Encyclopedia of Corrosion Technology, Second Edition

FFERRITE

Pure iron when heated to 1670F (910C) changes its internal crystalline structure from abody-centered cubic arrangement of atoms, alpha iron, to a face-centered cubic structure,gamma iron. At 2535F (1393C) it changes back to the body-centered cubic structure,delta iron, and at 2802F (1538C) the iron melts. When carbon is added to iron, it is foundthat it has only slight solid solubility in alpha iron (less than 0.001 percent at room tem-perature). On the other hand, gamma iron will hold up to 2.0% carbon in solution at2066F (1129C). The alpha iron containing carbon or any other element in solid solutionis called ferrite. Usually when not in solution in the iron the carbon forms a compound Fe3C(iron carbide), which is extremely hard and brittle and is known as cementite. The physicalproperties of the ferrite are approximately that of pure iron and are characteristic of themetal. The presence of cementite does not in itself cause steel to be hard, but rather it is theshape and distribution of the carbides in the iron that determine the hardness of the steel.

Since ferrite does not contain enough carbon to permit the formation of marten-site, it cannot be hardened by heat treatment. Therefore, steels composed of only ferriteare not hardenable by heat treatment.

The generic term ferritic steel is used to refer to carbon or low-alloy steels that containother phases in addition to ferrite. These steels are usually hardenable by heat treatment.

FERRITIC STAINLESS STEELS

The ferritic stainless steels are the simplest of the stainless steel family of alloys since theyare principally ironchromium alloys. They are magnetic, have body-centered cubic struc-tures, and possess mechanical properties similar to those of carbon steel, though less ductile.Refer to Table F.1 for the physical and mechanical properties of ferritic stainless steels.

This class of alloys usually contains 1518% chromium, although they can go aslow as 11% in special cases, under the influence of other alloying elements, or as high as30%. Continued additions of chromium will improve corrosion resistance in severe envi-ronments. Chromium additions are particularly beneficial in terms of resistance in oxi-dizing environments, at both moderate and elevated temperatures. Addition ofchromium is the most cost-effective means of increasing corrosion resistance of steel.

These materials are historically known as 400 series stainless as they were identifiedwith numbers beginning with 400 when the American Institute for Iron and Steel (AISI)had the authority to designate alloy compositions. Under the new UNS system, the oldthree-digit numbers were retained, such as the old 405, a basic 12% chromium, balanceiron material, which is now S40500.

Copyright 2004 by Marcel Dekker, Inc.

Corrosion resistance is rated good, although ferritic alloys do not resist reducing acids,such as hydrochloric. Mildly corrosive conditions and oxidizing media are handled satis-factorily. Type 403 finds wide application in nitric acid plants. Increasing the chromiumcontent to 24% and 30% improves the resistance to oxidizing conditions at elevated tem-peratures. These alloys are useful for all types of furnace parts not subject to high stress.

Ferritic stainless steels offer useful resistance to mild atmospheric corrosion andmost fresh waters. They will corrode with exposure to seawater atmospheres.

Type 405 (S40500)Type 405 stainless is designed for use in the as-welded condition; however, heat treatmentimproves corrosion resistance. The chemical composition is given in Table F.2.

This alloy is resistant to nitric acid, organic acids, and alkalies. It will be attacked bysulfuric, hydrochloric, hydrofluoric, and phosphoric acids as well as seawater. It is resis-tant to chloride stress corrosion cracking.

Table F.1 Physical and Mechanical Properties of Ferritic Stainless Steels

Type of alloy

Property 430 444 XM-27

Modulus of elasticity 106 29 29Tensile strength 103, psi 60 60 70Yield strength 0.2% offset 103, psi 35 40 56Elongation in 2 in., % 20 20 30Hardness, Brinell B-165 217 Rock. B-83Density, lb/in.3 0.278 0.28 0.28Specific gravity 7.75 7.75 7.66Specific heat (32212F), Btu/lbF 0.11 0.102 0.102Thermal conductivity, Btu/lbF

at 70F (20C) 15.1 17.5at 1500F (815C) 15.2

Thermal expansion coefficient (32212F) 106 in./in.F 6.0 6.1 5.9

Table F.2 Chemical Composition of Ferritic Stainless Steels

AISItype

Nominal composition (%)

C max. Mn max. Si max. Cr Othera

405 0.08 1.00 1.00 11.5014.50 0.100.30 Al430 0.12 1.00 1.00 14.0018.00430F 0.12 1.25 1.00 14.0018.00 0.15 S min.430(Se) 0.12 1.25 1.00 14.0018.00 0.15 Se min.444 0.025 1.00 1.00 max. 17.519.5 1.752.50 Mo446 0.20 1.50 1.00 23.0017.00 0.25 max. NXM27b 0.002 0.10 0.20 26.00aElements in addition to those shown are as follows: phosphorus0.06% max. in types 430F and 430(Se), 0.0 15% in XM-27; sulfur0.03% max. in types 405, 430, 444, and 446, 0.15% min. type 430F, 0.01% in XM-27; nickel1.00% max. in type 444, 0.15% in XM-27; titanium + niobium0.80% max. in type 444; copper0.02% in XM-27; nitrogen0.010% in XM-27.bE-Brite 26-1 Trademark of Allegheny Ludlum Industries Inc.


FApplications include heat exchanger tubes in the refining industry and other areaswhere exposure may result in the 885F (475C) or sigma temperature range. It has anallowable maximum continuous operating temperature of 1300F (705C) with an inter-mittent allowable temperature of 1500F (815C).

Type 409 (S40900)This is an 11% chromium alloy stabilized with titanium. It has the following composition:

The primary application for alloy 409 is in the automotive industry as mufflers,catalytic converters, and tailpipes. It has proven an attractive replacement for carbon steelbecause it combines economy and good resistance to oxidation and corrosion.

Type 430 (S43000)This is the most widely used of the ferritic stainless steels. The chemical compositionwill be found in Table F.2. In continuous service, type 430 may be operated to a maxi-mum temperature of 1500F (815C) and 1600F (870C) in intermittent service.However, it is subject to 885F (475C) embrittlement and loss of ductility at subzerotemperatures.

Type 430 stainless is resistant to chloride stress corrosion cracking and elevated sul-fide attack. Applications are found in nitric acid services, water and food processing,automobile trim, heat exchangers in petroleum and chemical processing industries,reboilers for desulfurized naphtha, heat exchangers in sour water strippers, and hydrogenplant effluent coolers. The compatibility of type 430 stainless steel with selected corro-dents is provided in Table F.3.

Stainless steel type 430F is a modification of type 430. The carbon content isreduced to 0.065%, manganese to 0.80%, and silicon to 0.30.7% while 0.5% molybde-num and 0.60% nickel have been added. This is an alloy used extensively in solenoidarmatures and top plugs. It has also been used in solenoid cores and housings operating incorrosive atmospheres.

Type 430F stainless should be considered when making machined articles from a17% chromium steel. The composition has been altered by increasing the manganesecontent to 1.25% and the phosphorus content to 0.06%, with the sulfur content at0.15% minimum and the addition of 0.60% molybdenum. This material will not hardenby heat treatment. It has been used in automatic screw machines for parts requiring goodcorrosion resistance such as aircraft parts and gears.

