Designation:B117–03
Standard Practice for
Operating Salt Spray(Fog)Apparatus1
This standard is issued under thefixed designation B117;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1.Scope
1.1This practice covers the apparatus,procedure,and conditions required to create and maintain the salt spray(fog) test environment.Suitable apparatus which may be used is described in Appendix X1.
1.2This practice does not prescribe the type of test speci-men or exposure periods to be used for a specific product,nor the interpretation to be given to the results.
1.3The values stated in SI units are to be regarded as standard.The inch-pound units in parentheses are provided for information and may be approximate.
1.4This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
2.Referenced Documents
2.1ASTM Standards:
B368Method for Copper-Accelerated Acetic Acid-Salt Spray(Fog)Testing(CASS Test)2
D609Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint,Varnish,Conversion Coatings,and Related Coating Products3
D1193Specification for Reagent Water4
D1654Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments3
E70Test Method for pH of Aqueous Solutions with the Glass Electrode5
E691Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method6
G85Practice for Modified Salt Spray(Fog)Testing7
3.Significance and Use
editorial英文3.1This practice provides a controlled corrosive environ-ment which has been utilized to produce relative corrosion resistance information for specimens of metals and coated metals exposed in a given test chamber.
3.2Prediction of performance in natural environments has seldom been correlated with salt spray results when used as stand alone data.
3.2.1Correlation and extrapolation of corrosion perfor-mance based on exposure to the test environment provided by this practice are not always predictable.
3.2.2Correlation and extrapolation should be considered only in cases where appropriate corroborating long-term atmo-spheric exposures have been conducted.
3.3The reproducibility of results in the salt spray exposure is highly dependent on the type of specimens tested and the evaluation criteria selected,as well as the control of the operating variables.In any testing program,sufficient repli-cates should be included to establish the variability of the results.Variability has been observed when similar specimens are tested in different fog chambers even though the testing conditions are nominally similar and within the ranges speci-fied in this practice.
4.Apparatus
4.1The apparatus required for salt spray(fog)exposure consists of a fog chamber,a salt solution reserv
oir,a supply of suitably conditioned compressed air,one or more atomizing nozzles,specimen supports,provision for heating the chamber, and necessary means of control.The size and detailed con-struction of the apparatus are optional,provided the conditions obtained meet the requirements of this practice.
4.2Drops of solution which accumulate on the ceiling or cover of the chamber shall not be permitted to fall on the specimens being exposed.
1This practice is under the jurisdiction of ASTM Committee G01on Corrosion
of Metals and is the direct responsibility of Subcommittee G01.05on Laboratory
Corrosion Tests.
Current edition approved October1,2003.Published October2003.Originally
approved in1939.Last previous edition approved in2002as B117–02.
2Annual Book of ASTM Standards,V ol02.05.
3Annual Book of ASTM Standards,V ol06.01.
4Annual Book of ASTM Standards,V ol11.01.
5Annual Book of ASTM Standards,V ol15.05.
6Annual Book of ASTM Standards,V ol14.02.7Annual Book of ASTM Standards,V ol03.02.
1
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4.3Drops of solution which fall from the specimens shall not be returned to the solution reservoir for respraying.
4.4Material of construction shall be such that it will not affect the corrosiveness of the fog.
4.5All water used for this practice shall conform to Type IV water in Specification D1193(except that for this practice limits for chlorides and sodium may be ignored).This does not apply to running tap water.All other water will be referred to as reagent grade.
5.Test Specimens
5.1The type and number of test specimens to be used,as well as the criteria for the evaluation of the test results,shall be defined in the specifications covering the material or product being exposed or shall be mutually agreed upon between the purchaser and the seller.
6.Preparation of Test Specimens
6.1Specimens shall be suitably cleaned.The cleaning method shall be optional depending on the nature of the surface and the contaminants.Care shall be taken that specimens are not recontaminated after cleaning by excessive or careless handling.
6.2Specimens for the evaluation of paints and other organic coatings shall be prepared in accordance with applicable specification(s)for the material(s)being exposed,or as agreed upon between the purchaser and the supplier.Otherwise,the test specimens shall consist of steel meeting the requirements of Practice D609and shall be cleaned and prepared for coating in accordance with the applicable procedure of Practice D609.
6.3Specimens coated with paints or nonmetallic coatings shall not be cleaned or handled excessively prior to test.
