1、Designation: D2688 151Standard 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 y
2、ear 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.1NOTEAn editorial correction was made to 13.3.2 in July 2016.1. Scope1.1 This test method covers the determination of the c
3、orro-sivity of water by evaluating pitting and by measuring theweight 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
4、is also afunction of the tendency for water and the materials 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 sys
5、tems using a side stream corrosion speci-men rack.1.3 The values stated in SI units are to be regarded asstandard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.4 This standard does not purpor
6、t to address all of thesafety concerns, if any, associated with its use. It is theresponsibility 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 Documents2.1 ASTM Standards:2D1129
7、 Terminology Relating to WaterD2331 Practices for Preparation and Preliminary Testing ofWater-Formed DepositsD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG16 Guid
8、e for Applying Statistics to Analysis of CorrosionData3. Terminology3.1 DefinitionsFor definitions of terms used in thisstandard, refer to Terminology 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 promot
9、eor inhibit corrosion, the corrosiveness of a material or thecorrosivity of water must be determined in relative, rather thanabsolute, terms. The tendency for a material to corrode isnormally determined by measuring its rate of corrosion andcomparing it with the corrosion rates of other materials in
10、 thesame water environment. Conversely, the relative corrosivityof water may be determined by comparing the corrosion rate ofa material in the water with the corrosion rates of the samematerial in other waters. Such tests are useful, for example, forevaluating the effects of corrosion inhibitors on
11、the corrosivityof water. Although this test methods is intended to determinethe corrosivity of water, it is equally useful for determiningcorrosiveness and corrosion rate of materials. Examples ofsystems in which this method may be used include but are notlimited to open recirculating cooling water
12、and closed chilledand hydronic heating systems.5. Composition of Specimens5.1 The specimens shall be similar in composition to thepiping in the system in which the corrosion test is being made.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility
13、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.Current edition approved June 1, 2015. Published June 2015. Originallyapproved in 1969. Last previous edition approved in 2011 a
14、s D2688 11. DOI:10.1520/D2688-15E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM Internatio
15、nal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. 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
16、(1)3(for example, drilling, reaming, and cutting specimens).7. Types of Corrosion7.1 General CorrosionCharacterized by uniform attack ofthe metal over the entire surface.7.2 PittingA form of localized corrosion, the depth,number, size, shape, and distribution of pits being pertinentcharacteristics.
17、It may be evaluated by counting the number, bynoting the size, shape, and distribution, and by measuring thedepth of pits in representative areas. 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 incor
18、rosion testing, since active corrosion sites may develop insuch locations. Crevices may exist at threads and joints andunder deposits, as well 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
19、 large specimen surface area relative to the crevicearea reduces this influence on the overall corrosion results.Light sanding is necessary to remove edges of coupon mark-ing.7.4 Edge CorrosionThe increased corrosion that occurs atedges of corrosion specimens, where the metal may be ofdifferent comp
20、osition or structure, must be given attention. Inthis method, specimens of a high ratio of surface area to edgearea reduce this effect. If an abnormally high degree of edgecorrosion is observed, the effect may be evaluated by measure-ment of the specimen dimensions previous to and followingexposure.