Chemical Weight Percent

Carbon 0.08Manganese 1Silicon 1Chromium 10.511.75Nickel 0.5Phosphorus 0.045Sulfur 0.045Titanium 0.6 % Cr min. to 0.75% maxIron Balance


Table F.3 Compatibility of Ferritic Stainless Steels with Selected Corrodentsa

Chemical 430 (F/C) 444 (F/C) XM-27 (F/C)

AcetaldehydeAcetamideAcetic acid 10% 70/21 200/93 200/93Acetic acid 50% x 200/93 200/93Acetic acid 80% 70/21 200/93 130/54Acetic acid, glacial 70/21 140/60Acetic anhydride 90% 150/66 300/149Aluminum chloride, aqueous x 110/43Aluminum hydroxide 70/21Aluminum sulfate xAmmonia gas 212/100Ammonium carbonate 70/21Ammonium chloride 10% 200/93Ammonium hydroxide 25% 70/21Ammonium hydroxide, sat. 70/21Ammonium nitrate 212/100Ammonium persulfate 70/21Ammonium phosphate 70/21Ammonium sulfate 1040% xAmyl acetate 70/21Amyl chloride xAniline 70/21Antimony trichloride xAqua regia 3:1 xBarium carbonate 70/21Barium chloride 70/21b

Barium sulfate 70/21Barium sulfide 70/21Benzaldehyde 210/99Benzene 70/21Benzoic acid 70/21Borax 5% 200/93Boric acid 200/93a

Bromine gas, dry xBromine gas, moist xBromine liquid xButyric acid 200/93Calcium carbonate 200/93Calcium chloride xCalcium hypochlorite xCalcium sulfate 70/21Carbon bisulfide 70/21Carbon dioxide, dry 70/21Carbon monoxide 1600/871Carbon tetrachloride, dry 212/100


FChemical 430 (F/C) 444 (F/C) XM-27 (F/C)

Carbonic acid xChloracetic acid, 50% water xChloracetic acid xChlorine gas, dry xChlorine gas, wet xChloroform, dry 70/21Chromic acid 10% 70/21 120/49Chromic acid 50% x xChromyl chlorideCitric acid 15% 70/21 200/93 200/93Citric acid, concentrated xCopper acetate 70/21Copper carbonate 70/21Copper chloride x xCopper cyanide 212/100Copper sulfate 212/100Cupric chloride 5% xCupric chloride 50% xEthylene glycol 70 /21Ferric chloride x 80/27Ferric chloride 10% in water 75/25Ferric nitrate 1050% 70/21Ferrous chloride xFerrous nitrateFluorine gas. dry xFluorine gas, moist xHydrobromic acid, dilute xHydrobromic acid 20% xHydrobromic acid 50% xHydrochloric acid 20% xHydrochloric acid 38% xHydrocyanic acid 10% xHydrofluoric acid 30% x xHydrofluoric acid 70% x xHydrofluoric acid 100% x xIodine solution 10% xLactic acid 20% x 200/93 200/93Lactic acid, concentrated xMagnesium chloride 200/93Malic acid 200/93Muriatic acid xNitric acid 5% 70/21 200/93 320/160Nitric acid 20% 200/93 200/93 320/160Nitric acid 70% 70/21 x 210/99Nitric acid, anhydrous x xNitrous acid 5% 70/21

Table F.3 Compatibility of Ferritic Stainless Steels with Selected Corrodentsa (Continued)


Type 430FR alloy has the same chemical composition as type 430F except for increasingthe silicon content to 1.001.50%. This alloy is used for solenoid valve magnetic core compo-nents, which must combat corrosion from atmospheric fresh water and corrosive environments.

Type 439L (S43035)The composition of this alloy is as follows:

Chemical 430 (F/C) 444 (F/C) XM-27 (F/C)

Phenol 200/93Phosphoric acid 5080% x 200/93 200/93Picric acid xSilver bromide 10% xSodium chloride 70/21b

Sodium hydroxide 10% 70/21 212/100 200/93Sodium hydroxide 50% x 180/82Sodium hydroxide, concentrated xSodium hypochlorite 30% 90/32Sodium sulfide to 50% xStannic chloride xStannous chloride 10% 90/32Sulfuric acid 10% x x xSulfuric acid 50% x x xSulfuric acid 70% x xSulfuric acid 90% x xSulfuric acid 98% x 280/138Sulfuric acid 100% 70/21 xSulfuric acid, fuming xSulfurous acid 5% x 360/182Thionyl chlorideToluene 210/99Trichloroacetic acid xWhite liquorZinc chloride 20% 70/21b 200/93

aThe chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. Compatibility is shown to the maximum allowable temperature for which data are available. Incompatibility is shown by an x. A blank space indicates that data are unavailable. When compatible, the corrosion rate is < 20 mpy.bPitting may occur.Source: PA Schweitzer. Corrosion Resistance Tables. 4th ed. Vols. 13 New York: Marcel Dekker, 1995.

Chemical Weight Percent

Carbon 0.07 max.Manganese 1.00 max.Silicon 1.00 max.Chromium 17.019.0Nitrogen 0.50Titanium 12 % C min.Aluminum 0.15 max.

Table F.3 Compatibility of Ferritic Stainless Steels with Selected Corrodentsa (Continued)


FThis alloy resists intergranular attack and formation of martensite in the as-welded heat-affected zone but is subject to 885F (475C) embrittlement.Alloy 439L is resistant to chloride stress corrosion, organic acids, alkalies, and nitric

acid. It will be attacked by sulfuric hydrochloric, hydrofluoric, and phosphoric acids, aswell as seawater.

Applications include heat exchangers, condensers, feedwater heaters, tube oil cool-ers, and moisture separator reheaters.

Type 444 (S44400)The chemical composition of this alloy will be found in Table F.2. This is a low-carbonalloy with molybdenum added to improve chloride pitting resistance. It is virtuallyimmune to chloride stress corrosion cracking. The alloy is subject to 885F (475C)embrittlement and loss of ductility at subzero temperatures.

The chloride pitting resistance of this alloy is similar to that of types 430 and 439L.Like all ferritic stainless steels, type 444 series relies on a passive film to resist corrosionbut exhibits rather high corrosion rates when activated. This characteristic explains theabrupt transition in corrosion rates that occur at particular acid concentrations. Forexample, it is resistant to very dilute solutions of sulfuric acid at boiling temperature butcorrodes rapidly at higher concentrations. The corrosion rates of type 444 in stronglyconcentrated sodium hydroxide solutions are also higher than those for austenitic stain-less steels. The compatibility of type 444 alloy with selected corrodents will be found inTable F.3. In general, the corrosion rate of type 444 is considered equal to that of type304 stainless steel.

This alloy is used for heat exchangers in chemical, petroleum, and food processingindustries as well as piping.

Type 446 (S44600)Type 446 is a heat-resisting grade of ferritic stainless steel. It has a maximum temperaturerating of 2000F (1095C) for continuous service and a maximum temperature rating of2150F (1175C) for intermittent service. The chemical composition will be found inTable F.2.

This nonhardenable chromium steel exhibits good resistance to reducing sulfurousgases and fuel-ash corrosion. It also has good general corrosion in mild atmospheric envi-ronments, fresh water, mild chemicals, and mild oxidizing conditions.

Applications include furnace parts, kiln linings, and annealing boxes.See Refs. 2 and 3.

FIBERGLASS

Fiberglass was developed during and immediately after World War II. Fiberglass ismade by a number of different processes, such as melt spinning or by drawing froma marble. At the present time E and C glass predominate, which are boroalumino-silicate and aluminosilicate glass, respectively. The major use is as a reinforcingmaterial for various plastic resins. To improve adhesion of these glasses to resins,various so-called binders have been developed, the most common of which are thesilanes.

Also refer to Thermoset Reinforcing Materials.


FIBER-REINFORCED PLASTICS (COMPOSITES)

Plastic resins, particularly the thermosets, require some type of reinforcing material toprovide strength and stability. Reinforcement is also used with thermoplasts on occasionto provide additional strength.