6.4Whenever it is desired to determine the development of corrosion from an abraded area in the paint or organic coating, a scratch or scribed line shall be made through the coating with a sharp instrument so as to expose the underlying metal before testing.The conditions of making the scratch shall be as defined in Test Method D1654,unless otherwise agreed upon between the purchaser and the seller.
6.5Unless otherwise specified,the cut edges of plated, coated,or duplex materials and areas containing identification marks or in contact with the racks or supports shall be protected with a suitable coating stable under the conditions of the practice.
N OTE1—Should it be desirable to cut test specimens from parts or from preplated,painted,or otherwise coated steel sheet,the cut edges shall be protected by coating them with paint,wax,tape,or other effective media so that the development of a galvanic effect between such edges and the adjacent plated or otherwise coated metal surfaces,is prevented.
7.Position of Specimens During Exposure
7.1The position of the specimens in the salt spray chamber during the test shall be such that the following conditions are met:
7.1.1Unless otherwise specified,the specimens shall be supported or suspended between15and30°from the vertical and preferably parallel to the principal direction offlow of fog through the chamber,based upon the dominant surface being tested.
7.1.2The specimens shall not contact each other or any metallic material or any material capable of acting as a wick.
7.1.3Each specimen shall be placed to permit unencum-bered exposure to the fog.
7.1.4Salt solution from one specimen shall not drip on any other specimen.
N OTE2—Suitable materials for the construction or coating of racks and supports are glass,rubber,plastic,or suitably coated wood.Bare metal shall not be used.Specimens shall preferably be supported from the bottom or the side.Slotted wooden strips are suitable for the support offlat panels.Suspension from glass hooks or waxed string may be used as long as the specified position of the specimens is obtained,if necessary by means of secondary support at the bottom of the specimens.
8.Salt Solution
8.1The salt solution shall be prepared by dissolving561 parts by mass of sodium chloride in95parts of water conforming to Type IV water in Specification D1193(except that for this practice limits for chlorides and sodium may be ignored).Careful attention should be given to the chemical content of the salt.The salt used shall be sodium chloride with not more than0.3%by mass of total impurities.Halides (Bromide,Fluoride,and Iodide)other than Chloride shall constitute less than0.1%by mass of the salt content.Copper content shall be less than0.3ppm by mass.Sodium chloride containing anti-caking agents shall not be used because such agents may act as corrosion inhibitors.See Table1for a listing of these impurity restrictions.Upon agreement between the purchaser and the seller,analysis may be required and limits established for elements or compounds not specified in the chemical composition given above.
TABLE1Maximum Allowable Limits for Impurity Levels in
Sodium Chloride A,B
Impurity Description Allowable Amount Total Impurities#0.3% Halides(Bromide,Fluoride and Iodide)excluding Chloride#0.1% Copper<0.3ppm
Anti-caking Agents0.0%
A A common formula used to calculate the amount of salt required by mass to achieve a5%salt solution of a known mass of water is:
.053X Mass of Water5Mass of NaCl required
The mass of water is1g per1mL.To calculate the mass of salt required in grams to mix1L of a5%salt solution,multiply.053by1000g(35.27oz.,the mass of 1L of water).This formula yields a result of53g(1.87oz.)of NaCl required for each liter of water to achieve a5%salt solution by mass.
The0.053multiplier for the sodium chloride used above is derived by the following:
1000g~mass of a full L of water!divided by0.95
~water is only95%of the total mixture by mass!yields1053g
This1053g is the total mass of the mixture of one L of water with a5%sodium chloride concentration.1053g minus the original weight of the L of water,1000g, yields53g for the weight of the sodium chloride.53g of total sodium chloride divided by the original1000g of water yields a0.053multiplier for the sodium chloride.
As an example:to mix the equivalent of200L(52.83gal)of5%sodium chloride solution,mix10.6kg(23.37lb)of sodium chloride into200L(52.83gal)of water. 200L of water weighs200,000g.200,000g of water x.053(sodium chloride multiplier)=10,600g of sodium chloride,or10.6kg.
B In order to ensure that the proper salt concentration was achieved when mixing the solution,it is recommended that the solution be checked with either a salimeter hydrometer or specific gravity hydrometer.When using a salimeter hydrometer,the measurement should be between4and6%at25°C(77°F).When using a specific gravity hydrometer,the measurement should be between1.0255and1.0400at 25°C
(77°F).
