and 1.4833) consist of chromium (16-26%), nickel (6-12%) and iron. Other alloying elements (e.g. molybdenum) may be added or modified according to the desired properties to produce derivative grades that are defined in the standards (e.g. 1.4404). The austenitic group contains more grades, that are used in greater quantities, than any other category of stainless steel. Austenitic stainless steels exhibit superior corrosion resistance to both ferritic and martensitic stainless steels. Corrosion performance may be varied to suit a wide range of service environments by careful alloy adjustment e.g. by varying the carbon or molybdenum content. These materials cannot be hardened by heat treatment and are strengthened by work-hardening. Unlike ferritic and martensitic stainless steels, austenitic grades do not exhibit a yield point. They offer excellent formability and their response to deformation can be controlled by chemical composition. They are not subject to an impact transition at low temperatures and possess high toughness to cryogenic temperatures. They exhibit greater thermal expansion and heat capacity, with lower thermal conductivity than other stainless or conventional steels. They are generally readily welded, but care is required in the selection of consumables and practices for more highly alloyed grades. Austenitic stainless steels are often described as non-magnetic, but may become slightly magnetic when machined or worked.

Duplex stainless steels (e.g. grade S31803) consist of chromium (18-26%) nickel (4-7%), molybdenum (0-4%), copper and iron. These stainless steels have a microstructure consisting of austenite and ferrite, which provides a combination of the corrosion resistance of austenitic stainless steels with greater strength. Duplex stainless steels are weldable, but care must be exercised to maintain the correct balance of austenite and ferrite. They are ferromagnetic and subject to an impact transition at low temperatures. Their thermal expansion lies between that of austenitic and ferritic stainless steels, while other thermal properties are similar to plain carbon steels. Formability is reasonable, but higher forces than those used for austenitic stainless steels are required.

Effect of Alloying on Structure and Properties

ChromiumChromium is by far the most important alloying element in stainless steel production. A minimum of 10.5% chromium is required for the formation of a protective layer of chromium oxide on the steel surface. The strength of this protective (passive) layer increases with increasing chromium content. Chromium prompts the formation of ferrite within the alloy structure and is described as ferrite stabiliser.

NickelNickel improves general corrosion resistance and prompts the formation of austenite (i.e. it is an austenite stabiliser). Stainless steels with 8-9% nickel have a fully austenitic structure and exhibit superior welding and working characteristics to ferritic stainless steels. Increasing nickel content beyond 8-9% further improves both corrosion resistance (especially in acid environments) and workability.

Molybdenum (and tungsten)Molybdenum increases resistance to both local (pitting, crevice corrosion, etc) and general corrosion. Molybdenum and tungsten are ferrite stabilisers which, when used in austenitic alloys, must be balanced with austenite stabilisers in order to maintain the austenitic structure. Molybdenum is added to martensitic stainless steels to improve high temperature strength.

NitrogenNitrogen increases strength and enhances resistance to localised corrosion. It is austenite former.

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CopperCopper increases general corrosion resistance to acids and reduces the rate of work-hardening (e.g. it is used in cold-headed products such as nails and screws). It is an austenite stabiliser.

CarbonCarbon enhances strength (especially, in hardenable martensitic stainless steels), but may have an adverse affect on corrosion resistance by the formation of chromium carbides. It is an austenite stabiliser.

Titanium (and niobium & zirconium)Where it is not desirable or, indeed, not possible to control carbon at a low level, titanium or niobium may be used to stabilise stainless steel against intergranular corrosion. As titanium (niobium and zirconium) have greater affinity for carbon than chromium, titanium (niobium and zirconium) carbides are formed in preference to chromium carbide and thus localised depletion of chromium is prevented. These elements are ferrite stabilisers.

SulphurSulphur is added to improve the machinability of stainless steels. As a consequence, sulphur-bearing stainless steels exhibit reduced corrosion resistance.

CeriumCerium, a rare earth metal, improves the strength and adhesion of the oxide film at high temperatures.

ManganeseManganese is an austenite former, which increases the solubility of nitrogen in the steel and may be used to replace nickel in nitrogen-bearing grades.

SiliconSilicon improves resistance to oxidation and is also used in special stainless steels exposed to highly concentrated sulphuric and nitric acids. Silicon is a ferrite stabiliser.

Stainless Steel Grade Designations

With the exception of the tables of applications for medical devices, stainless steels are primarily described by designations given in EN 10088 – Stainless Steels (for general purposes). These designations follow the Werkstoff numbering system for steels originally developed in German (e.g. 1.4301). The Werkstoff numbering system has also been used as the basis for other European Standards for steels (e.g. high temperature stainless steels). For simplicity, these additional standards have not been referenced in this text. However, their Werkstoff grade designations have been used to describe high temperature stainless steels and they are may be identified by the designation 1.48XX (e.g. 1.4818) to indicate high temperature applications. Common US designations are also given (e.g. AISI 303, ASTM S41050) to further aid recognition of the stainless steel alloys named for particular applications.

Medical (non-implant) devices are also described in terms of both EN 10088 and US designations, but in addition reference is made to specific standards applicable to medical devices (e.g. ISO 7153-1). Medical implants have specific material specifications (e.g. ISO 5832-1 and ISO 5832-9), which do not have an equivalent EN 10088 grade.

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Applications - Transport

AerospaceMaterials for aerospace applications are required to maintain the integrity of the structure (i.e. to be sufficiently robust to withstand their service environment) and to be inert (ie corrosion resistant). Stainless steels are used in aerospace applications because they are resistant to corrosion and high temperature oxidation and maintain their mechanical properties over a wide temperature range.

In aerospace applications, materials for each application are selected on the basis of their resistance to corrosion or high temperature oxidation and mechanical properties in a specific service environment. The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for aerospace applications. For applications where corrosion resistance is of primary importance, austenitic stainless steel grade 1.4301 (AISI 304) and its derivatives are suitable for mild environments with less than 200 ppm chloride (eg cabin components, internal fuel tanks, etc). Grade 1.4401 and its derivatives are suited to service environments where chloride is present in the atmosphere. Grades 1.4301 (AISI 304), 1.4401 (AISI 316) and their respective derivatives exhibit moderate oxidation resistance and are suitable for temperatures up to 870C. For applications where oxidation resistance is the primary feature, grades 1.4818 (ASTM S30415), 1.4835 (ASTM S30815), 1.4833 (AISI 309) and 1.4845 (AISI 310) may be used. These grades are suitable for temperatures up to 1150C.

Typical applications for stainless steels in aerospace applications are shown in the table below.

Aerospace Applications – Applications, Grades and Human Exposure

Application/Use Stainless Steel Human Exposure -Dermal ContactType EN 10088 Grade

Fuel tanks Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)

Transient exposure to producers, installers and users.

Exhaust components, high temperature engine and structural parts

Austenitic 1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4818 (ASTM S30415)[153 MA]1.4835 (ASTM S30815)[253 MA]1.4833 (AISI 309)1.4845 (AISI 310)

Transient exposure to producers, installers and users.

Other structural components (ambient temperature)

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)

Transient exposure to producers and installers. Limited transient to user.