Many types of fibers are used as reinforcing materials, with glass being the predom-inant material used. Other materials used include carbon, boron, silicon carbide, polyes-ter fibers, and aramid fibers. It is essential that the polymer and reinforcing fiber both beresistant to the chemical being handled and that they both be suitable for use at the max-imum temperature desired.

Additional information can be found by referring to the specific fiber and resin.

FILIFORM CORROSION

Metals with semipermeable coatings or films may undergo a type of corrosion resulting innumerous meandering threadlike filaments of corrosion beneath the coatings or films.The essential conditions for this form of corrosion to develop are generally high humidity(65% to 95% relative humidity at room temperature), sufficient water permeability ofthe film, stimulation by impurities, and the presence of film defects (mechanical damage,pores, insufficient coverage of localized areas, air bubbles, salt crystals, or dust particles).

The threadlike filaments of corrosion spread in a zigzag manner. The filaments are0.1 to 0.5 mm wide and grow steadily but do not cross each other. Each filament has anactive head and inactive tail. If an advancing head meets another filament, it gets divertedand starts growing in another direction.

Filiform corrosion has been observed on aluminum, steel, zinc, and magnesium,usually under organic coatings such as paints and lacquers. It has also been found undertin, enamel, and phosphate coatings. The attack does not damage the metal to any greatextent, but the coated surface loses its appearance.

On steel the tail is usually red-brown and the head blue, indicating the presence ofFe2O3 or Fe2O3 nH2O at the tail and Fe

2+ ions in the head as corrosion product. The growthmechanism is explained by the formation of a differential aeration cell. The head absorbs waterfrom the atmosphere because of the presence of a relatively concentrated solution of ferroussalts, and hydrolysis creates an acidic environment (pH 14). Oxygen that diffuses throughthe film tends to accumulate more at the interface between the head and tail. Lateral diffusionof oxygen serves to keep the main portion of the filament cathodic to the head.

Filiform corrosion can be prevented by reducing the relative humidity of the environ-ment to below 65%. Films having a very low water permeability will also provide protection.

See Refs. 1 and 4.

FLUOREL

See Fluoroelastomers.

FLUOROELASTOMERS (FKM)

Fluoroelastomers are fluorine-containing hydrocarbon polymers with a saturated structureobtained by polymerizing fluorinated monomers such as vinylidene fluoride, hexafluoroprene,


Fand tetrafluoroethylene. The result is a high-performance synthetic rubber with exceptionalresistance to oils and chemicals at elevated temperatures. Initially this material was used to pro-duce O-rings for use in severe conditions. Although this remains a major area of application,these compounds have found wide use in other applications because of their chemical resistanceat high temperatures and other desirable properties.

As with other rubbers, fluoroelastomers are capable of being compounded with var-ious additives to enhance specific properties for particular applications. Fluoroelastomersare suitable for all rubber processing applications, including compression molding, injec-tion molding, injection/compression molding, transfer molding, extrusion, calendering,spreading, and dipping.

These compounds possess the rapid recovery from deformation, or resilience, of atrue elastomer and exhibit mechanical properties of the same order of magnitude as thoseof conventional synthetic rubbers.

Fluoroelastomers are manufactured under various trade names by different manu-facturers. Three typical materials are listed below.

These elastomers have the ASTM designation of FKM.

Physical and Mechanical PropertiesThe general physical and mechanical properties of fluoroelastomers are similar to thoseof other synthetic rubbers. General-purpose compounds have a hardness of 7075Shore A. Formulations are produced that have hardnesses ranging from 45 to 95 ShoreA. At elevated temperatures, 250500F(121260C), hardness may decrease by 515points depending upon the polymer and the formulation. These variations must hetaken into account when specifying hardness of products to be used at elevatedtemperatures.

Fluoroelastomer compounds have good tensile strengths, ranging from 188 to 2900psi. In general, the tensile strength of any elastomer tends to decrease at elevated temper-atures; however, this loss in tensile strength is much less with the fluoroelastomers. Per-cent elongation at break is an indication of operating life. A high percentage is essentialwhen high resistance to bending stress is required for the application. These elastomershave a range of 100400%. The ability of fluoroelastomers to recover their originaldimension after compression and their exceptional thermal resistance make it possible tofabricate cured items with very low set compression values even under the most severeoperating conditions. These values become even more meaningful at elevated tempera-tures when it is realized that most rubbers have a maximum service temperature of lessthan 250F (121C). Table F.4 lists the physical and mechanical properties of the fluo-roelastomers.

The resilience of the fluoroelastomers makes them suitable for application as vibra-tion isolators at elevated temperatures and as vibration dampers (energy absorbers) atroom temperature. In the latter case, because of cost, they would normally be used only

Trade name Manufacturer

Viton DuPontTechnoflon AusimontFluorel 3M


in extremely corrosive atmospheres. These rubbers can be applied as coatings to fabrics oradhered to a variety of metals to provide fluid resistance to the substrate.

The temperature resistance of the fluoroelastomers is exceptionally good over awide temperature range. At high temperatures their mechanical properties are retainedbetter than those of any other elastomer. Compounds remain usefully elastic indefinitelywhen exposed to aging up to 400F (204C). Continuous service limits are generally con-sidered to be as in the table.

Table F.4 Physical and Mechanical Properties of Fluoroelastomersa

Specific gravity 1.8Specific heat 0.395Brittle point 25 to 75F (32 to 59C)Coefficient of linear expansion 88 106/F, 16 105/CThermal conductivityBtu-in./h-ft2 F at 100F 1.58kg-cal/cm-cm2-C-h at 38C 1.96Electrical propertiesDielectric constant at 1000 Hz

at 75F (24C) 10.5at 300F (149C) 7.1at 390F (199C) 9.1

Dissipation factor at 1000 Hzat 75F (24C) 0.034at 300F (149C) 0.273at 390F (199C) 0.391.19

Permeability, cm3 /cm2-cm-sec-atmat 75F (24C)

to air 0.0099 107

to helium 0.892 107

to nitrogen 0.0054 107

at 86F (30C)to carbon dioxide 0.59 107

to oxygen 0.11 107

Tensile strength, psi 18002900Elongation, % at break 400Hardness, Shore A 4595Abrasion resistance GoodMaximum temperature, continuous use 400F (205C)Compression set, %

at 70F (21C) 21at 300F (149C) 32at 392F (200C) 98

Tear resistance GoodResistance to sunlight Excellent Effect of aging NilResistance to heat Excellent

aThese are representative values since they may be altered by compounding.


F

On the low-temperature side, these rubbers are generally serviceable in dynamicapplications down to 10F (23C). Flexibility at low temperature is a function of thematerial thickness The thinner the cross-section, the less stiff the material is at every tem-perature. The brittle point at a thickness of 0.075 in. (1.9 mm) is in the neighborhood of50F (45C). This temperature can have a range of 25 to 75F (32 to 59C)depending upon the thickness and hardness of the material. Fluoroelastomers are rela-tively impermeable to air and gases, ranking about midway between the best and thepoorest elastomers in this respect. This permeability can he modified considerably by theway they are compounded. In all cases permeability increases rapidly with increasing tem-perature. Table F.4 provides some data on the permeability of the fluoroelastomers.

