1、Designation: D 2688 05Standard Test Method forCorrosivity of Water in the Absence of Heat Transfer(Weight Loss Method)1This standard is issued under the fixed designation D 2688; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、 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 is also afunction of the tendency for water and the materia
4、ls 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 This
5、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-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2
6、.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 2331 Practices for Preparation and Preliminary Testing ofWater-Formed DepositsD 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D19 on WaterG1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion
7、Test SpecimensG16 Guide for Applying Statistics to Analysis of CorrosionData3. Terminology3.1 Definitions: For definitions of terms used in these testmethods, refer to Terminology D 1129.4. Significance and Use4.1 Since the two tendencies are inseparable for a metal tocorrode and for water and the m
8、aterials it contains to promoteor 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 corrosi
9、on 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 water with the corrosion rates of the samematerial in other waters. Such tests are useful, for example, forevaluating the effec
10、ts of corrosion inhibitors on 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 ope
11、n 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 system in which the corrosion test is being made.6. Effect of Cold Working on Corrosion6.1 Cold working can be important in ca
12、using localizedcorrosion; however, plastic deformation can be minimized inspecimen preparation by following proper machining practices(1) (for example, drilling, reaming, and cutting specimens).7. Types of Corrosion7.1 General Corrosion is characterized by uniform attackof the metal over the entire
13、surface.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling of Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current ed
14、ition approved Jan. 1, 2005. Published January 2005. Originallyapproved in 1969. Last previous edition approved in 1999 as D 2688 94 (1999)e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vol
15、ume 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.7.2 Pitting is a form of localized corrosion, the depth,number, size, shape, and distribution of pits be
16、ing pertinentcharacteristics. 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 Corrosion is a
17、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 as in corrosion specimens. In thismethod, crevice corrosion may be in evidence where thespecimen is fastened to the holder
18、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 remove edges of coupon mark-ing.7.4 Edge Corrosion The increased corrosion that occursat edges of corrosion specimens, wher
19、e 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 abnormally high degree of edgecorrosion is observed, the effect may be evaluated by measure-ment of the specimen dimensions
20、 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 turbulent and high-velocity flow, particularly when softmetals and copper are involved, is characterized by continuousbroad
21、er-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 on the specimens maybe analyzed by the methods listed in Practices D 2331. Themost common constituents will be calcium, ma
22、gnesium, 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 contact with flowing water for a measured length of time.After removal from the system, these coupons are examined,clean
23、ed, 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 charac-teristics of the foreign matter on the coupons.10. Interferences10.1 Deviation in metal composition or surface prepa
24、rationof 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 insulatedfrom the coupon, constitutes a source of error in the results.10.3 Deviations in the velocity and direction of flow
25、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, deposits, or biological growths may affectlocal corrosivity; results should therefore be interpreted withcaution.11. Apparatus11
26、.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 asleeve that fits into the coupon hole and around the screw.NOTE 1The insulating washer may be eliminated if a non-metal sc
27、rewand 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 (0.375-in.) outside diameter PVC, CPVC, orTFE fluorocarbon rod, or equivalent, attached at one end to adrilled PVC, CPVC, or
28、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 witness mark to indicate the orientation of thetest specimen when it is mounted in the bypass rack.11.4 Bypass Specimen Rac
29、k, 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 Schedule 80 PVC or CPVC pipe.11.5 Dial Depth GageA gage with a knife-edge base,pointed probe, and dial indicator for measur
30、ement of pit depth.11.6 Emery Paper, Number 0.12. Materials12.1 Vapor Phase Inhibitor Paper. Envelopes constructedof vapor phase inhibitor paper are commercially available.13. Coupon Preparation13.1 In this procedure, coupons are to be made principallyfrom sheet metal; however, in a few cases, as wi
31、th 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 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
32、 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 stainless steel; use cold-rolledsteel free of rust spots for ferrous metal. Obtain stainless steelwith a No. 4 finish.
33、313.3.1 Shear 14-gage sheet metal material to the dimensionsof 13 by 75 mm (0.5 by 3.0 in.).13.3.2 Drill or punch a 5-mm (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
34、with an oversize drill.3Metals Handbook, Vol 1,American Society for Metals, Metals Park, OH 44073,1961, p. 430.D 2688 05213.3.4 Stamp identifying numbers or letters on the couponarea below the mounting hole.13.4 Cast Metal Coupon PreparationObtain rough cast-ings of the desired metal, measuring abou
35、t 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 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
36、.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 area between the edge and the mounting hole.13.4.5 The approximate weight of metal coupons, g, is asfollows:Steel
37、 10.35Cast Iron 11.65Copper 13.33Zinc 8.7FIG. 1 Installation of Corrosion CouponsD 2688 053Lead 16.6013.5 Cleaning Metal CouponsDegrease and clean corro-sion in specimens in accordance with Practice G1.14. Procedure14.1 Weigh the clean, dry specimens on an analyticalbalance to the nearest 0.1 mg.14.
38、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-free atmosphere.14.3 Store ferrous metal coupons in separate envelopesmade from vapor phase inhibitor-impregnated pap
39、er. 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 coupon with themetal screw and nut assembly. For added protection, attach thespecimen to the holder using a non-met
40、al 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 piping to arate that gives a flow velocity that corresponds to the normalflow in those parts of the system under prime
41、 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 Remove specimens from the system at chosen inter-vals. Since the corrosion will be high initially and then fall toa
42、 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. Removalof three or four sets of coupons at 4- to 7-day intervals isrecommended.14.7.2 Use long time intervals for the seco
43、nd 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.14.8 Protect the specimen if it cannot be examined, cleaned,and reweighed immediately after removal from the system.
44、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 coupons, wrap carefully in plastic film. Theinterim period between removal of specimens and reweighingshould be kept
45、 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 to the amount and nature of any adherentdeposit. Chemical analysis of the deposit may be performed inaccordance wi
46、th Practices D 2331, 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 coupons as well as possible with a plasticknife. Remove oily and greasy deposits in accordance withPractice G1. Rem
47、ove 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 materialto the identical cleaning procedure used for the test specimensand reweigh to determine the blank correction factor
48、 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 representative area with the dial depthgage. Record the resultant values as pit depths. The number,size, shape, and distri
49、bution 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 mils per year or millimetres per year assumingthat localized attack or pitting is not present and that thecorrosion is general (3).15.2 Calculation of the Corrosion Rate:15.2.1 To calculate the corrosion rate (3, 4, 5) in mil
