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Industrial Product Design: Materials for the Machinery

Wilfried Rahse[1]*

www.ChemBioEngRev.de ª 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ChemBioEng Rev 2014, 1, No. 3, 1–16 1

Abstract

The materials for production plants must be chemi-cally resistant under operating conditions for a longperiod of time. Typical materials are metals, espe-cially stainless steel, superalloys, and nonmetalssuch as graphite, borosilicate glass, and ceramics, aswell as plastics. The product manufacturers preferhighly alloyed stainless steel with ~17–18 % Cr and12 % Ni (AISI 304 and 316 grades). The danger ofpitting and stress corrosion decreases with increas-ing amounts of molybdenum. The pharmaceuticaland food industries utilize machinery in stainless

steel with surfaces in mirror finish to avoid infectionwith microorganisms in the entire plant. The sur-face smoothing is performed by mechanical meth-ods or by electropolishing. Besides stainless steel,the chemical industry takes advantage of nonferrousmetals, alloys, metallic oxides, and carbides as wellas plastics for processing and storage of aggressivesubstances. These materials are mainly used for lin-ings and coatings. In many cases, they are appliedby thermal spraying (sputtering).

Keywords: Hygiene, Plastics, Stainless steel, Superalloys, Surface polishing

Received: April 16, 2014; accepted: April 16, 2014

DOI: 10.1002/cben.201400009{

1 Motivation

The product design describes the development of a new prod-uct, which solves a customer’s needs by involving the customer.Product design includes product performance, handling, andproduct esthetics. The industrial production of specified prod-ucts requires optimally designed processes and the use ofappropriate materials for the machinery and equipment. Thechemical and mechanical stability has first priority, i.e., in par-ticular the corrosion and abrasion resistance of product-wettedareas. In addition, for food, pharmaceutical, biotechnology, andcosmetic preparations, and also for some other products, likeliquid detergents, product hygiene plays an essential role withregard to quality. Product hygiene means that microorganismsare absent or their numbers are below fixed limits. Certain mi-croorganisms must always be absent. Product hygiene requiresthat the production is carried out in an appropriate facility[1, 2]. In order to ensure the hygiene of the products and thesystem during production, the process is continuously moni-tored and recorded.

Design and materials of the machinery and equipment as wellas their processing are of great importance for the hygiene andproduct quality. The plant must be designed free of dead spaceto avoid the formation of biofilms. The occurrence of biofilmsmay be an indication of an incipient bio-corrosion, often trig-gered by sulfate-reducing anaerobic bacteria. On the other hand,a firm adhesion of microorganisms on the walls of equipmentmust be prevented. Furthermore, a suitable plant design withappropriate materials simplifies the system’s cleaning, allows aresidue-free draining, and reduces the wastewater pollution.

While some very large companies have specialists in the fieldof materials who develop optimal solutions for each process,most of the other companies are dependent on the knowledgeand experience of their employees from process development,project management, and production. During the purchase ofnew machinery and equipment, the material and its processingis usually defined in a joint discussion with the manufacturer.This contribution is intended to give the developers and opera-tors of plants some evidence on the properties of materials.This knowledge is important when ordering new machineryand for trouble-free production of high-quality products. Theremarks come from own experience and background in thebiotechnology and consumer goods industry, supported byreading the literature.

2 Relationship between Material andProduct Design

Chemical engineers who work in the field of product and pro-cess development for the food, chemical, or pharmaceutical in-dustry, must not only specify the materials when ordering

—————[1] Dr.-Ing. W. Rahse

Bahlenstraße 168, 40589 Dusseldorf, Germany.E-Mail: [email protected]

{English version of DOI: 10.1002/cite.201300191

equipment but, in addition, often the finish of wetted surfacesand welds. In many cases, specifications exist because the com-pany prescribes for some or all plants a standard stainless steel(such as AISI 316Ti, Din 1.4571); optionally, it also specifies asurface finish. Therefore, the storage in the company’s work-shops is reduced; furthermore, the processing in the plant con-struction is standardized. If a device requires a better materialgrade against chemical corrosion and abrasive wear, the deci-sion must be made between alternatives. Howsoever, the econ-omy (cost, repair, resistance, and cleaning cycles) of the materi-al stands against the product quality (metal contents andhygiene).

Quality includes product safety and product hygiene, whichrequire extensive plant hygiene. Especially in the pharmaceuti-cal and biotechnology industries, as well as for food and cos-metics, stainless steels are used with ground and polished sur-faces. On the one hand, the polishing of the product’s wettedsurfaces significantly increases corrosion resistance. On theother hand, a residue-free cleaning can be performed, avoidingcross-contamination and infection by microorganisms in theentire production plant; when, as a prerequisite, a dead space-free, fully drainable plant is available. Examples of avoidingdead spaces can be found in DIN EN 1672-2:2005 and theEuropean Hygienic Engineering and Design Group (EHEDG)(3-A and NSF International) brochures [1].

The adhesion of microorganisms, the formation of biofilms,the adhesion of product residues and deposits, and the devel-opment of crusts depend on the material and surface properties[2]. The same applies to the cleaning and disinfection of thesurfaces and the removal of residues with appropriate solu-tions. These parameters worsen over the years on account ofmechanical wear and chemical attack. Typical aging processesaffect mainly plastics (bellows, seals). Because rough surfaces,incipient corrosion, and the gradual formation of micro cracksoffer numerous opportunities for the microorganisms to ad-here, these are hygienically questionable [3] and not allowed.The DIN standard 1672-2 specifies that in the food industry,product contact surfaces must have an average surface rough-ness, Ra, of at least 0.8mm. The required processing of stainlesssteel by grinding/polishing or pickling/electropolishing isclearly reflected in the purchase price.

The cleanability of the plant is not only an essential qualitybut also a cost factor, because the system’s availability dependson the duration of cleaning. The cleaning method is a functionof the material, its surface smoothness, the distance betweenroughness mountains and the composition of cleaning agents(surfactants, oxidants, pH-value), as well as the cleaning condi-tions (flow, temperature). The pharmaceutical industry oftenproduces in electropolished equipment. The electropolishing ofthe surfaces ensures the necessary hygiene and a rather easycleaning. This allows reducing the duration and consumptionof cleaning solutions. In addition, it is possible to disinfect theproduction plant including the filling lines with 2-propanol,which regularly takes place in the cosmetic industry after clean-ing. Even higher demands on sterility are met with chemicaland steam sterilization.