Transport – Motor VehiclesMaterials for motor vehicle applications are required to maintain the integrity of the structure (i.e. to be sufficiently robust to withstand their service environment) and to be inert (i.e. corrosion resistant). Stainless steels are used in motor vehicle applications because they are resistant to corrosion and high temperature oxidation, offer energy absorption properties and maintain their mechanical properties over a wide temperature range.

The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for motor vehicle applications. For applications where corrosion resistance is of primary importance, austenitic stainless steel grade 1.4301 (AISI 304) and its derivatives are suitable for mild environments (e.g. interior components, fuel tanks, etc). Grade 1.4401 (AISI 316) and its derivatives

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are suited to applications where chloride is present in the service environments. For temperatures up to 870 C, grades 1.4301 (AISI 304), 1.4401 (AISI 316), 1.4512 (AISI 409) and their respective derivatives may be used for application requiring moderate oxidation resistance. For example, 1.4512 (AISI 409) is often used in exhaust systems for high volume production cars, while 1.4301 (AISI 304) and its derivatives are used in the exhaust systems for low volume luxury cars. Catalytic converters also use stainless steels for both internal and external components.

Typical applications for stainless steels in motor vehicle applications are shown in the table below.

Motor Vehicle Applications – Applications, Grades and Human Exposure

Application/Use Stainless Steel Human Exposure –Dermal ContactType EN 10088 Grade

Fuel tanks Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)

Transient exposure to producers and installers. No contact for users.

Exhaust systems Ferritic

Austenitic

1.4512 (AISI 409)1.45091.4301 (AISI 304)1.4307 (AISI 304L)


Hose clips Ferritic 1.4016 (AISI 430) Transient exposure to producers and installers. No contact for users.

Housings for catalytic converters and turbochargers

Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4818 (ASTM S30415)[153 MA]


Internal components for catalytic converters

Austenitic

Ferritic

1.4818 (ASTM S30415)[153 MA]1.4835 (ASTM S30815)[253 MA]1.4833 (AISI 309)1.4845 (AISI 310) - (AISI 442)1.4762 (AISI 446)

Transient exposure to producers. No contact for installers and users.

Internal components for turbochargers (eg rotors)

Austenitic 1.4835 (ASTM S30815)[253 MA]1.4845 (AISI 310)

Transient exposure to producers. No contact for installers and users.

Chassis for buses and trucks, structural components

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4003 (ASTM S41050)[3Cr12]

Transient exposure to producers. No contact for users.

Handrails, luggage racks, etc

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)1.4016 (AISI 430)

Frequent transient exposure to producers. Transient for users.

Internal and external trim (eg bumpers, door scuff plates, headlight bezels, etc)

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)1.4113 (AISI 434)1.4526 (AISI 436)

Transient exposure to producers and installers. Limited transient to user.

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RailwayMaterials for railway applications are required to maintain the integrity of the structure (i.e. to be sufficiently robust withstand their service environment) and to be inert (ie corrosion resistance). Stainless steels are used in railway applications because they are resistant to corrosion, easily fabricated and offer good mechanical properties.

The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for railway applications. Austenitic stainless steel grades 1.4301 (AISI 304) and 1.4310 (AISI 301) are suitable for mild service environments and have been used in the construction of railway carriages, while ferritic stainless steel 1.4003 (ASTM S41050) has been used for freight wagons. Stainless steel is selected for both applications because it does not need protective paint coatings and thus maintenance costs are reduced.

Stainless steel is also used extensively in railway buildings and construction applications. In particular, the fire resistant properties of stainless steel have been utilised in underground railway stations (e.g. wall cladding and tunnel linings). See architectural applications for further details.

Typical applications for stainless steels in railway applications are shown in the table below.

Railway Applications – Applications, Grades and Human Exposure


Carriage door skins, skins for carriages and locomotives

Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4310 (AISI 301)


Carriage chassis and structural components

Austenitic 1.4003 (ASTM S41050)[3Cr12]1.4301 (AISI 304)1.4307 (AISI 304L)

Frequent transient to producers. No contact for users.

Freight wagon chassis and structural components

Austenitic 1.4003 (ASTM S41050)[3Cr12] Frequent transient exposure to producers. Transient for users.

Railway exhaust systems

FerriticAustenitic

1.4512 (AISI 409)1.45091.4301 (AISI 304)1.4307 (AISI 304L)

Transient for producers, installers and users.

Carriage trim eg beading for windows, door handles, handrails, luggage racks, etc

Austenitic

Ferritic



Under-train components eg tubes for compressed air and water systems, battery boxes, etc

Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)

Frequent transient to producers. No contact for users.

MarineMaterials for marine applications are selected to maintain the integrity of the structure (i.e. to be sufficiently robust withstand their service environment) and to be corrosion resistant. Stainless steels are used in marine applications because they are resistant to corrosion, easily fabricated and offer good mechanical properties.

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The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for marine applications. Austenitic stainless steel grades 1.4401 (AISI 316) and its derivatives are suitable for coastal service environments, splash zone applications and intermittent submersion in seawater. Although 1.4401 and its derivatives were once known as “marine grade” stainless steel, they are no longer recommended for permanent contact with seawater. Superaustenitic stainless steels containing 6% molybdenum are now recommended for permanent immersion in seawater. Duplex stainless steels (e.g. 1.4462/ASTM S31803) may be used in brackish waters (eg estuaries where the chloride content of the water is less than that of the open sea). Superduplex stainless steels (e.g. 1.4410/ASTM S32750) may also be used in direct and prolonged contact with seawater (e.g. in offshore oil platforms).

Typical applications for stainless steels in marine applications are shown in the table below.

Marine Applications – Applications, Grades and Human Exposure


Coastal (land-based) handrails, housings for equipment, ladders, lamp posts, etc

Austenitic 1.4401 (AISI 316)1.4404 (AISI 316L)

Transient exposure to producers and installers. Transient for users.

Deck components for boats and ships eg deck eyes, brackets for anchor ropes, housings for equipment, shackles, handrails, etc

Austenitic

Precipitation Hardness

1.4401 (AISI 316)1.4404 (AISI 316L)1.4542 (17/4 PH)

Transient exposure to producers and installers. Transient for users.

Boat propeller shafts Austenitic 1.3964 (Nitronic 50) Transient exposure to producers and installers. Limited transient for users.

Submerged items -pipelines and grills for oil, sewage and water, risers for oil platforms, grills, heat exchangers for ships and coastal power plants, equipment attached to hulls of boats and ships

Austeniticwith 6% Mo

1.4547 (ASTM S31254)[254 SMO]1.4529

Transient exposure to producers and installers. Limited transient for users.

Prolonged contact items – pumps, winches, holding and storage vessels

Austeniticwith 6% Mo

1.4547 (ASTM S31254)[254 SMO]1.4529

Transient exposure to producers and installers. Limited transient for users.

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Applications – Commercial and Consumer

Consumer productsMaterials for consumer products are selected for their corrosion resistance, for their aesthetic appearance, ease of cleaning and mechanical strength. Stainless steels are used in white goods because they are resistant to corrosion, easily fabricated, offer good mechanical properties over a wide range of temperatures and are able to accept a range of pleasing finishes.

