1、Designation: D2688 11Standard Test Method forCorrosivity of Water in the Absence of Heat Transfer(Weight Loss Method)1This standard is issued under the fixed designation D2688; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the corro-sivity of water by evaluating pitting and by measuring th
3、eweight loss of metal specimens. Pitting is a form of localizedcorrosion: weight loss is a measure of the average corrosionrate. The rate of corrosion of a metal immersed in water is afunction of the tendency for the metal to corrode and is also afunction of the tendency for water and the materials
4、it containsto promote (or inhibit) corrosion.1.2 The test method employs flat, rectangular-shaped metalcoupons which are mounted on pipe plugs and exposed to thewater flowing in metal piping in municipal, building, andindustrial water systems using a side stream corrosion speci-men rack.1.3 The valu
5、es stated in SI units are to be regarded asstandard, other units Values given in parenthesis are forinformation only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priat
6、e safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD2331 Practices for Preparation and Preliminary Testing ofWater-Formed DepositsD2777 Practice for Determination of Preci
7、sion and Bias ofApplicable Test Methods of Committee D19 on WaterG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG16 Guide for Applying Statistics to Analysis of CorrosionData3. Terminology3.1 Definitions: For definitions of terms used in this testmethod, refer to Termin
8、ology D1129.4. Significance and Use4.1 Since the two tendencies are inseparable for a metal tocorrode and for water and the materials it contains to promoteor inhibit corrosion, the corrosiveness of a material or thecorrosivity of water must be determined in relative, rather thanabsolute, terms. The
9、 tendency for a material to corrode isnormally determined by measuring its rate of corrosion andcomparing it with the corrosion rates of other materials in thesame water environment. Conversely, the relative corrosivityof water may be determined by comparing the corrosion rate ofa material in the wa
10、ter with the corrosion rates of the samematerial in other waters. Such tests are useful, for example, forevaluating the effects of corrosion inhibitors on the corrosivityof water. Although this test methods is intended to determinethe corrosivity of water, it is equally useful for determiningcorrosi
11、veness and corrosion rate of materials. Examples ofsystems in which this method may be used include but are notlimited to open recirculating cooling water and closed chilledand hydronic heating systems.5. Composition of Specimens5.1 The specimens shall be similar in composition to thepiping in the s
12、ystem in which the corrosion test is being made.6. Effect of Cold Working on Corrosion6.1 Cold working can be important in causing localizedcorrosion; however, plastic deformation can be minimized inspecimen preparation by following proper machining practices(1) (for example, drilling, reaming, and
13、cutting specimens).1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Cu
14、rrent edition approved Feb. 1, 2011. Published April 2011. Originallyapproved in 1969. Last previous edition approved in 2005 as D2688 051. DOI:10.1520/D2688-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book o
15、f ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7. Types of Corrosion7.1 General CorrosionCharacterized by uniform attack ofthe metal
16、 over the entire surface.7.2 PittingA form of localized corrosion, the depth, num-ber, size, shape, and distribution of pits being pertinentcharacteristics. It may be evaluated by counting the number, bynoting the size, shape, and distribution, and by measuring thedepth of pits in representative are
17、as. Both sides of the couponsmust be examined.7.2.1 A system may be devised for grading pitting (2).7.3 Crevice CorrosionA pertinent factor to consider incorrosion testing, since active corrosion sites may develop insuch locations. Crevices may exist at threads and joints andunder deposits, as well
18、as in corrosion specimens. In thismethod, crevice corrosion may be in evidence where thespecimen is fastened to the holder and at coupon markings.Providing a large specimen surface area relative to the crevicearea reduces this influence on the overall corrosion results.Light sanding is necessary to
19、remove edges of coupon mark-ing.7.4 Edge Corrosion The increased corrosion that occursat edges of corrosion specimens, where the metal may be ofdifferent composition or structure, must be given attention. Inthis method, specimens of a high ratio of surface area to edgearea reduce this effect. If an