The choice of material depends on the chemistry and operat-ing conditions as well as the raw materials and product phases,i.e., solid, liquid, gas, multiphase systems. Theoretically, for

each part of the production line, e.g., tank farms, silos, mainplant, filling line, and product storage, another material mightcome into question. This means that the term plant design in-cludes not just the machinery and equipment of the core facil-ity. If the standard grade of stainless steel is not sufficient, thereare alternative materials for each part of the production plant.Examples are materials for silos made of glass-fiber-reinforcedplastic (GRP) or stainless steel, for acid baths made of steelwith rubber or with an acid-resistant plastic liner, such as poly-vinylidene fluoride (PVDF), for agitator vessels of borosilicateglass or enamel, for heat exchangers made of graphite or Has-telloy.

As an integral part of product design, the quality dependscrucially on the materials and surface finish in the entire plant.Further, they also affect the production costs.

3 Choice of Material

The materials are chosen on the basis of chemical, thermal,and mechanical stresses. Materials for the production plant canbe divided into metals, such as stainless steel, nickel, titanium,etc., and inorganic nonmetals, such as graphite, glass, andceramics, as well as organic polymers, e.g., plastics. For ma-chinery, the chemical, pharmaceutical, biotechnology, and foodindustry utilizes mainly alloyed stainless steel of high quality.Typically, they work with standard grades, mostly AISI 304 or316 qualities. If the following critical substances are involved inthe process, another grade or material must be chosen [4]:– strong organic and inorganic acids;– acidic gases, including chlorine and bromine;– chloride, bromide, and fluoride ions;– alkalis, especially at high temperatures;– molten salts;– hydrogen.

Several chemical processes on the material surface can trig-ger corrosion [5]. This ensues in various forms. The bestknown are probably surface corrosion, crack, contact, pitting,and stress corrosion. Further, fatigue cracking and intergranu-lar corrosion occur. The corrosion resistance of the material de-pends on its chemical composition (usually Fe alloy) and theprocessing conditions. From the outside, chemical substancesattack and abrade the surfaces by raw and auxiliary materials,intermediate, secondary, and end products. These attacks deter-mine the lifetime of the machinery in detail via:– chemistry of substances present in the process;– application time and temperature;– concentration of problematic substances, gases, liquids, sus-

pensions, melting, and solids;– pH;– presence of oxidizing or reducing substances;– presence of abrasives;– presence of salts, particularly of chlorides (Na, K, heavy met-

als).For many substances, corrosion data are available in the lit-

erature [4, 6]. For high-temperature and/or high-pressure reac-tions as well as for operations in the petrochemical industryspecial grades of steel are used. These steels are tailored to theapplication, and represent particularly economical solutions.


Without guidelines of the company, the choice of materialusually takes place after the price–performance ratio.

4 Stainless Steel

In the chemical apparatus, stainless steel is by far the mostcommon material. For a list of stainless steels, see EN 10088.1.In general, stainless steels have a chromium content of > 10.5 %and of sulfur and phosphorus contents of < 0.025 %, and car-bon content of < 1.2 %. They are characterized by forming athin protective layer on the surface in contact with air. Afterminor damage, the layer regenerates by itself, when the steel isexposed to air and moisture [2]. The weldability increases withdecreasing carbon content. Stainless steel can be improved insome properties by further alloy constituents. For this purpose,nickel and molybdenum are particularly suitable.

4.1 Standard Grade

Chemical, pharmaceutical, and food industries require mainlyhigh-alloy steels containing at least 17 % Cr (up to 30 %) and12 % Ni (up to 26 %) for the plant and machinery in produc-tion, besides C < 0.1 %, Si < 1 %, and Mn < 2 %. These form incontact with oxygen from the air a thin, invisible passivationlayer of chromium (III) oxide (Cr2O3), which protects the un-derlying metal. The addition of Ni improves the corrosion re-

sistance of stainless steel, because it oxidizes very slowly (incontrast to iron). But the standard stainless steels cannot meetall the requirements of the chemical apparatus. For example,the steels are additionally alloyed with 2–5 % Mo to avoid pit-ting and stress corrosion cracking. Other requirements lead tothe addition of Ti, Cu, Al, Nb, and others. The compositions offrequently used steels are listed in Tab. 1.

The standard grade AISI 304 (1.4301) is probably the firstcommercial stainless steel and currently most often processed.This austenitic, nonmagnetic material, and other AISI 304Lqualities with less carbon (1.4306 and 1.4307), which are easierto weld and polish, show good resistance to water, steam, mois-ture, fruit acids, and weak organic and inorganic acids. Thefood, beverage, pharmaceutical, and cosmetic industries usethese steel grades commonly in the processing of liquids. Forimproved cleaning and corrosion resistance, the product con-tact surfaces are usually ground and/or polished.

The stainless steel AISI 316Ti (1.4571) also includes Ti, toimprove the stability and weldability. Together with the addedMo, this steel shows increased chemical resistance, especiallyagainst intergranular corrosion, pitting, and stress corrosioncracking. As this alloy covers most requirements, it is widelyused in chemical apparatuses, providing the standard materialin many companies (chemicals, consumer goods). Owing tothe stabilization of the stainless steel with Ti, the electropolish-ing is difficult. Mechanical grinding of the surfaces causesmany scratches by the very hard particles from titanium car-bide, torn from the surface. This concerns the Ti, Nb-stabilized


Table 1. Comparison of material numbers (DIN EN-AISI) of high-alloy stainless steels, their composition, and relative prices. Example: Ma-terial number according to DIN EN: 1.4301; composition according to European standards EN: X5CrNi18-10, number after X = carbon con-tent multiplied by factor 100, 5 = 0.05 %, CrNi18-10 = 18 % Cr, 10 % Ni; Material number according to American Iron and Steel InstituteStandard: AISI 304; a) Calculated by alloy surcharges (according to a table from Stappert/Dusseldorf for wholesalers).