Being halogen-containing polymers, these elastomers are more resistant to burningthan are exclusively hydrocarbon rubbers. Normally compounded material will burn whendirectly exposed to flame but will stop burning when the flame is removed. Natural rubberand synthetic hydrocarbon rubbers under the same conditions will continue to burn whenthe flame is removed. However, it must be remembered that under an actual fire conditionfluoroelastomers will burn. During combustion, fluorinated products such as hydrofluoricacid can be given off. Special compounding can improve the flame resistance. One such for-mulation has been developed for the space program that will not ignite under conditionsof the NASA test, which specifies 100% oxygen at 6.2 psi absolute.

The fluoroelastomers will increase in stiffness and hardness when exposed togamma radiation from a cobalt-60 source. For dynamic applications, radiation exposureshould not exceed 1 107 roentgens. Higher dosages are permissible for static applica-tions. There is no evidence of radiation-induced stress cracking. There are other elas-tomers that exhibit superior radiation resistance. However, high temperatures arefrequently encountered along with exposure to radiation, and in many cases these ele-vated temperatures will rule out the more radiation-resistant elastomers.

Fluoroelastomers are particularly recommended when resistance to ozone, hightemperatures, or highly corrosive fluids is required in addition to radiation resistance.

The dielectric properties of the fluoroelastomers permit them to be used as insulatingmaterials at low tension and frequency in high-temperature applications and in the presenceof higher concentrations of ozone and highly aggressive chemicals. The values of the individualproperties can be greatly influenced by formulation but are generally in the following ranges:

Fluoroelastomers have been approved by the U.S. Food and Drug Administrationfor use in repeated contact with food products. More details are available in the FederalRegister Vol. 33, No. 5, Tuesday, January 9, 1968, Part 121Food Additives, Subpart

3000 h at 450F (232C )1000 h at 500F (260C )240 h at 550F (288C )48 h at 600F (313C )

Direct current resistivity 2 1013 ohm-cmDielectric constant 1015 Dissipation factor 0.010.05Dielectric strength 500 V/mil (2000 V/mm)


FFood Additives Resulting from Contact with Containers or Equipment and FoodAdditives Otherwise Affecting FoodRubber Articles Intended for Repeated Use.

The biological resistance of fluoroelastomers is excellent. A typical compoundtested against specification MIL E-5272C showed no fungus growth for 30 days. Thisspecification covers four common fungus groups.

Resistance to Sun, Weather, and OzoneBecause of their chemically saturated structure, the fluoroelastomers exhibit excellentweathering resistance to sunlight and especially to ozone. After 13 years of exposure inFlorida in direct sunlight, samples showed little or no change in properties or appearance.Similar results were experienced with samples exposed to various tropical conditions inPanama for a period of 10 years. Products made of this elastomer are unaffected by ozoneconcentrations as high as 100 ppm. No cracking occurred in a bent loop test after oneyear exposure to 100 ppm of ozone in air at 100F (38C) or in a sample held at 356F(180C) for several hundred hours. This property is particularly important consideringthat standard tests, such as in the automotive industry, require resistance to only 0.5 ppmozone.

Chemical ResistanceThe fluoroelastomers provide excellent resistance to oils, fuels, lubricants, most mineralacids, many aliphatic and aromatic hydrocarbons (carbon tetrachloride, benzene, toluene,xylene) that act as solvents for other rubbers, gasoline, naphtha, chlorinated solvents, andpesticides. Special formulations can be produced to obtain resistance to hot mineral acids,steam, and hot water.

These elastomers are not suitable for use with low-molecular-weight esters andethers, ketones, certain amines, or hot anhydrous hydrofluoric or chlorosulfonic acids.Their solubility in low-molecular-weight ketones is an advantage in producing solutioncoatings of fluoroelastomers. Table F.5 provides the compatibility of fluoroelastomerswith selected corrodents.

ApplicationsThe main applications for the fluoroelastomers are in those products requiring resistanceto high operating temperatures together with high chemical resistance to aggressive fluidsand to those characterized by severe operating conditions that no other elastomer canwithstand. By proper formulation, cured items can he produced that will meet the rigidspecifications of the industrial, aerospace, and military communities.

Recent changes in the automotive industry that have required reduction in environ-mental pollution, reduced costs, energy saving, and improved reliability have resulted inhigher operating temperatures, which in turn require a higher-performance elastomer.The main innovations resulting from these requirements are

Turbocharging More compact, more efficient, and faster enginesCatalytic exhaustsCx reductionSoundproofing


FTable F.5 Compatibility of Fluoroelastomers with Selected CorrodentsaMaximum

temp.Maximum

temp.

Chemical F C Chemical F C

Acetaldehyde x x Barium hydroxide 400 204Acetamide 210 199 Barium sulfate 400 204Acetic acid 10% 190 88 Barium sulfide 400 204Acetic acid 50% 180 82 Benzaldehyde x xAcetic acid 80% 180 82 Benzene 400 204Acetic acid, glacial x x Benzene sulfonic acid 10% 190 88Acetic anhydride x x Benzoic acid 400 204Acetone x x Benzyl alcohol 400 204Acetyl chloride 400 204 Benzyl chloride 400 204Acrylic acid x x Borax 190 88Acrylonitrile x x Boric acid 400 204Adipic acid 190 88 Bromine gas, dry, 25% 180 82Allyl alcohol 190 88 Bromine gas, moist, 25% 180 82Allyl chloride 100 38 Bromine liquid 350 177Alum 190 88 Butadiene 400 204Aluminum acetate 180 82 Butyl acetate x xAluminum chloride, aqueous 400 204 Butyl alcohol 400 204Aluminum fluoride 400 204 n-Butylamine x xAluminum hydroxide 190 88 Butyl phthalate 80 27Aluminum nitrate 400 204 Butyric acid 120 49Aluminum oxychloride x x Calcium bisulfide 400 204Aluminum sulfate 390 199 Calcium bisulfite 400 204Ammonia gas x x Calcium carbonate I90 88Ammonium bifluoride 140 60 Calcium chlorate 190 88Ammonium carbonate 190 88 Calcium chloride 300 149Ammonium chloride 10% 400 204 Calcium hydroxide 10% 300 149Ammonium chloride 50% 300 149 Calcium hydroxide, sat. 400 204Ammonium chloride, sat. 300 149 Calcium hypochlorite 400 204Ammonium fluoride 10% 140 60 Calcium nitrate 400 204Ammonium fluoride 25% 140 60 Calcium sulfate 200 93Ammonium hydroxide 25% 190 88 Carbon bisulfide 400 204Ammonium hydroxide, sat. 190 88 Carbon dioxide, dry 80 27Ammonium nitrate x x Carbon dioxide, wet x xAmmonium persulfate 140 60 Carbon disulfide 400 204Ammonium phosphate 180 82 Carbon monoxide 400 204Ammonium sulfate 1040% 180 82 Carbon tetrachloride 350 177Ammonium sulfide x x Carbonic acid 400 204Amyl acetate x x Cellosolve x xAmyl alcohol 200 93 Chloracetic acid, 50% water x xAmyl chloride 190 88 Chloracetic acid x xAniline 230 110 Chlorine gas, dry 190 88Antimony trichloride 190 88 Chlorine wet 190 88Aqua regia 3:1 190 88 Chlorine, liquid 190 88Barium carbonate 250 121 Chlorobenzene 400 204Barium chloride 400 204 Chloroform 400 204


Maximumtemp.

Maximumtemp.