The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for consumer products. Austenitic stainless steel grade 1.4305 (AISI 303) exhibits free-machining properties and, traditionally, has been used for ear studs. As EU legislation governing nickel release from products no longer permits the use of this material for such applications, alternative stainless steel grades, containing normal levels of sulphur, are available for applications not involving epithelization (eg 14301/AISI 304, 1.4401/AISI 316 and their derivatives). The free-machining properties of these stainless steel grades can be enhanced by the addition of other chemical elements (eg calcium). Until recently, 1.4401 (AISI 316) and 1.4404 (AISI 316L) have been used for jewellery involved in body piercing. However, because they contain >0.05% of nickel, EU legislation now prohibits their use for applications involving epithelization.

Stainless steels 1.4016 (AISI 430), 1.4301 (AISI 304), 1.4401 (AISI 316) and their derivatives are widely used in cabinets for, and internal components of, white goods (eg washing machines, refrigerators, etc).

Typical applications for stainless steels in consumer products are shown in the table below.

Consumer Products – Applications, Grades and Human Exposure


Belt buckles, bottle openers, candle holders, hip flasks, key ring fobs, money clips, torch bodies, casings for pens and pencils


Transient exposure to producers. Transient for users.

Jewellery eg earrings, ear studs, pendants, etc

Austenitic [1.4305 (AISI 303)]*1.4301 (AISI 304)1.4307 (AISI 304L) 1.4401 (AISI 316) 1.4404 (AISI 316L)

Transient exposure to producers. Prolonged and close contact for user.

Jewellery for body piercing

Austenitic 1.4401 (AISI 316) 1.4404 (AISI 316L)


Watch casings and straps

Austenitic [1.4305 (AISI 303)]*1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)


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Watch backs Austenitic

Ferritic

[1.4305 (AISI 303)]*1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)1.4016 (AISI 430)


Watch buckles Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)


Watch straps Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4372 (AISI 201)


Washing machine drums, casings andpanels for cookers, microwave ovens, refrigerators, freezers, toasters, washing machines and dish washers

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)1.4510

Transient exposure to producers and user.

Refrigerator and freezer components



Hot water tanks Austenitic

Ferritic

1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.45201.4521

Limited transient for user and transient contact for producer and installer.

Kitchen cabinets and worktops, sinks and drainers

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)1.4510


*- Not permitted for this use in EU countries.- Not permitted for use during epithelization in EU countries

LeisureMaterials for leisure products are selected for their corrosion resistance, for their aesthetic appearance, ease of cleaning and mechanical strength. Stainless steels are used in leisure goods because they are resistant to corrosion, easily fabricated, offer good mechanical properties over a wide range of temperatures and are able to accept a range of pleasing finishes.

For stainless steels used in sailing equipment see marine applications and for fishing/hunting knives see beverage, dairy and food applications (professional knives).

Typical applications for stainless steels in leisure products are shown in the table below.

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Leisure Products – Applications, Grades and Human Exposure


Golf clubs (heads of) Precipitation Hardening

1.4542 (17/4 PH) Frequent transient exposure to producers. Transient for users.

Golf shoes (plate for attaching studs)


Transient exposure to producers. No contact for user.

Model railway lines Ferritic 1.4016 (AISI 430) Transient exposure to producers and user.

Swimming pool filter grills, pipelines, watertreatment and filter units,


Transient exposure to producers and pool maintenance staff. No contact for users.

Swimming pool handrails, ladders and steps, pool liners


Transient exposure to producers and users.

Swimming pool ceiling tile and flume support brackets/fasteners

Austenitic 1.4539 (ASTM N08904)1.4438 (AISI 317L)

Transient exposure to producers and pool maintenance staff. No contact for users.

Computer discs (sliding gates for)


Transient exposure to producers and users.

Beverage/Dairy and Food Preparation, Processing and StorageThe Council of Europe has published “Guidelines on metals and alloys in contact with food”. The final draft version was submitted by the Danish delegation on 11.10.2000. Information from this document has been used to compile this section on the applications of stainless steel in the Beverage, Dairy and Food Industries.

Materials for beverage, dairy and food preparation, processing and storage are required to maintain the integrity of the structure (i.e. to be corrosion resistant and sufficiently robust to withstand their service environment) and to be inert (i.e. to impart neither colour nor flavour to foodstuffs or beverages). Stainless steels are widely used in these applications because they are resistant to corrosion, inert, easily cleaned and sterilised without loss of properties, and can be readily fabricated by a variety of techniques.

Materials for beverage, dairy and food preparation, processing and storage are selected on the basis of their resistance to corrosion in a specific service environment and, where appropriate, operation of the plant (whether continuous or batch operation with plant shutdowns) must also be considered. In practice, the majority of applications where stainless steel is used in contact with food, austenitic grades with 18% chromium provide an optimum balance of corrosion resistance (to a wide range of foodstuffs), cost and ease of fabrication. Nevertheless, ferritic, martensitic and duplex stainless steels are also used in beverage, dairy and food contact applications.

The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for beverage, dairy and food contact applications. Martensitic stainless steels may hardened by heat treatment and are suitable for moderately corrosive environments. For example, 1.4021 (AISI 420) is used for medium priced cutlery, while 1.4122 with a higher carbon and molybdenum is used for high quality cutlery. Martensitic stainless steel 1.4116 with high carbon,

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molybdenum and vanadium is used for cooks’ knives and professional knives. Ferritic stainless steels offer good corrosion resistance, are not hardenable by heat treatment and have limited formability. Grade 1.4016 (AISI 430) may be used in such applications as low price cutlery, hollow-ware, work surfaces and cabinets. The austenitic stainless steels offer good to excellent corrosion resistance, and are easily welded and fabricated. Grade 1.4031 (AISI 304) and its derivatives are used in mild environments (with chloride content less than 200 mg/l) for both domestic and professional cutlery, hollow-ware and kitchen utensils. Grade 1.4401 (AISI 316) and its derivatives are used in food processing, storage and transport equipment (e.g. pipe work) and are suitable for more aggressive service environments (with chloride contents up to 500 mg/l). At higher chloride contents and especially if combined with increased operating temperatures, the duplex stainless steels grades 1.4462 (ASTM S31803) and 1.4362 (ASTM S32304) are used for their resistance to stress-corrosion-cracking. For more aggressive service environments (e.g. steam heating systems and boilers), the superaustenitic (e.g. 1.4547) and superduplex (e.g. 1.4410) grades may be required.

Surface finish can have a significant impact on the performance of beverage, dairy and food plant and equipment. For this reason, specifications for beverage, dairy and food plant and equipment identify a variety of surface finish requirements. Design, workmanship, installation and commissioning have a significant effect on the performance of both the plant and its materials of construction. In general, smooth finishes are preferred and crevices/re-entrant features are avoided in plant and equipment design.

Typical applications for stainless steels in beverage, dairy and food plant and equipment are shown in the table below.

Beverage/Dairy and Food Preparation, Processing and Storage – Applications, Grades and Human Exposure

Application/Use Stainless Steel Human Exposure –Dermal Contact

Type EN 10088 Grade

Cutlery Austenitic

Martensitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4021 (AISI 420)1.41221.4016 (AISI 430)

Frequent transient contact for user and producer.