Material number(DIN EN 10088-1)

Steel composition(DIN EN 10088-1)

AISI standard,(and ASTM-International)

Estimated relative pricesa) [%] (V2A = 100 %); May 2013, Germany100 % = y € kg–1

Steel bary = 1.53

Sheety = 1.23

Seamless pipey = 2.32

1.4006 X12Cr13 410 30 – 26

1.4301 (V2A) X5CrNi18-10 304 100 100 100

1.4307 X2CrNi18-9 304L 100 100 100

1.4401 X5CrNiMo17-12-2 316 148 154 135

1.4404 X2CrNiMo17-12-2 316L 148 154 135

1.4435 X2CrNiMo18-14-3 316L 166 173 151

1.4439 X2CrNiMoN17-13-5 317LNM 184 193 172

1.4462 X2CrNiMoN22-5-3 – 117 126 100

1.4539 X1NiCrMoCu25-20-5 904L 274 282 247

1.4541 X6CrNiTi18-10 321 114 115 100

1.4563 X1NiCrMoCuN 31-27-4 – 311 – 281

1.4571 (V4A) X6CrNiMoTi17-12-2 316Ti 150 157 135

1.4580 X6CrNiMoNb17-12-2 316Nb 156 – 135

1.4762 X10CrAlSi25 446 41 48 34

steels (AISI 316Ti, 316Nb, and 321)that are less suitable for use in thepharmaceutical, food, biotechnology,and cosmetic industries. In these fields,the machinery must be polished to mir-ror finish. The engineers use for theseapplications some low-carbon grades,such as AISI 316L (1.4404 and 1.4435)or for lower requirements AISI 304L(1.4306 and 1.4307).

Most equipment is made in standardstainless steels (all AISI 304/316grades). In some cases, another materi-al, as mentioned in Tab. 1, is required.The standard qualities show a medium,mechanical stress tolerance, e.g., as ma-terial in mills, and a mean resistance tochemical agents. They represent aneconomic compromise, and are widely used in process indus-tries for processing of solids, suspensions, pastes, liquids, andliquids/gases at moderate temperatures.

In contrast, the mentioned aluminum-containing steel AISI446 (Tab. 1) is a specialist. The inexpensive high-temperaturesteel is used up to 1100 �C and shows a high resistance to sul-furous gases.

4.2 Corrosion

The choice of steel quality is based on the chemical and me-chanical resistance and processability, availability, and costs.Steel producers and distributors have published a series ofchemical resistance tables, mainly for pure liquids at ambienttemperature. In the literature [4, 6, 7], extensive data collectionsexist. It is widely known that stainless steels are attacked bymany acids. Less known, but a big problem, is the pitting andstress corrosion cracking, caused by halide ions, preferablychloride ions [2, 7]. These effects occur in particular at elevatedion concentrations (> 50 ppm) and temperatures, increased incombination with low pH values. The corrosion starts at a flawin the passivation layer. In addition, movements of the liquidhave an impact. The extent of damage increases in stagnantaqueous fluids due to the formation of local elements. There-fore, it is advisable after cleaning, to drain off the water, andthen to dry the plant for a longer standstill.

Accompanying substances affect corrosion, either positivelyor negatively. Therefore, in complex cases, some simple mea-surements of the product mixture must be carried out in thelaboratory. However, the corrosion resistance against chloridecan be determined by measuring the electric potential in chlo-ride solutions as a function of temperature (Fig. 1). Measure-ments showed that AISI 304 stainless steels are not suitable forprocessing chloride-containing solutions. Depending on theconcentration, at elevated temperatures all AISI 316 stainlesssteels are not sufficiently stable. Higher levels of alloyed Moprovide the required chemical resistance; especially the grades1.4439, 1.4539, and 1.4563 (Tab. 1). By progressive alloying,the stability increases significantly against a variety of chemi-cals. Unfortunately, by this alloying the commodity prices rise.

In many cases, the material AISI 317LNM (1.4439) representsa good compromise between the required resistance and costs.

From the chemical perspective, both materials 1.4539 and1.4563 are best suitable against chloride induced pitting. Theresistance must be ensured throughout the facility, taking intoaccount the temperatures. In addition to the machinery andequipment, this concerns all piping, valves, sensors, and welds.The welds should be derived from a similar material, and beperformed (automatically) in high quality. In all cases, the weldmust be post-treated by careful pickling and optionally grind-ing/polishing. By carbide formation, the Cr content can belowered at the weld, leading in extreme cases to intergranularcorrosion. Properly executed welds form in air a closed, contin-uous passivation layer in one or two days.

Basically, it is possible to significantly reduce the risk ofchemical and/or microbial corrosion by careful processing ofthe machinery, and the other system components. The surfacesincluding welds should be smooth without scratches or otherdamage. Pipes, valves and pumps must be connected free oftensions and vibrations. In addition, constant cleanings in thetemperature range of 50–85 �C improve the hygiene. A varietyof acidic and alkaline cleaning solutions, optionally mixed withoxidizing agents, are applied one after the other in CIP systems[8]. Stagnant fluid areas are to be avoided.

4.3 Smoothing the Metal Surfaces

4.3.1 Preparations

The manufacture of machinery and equipment requires the pro-cessing of stainless steel in the form of sheets, seamless pipes,and partly steel bars (for shafts). These materials are available indifferent qualities with surfaces that are smooth, polished,brushed, or shiny polished [9]. The average Ra of cold-rolledsheets is in the range of 0.2–0.5 mm [1], depending on the pre-treatment. This starting material facilitates further operations forthe production of machinery with surfaces in mirror finish.

For cleaning and smoothing the steel surfaces, several meth-ods (Tab. 2) exist. The procedures are usually applied individu-ally or in combination. Absolutely necessary steps represent


Figure 1. Measurements of the electric potential as function of the temperature in 3 % so-dium chloride solution, using various stainless steels (WNr. = material number DIN EN).

the precleaning of the machinery and the pickling of all welds.A smoothing of the surfaces may be carried out chemically ormechanically. If subsequently an electropolishing follows, theequipment always must be completely pickled.

For a perfect result of the pickling, a previous cleaning of thesurfaces is required. In the procedure, the dirt and residue fromthe stickers are removed and a pretreatment for degreasing exe-cuted. Alkaline solutions at elevated temperatures provide goodresults. Clinging dirt, slag residues, or scale layers can be re-moved with stainless steel brushes or by electrolytic processesor ultrasound. Only completely purified surfaces are able toform a continuous passivation layer.

4.3.2 Mechanical Procedures

Through blasting, brushing, grinding, buffing, pickling, andpolishing, esthetic structures on stainless steel surfaces arise forgoods in the private and public sector (gates, railings, wall cov-erings, household items, and appliances). In the industrial sec-tor, however, the surfaces must be corrosion resistant and easilycleanable. Size, accessibility, and application of the metal sur-face determine the method for smoothing. On large areas, suchas the interior walls of a stirred tank, the smoothing is per-formed mechanically by hand with the aid of grinding and pol-ishing machines. Fissured surfaces are preground in a first stepwith coarse sandpaper (grade 60 or 80). Each subsequent steprequires a finer grain size in the gradation up to the maximumfactor of 2, that is, with pastes grit 120, 240–320 and with sand-

ing belts grit P 120, P 240, P 320–600 (Tab. 3) until the desiredtarget (approximately Ra = 0.2–0.4 mm) is reached.