Chlorosulfonic acid x x Methyl chloride 190 88Chromic acid 10% 350 177 Methyl ethyl ketone x xChromic acid 50% 350 177 Methyl isobutyl ketone x xCitric acid 15% 300 149 Muriatic acid 350 177Citric acid, concentrated 400 204 Nitric acid 5% 400 204Copper acetate x x Nitric acid 20% 400 204Copper carbonate 190 88 Nitric acid 70% 190 88Copper chloride 400 204 Nitric acid, anhydrous 190 88Copper cyanide 400 204 Nitrous acid, concentrated 90 32Copper sulfate 400 204 Oleum 190 88Cresol x x Perchloric acid 10% 400 204Cupric chloride 5% 180 82 Perchloric acid 70% 400 204Cupric chloride 50% I80 82 Phenol 210 99Cyclohexane 400 204 Phosphoric acid 5080% 300 149Cyclohexanol 400 204 Picric acid 400 204Dichloroethane (ethylene dichloride) 190 88 Potassium bromide 30% 190 88Ethylene glycol 400 204 Salicylic acid 300 149Ferric chloride 400 204 Sodium carbonate 190 88Ferric chloride 50% in water 400 204 Sodium chloride 400 204Ferric nitrate 1050% 400 204 Sodium hydroxide 10% x xFerrous chloride 180 82 Sodium hydroxide 50% x xFerrous nitrate 210 99 Sodium hydroxide, concentrated x xFluorine gas, dry x x Sodium hypochlorite 20% 400 204Fluorine gas, moist x x Sodium hypochlorite, concentrated 400 204Hydrobromic acid, dilute 400 204 Sodium sulfide to 50% 190 88Hydrobromic acid 20% 400 204 Stannic chloride 400 204Hydrobromic acid 50% 400 204 Stannous chloride 400 204Hydrochloric acid 20% 350 177 Sulfuric acid 10% 350 149Hydrochloric acid 38% 350 177 Sulfuric acid 50% 350 149Hydrocyanic acid 10% 400 204 Sulfuric acid 70% 350 149Hydrofluoric acid 30% 210 99 Sulfuric acid 90% 350 149Hydrofluoric acid 70% 350 177 Sulfuric acid 98% 350 149Hydrofluoric acid 100% x x Sulfuric acid 100% 180 88Hypochlorous acid 400 204 Sulfuric acid, fuming 200 93Iodine solution 10% 190 88 Sulfurous acid 400 204Ketones, general x x Thionyl chloride x xLactic acid 25% 300 149 Toluene 400 204Lactic acid, concentrated 400 201 Trichloroacetic acid 190 88Magnesium chloride 390 199 White liquor 190 88Malic acid 390 199 Zinc chloride 400 204Manganese chloride 180 82aThe chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. Compatibility is shown to themaximum allowable temperature for which data are available. Incompatibility is shown by an x. Source: PA Schweitzer. Corrosion Resistance Tables. 4th ed. Vols. 13. New York: Marcel Dekker, 1995.

Table F.5 Compatibility of Fluoroelastomers with Selected Corrodentsa (Continued)


!""

FIn addition, the use of lead-free fuels, alternative fuels, sour gasoline lubricants, and anti-freeze fluids have caused automotive fluids to be more corrosive to elastomers. At thepresent time, fluoroelastomers are being applied as shaft seals, valve stem seals, O-rings(water-cooled cylinders and injection pumps), engine head gaskets, filter casing gaskets,diaphragms for fuel pumps, water pump gaskets, turbocharge lubricating circuit bellows,carburetor accelerating pump diaphragms, carburetor needle-valve tips, fuel hoses, andseals for exhaust gas pollution-control equipment.

In the field of aerospace applications, the reliability of materials under extremeexposure conditions is of prime importance. The high- and low-temperature propertiesof the fluoroelastomers have permitted them to give reliable performance in a numberof aircraft and missile components, specifically manifold gaskets, coated manifold gas-kets, coated fabrics, firewall seals, heat-shrinkable tubing and fittings for wire andcable, mastic adhesive sealants, protective coatings, and numerous types of O-ringseals.

The ability of the fluoroelastomers to seal under extreme vacuum conditions in therange of 109 mm Hg is an additional feature that makes these materials useful for com-ponents used in space.

The exploitation of oil fields in difficult areas such as desert or offshore sites hasincreased the problems of high temperatures and pressures, high viscosities, and high alka-linity. These extreme operating conditions require elastomers that have a high chemicalresistance, thermal stability, and overall reliability to reduce maintenance. The same prob-lems exist in the chemical industry. The fluoroplastics provide a solution to these problemsand are used for O-rings, V-rings, U-rings, gaskets, valve seats, diaphragms for meteringpumps, hoses, expansion joints, safety clothing and gloves, linings for valves, and mainte-nance coatings.

An important application for these elastomers is in the production of coatings andlinings. Their chemical stability solves the problem of chemical corrosion by making itpossible to use them for such purposes as

A protective lining for power station stacks operated with high-sulfur fuelsA coating on rolls for the textile industry to permit scouring of fabricsTank linings for the chemical industry

See Refs. 5 and 6.

FLUORINATED ETHYLENE PROPYLENE (FEP)

FEP is a fully fluorinated thermoplast with some branching but consists mainly of linearchains having the following formula:

F F F F F| | | | |

C C C C C | | |

|| |

F F F FF C F

|F


FEP has a maximum operating temperature of 375F (190C). After prolonged expo-sure at 400F (204C) it exhibits changes in physical strength. It is a relatively soft plas-tic with lower tensile strength, wear resistance, and creep resistance than other plastics.It is insensitive to notched impact forces and has excellent permeation resistance exceptto some chlorinated hydrocarbons. Table F.6 lists the physical and mechanical proper-ties. FEP may he subject to permeation by specific materials. Refer to Permeation fordetails.

FEP basically exhibits the same corrosion resistance as PTFE, with a few excep-tions, but at lower operating temperatures. It is resistant to practically all chemicals, theexceptions being extremely potent oxidizers, such as chlorine trifluoride and related com-pounds. Some chemicals will attack FEP when present in high concentrations at or nearthe service temperature limit. Refer to Table F.7 for the compatibility of FEP withselected corrodents. Reference 6 lists the compatibility of FEP with a wide range ofselected corrodents.

FLUOROCARBON RESINS

Fluorocarbon resins are organic compounds in which the hydrogen atoms have beenreplaced by fluorine. They are fully fluorinated, while fluoropolymer resins are only par-tially fluorinated. Included in this group of resins are polytetrafluoroethylene (PTFE),fluorinated ethylene propylene (FEP), and perfluoralkoxy (PFA). They are characterizedby the following properties:

1. Nonpolarity: The carbon backbone of the linear polymer is completely sheathed by the tightly held electron cloud of fluorine atoms, with electronegatives bal-anced.

2. High CF and CC bond strengths.3. Low interchain forces: Interactive forces between the two adjacent polymer

chains are significantly lower than the bond forces within one chain.4. Crystallinity.5. High degree of polymerization.

Table F.6 Physical and Mechanical Properties of FEP

Specific gravity 2.15Water absorption 24 h at 73F (23C ), % 0.01Tensile strength at 73F (23C) psi 27003100Modulus of elasticity in tension at 73F (23C ) 105 psi 0.9Compressive strength, psi 16,000Flexural strength, psi 3000Izod impact strength, notched at 73F (23C) no breakCoefficient of thermal expansion, in./in. F 105 8.310.5Thermal conductivity Btu/h/ft2/F/in. 0.11Heat distortion temperature, at 66 psi F/C 158/70Resistance to heat at continuous drainage, F/C 400/204Limiting oxygen index, % 95Flame spread Nonflammable


FTable F.7 Compatibility of FEP with Selected CorrodentsaMaximum

temp.Maximum

temp.