Cooking utensils, cooks knives, professional knives

Austenitic

Martensitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4021 (AISI 420)1.41221.41161.4016 (AISI 430)

Transient for user and frequent transient contact for producer.

Cabinets, hollow-ware, work surfaces

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)

Frequent transient contact for producer, installer and user.

Cooking, processing and storage tanks & vessels, pumps, pipelines and tubes, taps and valves

Austenitic

Duplex

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4547 (ASTM S31254)[254 SMO]1.4362 (ASTM S32034)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]

Transient contact for producer, installer and user.

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Type EN 10088 GradeBoilers and steam heaters

Austenitic

Duplex

1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4547 (ASTM S31254)[254 SMO]1.4362 (ASTM S32034)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]

Limited transient for user and frequent transient contact for producer and installer.

Hot water tanks Austenitic

Ferritic

1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.45201.4521

Limited transient for user and transient contact for producer and installer.

Cookers, heaters, ovens – internal panels, burners, conveyors, grills, shelves and baking trays

Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4818 (ASTM S30415)[153 MA]1.4835 (ASTM S30815)[253 MA]1.4845 (AISI 310)

Limited transient for user and frequent transient contact for producer and installer.

Trim (external) for domestic cookers and ovens

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)

Limited transient for user and frequent transient contact for producer.

Beer kegs Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)

Limited transient for user and for producer. Frequent transient contact for delivery personnel.

Wine storage vats, pipelines, pumps and valves

Austenitic 1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)

Transient for user and frequent transient contact for producer and installer.

Saucepans, kettles, confectionery moulds

1.4301 (AISI 304)1.4307 (AISI 304L)1.4016 (AISI 430)

Transient for user and frequent transient contact for producer.

Flooring, walkways, hand rails and structural building components (eg ladders, joists, columns, beams, etc),


Transient for producer and installer. Minimal exposure with flooring and structural components for user. Transient exposure to hand rails and ladders for user.

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Type EN 10088 GradeFasteners Austenitic

Martensitic

Ferritic

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4547 (ASTM S31254)[254 SMO]1.4006 (AISI 410)1.4057 (AISI 431)1.4021 (AISI 420)1.4028 (AISI 420)1.4016 (AISI 430)

Limited transient for user and producer. Frequent transient contact for installer.

* 1.4305 (AISI 303) is used for machined parts (eg shafts for pumps and valve mechanisms) and fasteners that require corrosion resistance to cleaning agents, but that do not come into direct contact with foodstuff.

Drinking water/sewage and waste water treatmentMaterials for drinking water/sewage and waste water treatment are required to maintain the integrity of the structure (i.e. to be corrosion resistant and sufficiently robust withstand their service environment) and to be inert (i.e. to have minimal metal release into water). Stainless steels are widely used in drinking water/sewage and waste water treatment because they are resistant to corrosion, inert and easily cleaned, and can be readily fabricated by a variety of techniques.

In drinking water, sewage and waste water, materials for each application are selected on the basis of their resistance to corrosion in a specific service environment. The selection of a suitable grade of stainless steel must also include consideration the operation of the plant (whether continuous or batch operation with plant shutdowns).

Although it is difficult to provide a list of stainless steel grades used for specific applications, the following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for pharmaceutical applications. The austenitic stainless steel grade 1.4031 (AISI 304) and its derivatives are used in mild environments where the chloride content is less than 200 mg/l, while grade 1.4401 (AISI 316) and its derivatives may be used with chloride contents up to 500 mg/l. At higher chloride contents and especially if combined with increased operating temperatures and high chlorine content waters, the duplex stainless steels grades 1.4462 (ASTM S31803) and 1.4362 (ASTM S32304) are used for their resistance to stress-corrosion-cracking. For more aggressive service environments, the superaustenitic (e.g. 1.4547) and superduplex (e.g. 1.4410) grades may be required.

Ferritic and martensitic stainless steels are used, but to a much lesser extent, in drinking water/sewage and waste water treatment. Generally, ferritic and martensitic stainless steels contain less than 1% nickel. Martensitic stainless steels are used in situations that require high hardness/high strength and moderate corrosion resistance (eg grids handling abrasive materials, fasteners, etc). Ferritic stainless steels resist atmospheric corrosion and stress-corrosion-cracking, but their use in water treatment is limited.

Surface finish tends to have a significant impact on the performance of drinking water/sewage and waste water treatment plant and equipment. For this reason, specifications for drinking water/sewage and waste water treatment plant and equipment have a variety of surface finish requirements. Design, workmanship, installation and commissioning have a significant effect on the performance of both the plant and its materials of construction.

Typical applications for stainless steels in drinking water/sewage and waste water treatment plant and equipment are shown in the table below.

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Drinking water/sewage and waste water treatment Plant and Equipment – Applications, Grades and Human Exposure


Processing and storage tanks/vessels, pumps, pipelines and tubes, taps and valves.

Austenitic

Duplex

MartensiticFerritic

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4547 (ASTM 31254) [254 SMO]1.4362 (ASTM S32304)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]1.4057 (AISI 431)1.4016 (AISI 430)


Tubing for seawater desalination plants

Ferritic 1.4592 Transient for producers, installers and users.

Fasteners Austenitic

Martensitic

Ferritic

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4547 (ASTM S31254)[254 SMO]1.4006 (AISI 410)1.4057 (AISI 431)1.4021 (AISI 420)1.4028 (AISI 420)1.4016 (AISI 430)


Flooring, walkways, hand rails and structural building components (eg ladders, joists, columns, beams, etc),


Transient for producers and installers. Minimal exposure with flooring and structural components user. Transient exposure to hand rails and ladders for user.

* 1.4305 (AISI 303) is used for machined parts (eg shafts for pumps and valve mechanisms) and fasteners that require corrosion resistance to cleaning agents, but that do not come into direct contact with drinking water.

Medical Devices and ImplantsIt is important to distinguish between stainless steel grades used for implant applications and the commercial grade stainless steels [e.g. 1.4305 (AISI 303), 1.4301 (AISI 304) and 1.4401 (AISI 316)] used for other medical devices (eg dental scalers, dental explorers, dental and surgical forceps, kidney dishes, theatre tables, etc). In the EU, the Medical Device Directive defines implants as medical devices that are exposed to human tissue for more than 30 days.

This definition means that commercial grade stainless steels can be used in contact with human tissue for up to 30 days. For example, 1.4401 (AISI 316) pins can be used in conjunction with fixation devices to aid repair of fractured bones. These pins (or rods) pass through the skin (and underlying tissue) and are fixed into bone on either side of the fracture. Although these pins are machined, grades

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303 or 304 are not used for this application. Grade 316 is generally considered the minimum requirement and in many cases implant grade material would be used.

ISO standards 5832-1 and 5832-9 specify wrought stainless steel and high-nitrogen stainless steel, respectively, for surgical implants. These materials were originally developed from 1.4401 (AISI 316) stainless steel, but their chemical composition is now enhanced (i.e. higher chromium, nickel and molybdenum contents). In addition, implant grade stainless steels have specific requirements for resistance to pitting corrosion and for cleanliness that do not apply to commercial stainless steels [eg 1.4401 (AISI 316)]. Hence, special production routes (i.e. vacuum melting or electroslag refining) are used to produce "clean" implant steels.