The coarse abrasives eliminate the imperfections in the metalsurface, such as sanding marks, nicks, and hairlines. With pro-gressively finer grits all scratches disappear, even the invisibleones. The high-gloss finish requires appropriate polishingpastes and sanding belts, discs, and high-speed machines. Thegrinding result is highly dependent on the skill of the polishers,their expertise, and equipment (grinding wheel machine, sand-ing pastes). During the ‘‘dry’’ applications in steel polishing,waxes and kerosene are used as a lubricant and a coolant. Forthe smoothing of stainless steel, the polisher needs in graduatedgrain sizes not only sanding particles, made of alumina, silica,or zirconia but also aluminum carbide and silicon carbide andsometimes diamond dust. These mechanical methods removethe scratches, but the base material is not eroded appreciably.The result of extensive polishing is shown in Fig. 2, in the caseof a large two-shaft mixer.

4.3.3 Pickling

Pickling [9] is the process for removing scale layers after heattreatments, residues from welding, annealing colors, sandingdust, abraded metal, external rust, and chromium carbide(which can arise during drilling without a coolant). By actionof the acid (usually nitric acid mixed with hydrofluoric, HFacid), a metal erosion of 1–5 mm occurs at ~ 40 (+ 20) �C. Forsome parts of the plant or for the entire apparatus, the acid


Table 2. Improving stainless steel surfaces.

Procedure Action Execution Achievable roughnessRa [mm] (mean value)

Cleaning as upstream process step Removing coarse dirt High pressure cleaning, steam cleaning(140 �C)

–

Removing dirt and grease, possiblysupported by ultrasound

Dipping into a surfactant-alkaline cleaningsolution, or: spraying with a mixture ofphosphoric acid/surfactant

–

Removing tough dirt Stainless steel brush, electrolytic processes –

Removal of caking Ultrasound –

Mechanical smoothing Making of a clean, matte layer Blasting of surfaces with quartz sand or beadsof glass or of stainless steel or carbon dioxide

< 1.2

Satinized matte structure Brushes (coarse to very fine) –

Shiny, planar surface Buffing (felt disc with decreasing grain sizesof the pastes)

–

Smooth surface (up to mirrorfinish)

Grinding or polishing (with decreasing grainsize)

up to 0.1

Chemical smoothing Passivation layer Accelerated formation with dilute nitric acid –

Removal of scale layers after heattreatment, and of tarnishing afterwelding, further of external rust

Pickling with acids (mixture of nitricand hydrofluoric) in the bath or by spraying

0.5–1.0

Smooth surface (up to mirror finish) Electropolishing, 0.2–0.5

plasma polishing < 0.01

bath is applied. Pickling ensures the subsequent formation of acomplete passive layer, to protect the metal against corrosion.After rinsing with soft water, the formation of the layer beginsin contact with air on the clean surface. Two to eight hours lat-er, the passivation layer is completely present in a thickness ofabout 20 nm. By the addition of oxidizing agents, such as dilutenitric acid or hydrogen peroxide, the layer is formed immedi-ately on all surfaces. In the food and pharmaceutical industries,the passivation is preferably carried out with citric acid at tem-peratures above 40 �C over a period of a few hours.

Pickling is advisable before a mechanical polishing; but con-stitutes an indispensable part of electropolishing. It takes place

with acid mixtures in a dipping and spraying process, or bypumping through tubes (Tab. 4). Welds must always be pickled.If it is not done with the whole apparatus in the bath, the acidis often applied in the form of a paste with a brush. Carefulpickling allows the formation of a passive layer on the welds toprevent corrosion. In addition, pickling improves the appear-ance (Fig. 3). To generate a complete passivation, pickling is inuse for stainless steels, nickel alloys, titanium, and titaniumalloys (Fig. 4). Normal steel, copper, aluminum, and their alloysare cleaned and pickled before electropolishing, chemical de-burring and polishing, anodizing and plating.

4.3.4 Electropolishing

Depending on the diameter and length of tubes, a mechanicalsmoothing of the inner surfaces is difficult to accomplish. Andespecially for small parts, such as pipe bends, fittings, valves,sensors, and pumps, pickling/electropolishing is the appropri-ate method. But large apparatuses, preferably for the pharma-ceutical and biotechnology industry, are also electropolished.The method [11] begins with a cleaning of the metal surfaceswith alkali followed by pickling. Then, electrolysis expires in amixture of concentrated sulfuric and phosphoric acid at ele-vated temperatures (see Tab. 4). The steel parts are placed in abasket, which is connected as the anode. By applying a DC


Table 3. Classification of the grade for abrasive pastes and abrasive papers/sanding belts. a)FEPA: Federation Europeenne des Fabricantsde Produits Abrasifs; b)ANSI: American National Standards Institute, c)[1].

Abrasive grit for pastes,according to

Average grain size of pastesdP [mm]

Abrasive gritfor sandpaperand sanding belts

Average grain sizesof sandpaper andsanding belts dP [mm]

Achievable roughness,mean valuec)

Ra [mm]

FEPAa) ANSIb) FEPA ANSI FEPA

60 – 260 – P20 1000

80 – 185 – P60 269 3.5

100 100 129 125 P120 125 1.1

180 180 69 70 P240 58.5 0.2–0.5

220 220 58 58 P320 46.2 0.15–0.4

320 360 29 28 P600 25.8 0.1–0.25

360 400 23 23 P1000 18.3

400 500 17 18 P2000 10.3

Table 4. Acid treatment of stainless steel [10, 11].

Action Acid (mixture) (Nitric, sulfuric,phosphoric acid)

Hydrofluoric acid[%]

Additives [%](Type)

Temperature[�C]

Duration[min]

Pickling ‘‘classic’’ 10–28 %; HNO3 (50 %) 3–8 0.1 (Surfactants) 15–60 20–300

Pickling‘‘nitrate-free’’

10–25 %; H2SO4 /H3PO4 3–5 1–5 (H2O2) 15–60 20–300

Elektropolishing 1:1; H2SO4 (96 %)/H3PO4

(86 %)– – 40–75 2–20

Figure 2. Large twin-shaft mixer with clean surfaces, polishedto a mirror finish on walls, shafts, and tools. Courtesy of NaraMachinery Co., Ltd. Europe.

voltage (Fig. 5), the ‘‘hills, mountains, and elevations’’ on thesurfaces dissolve, by forming ions. Either they remain dissolvedor fall as mud at the cathode on the ground. During the elec-tropolishing, about 10–40 mm of steel are dissolved from theentire surface, depending on the time, temperature, composi-tion of the acids, and the applied voltage. Thus, not only thecraters but also the inhomogeneous superficial layers andridges disappear. The average roughness is halved by the pro-cess. All these advantages especially appreciate the pharmaceu-tical industry and produced in electropolished plants.