8.2The pH of the salt solution shall be such that when atomized at35°C(95°F)the collected solution will
be in the pH range from6.5to7.2(Note3).Before the solution is atomized it shall be free of suspended solids(Note4).The pH measurement shall be made at25°C(77°F)using a suitable glass pH-sensing electrode,reference electrode,and pH meter system in accordance with Test Method E70.
N OTE3—Temperature affects the pH of a salt solution prepared from water saturated with carbon dioxide at room temperature and pH adjust-ment may be made by the following three methods:
(1)When the pH of a salt solution is adjusted at room temperature,and atomized at35°C(95°F),the pH of the collected solution will be higher than the original solution due to the loss of carbon dioxide at the higher temperature.When the pH of the salt solution is adjusted at room temperature,it is therefore necessary to adjust it below6.5so the collected solution after atomizing at35°C(95°F)will meet the pH limits of6.5to 7.2.Take about a50-mL sample of the salt solution as prepared at room temperature,boil gently for30s,cool,and determine the pH.When the pH of the salt solution is adjusted to6.5to7.2by this procedure,the pH of the atomized and collected solution at35°C(95°F)will come within this range.
(2)Heating the salt solution to boiling and cooling to35°C(95°F)and maintaining it at35°C(95°F)for approximately48h before adjusting the pH produces a solution the pH of which does not materially change when atomized at35°C(95°F).
(3)Heating the water from which the salt solution is prepared to35°C (95°F)or above,to expel carbon dioxide,and adjusting the pH of the salt solution within the limits of6.5to7.2produces a solution the pH of which does not materially change when atomized at35°C(95°F).
N OTE4—The freshly prepared salt solution may befiltered or decanted before it is placed in the reservoir,or the end of the tube leading from the solution to the atomizer may be covered with a double layer of cheesecloth to prevent plugging of the nozzle.
N OTE5—The pH can be adjusted by additions of dilute ACS reagent grade hydrochloric acid or sodium hydroxide solutions.
9.Air Supply
9.1The compressed air supply to the Air Saturator Tower shall be free of grease,oil,and dirt before use by passing through well-maintainedfilters.(Note6)This air should be maintained at a sufficient pressure at the base of the Air Saturator Tower to meet the suggested pressures of Table2at the top of the Air Saturator Tower.
N OTE6—The air supply may be freed from oil and dirt by passing it through a suitable oil/water extrac
tor(that is commercially available)to stop any oil from reaching the Air Saturator Tower.Many oil/water extractors have an expiration indicator,proper preventive maintenance intervals should take these into account.
9.2The compressed air supply to the atomizer nozzle or nozzles shall be conditioned by introducing it into the bottom of a towerfillwed with water.A common method of introduc-ing the air is through an air dispersion device(X1.4.1).The level of the water must be maintained automatically to ensure adequate humidification.It is common practice to maintain the temperature in this tower between46and49°C(114–121°F)to offset the cooling effect of expansion to atmospheric pressure during the atomization process.Table2in9.3of this practice shows the temperature,at different pressures,that are com-monly used to offset the cooling effect of expansion to atmospheric pressure.
9.3Careful attention should be given to the relationship of tower temperature to pressure since this relationship can have a direct impact to maintaining proper collection rates(Note7). It is preferable to saturate the air at temperatures well above the chamber temperature as insurance of a wet fog as listed in Table2.
N OTE7—If the tower is run outside of these suggested temperature and pressure ranges to acheive p
roper collection rates as described in10.2of this practice,other means of verifying the proper corrosion rate in the chamber should be investigated,such as the use of control specimens (panels of known performance in the test conducted).It is preferred that control panels be provided that bracket the expected test specimen performance.The controls allow for the normalization of test conditions during repeated running of the test and will also allow comparisons of test results from different repeats of the same test.(Refer to Appendix X3, Evaluation of Corrosive Conditions,for mass loss procedures).
10.Conditions in the Salt Spray Chamber
10.1Temperature—The exposure zone of the salt spray chamber shall be maintained at35+1.1−1.7°C (95+2−3°F).Each set point and its tolerance represents an operational control point for equilibrium conditions at a single location in the cabinet which may not necessarily represent the uniformity of conditions throughout the cabinet.The tempera-ture within the exposure zone of the closed cabinet shall be recorded(Note8)at least twice a day at least7h apart(except on Saturdays,Sundays,and holidays when the salt spray test is not interrupted for exposing,rearranging,or removing test specimens or to check and replenish the solution in the reservoir)
N OTE8—A suitable method to record the temperature is by a continu-ous recording device or by a the
rmometer which can be read from outside the closed cabinet.The recorded temperature must be obtained with the salt spray chamber closed to avoid a false low reading because of wet-bulb effect when the chamber is open.