ISO 7153-1 specifies stainless steel for surgical and dental instruments. It should be stressed that the grades in ISO 7153-1 are generic, although there is a reference to another little used ISO steel standard. This standard also provides an indication of typical applications for each grade. The steel grades given in the standard represent typical commercial steel compositions, which should be readily available. Therefore, they are not special steels and certainly not specifically prepared for surgical applications. They are, however, used worldwide by all dental and surgical instrument manufacturers for their non-implant products.

Grade 1.4305 (AISI 303) stainless steel is used in medical devices, where its free-machining properties enhance the ease of manufacture. For example, medical devices with screw threads, with drilled and/or tapped holes. Handles of multi-part dental instruments are often manufactured in grade 303. In this application, its lower corrosion resistance is not a disadvantage. The handle rarely comes into contact with the patient and, if it does, contact is transient. The dentist is not at risk from contact dermatitis, because latex gloves are worn to reduce the risk of cross-contamination. Grade 304 has applications in medical device applications, where good corrosion resistance and moderate strength are required (e.g. dental impression trays, hollowware, retractors, guide pins, etc). Once again, most of these applications involve minimal and transient contact with patients.

Martensitic stainless steel [e.g. grades 1.4006 (AISI 410), 1.4021 (AISI 420), 1.4028 (AISI 429) and 1.4125 (AISI 440C)] is used extensively for dental and surgical instruments. These stainless steels can be hardened and tempered by heat treatment. Thus, they are capable of developing a wide range of mechanical properties (i.e. high hardness for cutting instruments and lower hardness with increased toughness for load-bearing applications). Martensitic stainless steels used in medical devices usually contain up to 1% nickel. Although there are some martensitic grades with higher nickel contents, these grades are not generally used for medical device applications.

Implants have very specific surface finish requirements. In many cases, the surfaces are highly polished and/or electropolished. Polished surfaces offer enhanced corrosion resistance and, in the case of an electropolished finish, a chemically clean surface. Furthermore implants are subject to stringent cleaning regimes designed to remove microbiological contamination, which again assists corrosion resistance, and are used in the sterile condition. Non-implant medical devices also have smooth and often highly polished surfaces. Electropolishing is widely used for dental and surgical instruments. The non-glare surface finishes also follow the standard polishing route, but are finished with a Scotchbrite mop instead of a polishing mop. Once again, these devices are cleaned and sterilised prior to use.

Typical applications for stainless steels in non-implant and impact medical devices are shown in the following tables. Note: The table for non-implant medical devices shows some grades in parentheses, eg (440B), to indicate their chemical composition is similar, but not directly equivalent, to the designated ISO 7153-1 grade.

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Non-Implant Medical Devices – Applications, Grades and Human Exposure

Application/Use Stainless Steel Human Exposure –Dermal ContactType Grade

AISI EN 10088

EN ISO 7153-1

Bone curettes Martensitic 420----303

1.40211.4034(1.4116)1.41161.41221.4305

BDHIKN

Transient for patient. User protected by gloves.

Bone-cutting forceps Martensitic 420--

1.40211.40341.4116

BDI


Bone Rongeurs Martensitic 420420---

1.40211.40281.4034(1.4116)1.4116

BCDHI


Chisels & gouges Martensitic

Austenitic

420-440A---303

1.40211.4034(1.4109)(1.4116)1.41161.41221.4305

BDGHIKN


Conchotomes Martensitic 420---

1.40211.4034(1.4116)1.4116

BDHI


Dental chiselsDental curettesDental scalers

Martensitic 420-(440B)440B440C

1.40281.40341.4112--

CDR--


Dental extraction forcepsDental filling instrumentsDental root elevators

Martensitic 420420440A(440B)

1.40211.4028-1.4112

BC-R


Dental impression trays Austenitic 304(304L)

1.4301(1.4307)

M Transient for patient. User protected by gloves.

Dental explorers Martensitic

Austenitic

420420-(440B)301

1.40211.40281.40341.41121.4310

BCDRO


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AISI EN 10088

ISO7153-1

Dental extraction forcepsDental filling instrumentsDental root elevators

Martensitic 420420440A(440B)

1.40211.4028-1.4112

BC-R


Dental impression trays, internal panels and trays for sterilising units

Austenitic 304(304L)

1.4301(1.4307)


Dental tweezers Martensitic

Austenitic

410420420304(304L)301

1.40061.40211.40281.4301(1.4307)1.4310

ABCM

O


Dressing forcepsTissue forceps

Martensitic 410 1.4006 A Transient for patient. User protected by gloves.

ForcepsForceps with bow handlesBranch forceps

Martensitic 420 1.4021 B Transient for patient. User protected by gloves.

Guide pins Martensitic

Austenitic

410420420304(304L)303

1.40061.40211.40281.4301(1.4307)1.4305

ABCM

N


Knives Martensitic - 1.4116 I Transient for patient. User protected by gloves.

Laboratory & Orthodontic Pliers

Martensitic 420420(440B)440C

1.40211.40281.4112-

BCR-


Orthodontic wire and tape

Austenitic(min 13%

Cr)

304(304L)

1.4301(1.4307)

M Prolonged and close contact with internal tissues of patient. User protected by gloves.

Probes Martensitic 420303

1.40211.4305

BN


Retractors Martensitic

Austenitic

410420304(304L)

1.40061.40211.4301(1.4307)

AB

M


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AISI EN 10088

ISO7153-1

Scalpels Martensitic ---440A

1.4034(1.4116)-1.4109

DEFG


Shears Martensitic 440A 1.4109 G Transient for patient. User protected by gloves.

Scissors with carbide inserts Scissors

Martensitic 420

420---

1.4021

1.40281.4034(1.4116)1.4116

B

CDHI


Wire-cutting pliersDrills, TapsCountersink cutters for Bone screws

Martensitic ---(440B)

1.4034(1,4116)1.41161.4112

DHIR


Dental clamps and support bands for dental fillings


1.4301(1.4307)


Laboratory spatulas and mixing knives

Martensitic

Austenitic

410420304(304L)

1.40061.40211.4301(1.4307)

ABM

No patient contact. Very limited contact with user.

Dental syringes and amalgam carriers


1.4301(1.4307)


Plunger rods for dental syringes and amalgam carriers

Austenitic 303 1.4305 N No patient contact. Very limited contact with user.

Screws, nuts, rivets Martensitic

FerriticAustenitic

410420430304, (304L)303301316316L

1.40061.40211.40161.4301(1.4307)1.43051.43101.44011.4404

ABLM

NOP

Very limited contact with user or patient.

Screwdrivers for bone screws

Ferritic 430 1.4016 L Transient for patient. User protected by gloves.

Springs MartensiticAustenitic

420301

1.40211.4310

BO

Very limited contact with user or patient.