Microscopy images, as shown in Fig. 6, demon-strate that edges are converted into roundness. Forthe achievement of the same smoothness (Ra val-ues of ~0.2mm), electropolishing is a superiormethod. It neither leaves residues nor influencesthe surface mechanically. The method can be com-pletely reproduced worldwide. In contrast to me-chanical polishing, the electropolishing leads, be-sides the smoothing, to a (desired) significanterosion of inhomogeneous layers in the superficialareas. During mechanical polishing, the surfacesare (minimal) deformed by heat and pressure. Of-ten, there remain microscopic scratches and tracesof metal dust and polishing paste. Advantageously,

the mechanical smoothing allows to start with raw materialsurfaces of much higher average roughness (> 3 mm). By usingpastes and sanding belts of various grits, especially when suc-cessively applied, there is a gradual improvement of the surface.In contrast, the electropolishing is usually carried out with amaterial having an average surface roughness of about 0.5 mm.Therefore, some parts like the welding seams must often bemechanically preprocessed.

In the electropolishing process, Fe and Ni dissolve relativelyquickly. Thus, the resulting surface is rich in Cr. Cr determinesthe appearance and corrosion resistance by the passivationlayer formed. Electropolishing of titanium-stabilized stainlesssteel is difficult, because TiC does not dissolve, and the carboncontent of the steel is relatively high. Therefore, similar alloyswithout stabilization and with reduced carbon content (AISI316L, 1.4404, 1.4435) are preferred. After the electrolysis treat-ment of work pieces, a rinsing with nitric acid takes place. Thisconverts the hardly soluble heavy metal salts (sulfates andphosphates) in slightly soluble nitrates. The metal nitrates canbe rinsed off with water, leaving a completely clean metal sur-face.

4.3.5 Plasma Polishing

The new electrolytic polishing method for metals provides ex-tremely smooth surfaces with low average roughness values.These are, with Ra values lower than 0.01 mm, more than afactor of 10 below electropolishing. In the procedure, the(untreated) metallic work pieces are placed in a bath and con-nected to the anode. The bath consists, in contrast to electro-polishing, not of acids but of an aqueous salt solution (2 %).According to information from Plasotec, by applying a highvoltage (> 300 V), a process-induced ignition and spreading ofplasma occurs. This encloses the work pieces as a thin gas layer.Thermal, chemical, and electrochemical processes give a shineon the surfaces that is not achievable with other polishingmethods. The temperature of the work pieces remains below100 �C. A minimal weight loss resulted during the treatment,caused by the leveling of microroughness and the removal ofridges. Furthermore, organic and inorganic surface contami-nants are removed by oxidation.

The amount of abraded metal can be controlled by the pro-cessing time. The typical metal removal is 3–30mm at a rate of3–10mm min–1, wherein the geometric shape is maintained.


Figure 3. Pickling of large equipment in acid baths (right: 90 m3). Courtesy ofSiedentop and Poligrat.

Figure 4. Untreated and pickled stainless steel fitting, alongwith a titanium sheet. Courtesy of Poligrat.

Figure 5. Smoothing of steel surfaces by electropolishing (2–20minutes at 40–75 �C).

Plasma-polished metals exhibit higher corrosion resistancethan the starting material. Figs. 7 and 8 demonstrate the resultsof the plasma polishing on photo shoots in the microscope.The first example is a laser-drilled stainless steel sheet together

with additional images from the scanning electron microscope(SEM). In the second example, a rasp made of a titanium alloyis shown, which obtains a completely smooth surface by plas-ma polishing.

5 Nonferrous (NF)Metals and Alloys

Nickel (Ni 99.2, alloy 200, 2.4066)shows under reducing conditions (ab-sence of air) in the entire temperaturerange an excellent resistance to alkalis.Furthermore, Ni is resistant to dry ha-logens and hydrogen halides. In weaklyoxidizing media, it forms an oxide layerfor protection against acids. But inhighly oxidizing media such as nitricacid or bleach, Ni may corrode rapidly.Caution is advised when using otheracids and/or in the presence of chlorideions from Fe, Ni, and Cu compounds.

For maximum mechanical andchemical requirements of the material,nickel alloys are used, such as for theconstruction of some chemical reactorsand turbines (aircraft, power plants).They show highest stability and goodresistance to pitting, crevice corrosion,and stress corrosion cracking, as well asexcellent resistance to acids, e.g., HCl,


Figure 6. Mixers and heat exchanger, electropolished to prevent the formation of deposits, and a filter plate in 50-fold magnification.Courtesy of Poligrat.

Figure 7. Laser boreholes spaced 150mm in stainless steel (AISI 316L, 1.4404); microscopyand SEM images; left: initial state, right: after plasma polishing. Courtesy of Plasotec.

and caustic solutions, even at high temperatures. Caution is ad-vised in the presence of heavy metal chlorides, similar to pureNi. Under the brand names Monel, Inconel, Hastelloy, Nicro-fer, and others, several comparable nickel alloys of high corro-sion resistance are available (Tab. 5). For each application, asuitable alloy exists.

Incoloy (alloy 625) is used industrially for the constructionof evaporators for phosphoric acid. The alloy 825 is approvedas material for pickling baths, but also in plants for the produc-tion of sulfuric and phosphoric acid, and for the concentratingof sodium hydroxide solution. Hastelloy B2 and C4 are also

suitable for wet chlorine and any acid, in particular, hydrochlo-ric acid, at elevated temperatures. Monel (400, 401, and 404) isa Ni/Cu alloy with 30–53 % Cu and the only resistant metalagainst fluorine, hydrogen fluoride, and hot concentrated hy-drofluoric acid. The superalloys based on Ni represent a conti-nuation of the stainless steel variants in which the Ni- and Mocontent is continuously increased at the expense of the ironand chromium content.