10.2Atomization and Quantity of Fog—Place at least two clean fog collectors per atomizer tower within the exposure zone so that no drops of solution will be collected from the test specimens or any other source.Position the collectors in the proximity of the test specimens,one nearest to any nozzle and the other farthest from all nozzles.A typical arrangement is shown in Fig.1.The fog shall be such that for each80 cm2(12.4in.2)of horizontal collecting area,there will be collected from1.0to2.0mL of solution per hour based on an average run of at least16h(Note9).The sodium chloride concentration of the collected solution shall be561mass% (Notes9-11).The pH of the collected solution shall be6.5to 7.2.The pH measurement shall be made as described in8.2 (Note3).
N OTE9—Suitable collecting devices are glass or plastic funnels with TABLE2Suggested Temperature and Pressure guideline for the top of the Air Saturator Tower for the operation of a test at35°C
(95°F)
Air Pressure,kPa Temperature,°C Air Pressure,PSI Temperature,°F 834612114
964714117
1104816119
1244918
121
the stems inserted through stoppers into graduated cylinders,or crystal-lizing dishes.Funnels and dishes with a diameter of 10cm (3.94in.)have an area of about 80cm 2(12.4in.2).
N OTE 10—A solution having a specific gravity of 1.0255to 1.0400at 25°C (77°F)will meet the concentration requirement.The sodium chloride concentration may also be determined using a suitable salinity meter (for example,utilizing a sodium ion-selective glass electrode)or colorimetrically as follows.Dilute 5mL of the collected solution to 100mL with distilled water and mix thoroughly;pipet a 10-
mL aliquot into an evaporating dish or casserole;add 40mL of distilled water and 1mL of 1%potassium chromate solution (chloride-free)and titrate with 0.1N silver nitrate solution to the first appearance of a permanent red coloration.A solution that requires between 3.4and 5.1mL of 0.1N silver nitrate solution will meet the concentration requirements.
N OTE 11—Salt solutions from 2to 6%will give the same results,though for uniformity the limits are set at 4to 6%.
10.3The nozzle or nozzles shall be so directed or baffled that none of the spray can impinge directly on the test specimens.
11.Continuity of Exposure
11.1Unless otherwise specified in the specifications cover-ing the material or product being tested,the test shall be continuous for the duration of the entire test period.Continu-ous operation implies that the chamber be closed and the spray operating continuously except for the short daily interruptions necessary to inspect,rearrange,or remove test specimens,to check and replenish the solution in the reservoir,and to make necessary recordings as described in Section 10.Operations shall be so scheduled that these interruptions are held to a minimum.
12.Period of Exposure
12.1The period of exposure shall be as designated by the specifications covering the material or product being tested or as mutually agreed upon between the purchaser and the seller.
N OTE 12—Recommended exposure periods are to be as agreed upon between the purchaser and the seller,but exposure periods of multiples of 24h are suggested.
13.Cleaning of Tested Specimens
13.1Unless otherwise specified in the specifications cover-ing the material or product being tested,specimens shall be treated as follows at the end of the test:
13.1.1The specimens shall be carefully removed.
13.2Specimens may be gently washed or dipped in clean running water not warmer than 38°C (100°F)to remove salt deposits from their surface,and then immediately dried.14.Evaluation of Results
14.1A careful and immediate examination shall be made as required by the specifications covering the material or product being tested or by agreement between the purchaser and the seller.
15.Records and Reports
15.1The following information shall be recorded,unless otherwise prescribed in the specifications covering the material or product being tested:
15.1.1Type of salt and water used in preparing the salt solution,
15.1.2All readings of temperature within the exposure zone of the chamber,
15.1.3Daily records of data obtained from each fog-collecting device including the following:
15.1.3.1V olume of salt solution collected in millilitres per hour per 80cm 2(12.4in.2),
15.1.3.2Concentration or specific gravity at 35°C (95°F)of solution collected,and
15.1.3.3pH of collected
solution.