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AISI EN 10088

ISO7153-1

Solid handles MartensiticFerritic

Austenitic

410420430303

1.40061.40211.40161.4305

ABLN


Hollow handles Austenitic 304(304L)

1.4301(1.4307)


Non-Active Implant Medical Devices – Applications, Grades and Human Exposure

Application/Use Stainless Steel Human Exposure –Dermal and

Subcutaneous Type Grade

Bone Plates Austenitic ISO 5832-1 Composition D or E Prolonged and close contact with internal tissues of patient. User protected by gloves.

Bones Screws Austenitic ISO 5832-1 Composition D or E Prolonged and closecontact with internal tissues of patient. User protected by gloves.

Keys for Bone Screws Austenitic

Martensitic

ISO 5832-1 Composition D or EISO 7153-1 Grade M or NISO 7153-1 Grade A, B or C


Femoral Fixation Devices

Austenitic ISO 5832-1 Composition D or E Prolonged and close contact with internal tissues of patient. User protected by gloves.

Intramedullary nails and pins

Austenitic ISO 5832-1 Composition D or EISO 5832-9

Prolonged and close contact with internal tissues of patient. User protected by gloves.

Neurosurgical implants(aneurysm clips)


Orthopaedic ImplantsAnkle, Elbow, Finger, Hip, Knee, Shoulder, Toe, Wrist

Austenitic ISO 5832-1 Composition D or EISO 5832-9


Osteosynthesis BS 3531 & BS EN ISO 14602 & BS EN ISO 14630


Skeletal pins and wires Austenitic ISO 5832-1 Composition D or E Prolonged and close contact with internal tissues of patient. User protected by gloves.

Staples with parallel legs


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PharmaceuticalPharmaceutical applications, in common with food and beverage, demand that the materials of construction maintain the integrity of the structure (i.e. they are corrosion resistant) and are inert (i.e. they release insignificant quantities of contaminants into the product). Stainless steels are widely used in the pharmaceuticals industry because they are resistant to corrosion, inert and easily cleaned.

Although grade 1.4401 (AISI 316) and its derivatives are the most widely used stainless steels in pharmaceutical plant and are considered by many as the industry standard, materials for each application are selected on the basis of their resistance to corrosion in a specific service environment. The selection of a suitable grade of stainless steel must also include consideration of the cleaning regime and cleaning agents used in the plant. Furthermore, the operation of the plant (whether continuous with a “clean in place” system or batch operation with shutdowns to clean the plant) may also influence the choice of material.

In view of the remarks made above, it is difficult to provide a list of stainless steel grades used for specific applications. However, the following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for pharmaceutical applications. The austenitic stainless steel grade 1.4031 (AISI 304) and its derivatives are used in mild environments where the chloride content is less than 200 mg/l, while grade 1.4401 (AISI 316) and its derivatives may be used with chloride contents up to 500 mg/l. At higher chloride contents and especially if combined with increased operating temperatures, the duplex stainless steels grades 1.4462 (ASTM S31803) and 1.4362 (ASTM S32304) are used for their resistance to stress-corrosion-cracking. For more aggressive service environments, the superaustenitic (e.g. 1.4547) and superduplex (e.g. 1.4410) grades may be required.

Surface finish has a significant impact on the performance of pharmaceutical plant and equipment. For this reason, specifications for pharmaceutical plant and equipment usually have very specific surface finish requirements. In many cases, the surfaces are highly polished and/or electropolished. Polished surfaces offer enhanced corrosion resistance and, in the case of an electropolished finish, a chemically clean surface.

Design, workmanship, installation and commissioning have a significant affect on the performance of both the plant and its materials of construction.

Typical applications for stainless steels in pharmaceutical plant and equipment are shown in the table below.

Pharmaceutical Plant and Equipment – Applications, Grades and Human Exposure


Processing and reaction vessels, storage tanks and vessels, pumps, pipelines and tubes, heat exchangers, scrubber units, taps and valves

Austenitic

Duplex

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4438 (AISI 317L)1.4539 (904L)1.4547 (ASTM S31254)[254 SMO]1.4362 (ASTM S32304)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]

Frequent transient for producer and installer. Transient for user.

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Flooring, hand rails and structural building components (eg ladders, joists, columns, beams, wall cladding, etc)


Frequent transient for producer and installer. Minimal exposure with flooring and structural components user. Transient exposure to hand rails and ladders for user.


Martensitic

Ferritic

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4438 (AISI 317L)1.4539 (904L)1.4547 (ASTM S31254)[254 SMO]1.4006 (AISI 410)1.4057 (AISI 431)1.4021 (AISI 420)1.4028 (AISI 420)1.4016 (AISI 430)

Transient for producer, installer and user. No contact with pharmaceutical products.

* 1.4305 (AISI 303) is used for machined parts (eg shafts for pumps and valve mechanisms) and fasteners that require corrosion resistance to cleaning agents, but that do not come into direct contact with pharmaceutical products.

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Applications - Industrial

Chemical/Process IndustriesMaterials used by the Chemical/Process Industries are required to maintain the integrity of the structure (i.e. to be corrosion resistant and sufficiently robust to withstand their service environment). Stainless steels are widely used in the chemical/process industries because they are resistance to corrosion, inert and easily cleaned, and can be readily fabricated by a variety of techniques.

Although grade 1.4401 (AISI 316) and its derivatives are the most widely used stainless steels in the chemical/process industries and are considered by many as the industry standard, materials for each application are selected on the basis of their resistance to corrosion in a specific service environment. The selection of a suitable grade of stainless steel must also include consideration the operation of the plant (whether continuous or batch operation with plant shutdowns).

Although it is difficult to provide a list of stainless steel grades used for specific applications, the following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for pharmaceutical applications. The austenitic stainless steel grade 1.4031 (AISI 304) and its derivatives are used in mild environments where the chloride content is less than 200 mg/l, while grade 1.4401 (AISI 316) and its derivatives may be used with chloride contents up to 500 mg/l. At higher chloride contents and especially if combined with increased operating temperatures, the duplex stainless steels grades 1.4462 (ASTM S31803) and 1.4362 (ASTM S32304) are used for their resistance to stress-corrosion-cracking. For more aggressive service environments, the superaustenitic (e.g. 1.4547) and superduplex (e.g. 1.4410) grades may be required.

Ferritic and martensitic stainless steels are, to a lesser extent, used by chemical/process industries. Generally, ferritic and martensitic stainless steels contain less than 1% nickel. Martensitic stainless steels are used in situations that require high hardness/high strength and moderate corrosion resistance (eg chutes handling abrasive materials, fasteners, crushing/cutting equipment, etc). Ferritic stainless steels are used where resistance to cyclic oxidation and resist stress-corrosion-cracking is required (e.g. extraction hoods for temperature drying process, where chlorides are contained in the fume).

Surface finish tends to have a significant impact on the performance of chemical/process plant and equipment. For this reason, specifications for chemical/process plant and equipment have a variety of surface finish requirements. Design, workmanship, installation and commissioning have a significant effect on the performance of both the plant and its materials of construction.

Typical applications for stainless steels in chemical/process plant and equipment are shown in the table below.

Chemical/Process Industries Plant and Equipment – Applications, Grades and Human Exposure


Processing and reaction vessels, storage tanks and vessels, pumps, pipelines and tubes, heat exchangers, taps and valves. Fume extraction systems (eg fume hoods and ducting) and scrubber units.