For extreme conditions, Nickel alloys, also the special mate-rials Ti, Zr, and Ta are encountered in chemical apparatuses. Tiis resistant to dilute sulfuric acid, hydrochloric acid, chloride-containing solutions, cold nitric acid, and most organic acidsand bases as well as against sodium hydroxide. In concentratedsulfuric acid, however, it dissolves with the formation of thepurple titanium sulfate. A thin, dense zirconium oxide layer isformed on contact with atmospheric oxygen and passivates themetal. Zr is therefore insoluble in acids and alkalis. Only aquaregia and hydrofluoric acid can attack the metal.

Comparable to Zr, Ta is protected by a thin superficial oxidelayer of tantalum (V)-oxide. Because of the strong passivation,Ta is insoluble in acids, even in aqua regia, and can be usedtherefore almost universally up to 150 �C (Fig. 9). The chemicaland pharmaceutical apparatus engineering used tantalum oftenas alloy with 2.5% tungsten for increased stability. The metal isattacked only by hydrofluoric acid and oleum (a mixture of sul-furic acid and sulfur trioxide) and molten salts. As base metal,Ta reacts with oxygen or halogens at temperatures above 300 �C.


Figure 8. Effect of plasma polishing, demonstrated on a toolmade of a titanium alloy. Courtesy of Plasotec.

Table 5. Composition of important nickel alloys (in [%]), ordered by increasing Ni and Mo contents and decreasing Fe and Cr contents;materials for extreme chemical attack.

Alloy No.Brand nameMaterial number

Ni Fe Co Cr Mo W Si Mn C

825Incoloy2.4858

38.0–46.0 27.0 – 19.5–23.5 2.5–3.0 – 0.5 1.0 0.025

G3Inconel, Nicrofer,Hastelloy2.4619

39.0–50.0 18.0–21.0 5.0 21.0–23.5 6.0–8.0 1.5 1.5 1.0 0.015

XHastelloy2.4669

47.0 18.5 1.5 22.0 9.0 0.6 1.0 1.0 0.1

625Inconel, Nicrofer2.4856

62.0 5.0 1.0 21.5 9.0 – 0.5 0.5 0.1

C4Nicrofer, Hastelloy2.4610

65.0 3.0 2.0 14.0–18.0 14.0–17.0 – 0.08 1.0 0.015

B3/B4Hastelloy, Nicrofer2.4600

65.0 1.0–6.0 2.5–3.0 0.3–3.0 26.0–32.0 0–3.0 0.01–0.05 1.5–3.0 0.01

B2Hastelloy2.4617

69.0 2.0 1.0 1.0 26.0–30.0 – 0.1 1.0 0.02

The prices vary greatly. They are dependent on the qualityand application shape. In 2013, the following prices per kilo-gram were published for the metals: Ti (ingot): 15–20.50 €, Zr(99.6 %): 25–115 €, Ta (> 99.8 %): 290–400 €, calculated with anexchange rate of 1.34 $/€. The high price of Ta is relativizedby the long life of the equipment and the high credit note afterscrapping the system. An estimate from 1997 gives the follow-ing price ratios [12], if the stainless steel AISI 316Ti is setto 100 %: Ti = 270 %, Hastelloy = 470 %, Ta = 2070 %, andgraphite = 145 %.

Using platings, linings, or superficial coatings, the base mate-rial of the plant and machinery is protected and separated fromthe corrosive medium. Stainless steels, special alloys, and super-alloys can be applied over rolling plating or explosion plating(about 3 mm thick plates). For this, various methods have beendeveloped [13]. Thin protective layers can be applied via sput-tering processes.

6 Inorganic Nonmetallic Materials

Inorganic materials such as borosilicate glass or graphite are inuse because of their extreme resistance to most aggressivechemicals. The glass can be combined with superalloys forheating and vaporizing. Other inorganic compounds are suit-able for the formation of a coating layer on a base material suchas steel. These coatings are performed by spraying on multiplelayers, and stand in competition to the plastic and plastic inli-ners. The layer thickness reaches 300mm. Chemical resistances,pressure, and temperatures as well as the mechanical load ca-pacity determine the best coating material. Known examplesare enamel, aluminum oxide, and zirconium dioxide. Mixers,reactors, absorber columns, membranes, mills, pumps, andmany other machinery can be coated with corrosion-resistantoxides or carbides using a spray method. In addition to theknown methods, i.e., flame and high-velocity flame sprayingwith powders, arc and plasma spraying, and cold spraying, andits variants, e.g. vacuum arc and vacuum-plasma and high-fre-

quency plasma spraying, there are new processes such as laserspraying and molten bath [13]. Except the sinter and melt pro-cedures, the aluminum oxide can be processed in the form oftiles, mosaic tiles, and strips [14].

Besides the carbides and oxides, almost all metallic materialsand alloys can be applied with these spray processes. The metalin the form of a wire, rod, or powder melts in the spray gun. Inthe electric arc spraying, the metal wire is melted at 4000 �C atthe top and applied via an inert carrier gas, Ar or N2, on theworkpiece in a layer thickness of 0.2–20 mm. This is also possi-ble for the superalloys and special metals.

6.1 Borosilicate Glass

Owing to its extreme resistance to aggressive chemicals and su-perior hygienic properties, borosilicate glass has been proven inmany laboratory and pilot plants as well as in small produc-tions. The pharmaceutical industry often uses this material,which is assigned to the highest (best) hydrolytic class 1 (ameasure of the alkalinity of the glass according to ISO 719).Borosilicate glass is resistant to all chemicals except hydrofluo-ric acid and hot phosphoric acid, and is characterized by highthermal stability and resistance to sudden temperature changes.Possible temperatures are –50 to 200 �C, limited by the bellowsand sealing materials. The glass itself withstands –196 �C (liq-uid nitrogen) up to 250 �C. Many parts of a production linemay consist of glass in combination with other special materi-als, for example, Ta or Hastelloy, for processing the corrosivechemicals (Fig. 10). The glass limits the size of tanks, reactors,and pipelines and the height of the operating pressure. Only at-mospheric, reduced pressure or minimal excess pressure can beapplied, depending on the size of the components.

Also, to observe processes such as the operations in the ap-paratuses, the installations are built of transparent material.During the tension-free construction of the system, it is neces-sary, similar to using graphite, to pay attention to the fragilityof small components.