20、abnormally high degree of edgecorrosion is observed, the effect may be evaluated by measure-ment of the specimen dimensions previous to and followingexposure. Use of a specimen of less thickness may also reducethe edge effect in weight loss.7.5 Impingement Attack (Erosion-Corrosion) associatedwith t
21、urbulent and high-velocity flow, particularly when softmetals and copper are involved, is characterized by continuousbroader-type pits and bright metal from which protective filmshave been scoured away. Some under-cutting also may bepresent.8. Water-Formed Deposits8.1 Water-formed deposits observed
22、on the specimens maybe analyzed by the methods listed in Practices D2331. Themost common constituents will be calcium, magnesium, alu-minum, zinc, copper, iron, carbonate, phosphate, sulfate, chlo-ride, and silica.9. Summary of Test Method9.1 Carefully prepared, weighed metal coupons are installedin
23、 contact with flowing water for a measured length of time.After removal from the system, these coupons are examined,cleaned, and reweighed. The corrosivity and fouling character-istics of the water are determined from the difference in weight,the depth and distribution of pits, and the weight and ch
24、arac-teristics of the foreign matter on the coupons.10. Interferences10.1 Deviation in metal composition or surface preparationof the coupons may influence the precision of the results.10.2 The presence of different metals in close proximity tothe coupon, (within 76 mm (3 in.), even if they are insu
25、latedfrom the coupon, constitutes a source of error in the results.10.3 Deviations in the velocity and direction of flow past thecoupons may influence the precision of the results.10.4 Results are directly comparable only for the watertemperature to which the coupon is exposed.10.5 Crevices, deposit
26、s, or biological growths may affectlocal corrosivity; results should therefore be interpreted withcaution.11. Apparatus11.1 Coupon SpecimensPrepare coupons in accordancewith Section 13.11.2 Insulating Washer, Screw, and NutUse for attachingthe coupon to the mounting rod. The insulating washer has as
27、leeve that fits into the coupon hole and around the screw.NOTE 1The insulating washer may be eliminated if a non-metal screwand nut are used. Screws and nuts of nylon or TFE fluorocarbon have beenfound satisfactory for this purpose.11.3 Specimen Mounting PlugUse a 152-mm (6-in.)length of 9.5-mm (0.3
28、75-in.) outside diameter PVC, CPVC, orTFE fluorocarbon rod, or equivalent, attached at one end to adrilled PVC, CPVC, or malleable iron pipe plug, and having aflat surface and a hole at the other end suitable for attachmentof the test specimen. The pipe plug shall have a saw slot orother suitable wi
29、tness mark to indicate the orientation of thetest specimen when it is mounted in the bypass rack.11.4 Bypass Specimen Rack, as illustrated in Fig. 1, forinstallation of coupon specimens. The piping, valves, andfittings of the corrosion rack shall be constructed of 1 in.Schedule 40 carbon steel or Sc
30、hedule 80 PVC or CPVC pipe.11.5 Dial Depth GageA gage with a knife-edge base,pointed probe, and dial indicator for measurement of pit depth.11.6 Emery Paper, Number 0.12. Materials12.1 Vapor Phase Inhibitor PaperEnvelopes constructedof vapor phase inhibitor paper are commercially available.13. Coupo
31、n Preparation13.1 In this procedure, coupons are to be made principallyfrom sheet metal; however, in a few cases, as with cast iron orcast bronze, it may be necessary to prepare coupons fromcastings.13.2 Use a coupon size of 13 by 76 by 1.6 mm (0.5 by 3.0by 0.0625 in.) for all sheet metals; and a 13
32、 by 76 by 3 mm (0.5by 3.0 by 0.125 in.) for cast metals. Other sizes are suitable,providing the total area is about 259 mm2(4 in.2), the principalrequirement being to keep the flat area large compared to theedge area.13.3 Sheet Metal Coupon PreparationObtain sheet metalof the type desired except for
33、 stainless steel; use cold-rolledsteel free of rust spots for ferrous metal. Obtain stainless steelwith a No. 4 finish.313.3.1 Shear 14-gage sheet metal material to the dimensionsof 13 by 75 mm (0.5 by 3.0 in.).3Metals Handbook, Vol 1,American Society for Metals, Metals Park, OH 44073,1961, p. 430.D
34、2688 11213.3.2 Drill or puncha5mm(0.019 in.) hole with its centerabout 3 mm (18 in.) from one end of the coupon.13.3.3 Deburr all sharp edges on the coupon specimen usinga file or emery belt, and deburr the hole with an oversize drill.13.3.4 Stamp identifying numbers or letters on the couponarea bel