Acetaldehyde 200 93 Barium hydroxide 400 204Acetamide 400 204 Barium sulfate 400 204Acetic acid 10% 400 204 Barium sulfide 400 204Acetic acid 50% 400 204 Benzaldehydeb 400 204Acetic acid 80% 400 204 Benzeneb,c 400 204Acetic acid, glacial 400 204 Benzene sulfonic acid 10% 400 204Acetic anhydride 400 204 Benzoic acid 400 204Acetoneb 400 204 Benzyl alcohol 400 204Acetyl chloride 400 204 Benzyl chloride 400 204Acrylic acid 200 93 Borax 400 204Acrylontrile 400 204 Boric acid 400 204Adipic acid 400 204 Bromine gas, dryc 200 93Allyl alcohol 400 204 Bromine gas, moistc 200 93Allyl chloride 400 204 Bromine liquidb,c 400 204Alum 400 204 Butadienec 400 204Aluminum acetate 400 204 Butyl acetate 400 204Aluminum chloride, aqueous 400 204 Butyl alcohol 400 204Aluminum chloride, dry 300 149 n-Butylamineb 400 204Aluminum fluoridec 400 204 Butyl phthalate 400 204Aluminum hydroxide 400 204 Butyric acid 400 204Aluminum nitrate 400 204 Calcium bisulfide 400 204Aluminum oxychloride 400 204 Calcium bisulfite 400 204Aluminum sulfate 400 204 Calcium carbonate 400 204Ammonia gasc 400 204 Calcium chlorate 400 204Ammonium bifluoridec 400 204 Calcium chloride 400 204Ammonium carbonate 400 204 Calcium hydroxide 10% 400 204Ammonium chloride 10% 400 204 Calcium hydroxide, sat. 400 204Ammonium chloride 50% 400 204 Calcium hypochlorite 400 204Ammonium chloride, sat. 400 204 Calcium nitrate 400 204Ammonium fluoride 10%c 400 204 Calcium oxide 400 204Ammonium fluoride 25%c 400 204 Calcium sulfate 400 204Ammonium hydroxide 25% 400 204 Caprylic acid 400 204Ammonium hydroxide, sat. 400 204 Carbon bisulfidec 400 204Ammonium nitrate 400 204 Carbon dioxide, dry 400 204Ammonium persulfate 400 204 Carbon dioxide, wet 400 204Ammonium phosphate 400 204 Carbon disulfide 400 204Ammonium sulfate 1040% 400 204 Carbon monoxide 400 204Ammonium sulfide 400 204 Carbon tetrachlorideb,c,d 400 204Ammonium sulfite 400 204 Carbonic acid 400 204Amyl acetate 400 204 Cellosolve 400 204Amyl alcohol 400 204 Chloracetic acid, 50% water 400 204Amyl chloride 400 204 Chloracetic acid 400 204Anilineb 400 204 Chlorine gas, dry x xAntimony trichloride 250 121 Chlorine gas, wetc 400 204Aqua regia 3:1 400 204 Chlorine liquidb 400 204Barium carbonatec 400 204 Chlorobenzenec 400 204Barium chloride 400 204 Chloroformc 400 204


Maximumtemp.

Maximumtemp.


Chlorosulfonic acidb 400 204 Manganese chloride 300 149Chromic acid 10% 400 204 Methyl chloridec 400 204Chromic acid 50% 400 204 Methyl ethyl ketonec 400 204Chromyl chloride 400 204 Methyl isobutyl ketonec 400 204Citric acid 15% 400 204 Muriatic acidc 400 204Citric acid, concentrated 400 204 Nitric acid 5%c 400 204Copper acetate 400 204 Nitric acid 20% 400 204Copper carbonate 400 204 Nitric acid 70%c 400 204Copper chloride 400 204 Nitric acid, 400 204Copper cyanide 400 204 Nitrous acid, concentrated 400 204Copper sulfate 400 204 Oleum 400 204Cresol 400 204 Perchloric acid 10% 400 204Cupric chloride 5% 400 204 Perchloric acid 70% 400 204Cupric chloride 50% 400 204 Phenolc 400 204Cyclohexane 400 204 Phosphoric acid 5080% 400 204Cyclohexanol 400 204 Picric acid 400 204Dichloroacetic acid 400 204 Potassium bromide 30% 400 204Dichloroethane (ethylene dichloride)c 400 204 Salicylic acid 400 204Ethylene glycol 400 204 Silver bromide 10% 400 204Ferric chloride 400 204 Sodium carbonate 400 204Ferric chloride 50% in waterb 260 127 Sodium chloride 400 204Ferric nitrate 1050% 260 127 Sodium hydroxide 10%b 400 204Ferrous chloride 400 204 Sodium hydroxide 50% 400 204Ferrous nitrate 400 204 Sodium hydroxide, concentrated 400 204Fluorine gas, dry 200 93 Sodium hypochlorite 20% 400 204Fluorine gas, moist x x Sodium hypochlorite concentrated 400 204Hydrobromic acid, dilute 400 204 Sodium sulfide to 50% 400 204Hydrobromic acid 20%c,d 400 204 Stannic chloride 400 204Hydrobromic acid 50%c,d 400 204 Stannous chloride 400 204Hydrochloric acid 20%c,d 400 204 Sulfuric acid 10% 400 204Hydrochloric acid 38% 400 204 Sulfuric acid 50% 400 204Hydrocyanic acid 10% 400 204 Sulfuric acid 70% 400 204Hydrofluoric acid 30%c 400 204 Sulfuric acid 90% 400 204Hydrofluoric acid 70%c 400 204 Sulfuric acid 98% 400 204Hydrofluoric acid 100%c 400 204 Sulfuric acid 100% 400 204Hypochlorous acid 400 204 Sulfuric acid, fumingc 400 204Iodine solution 10%c 400 204 Sulfurous acid 400 204Ketones, general 400 204 Thionyl chloridec 400 204Lactic acid 25% 400 204 Toluenec 400 204Lactic acid, concentrated 400 204 Trichloroacetic acid 400 204Magnesium chloride 400 204 White liquor 400 204Malic acid 400 204 Zinc chlorided 400 204

aThe chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. Compatibility is shown to themaximum allowable temperature for which data are available. Incompatibility is shown by an x. bMaterial will be absorbed.cMaterial will permeate.dMaterial can cause stress cracking.Source: PA Schweitzer. Corrosion Resistance Tables. 4th ed. Vols. 13. New York: Marcel Dekker, 1995.

Table F.7 Compatibility of FEP with Selected Corrodentsa (Continued)


"

FThese properties provide the following advantages to these materials:1. High melting point2. High thermal stability3. High upper service temperatures4. Inertness to chemical attack by almost all chemicals5. Low coefficient of friction6. Low water absorbability7. Weatherability8. Flame resistance9. Toughness

Listed in the table are the properties of the fluorocarbon resins.

For more information on the fluorocarbon resins, refer to the specific resin andthermoplasts.

FLUOROPOLYMER RESINS

The fluoropolymers are resistant to a broader range of chemicals at higher temperaturesthan chlorinated or hydrogenated polymers, polyesters, and polyamides. However, theirproperties are significantly different from those of fully fluorinated resins (fluorocarbons).Included in this category are ethylene tetrafluoroethylene (ETFE), sold under the tradename of Tefzel by DuPont; polyvinylidene fluoride (PVDF), sold under the trade namesof Kynar by Elf Atochem, Solef by Solvay, Hylar by Ausimont USA, and Super Pro andIso by Asahi/America; and ethylene chlorotrifluoroethylene (ECTFE), sold under thetrade name of Halar by Ausimont USA.

