ASTM A896-1989(2004) Standard Practice for Conducting Case Studies on Galvanized Structures《镀锌结构导电壳研究的标准规程》.pdf

1、Designation: A 896 89 (Reapproved 2004)Standard Practice forConducting Case Studies on Galvanized Structures1This standard is issued under the fixed designation A 896; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las

2、t 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 practice sets forth the procedures for conductingcase studies of galvanized installations. It is intended forstruct

3、ural members and other permanent parts of the installa-tion, such as railings and other such fabrications.1.2 Included in this practice are recommendations for thevisual inspection of the galvanized structure, measurement ofcoating thickness, and reporting of results.1.3 The values stated in SI unit

4、s are to be regarded as thestandard.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-priate safety and health practices and determine the applica-bility of regulatory limi

5、tations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 499 Test Method for Measurement of Coating Thicknessby the Magnetic Method: Nonmagnetic Coatings on Mag-netic Basis MetalsE 376 Practice for Measuring Coating Thicknesses byMagnetic-Field or Eddy Current (Electromagnetic) TestMethods3

6、. Significance and Use3.1 This practice is applicable to galvanized structuresexposed to the atmosphere or to plant environments, includingbuildings, bridges, and industrial plant constructions.3.2 It provides for the collection of data to document theprotection afforded by the galvanized coating.3.

7、3 Method A for conducting a coating thickness surveyaims essentially at an assessment of the general condition ofthe galvanized structure, at the time of the inspection, by takingthickness measurements on several members of the structure.3.4 Method B provides for accurate monitoring of thecoating th

8、ickness decrease as a function of time, at specificlocations on the structure, in order to assess the corrosivity ofthe environment, the effect of orientation, elevation, or otherfactors.3.5 Method B is not an alternate procedure to Method A, butis complementary and optional.4. Apparatus4.1 Surface

9、Preparation:4.1.1 Water.4.1.2 Cloths, for washing and drying.4.1.3 Soft Fiber Bristle Brush.4.2 Coating Thickness Measurement:4.2.1 Thickness Gage.4.2.2 Steel Calibration Plates and Foils.4.2.3 Permanent Marker.4.2.4 Tape Measure.4.2.5 Center Punch.4.2.6 Hammer.4.3 Electronic Magnetic Flux Gage The

10、use of an elec-tronic magnetic-flux gage in accordance with Method B 499 isrecommended. Instruments with an accuracy of 63to65%are commercially available.4.3.1 Probes having a constant pressure feature will mini-mize operator error.4.3.2 The probe assembly should have a probe support ifmeasurements

11、are to be made on rounded or curved surfaces.4.4 Hand-Held Magnetic GageA hand-held magneticgage using the magnetic attraction principle in accordance withPractice E 376 may be used for Method A.5. General Procedure5.1 Background Information:5.1.1 Wherever possible, obtain information on the tonnage

12、and cost of the steel work, the cost of galvanizing, andestimates of alternative coating costs (initial and maintenance)if the steelwork had been coated by another method. Determineif there are areas of the installation which were painted ratherthan galvanized, or painted over galvanizing.1This prac

13、tice is under the jurisdiction of ASTM Committee A05 on MetallicCoated Iron and Steel Products and is the direct responsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specifications.Current edition approved May 1, 2004. Published June 2004. Originallyapproved in 1989. Last previous

14、edition approved in 1999 as A 896 - 89 (1999).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.1Copyright ASTM

15、 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.2 Determine if any problems were experienced duringfabrication, galvanizing, construction, and operation.5.2 Corrosive Environment Identification:5.2.1 The galvanized installation should be divide

16、d accord-ing to the various corrosive environments to which it isexposed. For example, plant atmospheres could be categorizedwith respect to the processing step. Sheltered versus boldlyexposed areas can be considered as two different environments.5.2.2 Pertinent data relating to the corrosive enviro

17、nmentsshould be obtained, such as types of chemical present, concen-tration of fumes, occurrence of spills, temperature fluctuations,amount of rainfall, or the use of de-icing salts.5.3 Visual Inspection:5.3.1 Observe the overall appearance of the galvanizedstructure, and the appearance of each type

18、 of plant environ-ment, if applicable. Note such characteristics as color andspangle of the galvanized coating, the presence of rust orstaining, and the condition of other coatings, such as paint.Take note of chemical spills or leaks, the presence of fumes orhigh humidity, and effects of orientation

19、, elevation, design, orany other factors causing localized or nonuniform corrosion.5.3.2 The condition of the galvanized coating may varyaccording to section thickness or geometry of the steel. Forexample, there may be differences with respect to light versusheavy sections or handrails versus beams.