N OTE —This figure shows a typical fog collector arrangement for a single atomizer tower cabinet.The same fog collector arrangement is also applicable for multiple atomizer tower and horizontal (“T”type)atomizer tower cabinet constructions as well.
FIG.1Arrangement of Fog
Collectors
15.2Type of specimen and its dimensions,or number or description of part,
15.3Method of cleaning specimens before and after testing, 15.4Method of supporting or suspending article in the salt spray chamber,
15.5Description of protection used as required in6.5, 15.6Exposure period,
15.7Interruptions in exposure,cause,and length of time, and
15.8Results of all inspections.
N OTE13—If any of the atomized salt solution which has not contacted the test specimens is returned to the reservoir,it is advisable to record the concentration or specific gravity of this solution also.
16.Keywords
16.1controlled corrosive environment;corrosive condi-tions;determining mass loss;salt spray(fog)exposure
APPENDIXES
(Nonmandatory Information)
X1.CONSTRUCTION OF APPARATUS
X1.1Cabinets
X1.1.1Standard salt spray cabinets are available from several suppliers,but certain pertinent accessories are required before they will function according to this practice and provide consistent control for duplication of results.
X1.1.2The salt spray cabinet consists of the basic chamber, an air-saturator tower,a salt solution reservoir,atomizing nozzles,specimen supports,provisions for heating the cham-ber,and suitable controls for maintaining the desired tempera-ture.
X1.1.3Accessories such as a suitable adjustable baffle or central fog tower,automatic level control for the salt reservoir, and automatic level control for the air-saturator tower are pertinent parts of the apparatus.
X1.1.4The size and shape of the cabinet shall be such that the atomization and quantity of collected solution is within the limits of this practice.
X1.1.5The chamber shall be made of suitably inert mate-rials such as plastic,glass,or stone,or constructed of metal and lined with impervious plastics,rubber,or epoxy-type materials or equivalent.
X1.1.6All piping that contacts the salt solution or spray should be of inert materials such as plastic.Vent piping should be of sufficient size so that a minimum of back pressure exists and should be installed so that no solution is trapped.The exposed end of the vent pipe should be shielded from extreme air currents that may causefluctuation of pressure or vacuum in the cabinet.
X1.2Temperature Control
X1.2.1The maintenance of temperature within the salt chamber can be accomplished by several methods.It is generally desirable to control the temperature of the surround-ings of the salt spray chamber and to maintain it as stable as possible.This may be accomplished by placing the apparatus in a constant-temperature room,but may also be achieved by surrounding the basic chamber of a jacket containing water or air at a controlled temperature.
X1.2.2The use of immersion heaters in an internal salt solution reservoir or within the chamber is detrimental where heat losses are appreciable because of solution evaporation and radiant heat on the specimens.
X1.3Spray Nozzles
X1.3.1Satisfactory nozzles may be made of hard rubber, plastic,or other inert materials.The most commonly used type is made of plastic.Nozzles calibrated for air consumption and solution-atomized are available.The operating characteristics of a typical nozzle are given in Table X1.1.
X1.3.2It can readily be seen that air consumption is relatively stable at the pressures normally used,but a marked reduction in solution sprayed occurs if the level of the solution is allowed to drop appreciably during the test.Thus,the level of the solution in the salt reservoir must be maintained auto
matically to ensure uniform fog delivery during the test.8 X1.3.3If the nozzle selected does not atomize the salt solution into uniform droplets,it will be necessary to direct the spray at a baffle or wall to pick up the larger drops and prevent them from impinging on the test specimens.Pending a com-plete understanding of air-pressure effects,and so forth,it is important that the nozzle selected shall produce the desired 8A suitable device for maintaining the level of liquid in either the saturator tower or reservoir of test solution may be designed by a local engineering group,or may be purchased from manufacturers of test cabinets as an accessory.
TABLE X1.1Operating Characteristics of Typical Spray Nozzle Siphon
Height
,cm
Air Flow,dm3/min Solution Consumption,cm3/h
Air Pressure,kPa Air Pressure,kPa
34691031383469103138 101926.531.5362100384045845256 201926.531.536636276037204320 301926.531.5360138030003710 401926.631.536078021242904
Siphon
Height,
in.
Air Flow,
L/min
Solution
Consumption,mL/h
Air Pressure,psi Air Pressure,psi
51015205101520 41926.531.5362100384045845256 81926.531.536636276037204320 121926.531.5360138030003710 161926.631.53607802124
2904
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