35、ow the mounting hole.13.4 Cast Metal Coupon PreparationObtain rough cast-ings of the desired metal, measuring about 19 by 114 by 6 mm(34 by 412 by14 in.) from a commercial foundry or elsewhere.13.4.1 Surface grind to the dimensions of 13 by 102 by 3mm (0.5 by 4.0 by 0.125 in.) and a surface roughnes
36、s of about124 in.13.4.2 Drill a 7-mm (932-in.) hole with its center about 8mm (516 in.) from one end of the coupon.13.4.3 Deburr all sharp edges on the coupon specimen usinga file or emery belt, and deburr the hole with an oversize drill.13.4.4 Stamp identifying numbers or letters on the smallcoupon
37、 area between the edge and the mounting hole.13.4.5 The approximate weight of metal coupons, g, is asfollows:Steel 10.35Cast Iron 11.65Copper 13.33Zinc 8.7FIG. 1 Installation of Corrosion CouponsD2688 113Lead 16.6013.5 Cleaning Metal CouponsDegrease and clean corro-sion in specimens in accordance wi
38、th Practice G1.14. Procedure14.1 Weigh the clean, dry specimens on an analyticalbalance to the nearest 0.0001 g.14.2 After weighing, store the specimens in a desiccatoruntil ready for use. If storing in a desiccator is inconvenient orimpractical, use an alternative method for providing acorrosion-fr
39、ee atmosphere.14.3 Store ferrous metal coupons in separate envelopesmade from vapor phase inhibitor-impregnated paper. Storenonferrous metal coupons in sealed plastic envelopes orwrapped in plastic film.14.4 Attach the coupon to the mounting rod, using aninsulating washer to preclude any contact of
40、coupon with themetal screw and nut assembly. For added protection, attach thespecimen to the holder using a non-metal screw and nut.14.5 Install the holder and coupon assembly in a suitableline or in a bypass piping arrangement as shown in Fig. 1.14.6 Adjust the rate of flow of water in the test pip
41、ing to arate that gives a flow velocity that corresponds to the normalflow in those parts of the system under prime consideration.Normally, the flow velocity will be in the range from 0.4 to 1.8m (1.5 to 6 ft)/s. Check and readjust the flow as necessary tomaintain the desired rate. See Table 1.14.7
42、Remove specimens from the system at chosen inter-vals. Since the corrosion will be high initially and then fall toa lower, nearly constant rate, two time series should be chosen.14.7.1 Use short time intervals for the first time series inorder to establish the rate at which passivity occurs. Removal
43、of three or four sets of coupons at 4- to 7-day intervals isrecommended.14.7.2 Use long time intervals for the second time series inorder to establish the mean steady-state corrosion rate. Re-moval of the first coupons after 1 month and the remainingcoupons at 1 to 3-month intervals is recommended.1
44、4.8 Protect the specimen if it cannot be examined, cleaned,and reweighed immediately after removal from the system.Dry between paper towels. Store the ferrous metal coupons inseparate envelopes made from vapor phase inhibitor-impregnated paper or wrap carefully in plastic film. Fornonferrous metal c
45、oupons, wrap carefully in plastic film. Theinterim period between removal of specimens and reweighingshould be kept to a minimum and in no case should it exceed1 week.14.9 Examine the specimen and record either by photographor by description the appearance of the specimen, payingparticular attention
46、 to the amount and nature of any adherentdeposit. Chemical analysis of the deposit may be performed inaccordance with Practices D2331, but this step is optional.14.10 For ferrous coupons, use one of the following alter-native procedures for cleaning the coupon prior to reweighing.14.10.1 Clean the c
47、oupons as well as possible with a plasticknife. Remove oily and greasy deposits in accordance withPractice G1. Remove remaining loose corrosion products bybrushing with a bristle brush. Remove corrosion products inaccordance with Practice G1.14.11 Subject a weighed blank coupon of the same materialt
48、o the identical cleaning procedure used for the test specimensand reweigh to determine the blank correction factor to beapplied to the coupon weight losses.14.12 Reweigh each coupon to the nearest 0.1 mg.14.13 If pitting (see 7.2) is apparent on the coupon, measurethe depth of the pits in a represen
49、tative area with the dial depthgage. Record the resultant values as pit depths. The number,size, shape, and distribution of the pits shall also be determinedand recorded.14.14 Record the appearance of the cleaned, weighed cou-pon as“ protected,” “moderate localized,” “moderate pitting,”or“ severe pitting,” by comparing the coupon with the illustra-tions given in Fig. 2.15. Calculation15.1 Corrosion rates are normally calculated as an averagepenetration in millimeters per year (or as mils per year) ormillimeters per year assuming that localized attack or pitt