21、 Use of a specimen of less thickness may also reducethe edge effect in weight loss.7.5 Impingement Attack (Erosion-Corrosion)associatedwith turbulent and high-velocity flow, particularly when softmetals and copper are involved, is characterized by continuousbroader-type pits and bright metal from wh
22、ich protective filmshave been scoured away. Some under-cutting also may bepresent.8. Water-Formed Deposits8.1 Water-formed deposits observed on the specimens maybe analyzed by the methods listed in Practices D2331. Themost common constituents will be calcium, magnesium,aluminum, zinc, copper, iron,
23、carbonate, phosphate, sulfate,chloride, and silica.9. Summary of Test Method9.1 Carefully prepared, weighed metal coupons are installedin 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 fou
24、ling character-istics of the water are determined from the difference in weight,the depth and distribution of pits, and the weight and charac-teristics of the foreign matter on the coupons.10. Interferences10.1 Deviation in metal composition or surface preparationof the coupons may influence the pre
25、cision of the results.10.2 The presence of different metals in close proximity tothe coupon, (within 76 mm (3 in.), even if they are insulatedfrom 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 precisio
26、n of the results.10.4 Results are directly comparable only for the watertemperature to which the coupon is exposed.10.5 Crevices, deposits, or biological growths may affectlocal corrosivity; results should therefore be interpreted withcaution.11. Apparatus11.1 Coupon SpecimensPrepare coupons in acco
27、rdancewith Section 13.11.2 Insulating Washer, Screw, and NutUse for attachingthe coupon to the mounting rod. The insulating washer has asleeve 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 ny
28、lon or TFE fluorocarbon have beenfound satisfactory for this purpose.11.3 Specimen Mounting PlugUse a 152-mm (6-in.)length of 9.5-mm (0.375-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
29、 surface and a hole at the other end suitable for attachmentof the test specimen. The pipe plug shall have a saw slot orother suitable witness 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, forinstallati
30、on of coupon specimens. The piping, valves, andfittings of the corrosion rack shall be constructed of 2.5 cm (1in.) Schedule 40 carbon steel, stainless steel, or Schedule 80PVC or CPVC pipe. If necessary, the rack can be constructedof 16.8-mm (34-in.) Schedule 40 carbon steel, stainless steel, orSch
31、edule 80 PVC or CPVC pipe. This allows for a lower flowrate to achieve adequate velocity but leaves less clearancearound the coupon and may trap more debris. If a 16.8-mm(34-in.) rack is used, a strainer should be installed ahead of therack to prevent debris from entering the rack.11.5 Dial Depth Ga
32、geA 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.Vapor phase inhibitor paper for wrapping coupons is al
33、socommercially available.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D2688 151213. Coupon 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 nec
34、essary 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 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 be
35、ing to keep the flat area large compared to theedge area.13.3 Sheet Metal Coupon PreparationObtain sheet metalof the type desired except for stainless steel; use cold-rolledsteel free of rust spots for ferrous metal. Obtain stainless steelwith a No. 4 finish (3).13.3.1 Shear 14-gage sheet metal mate
36、rial to the dimensionsof 13 by 75 mm (0.5 by 3.0 in.).13.3.2 Drill or puncha5mm(0.19 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 identif
37、ying numbers or letters on the couponarea below the mounting hole.13.4 Cast Metal Coupon Preparation Obtain 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.FIG. 1 Installation of Corrosion CouponsD2688 151313.4.1 Surf
38、ace grind to the dimensions of 13 by 102 by 3mm (0.5 by 4.0 by 0.125 in.) and a surface roughness 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 debur
39、r the hole with an oversize drill.13.4.4 Stamp identifying numbers or letters on the smallcoupon 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 8.7Lead 16.6013.5 Cleaning Metal CouponsDegrease and
40、 clean corro-sion in specimens in accordance with Practice .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 a
41、lternative method for providing acorrosion-free atmosphere.14.3 Store coupons in separate envelopes made from vaporphase inhibitor-impregnated paper or in envelopes andwrapped in vapor-phase inhibitor-impregnated paper.14.4 Attach the coupon to the mounting rod, using a plasticscrew and nut or using
42、 an insulating washer to preclude anycontact of coupon with the metal screw and nut assembly. Foradded protection, attach the specimen to the holder using anon-metal screw and nut.14.5 The coupons should be placed into the corrosioncoupon rack following the galvanic series in seawater. Thismeans tha
43、t the most active (least noble) metal be first in theflow path. Other coupons follow the galvanic series. Thisprevents the more noble metal from cathodically depositing onthe more active metal or alloy.14.6 Install the holder and coupon assembly in a suitableline or in a bypass piping arrangement as
44、 shown in Fig. 1.14.7 Adjust the rate of flow of water in the test piping 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 readjus
45、t the flow as necessary tomaintain the desired rate. See Table 1.14.8 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.14.8.1 Use short time intervals for the first time s
46、eries inorder to establish the rate at which passivity occurs. Removalof three or four sets of coupons at 4 to 7-day intervals isrecommended.14.8.2 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 mont
47、h and the remainingcoupons at 1 to 3-month intervals is recommended.14.9 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-impre
48、gnated paper or wrap carefully in plastic film. Fornonferrous metal coupons, 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.14.10 Examine the specimen and record either by photo-graph or b
49、y description the appearance of the specimen, payingparticular attention 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.14.11 For ferrous coupons, use one of the following alter-native procedures for cleaning the coupon prior to reweighing.14.11.1 Clean the coupons as well as possible with a plasticknife. Remove oily and greasy deposits in accordance withPractice . Remove remaining loose corrosion products bybrushing with a bristle brush. R