Austenitic

Duplex

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4438 (AISI 317L)1.4539 (904L)1.4547 (ASTM S31254)[254 SMO]1.4362 (ASTM S32304)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]1.45211.4592

Transient for producer, installer and user.

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Crushing/cutting equipment, mechanical handling equipment (chutes/conveyors) for abrasive materials

Martensitic 1.4006 (AISI 410)1.4057 (AISI 431)1.4005 (AISI 303)*



Martensitic

Ferritic



Flooring, walkways, hand rails and structural building components (eg ladders, joists, columns, beams, wall cladding, etc)


Transient for producer and installer. Minimal exposure with flooring and structural components user. Transient exposure to hand rails and ladders for user.

* Resulfurised grade 303.

Nuclear IndustryMaterials used by the Nuclear Industry are required to maintain the integrity of the structure (i.e. they must be corrosion and radiation resistant and sufficiently robust to withstand their service environment). Stainless steels are widely used in the nuclear industry because they are resistance to corrosion and can be readily fabricated by a variety of techniques. Materials for each application are selected on the basis of their resistance to corrosion in a specific service environment.

In view of the remarks made above, it is difficult to provide a list of stainless steel grades used for specific applications. Although similar considerations to those used for the chemical/process industries apply to nuclear applications, the presence of high radiation fluxes may require additional measures. For example, boron is added to the austenitic stainless steel grade 1.4031 (AISI 304) as a neutron moderator. In addition, the cobalt content of stainless steels used for nuclear applications is often subject to strict limits (e.g. less than 0.3% cobalt for British Nuclear Fuels).

Surface finish tends to have a significant impact on the performance of nuclear plant and equipment. For this reason, specifications for nuclear plant and equipment have a variety of surface finish requirements. Design, workmanship, installation and commissioning have a significant affect on theperformance of both the plant and its materials of construction.

Typical applications for stainless steels in nuclear plant and equipment are shown in the table below.

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Nuclear Plant and Equipment – Applications, Grades and Human Exposure


Processing and reaction vessels, storage tanks and vessels, pumps, pipelines and tubes, heat exchangers, taps and valves. Fume extraction systems (eg fume hoods and ducting) and scrubber units.

Austenitic

Duplex

Martensitic

Ferritic

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4401 (AISI 316L)1.4571 (AISI 316Ti)1.4438 (AISI 317L)1.4539 (904L)1.4547 (ASTM S31254)[254 SMO]1.4362 (ASTM S32304)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]1.4006 (AISI 410)1.4021 (AISI 420)1.4028 (AISI 420)1.4057 (AISI 431)1.4016 (AISI 430)1.45211.4592

Transient for producers. Very limited exposure for installers and user due to nature of the processes.

Containment flasks for nuclear waste

Austenitic 1.4301 (AISI 304) with boron and low cobalt content






Martensitic

Ferritic



* Resulfurised grade 303

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EngineeringStainless steels are used in extensively in general engineering applications. For example, cement production, furnaces, heating and ventilating, heat treatment furnaces, machined parts, tooling/jigs/fixtures, power generation and waste incinerators. Materials for general engineering applications are required to maintain the integrity of the structure (i.e. to be resistant to corrosion or high temperatures and sufficiently robust to withstand their service environment). Stainless steels are widely used in general engineering applications because they are resistance to corrosion or high temperatures and can be readily fabricated by a variety of techniques.

Materials for each application are selected on the basis of their resistance to a specific service environment. The austenitic stainless steel grade 1.4031 (AISI 304) and its derivatives are used in mild corrosive environments where the chloride content is less than 200 mg/l, while grade 1.4401 (AISI 316) and its derivatives may be used in more aggressive environments with chloride contents up to 500 mg/l. At higher chloride contents and especially if combined with increased operating temperatures, the duplex stainless steels grades 1.4462 (2205) and 1.4362 (2304) are used for their resistance to stress-corrosion-cracking. For more aggressive corrosion service environments, the superaustenitic (e.g. 1.4547) and superduplex (e.g. 1.4410) grades may be required.

The austenitic stainless steels 1.4301 (AISI 304), 1.4401 (AISI 316) and their respective derivatives are suitable for applications up to 870 C. For higher operating temperatures, other austenitic stainless steels (e.g. 1.4818, 1.4833, 1.4835 and 1.4845) are used. Certain grades of stainless steel can operate at temperatures up to 1150 C.

Ferritic and martensitic stainless steels are widely used in general engineering applications. Generally, ferritic and martensitic stainless steels contain less than 1% nickel. Martensitic stainless steels are used in situations that require high hardness/high strength and moderate corrosion resistance (eg chutes handling abrasive materials, fasteners, crushing/cutting equipment, etc). Ferritic stainless steels are resistant to cyclic oxidation and also resist stress-corrosion-cracking (e.g. extraction hoods for temperature drying process, where chlorides are contained in the fume).

Specifications for general engineering applications have a variety of surface finish requirements. Design, workmanship, installation and commissioning have a significant effect on the performance of both the plant and its materials of construction.

Typical applications for stainless steels in general engineering applications are shown in the table below.

General Engineering – Applications, Grades and Human Exposure


Crushing/cutting equipment, mechanical handling equipment (chutes/conveyors) for abrasive materials

Austenitic

Martensitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4006 (AISI 410)1.4057 (AISI 431)1.4021 (AISI 420)1.4028 (AISI 420)1.4003 (ASTM S41050)[3Cr12]


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Ducting, flues, chimneys and chimney liners for heating and ventilating, power generation and waste incinerators.

Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4539 (904L)1.4547 (ASTM S31254) [254 SMO]1.45211.4592


High temperature components (eg burners, conveyors, hearths and hoppers, heat reflectors, etc) for furnaces, heaters, cement production and waste incinerators

Austenitic 1.4541 (AISI 321)1.4401 (AISI 316)1.4401 (AISI 316L)1.4818 (ASTM S30415)[153 MA]1.4835 (ASTM S30815)[253 MA]1.4833 (AISI 309)1.4845 (AISI 310)

Transient for producer and installer. Minimal for user.

Jigs, fixtures and tooling for assembly,brazing, machining and welding operations

Austenitic

Martensitic

Ferritic

1.4305 (AISI 303)*1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)1.4006 (AISI 410)1.4057 (AISI 431)1.4021 (AISI 420)1.4028 (AISI 420)1.4016 (AISI 430)

Transient for producers and users.

Machined components (eg drive shafts for pumps)

Austenitic 1.4305 (AISI 303)* - (AISI 303Se)1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)1.4021 (AISI 416)1.4028 (AISI 420F)

Transient for producers and users.

Steam generation and heat exchangers for power generation

Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4539 (904L)1.4547 (ASTM S31254)[254 SMO]

Transient for producers and installers. Minimal for users.



Transient for producer and installer. Minimal exposure with flooring and structural components user. Transient exposure to hand rails and ladders for user.