The polarity of these resins is increased as the result of substituting hydrogen orchlorine, which have different electronegatives relative to fluorine. The length of theirbonds to the carbon backbone also differs from those with fluorine. The centers of elec-tronegativity and electropositivity are not held as tightly as with carbonfluorine bonds.As a result, differential separation of charge can be induced chemically between atoms inadjacent chains to permit electrostatic interaction between chains. Higher mechanical

Property ASTM Standard PTFE FEP PFA

Specific gravity D792 2.132.22 2.15 2.15Tensile strength, psi D638 25004000 3400 3600Elongation, % D638 200400 325 300Flexural modulus, psi D790 27000 90000 90000Impact strength, ft-lb/in. D256 3.5 no break no breakHardness. Shore D D2240 5065 56 60Coefficient of friction D1894 0.1 0.2 0.2Upper service temp., F/C UL746B 500/260 400/204 500/260Flame rating UL94 VO VO VOLimiting oxygen index, % D2863 95 95 95Chemical/solvent resistance D543 outstandingWater absorption, 24 h D570 0.01 0.01 0.03


properties are produced because of the increased interpolymer chain attraction along withthe interlocking of differently sized atoms. In addition, the increased polarity/interpoly-mer attraction reduces the permeation of penetrants through the resin. Because of thesubstitution of hydrogen or of hydrogen and chlorine for fluorine, chemical and thermalstability are sacrificed.

The chemical stability is affected by the arrangement of the substituting elementsalong the polymer chain. Solubility can be a leading indicator. For example, ETFE has noknown solvent under ordinary circumstances, while PVDF is soluble in common indus-trial ketones (e.g., methyl ethyl ketone) and ECTFE is soluble in some fluorinated sol-vents. While the fully fluorinated polymers are resistant to strong acids and alkalies, thesubstituted polymers are adversely affected. However, these resins do possess advanta-geous properties both mechanical and chemically resistant. Typical properties of the fluo-ropolymer resins are shown in the table.

For additional information, see the specific fluoropolymer and thermoplast.

FLUOROSILICONE RUBBER

See Silicone Rubbers and Fluorosilicone.

FORMS OF CORROSION

The several forms of corrosion to which a metal may be subjected are

1. Electrochemical corrosion2. Uniform corrosion3. Intergranular corrosion4. Galvanic corrosion5. Crevice corrosion6. Pitting7. Erosion corrosion8. Stress corrosion cracking (SCC)

Property ASTM Std ETFE PVDF ECTFE

Specific gravity D792 1.70 1.78 1.68Tensile strength, psi D638 6300 4500 7000Elongation, % D638 300 50 210Flexural modulus, psi 105 D790 1.7 2.5 2.4Impact strength ft-lb/in. D256 no break 2 no breakHardness, Shore D D2240 67 78 75Coefficient of friction D1894 0.4Upper service temperature, F/C UL746 300/150 300/150 300/150Flame rating UL94 VO VO VOLimiting oxygen index, % D2863 30 30 30Chemical/solvent resistance D543 excellent fair goodWater absorption, 24 h D570 0.03 0.03 0.1


!

F9. Biological corrosion10. Dezincification (dealloying)11. Concentration cell12. Embrittlement13. Filiform corrosion14. Corrosion fatigue15. Fretting corrosion16. Graphitization

Not all of these forms of corrosion are present in all applications, but it is possible to havemore than one form present. In addition, not all metals are subject to all of these forms ofcorrosion. Understanding when each of these forms of corrosion could be present willpermit the designer to take steps to eliminate the condition or to keep the corrosionwithin acceptable limits. Refer to the specific form of corrosion for details.

FRETTING CORROSION

Wear is a surface phenomenon that occurs by displacement and detachment of materials.Corrosive wear is the aggravation by corrosion of the wear process. The chemical reactionmay take place first, followed by the removal of the corrosion products by mechanical abra-sion. Conversely, mechanical action may precede chemical action in which small particlesdislodged by abrasion react with the environment. In both cases, the wear rate is increased.

Fretting is also a wear phenomenon occurring between two mating surfaces underloading and having a relative slip of extremely small amplitude, such as would be causedby vibration. Under such conditions, the minute protrusions of one surface, ploughthrough the mating surface, dislodging metallic particles or breaking the protective film.Fretting corrosion is the aggravation of this action in the presence of a corrosive liquid.

Fretting corrosion damage is characterized by discoloration of the metal surface andthe formation of pits. Fatigue cracks may nucleate at the pits. Fretting corrosion results inthe loosening of parts, sometimes seizure of the parts because of the accumulation of cor-rosion products, loss of dimensional accuracy, and at times fatigue failure. As loads increase,the magnitude of damage also increases, but it will decrease with increasing temperature andincreasing moisture. This is an indication that the mechanism is not fully electrochemical.

Fretting and fretting corrosion are encountered in joints, connecting rods, shrinkfits, oscillating bearings, splices, and couplings and in many parts of vibrating machinery.

Fretting corrosion can be minimized by reducing wearing action, such as by lubri-cating the wearing surfaces. This is why increased moisture, through its lubricating effect,reduces fretting corrosion. The use of rubber, Teflon, or any material of high elastic strainlimit inserted between the two surfaces will prevent fretting. Induction of residual stressesthrough shot peening is helpful in preventing fatigue crack propagation initiated by fret-ting. If practical, the elimination of vibration is ideal.

FUEL ASH CORROSION

Low-grade fuel oils contain elements, particularly vanadium and sodium, that cause accel-erated high-temperature corrosion. At temperatures above 1200F (650C), vanadiumoxide vapor and sodium sulfate react to form sodium vanadate, which in turn can react with


metal oxides on the surfaces of heater tubes, tubesheets, etc. The resulting slag can becomea low-melting eutectic mixture that is a molten solvent for metal oxides. The slag dissolvesprotective metal oxides and prevents their reforming. Sulfur in the fuel accelerates the actionby means of sulfidation and by additional lowering of the melting point of the vanadiumoxide flux. Failures resulting from this mechanism tend to be rapid.

Concentrations of less than 5 ppm vanadium appear to have little effect. Concen-trations of up to 20 ppm vanadium are safe as long as the maximum metal temperature isless than 1550F (845C). For concentrations of vanadium in excess of 20 ppm, the safemaximum temperature is 1200F (650C).

Practically all alloys are susceptible to fuel ash corrosion. However, alloys having ahigh content of nickel and chromium (50 Cr50 Ni) offer good protection. The rate ofcorrosion decreases at very low air concentrations. Reducing the amount of excess air toless than 5% will control fuel ash corrosion.

Also see High-Temperature Corrosion.

FURAN RESINS

Also see Polymers and Thermoset Polymers. Since there are different formulations ofthe furan resins, the supplier should be checked as to the compatibility of a particularresin with the corrodents to be encountered. Corrosion charts will indicate the compati-bility of at least one formulation.

The strong point of the furan resins is their excellent resistance to solvents in com-bination with acids and alkalies. They are compatible with the following corrodents:

The furans are not resistant to bleaches, such as peroxides and hypochlorites, con-centrated sulfuric acid, phenol and free chlorine, or higher concentrations of chromic ornitric acids.

Refer to Table F.8 for the compatibility of furan resins with selected corrodents. See Refs. 68, 9.

Solvents

Acetone Methyl ethyl ketoneBenzene PerchlorethyleneCarbon disulfide StyreneChlorobenzene TolueneEthanol TrichloroethyleneEthyl acetate XyleneMethanol

Acids

Acetic PhosphoricHydrochloric 60% Sulfuric5% Nitric

Bases

Dimethylamine Sodium sulfideSodium carbonate Sodium hydroxide


FTable F.8 Compatibility of Furan Resins with Selected CorrodentsaMaximum

temp.Maximum

temp.