6.2 Vitreous Enamel

When carrying out reactions under pressure, enameled reactors(Fig. 11), tanks, columns, pipes, and valves are used for aggres-sive substances in the pressure range of –1 to 6 bar with tem-peratures of –25 to 200 �C. On the wetted steel surfaces of thestirred vessel, the manufacturer applies two to five layers ofa thickness from 1.4 to 2 mm, up to a volume of 80 m3

(EN 15159-01:2006). The enamel layer is made of glass-form-ing oxides such as borax (B2O3), quartz (SiO2), and feldspar(Si, Al, B, K, Na . . .), besides clay (Al2O3) and various heavymetal oxides. Enamel shows extremely good chemical resis-tance in an acidic environment, as with all glasses. Because ofthe chemical properties of silicates, they are not suitable for thealkaline region.


Figure 9. Equipment with product wetted parts made of Ta;a) steel vessel with Ta lining (explosion bonded); b) Ta tank;c) vertical bajonet heater, bottom plate made of steel with a tan-talum lining, tantalum tubes (Ta + 2.5 % W); d) column shell ofstainless steel with Ta lining (di = 1.1 m); e) heat exchanger madeof steel (stainless steel compensator) with Ta + 2.5 % W- tubes.Courtesy of Tantec.

6.3 Graphite

Graphite is used in chemical apparatus engineering for heat ex-changers, coolers, and condensers as well as falling-film eva-porators and absorbers, especially for the production and pro-cessing of mineral acids, such as hydrochloric, sulfuric,hydrofluoric, and phosphoric acid. For heat exchangers, largeheat exchange areas exist (over 2000 m2). The standard versionoperates up to 6 bar/180 �C (Fig. 12), special designs up to12 bar.Graphite tubes are also used as support material for micro- andultrafiltration membranes with zirconia or alumina as filterlayer. These combinations allow the crossflow separation of(aggressive) liquids from solids at high superficial velocities(Fig. 13).

7 Plastics

To ensure chemical stability, coatings are in use atpresent [15]. These originate not only from metals(e.g., superalloys) but also from nonmetals. As dis-cussed, typical inorganic materials are oxides,graphite, and glasses. Widespread organic materialsrepresent the different polymers with interestingproperties regarding the processability and chemi-cal stability [16].

In chemical plants, various plastics are used,mainly because the plastic materials offer high cor-


Figure 10. Plants partly or entirely made of borosilicate glass; a) small pharmaceutical plant; b) condenser; c) extraction and rectificationcolumn; d) gas absorber; and e) chemical reactor. Courtesy of QVF.

Figure 11. Anchor and turbostirrer in enameled chemical reactors (Jurec, Wiki-pedia, GNU Free Documentation).

Figure 12. Shell and tube heat exchanger with Diabon-tubes,right: graphite block heat exchanger. Courtesy of SGL-Carbon.

rosion resistance and cost advantages in comparison to othervariants. Examples (Fig. 14) are containers, large tanks, bigbags, silos, piping, pumps, valves, bellows, and sealings, inwhich the liquids come in contact only with plastic. The chemi-cal resistance of steel machinery and equipment, especially offiberglass tanks, is ensured by lining and coating with suitableplastics (Tab. 6) [17]. Alternatively, the manufacturer uses plas-tic inliners in containers or equipment made entirely of plastic.Inliners are hanged bags without a fixed connection to the basematerial.

The stability and chemical resistance of plasticsis limited in temperature. All plastic materials tol-erate 50 �C, several plastics 90 �C, and only a few,such as polytetrafluoroethylene (PTFE) and similarcompounds (see Tab. 6), even up to 200 �C. PTFE[18] is a widely used material for sealings, coatingsand linings. It requires special methods, becausePTFE cannot be processed by injection molding, asopposed to perfluoroalkoxy alkanes (PFA).

In general, the maximum working temperaturemay be higher for short-term use as in continuousoperation. Temperature limits and the chemical re-sistance [19] of some typical fluids are shown incorrosion Tab. 7. Sealing materials [20], such as

O-rings, are often made of elastic polymers, e.g., of ethylenepropylene diene monomer (EPDM) for sterile double mechani-cal seals. Always, the chemical resistance must be verified indetail in corrosion tables and/or in experiments. High attentionis always necessary for polar solvents (acetone), aromatic andchlorinated hydrocarbons, as well as for strong acids and bases.

Sealless pumps of high chemical stability up to 180 �C arecoated with plastics (Fig. 15). Aggressive, hazardous liquids canbe transported safely with a PFA-lined centrifugal pump,equipped with a magnetic drive (conforms to DIN EN 22858).This sealless centrifugal pump is resistant to corrosion. The liq-uids come in contact only with PFA, a polymer similar toTeflon. The polymer is a further development of PTFE and canbe processed as a typical thermoplastic. In another type ofpumps, the housing and the impeller are made completely ofplastics, accordingly to the chemical and thermal requirement,out of PP (polypropylene) or PVDF.

GRP represents a fiber-plastic composite made of a plasticand fiberglass [21]. As base, thermosets, e.g., polyester or epoxyresin, and thermoplastics (PA, polyamide) are used. GRP, alsocalled GFK (glasfaserverstarkter Kunststoff), shows an excellentcorrosion resistance in aggressive environments, especially in


Figure 13. Inorganic microfiltration membrane, consisting of agraphite support tube, and a thin zirconia layer at the inner sur-faces (adjusted to an average pore size of 0.14 mm).

Figure 14. Storage silos for bulk materials: a) silos with flexible walls for plastic pellets; b) emptying of a big bag; c) discharge aid for aflexible silo; and d) glass-fiber reinforced polyester silo. Courtesy of A.B.S. Silo and Conveyor Systems (a, b, c) and Hans Gaab (d).

Figure 15. Two different sealless centrifugal pumps with magnetic drive for ag-gressive liquids; left: PFA lined pump, courtesy of CP Pumps. Right: impeller andhousing completely made of plastic, courtesy of Schmitt centrifugal pumps.

mineral acids (Fig. 16). In addition, in special cases, a liningimproves the chemical resistance. Therefore, GRP is not only asuitable material at normal and moderate temperatures (up to80 �C) for the production equipment and container in thechemical industry but also an economical solution in compari-son to stainless steel. Pure GRP is problematic for use in thepharmaceutical, biotechnology, and cosmetic industries, be-cause microorganisms can penetrate into the material, unat-tainable for the cleaning solutions. In these and similar applica-tions, polished stainless steel represents the better material.

The author has declared no conflict of interests.