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Martensitic

Ferritic



* Resulfurised grade 303

Oil/Offshore IndustryMaterials for the Oil/Offshore Industry are required to maintain the integrity of the structure (i.e. they must possess both internal and external corrosion resistance and be sufficiently robust to withstand their service environment). Stainless steels are widely used in the oil/offshore industry because they are resistant to corrosion, strong and can be readily fabricated by a variety of techniques. Materials for each application are selected on the basis of their resistance to corrosion in a specific service environment.

In view of the remarks made above, it is difficult to provide a list of stainless steel grades used for specific applications. Similar considerations to those used for the chemical/process industries apply to oil/offshore applications. The presence of high sulphur content in some crude oil in combination with stress and temperature may require additional measures to prevent stress-corrosion-cracking. For example, the hardness of austenitic stainless steels may be limited to a maximum of 22 HRc (ie Rockewell hardness C scale) for sour gas applications. In addition, offshore applications may also require resistance to seawater corrosion.

Surface finish tends to have a significant impact on the performance of oil/offshore plant and equipment. For this reason, specifications for oil/offshore plant and equipment have a variety of surface finish requirements. Design, workmanship, installation and commissioning have a significant affect on the performance of both the plant and its materials of construction.

Typical applications for stainless steels in oil/offshore plant and equipment are shown in the table below.

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Oil/Offshore Plant and Equipment – Applications, Grades and Human Exposure


Processing and reaction vessels, storage tanks and vessels, pumps, pipelines and tubes, heat exchangers, fasteners and valves. Fume extraction systems (eg ducting) and scrubber units.

Austenitic

Duplex

1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4571 (AISI 316Ti)1.4438 (AISI 317L)1.4539 (904L)1.4547 (ASTM S31254)[254 SMO]1.4362 (ASTM S32304)[2304]1.4462 (ASTM S31803)[2205]1.4410 (ASTM S32750)[2507]


Fire resistant walls for accommodation blocks

Austenitic

Duplex

1.4401 (AISI 316)1.4404 (AISI 316L)1.4462 (ASTM S31803)[2205]

Transient for producers. Very limited exposure for installers and user.

Flooring, walkways, hand rails and structural components (eg ladders, joists, columns, beams, etc)


Transient for producers. Very limited exposure for installers and user.

CryogenicsMaterials for cryogenic applications are selected for their mechanical strength and toughness (impact resistance) at low temperatures. Austenitic stainless steels are used in cryogenic applications because they do not undergo metallurgical phases changes or ductile/brittle fracture transitions (i.e. they remain ductile) to temperatures below –250 C.

Typical applications for stainless steels in cryogenic applications are shown in the table below.

Cryogenic Applications – Applications, Grades and Human Exposure


Liquid gas production and containment eg pipelines, storage vessels, valves and pumps. Refrigeration and freezer units. Liquid gas fuel tanks for missiles and rockets. Containment systems for super-cooled magnetic devices, etc


Frequent transient exposure to producers. Limited transient for users.

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Applications – Construction/Architectural

Architectural/ConstructionMaterials for Architectural/Construction applications are required to maintain the integrity of the structure (i.e. to be sufficiently robust withstand their service environment), to be inert (i.e. corrosion resistant) and where appropriate, aesthetically pleasing. Stainless steels are widely used in architectural/construction applications because they are resistance to corrosion, inert and easily cleaned, can be readily fabricated by a variety of techniques and can accept a variety of aesthetically pleasing finishes.

In architectural/construction applications, materials for each application are selected on the basis of their resistance to corrosion in a specific service environment. The following examples may serve to indicate the considerations made in selecting a suitable grade of stainless steel for architectural/construction applications. The austenitic stainless steel grade 1.4031 (AISI 304) and its derivatives are suitable for external rural and mild urban environments, where pollution is minimal. Grade 1.4401 (AISI 316) and its derivatives are suited to external urban applications, where traffic or industrial pollution are significant feature, and coastal environments, where chloride is present in theatmosphere. In warmer coastal climates, where high ambient temperatures are experienced, the duplex stainless steels grades 1.4462 (ASTM S31803) and 1.4362 (ASTM S32304) may be used. In external rural environments, the ferritic stainless steel 1.4016 (AISI 430) has been successfully used to a limited extent. Austenitic grade 1.4307 (AISI 304L) and its derivatives and ferritic grade 1.4016 (AISI 430) are used for internal architectural/construction applications.

Surface finish has an impact on the performance of architectural/construction products. For this reason, specifications for architectural/construction applications have a variety of surface finish requirements. In general, the surface finish of architectural/construction products that are unseen by the general public are not critical. In contrast, the surface finish of items viewed by the public can be an important feature of a building or structure. Manufacturers recommend the use of smooth, polished surface finishes for architectural/construction applications, because they resist the accumulation of dirt and are easily cleaned. In situations where a dull finish is desired, brushed and patterned finishes are sometimes used to reflect the light and reduce glare. Roughened surfaces are not recommended for architectural/construction applications visible to the public. Design, workmanship, installation and commissioning have a significant affect on the performance of both the plant and its materials of construction. Manufacturers recommend that architectural/construction structures made in stainless steel are subject to regular cleaning with water.

Typical applications for stainless steels in architectural/construction applications are shown in the table below.

Architectural/Construction Applications – Applications, Grades and Human Exposure


Cladding/walling (external) for buildings, tunnel linings, guttering, roof channels and downpipes. Roofs, balustrades

Austenitic

Ferritic



Chimney liners, ducting, flues


Transient for producers and installers. No contact for user.

Culverts Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)

Transient for producers and installers. No contact for user.

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Flooring, walkways, structural building components - beams, brackets, channels, hollow sections, columns, joists, etc

Austenitic

Duplex

1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)1.4462 (ASTM S31803)[2205]

Transient for producers and installers. Minimal exposure with flooring and structural components user.

Fasteners – bolts, nuts, rivets and screws

Austenitic

Martensitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4541 (AISI 321)1.4401 (AISI 316)1.4404 (AISI 316L)1.4547 (ASTM S31254)[254 SMO]1.4006 (AISI 410)1.4057 (AISI 431)1.4005 (AISI 303)*1.4016 (AISI 430)


Masonry brackets Austenitic

Ferritic

1.4301 (AISI 304)1.4307 (AISI 304L)1.4401 (AISI 316)1.4404 (AISI 316L)1.4003 (ASTM S41050)[3Cr12]1.4016 (AISI 430)

Transient for producers and installers. No contact for users.

Internal cladding and walling for buildings, wall and ceiling tiles, elevator/lift panels, door handles, hand rails

Austenitic

Ferritic


Transient for producers and installers. Transient to user.

Door handles, hand rails, lamp posts, ladders, street furniture and structures (eg bus stops, telephone booths, etc),

Austenitic

Duplex



Bridges and bridge components

Austenitic

Duplex



Reinforcing bars for concrete structures (eg motorway road bridges and elevated sections, marinas and marine structures).



Urinal and toilet bowels


Transient for producers and installers. Minimal contact for users.

Wall ties Austenitic 1.4301 (AISI 304)1.4307 (AISI 304L)


Window frames, glazing support brackets

Window hinges

Austenitic

Ferritic



* Resulfirised grade 303

STAINLESS STEELS - APPLICATIONS, GRADES AND HUMAN EXPOSURE

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