Acetaldehyde x x Bromine liquid 3% max. 300 149Acetic acid 10% 212 100 ButadieneAcetic acid 50% 160 71 Butyl acetate 260 127Acetic acid 80% 80 27 Butyl alcohol 212 100Acetic acid, glacial 80 27 n-Butylamine x xAcetic anhydride 80 27 Butyric acid 260 127Acetone 80 27 Calcium bisulfite 260 127Acetyl chloride 200 93 Calcium chloride 160 71Acrylic acid 80 27 Calcium hydroxide, sat. 260 127Acrylonitrile 80 27 Calcium hypochlorite x xAdipic acid 25% 280 138 Calcium nitrate 260 127Allyl alcohol 300 149 Calcium oxideAllyl chloride 300 149 Calcium sulfate 260 127Alum 5% 140 60 Caprylic acid 250 121Aluminum chloride, aqueous 300 149 Carbon disulfide 160 71Aluminum chloride, dry 300 149 Carbon dioxide. dry 90 32Aluminum fluoride 280 138 Carbon dioxide, wet 80 27Aluminum hydroxide 260 127 Carbon disulfide 260 127Aluminum sulfate 160 71 Carbon tetrachloride 212 100Ammonium carbonate 240 116 Cellosolve 240 116Ammonium hydroxide 25% 250 121 Chloracetic acid, 50%, water 100 38Ammonium hydroxide, sat. 200 93 Chloracetic acid 240 116Ammonium nitrate 250 121 Chlorine gas, dry 260 127Ammonium persulfate 260 127 Chlorine gas, wet 260 127Ammonium phosphate 260 127 Chlorine, liquid x xAmmonium sulfate 1040% 260 127 Chlorobenzene 260 127Ammonium sulfide 260 127 Chloroform x xAmmonium sulfite 240 116 Chlorosulfonic acid 260 127Amyl acetate 260 127 Chromic acid 10% x xAmyl alcohol 278 137 Chromic acid 50% x xAmyl chloride x x Chromyl chloride 250 121Aniline 80 27 Citric acid 15% 250 121Antimony trichloride 250 121 Citric acid, concentrated 250 121Aqua regia 3:1 x x Copper acetate 260 127Barium carbonate 240 Il6 Copper carbonateBarium chloride 260 127 Copper chloride 260 127Barium hydroxide 260 127 Copper cyanide 240 116Barium sulfide 260 127 Copper sulfate 300 149Benzaldehyde 80 27 Cresol 260 127Benzene 160 71 Cupric chloride 5% 300 149Benzene sulfonic acid 10% 160 71 Cupric chloride 50% 300 149Benzoic acid 260 127 Cyclohexane 141 60Benzyl alcohol 80 27 CyclohexanolBenzyl chloride 140 60 Dichloroacetic acid x xBorax 140 60 Dichloroethane (ethylene dichloride) 250 121Boric acid 300 149 Ethylene glycol 160 71Bromine gas, dry x x Ferric chloride 260 127Bromine gas, moist x x Ferric chloride 50%, water 160 71


REFERENCES

1. HI-I UIlhig. Corrosion and Corrosion Control. New York: John Wiley, 1963.2. CP Dillon. Corrosion Resistance of Stainless Steels. New York: Marcel Dekker, 1995.3. PA Schweitzer. Stainless steel. In: PA Schweitzer, ed. Corrosion and Corrosion Protection Handbook

2nd ed. New York: Marcel Dekker, 1989, pp 7981.4. JHW deWit. Inorganic and organic coatings. In: P Marcus and J Oudar, eds. Corrosion Mechanisms in

Theory and Practice. New York: Marcel Dekker, 1995, pp 602609.5. PA Schweitzer. Corrosion Resistance of Elastomers. New York: Marcel Dekker, 1990.

Maximum temp.

Maximum temp.


Ferric nitrate 1050% 160 71 Perchloric acid 10% x xFerrous chloride 160 71 Perchloric acid 70% 260 127Ferrous nitrate Phenol x xFluorine gas, dry x x Phosphoric acid 50 212 100Fluorine gas, moist x x Picric acidHydrobromic acid, dilute 212 100 Potassium bromide 30% 260 127Hydrobromic acid 20% 212 100 Salicylic acid 260 127Hydrobromic acid 50% 212 100 Silver bromide 10%Hydrochloric acid 20% 212 100 Sodium carbonate 212 100Hydrochloric acid 38% 80 27 Sodium chloride 260 127Hydrocyanic acid 10% 160 71 Sodium hydroxide 10% x xHydrofluoric acid 30% 230 110 Sodium hydroxide 50% x xHydrofluoric acid 70% 140 60 Sodium hydroxide, concentrated x xHydrofluoric acid 100% 140 60 Sodium hypochlorite 15% x xHypochlorous acid x x Sodium hypochlorite, concentrated x xIodine solution 10% x x Sodium sulfide to 10% 260 127Ketones, general 100 38 Stannic chloride 260 127Lactic acid 25% 212 100 Stannous chloride 250 121Lactic acid, concentrated 160 71 Sulfuric acid 10% 160 71Magnesium chloride 260 127 Sulfuric acid 50% 80 27Malic acid 10% 260 127 Sulfuric acid 70% 80 27Manganese chloride 200 93 Sulfuric acid 90% x xMethyl chloride 120 49 Sulfuric acid 98% x xMethyl ethyl ketone 80 27 Sulfuric acid 100% x xMethyl isobutyl ketone 160 71 Sulfuric acid, fuming x xMuriatic acid 80 27 Sulfurous acid 160 71Nitric acid 5% x x Thionyl chloride x xNitric acid 20% x x Toluene 212 100Nitric acid 70% x x Trichloroacetic acid 30% 80 27Nitric acid, anhydrous x x White liquor 140 60Nitrous acid, concentrated x x Zinc chloride 160 71Oleum 190 88

aThe chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. Compatibility is shown to themaximum allowable temperature for which data are available. Incompatibility is shown by an x. A blank space indicates that data are unavailable.Source: PA Schweitzer. Corrosion Resistance Tables. 4th ed. Vols. 13. New York: Marcel Dekker, 1995.

Table F.8 Compatibility of Furan Resins with Selected Corrodentsa (Continued)


F6. PA Schweitzer. Corrosion Resistance Tables. 4th ed. Vols. 13. New York: Marcel Dekker, 1995.7. GT Murray. Introduction to Engineering Materials. New York: Marcel Dekker, 1993.8. JH Mallinson. Corrosion Resistant Plastics in Chemical Plant Design. New York: Marcel Dekker,

1988.9. PA Schweitzer. Corrosion Resistant Piping Systems. New York: Marcel Dekker, 1994.


Table of ContentsFFERRITEFERRITIC STAINLESS STEELSType 405 (S40500)Type 409 (S40900)Type 430 (S43000)Type 439L (S43035)Type 444 (S44400)Type 446 (S44600)

FIBERGLASSFIBER-REINFORCED PLASTICS (COMPOSITES)FILIFORM CORROSIONFLUORELFLUOROELASTOMERS (FKM)Physical and Mechanical PropertiesResistance to Sun, Weather, and OzoneChemical ResistanceApplications

FLUORINATED ETHYLENE PROPYLENE (FEP)FLUOROCARBON RESINSFLUOROPOLYMER RESINSFLUOROSILICONE RUBBERFORMS OF CORROSIONFRETTING CORROSIONFUEL ASH CORROSIONFURAN RESINSREFERENCES

Encyclopedia of Corrosion Technology, Second Edition

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