Wilfried Rahse was the direc-tor of process development atHenkel AG & KGaA. In R&D/Technology Laundry andHomecare, his focus was prod-uct design and development ofinnovative processes and prod-ucts for safeguarding the futureas well as biotechnology(downstream processing of en-zymes). His efforts promotedthe erection of major produc-tion plants for enzyme pro-

cessing, Megaperls, and of superheated steam drying. Aftera short retirement period, he joined ATS-License GmbH(Cosmeceuticals) in 2010 as a partner for product develop-ment. Born 1947 in Berlin, he studied chemistry and chemi-cal engineering at the TU Berlin and graduated in 1976 withhis PhD. After his assistantship (1971–77), he worked forHenkel in process development, production, and environ-mental technology for 30 years.


Table 6. A method for lining and coating of equipments and components with plastics; polymers partially reinforced with fibers, non-wovens, mica, carbon fibers, and glass slides. FEP–fluorinated ethylene propylene; E-CTFE–ethylene chloro trifluoro ethylene; HDPE–highdensity polyethylene; PIB–polyisobutylene; PA–polyamide, and PES–polyethersulfone; the other abbreviations are explained in Tab. 7.

Process Principle Plastic (examples, abbreviations see also Tab. 7) Layer thickness[mm]

Lining with plates, tiles Stick on and weld together of preformedpanels

PE, PP, PVC, PVDF, PU, (PU)-elastomer(Vulkollan), GFK, PFA, FEP, E-CTFE

3–20

Lining with sheetsor laminates

Stick on and weld together; application andhardening of impregnated glass fiber mats

HDPE (high-density), PVC, PIB(polyisobutylene), rubber, resins (epoxy,furan, vinyl ester, polyurethane)

3–12

Smooth over, paint Applying a ceramic reinforced epoxy resin,or other systems

Various resins (epoxy, vinyl ester, polyester) about 2

Dipping All-round seamless coating PVC systems with adhesion promoter 1–8

Thermal spraying, sputtern(primarily flame spraying)

Melting in the spraying unit, heat supplyto the workpiece by the flame

All thermoplastics, sprayable resins(epoxy, novolac, vinyl ester, bisphenol,and mixtures thereof), and rubbers (systems)

0.03–3

Injection molding in anadapted form

Insertion and fixing of the moldings Many thermoplastics about 0.5–5

Powder coating Sprinkle the powder on the workpiece bya flat spray nozzle and thenthe powder melts by heat

PE, PA (polyamide), PU, Powder coatings,epoxy and polyester resins

0.015–0.03

Electrostatic powder coating Negatively charged powder meets positivelycharged component and then the powdermelts by heat

PE, PA, PVC, polyester, PU, epoxy andpolyacrylate resins

0.04–0.6 (up to 1)

Fluidized bed sintering Placing the preheated component in a fluidizedbed, and the powder melts at the surface

PE, PA, PES, epoxy resin about 0.1–0.3

Sewer renovation A long hose with a wound up resin/hardenersoaked tissue is inflatedand hardens in the old pipe

Unsaturated polyester resins (UP resins),according to DIN 18820

about 1–3

Figure 16. GFK-storage tanks for liquids: a) demineralized watertank PVDF/GRP; b) two acid tanks for 33 % hydrochloric acid,each 1000 m3 in size. Courtesy of Christen & Laudon.


Table 7. Plastic materials in chemical apparatus engineering for tanks, containers, big bags and silos (t), inliners and lining material (i),pipes (p), coatings (c) and sealings (s). a)Depending on the application.

Material (chemical name) Abbreviations Application Maximum operationtemperaturea) [�C]

Characteristics of corrosion resistance

Polyvinyl chloride(without plasticizer)

PVC p 60 Resistant to most acids, alkaline and salt sol-utions, furthermore to water-miscible organ-ic compounds; Not resistant to aromatic andchlorinated hydrocarbons

Polyvinyl chloride,after chlorination

PVC-C p 90 Same features as for PVC, but for highertemperatures

Polyethylene PE t, p 60 (40–90,increasing withcrystallinity)

Resistant to aqueous solutions of acids,alkalis, salts and several organic liquids;Not resistant to oxidizing acids

Polypropylene(heat stabilized)

PP t, i, p, c 90 Analog to PE, but for higher temperatures

Polyvinylidene fluoride PVDF i, p, c, s 130 Resistant to acids, salt solutions, aliphaticand aromatic and chlorinated hydrocarbons,alcohols and halogens; Limited resistance toketones, esters, ethers, organic bases andalkalis

Polytetrafluoro-ethylene PTFE i, p, c, s 180–200 Resistant to almost all chemicals

Perfluoroalkoxy-polymer(Teflon, and other)

PFA i, p. c, s 180–200 Similar to PTFE, but meltable for processing

Glass-fibre reinforced polyesterresin

GFK-UP t, p 80 Resistant to acids and aqueous salt solutions,oils and glycerolNot resistant to many organic hydrocarbons

Glass-fibre reinforcedepoxy resin

GFK-EP t, p 100 Analog to GFK-UP

Nitrile-butadiene rubber NBR i, c, s –30 up to 70 inaqueous, 90 ingaseous systems

Resistant to oil, gasoline, and aliphatichydrocarbons; Not resistant to oxidizingsubstances, benzene, esters

Fluoronated hydrocarbon(e.g., Viton)

FKM s –25 up to 200 Resistant to ozone, oils and many organicsolvents, best chemical stability of allelastomers; Not resistant to polar solvent(acetone), glycols, organic acids and bases

Ethylene propylenediene monomer

EPDM s 90 Resistant to ozone, and to many aggressivechemicals, also diluted acids;Not resistant to oils, fats and petroleumproducts

Polyacrylate rubber ACM i, c, s –10 up to 150 Resistant to ozone, hot oil and oxidizingenvironment;Not resistant to moisture, acids and bases

Silicone rubber VMQ (ASTM)/MVQ (DIN, ISO)

s –55 up to 100(oxygen, water) 210for hot air

Resistant to oil and fats, glycols, ozone;Not resistant to aromatic and chlorinatedhydrocarbons, superheated steam, acids andbases

Polyurethane PU i, c, s –50 up to 130 Lining and coating material; PU formsresistant casted seals, single use only;Resistant to oils and fats, diluted acids;Not resistant to bases

References

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The materials for production plantsmust be chemically resistant underoperating conditions for a long time.In addition, they often must meethygienic requirements. In this work,evidence is given to the developers andoperators of plants on the properties ofrelevant materials during the planningand design stage before newmachinery is purchased.

Industrial Product Design:Materials for the Machinery

W. Rahse

ChemBioEng Rev. 2014, 1 (3),XXX L XXX

DOI: 10.1002/cben.201400009

book 1,6 mb

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