20、5.3.3 The use of high silicon steels may be apparent, andshould be noted.5.3.4 Fasteners should be inspected. Look for rust, staining,or mechanical damage.5.4 Coating Thickness Survey:5.4.1 Method A:5.4.1.1 The selection of structural members should be basedmainly on the section thickness. A minimum

21、 of three represen-tative members from each of the two categories of sectionthickness, light (bracing) and heavy (column, beam) should besurveyed for each corrosive environment. Selection of suitablelocations for coating thickness measurements is at the discre-tion of the inspector and may be based

22、on factors such asorientation or accessibility. Take measurements in areas wherethe coating is uniform.5.4.1.2 Fasteners should be surveyed where their size per-mits. Measurements should be made on the center of boltheads, or on the flat parts of bolt heads or nuts.5.4.1.3 Calibrate the coating thic

23、kness gage against properreference materials before making measurements.5.4.1.4 Clean the surface, using a fine fiber brush or bywashing with water and drying, or both. Avoid removing any ofthe coating material or the film of basic zinc salts.5.4.1.5 At each location, make a minimum of five measure-

24、ments and determine the mean coating thickness.5.4.2 Method B:5.4.2.1 A minimum of three locations should be surveyedfor each corrosive condition or position of interest. Thelocations need not be on the same steel member. Selection ofsuitable locations is at the discretion of the inspector. Takemeas

25、urements in areas where the coating is uniform.5.4.2.2 Calibrate the coating thickness gage with properreference materials before the survey is started. Calibrationsshould be checked periodically to ensure continued accuracy ofmeasurements and again at the end of the survey.5.4.2.3 Clean the surface

26、, using a fine fiber bristle brush orby washing with water to remove dirt and dust, or both.WarningDo not abrade with emery paper or wire brush, orclean in any manner that would tend to remove the zinc coatingor the film of basic zinc salts. By removing the basic zinc saltsfilm, corrosion can be acc

27、elerated.5.4.2.4 Twenty-five measurements should be made at eachlocation within an area 50 by 50 mm 2 by 2 in. square, andthe mean (X) and the 90 % confidence limit on the mean (Sm90)should be determined (see Appendix X1). A different test areashould be surveyed if Sm90 is greater than 6 m 0.3 mil.

28、Ifpossible, use a template with 25 small holes (approximately 4mm diameter) ina5by5grid, with outside corner measure-ments 50 by 50 mm 2 by 2 in. Holes should be 12.5 mm 0.5in. apart horizontally and vertically. The grid should becentered in a larger square measuring 75 by 75 mm 3 by 3 in.with outsi

29、de corners containing small holes (see Fig. 1). Put thetemplate on the cleaned surface and mark the 29 holes with afelt tip marker. Measurements are to be taken starting with thetop left and recorded on the report form in the same order asmeasured on the grid.5.4.2.5 To make test areas easier to loc

30、ate for future surveys,center punch the outside corners of the 75 by 75 mm square 3by 3 in. so identification marks do not interfere with coatingmeasurements. If punching is not possible, use paint or otherpermanent marker (less desirable). If possible, take a photo-graphic record to properly docume

31、nt the position of eachstructural member on which measurements were made inrelation to the plant layout.FIG. 1 Template (not to scale)A 896 89 (2004)25.4.2.6 Periodic surveys should be conducted. An initialtwo-year interval is recommended for the first several years.Depending on the nature of the da

32、ta collected at the time of thesecond inspection, longer intervals may be considered.5.4.2.7 The same thickness gage, or at least the same type ofinstrument as used in subsequent surveys. The steel calibrationplate should be the same for each survey.5.5 Photographs:5.5.1 Obtain an overall photograph

33、ic view of the installa-tion, from several angles, if possible.5.5.2 Photograph each corrosive environment where mea-surements are made, show the relation of the site to the generalplant layout. If possible, show the fumes or chemicals thatwould normally be present.5.5.3 Take close-up photographs wh

34、ere appropriate.5.5.3.1 Include close-up photographs of areas where actualmeasurements were made.5.5.3.2 Take close-up photographs of other areas pertinentto the study, such as those areas showing concentrated corro-sion, coating damage, staining, etc., that is not typical of thegalvanized structure

35、 as a whole.5.5.3.3 Take close-ups of fasteners.5.5.3.4 Take close-ups of painted or other coated areas.6. Report6.1 Report sheets are provided in Appendix X2.6.2 State the name of the company of installation and itslocation. Describe the type of structure if an industrial plant.6.3 The inspector sh

36、ould state his or her name, companycontact, date of the inspection, and type of thickness measuringequipment used.6.4 Present any data that is available regarding tonnage andcost of the steel, and comparison costs of galvanizing versusother coating systems.6.5 Visual Inspection:6.5.1 Report the gene

37、ral appearance of the galvanizedstructure or installation, and any noticeable changes since thelast inspection. Report coating characteristics such as color,spangle, stains, rust, and condition of paint coatings, fasteners,and high silicon steels within each type of environment, ifapplicable.6.5.2 R

38、elate the photographs to the locations discussed inthe report.6.6 Coating Thickness Measurement:6.6.1 Method AState the range of average coating thick-nesses measured on structural members, including high siliconsteels, and on fasteners. Make mention of differences in coatingthickness that may arise

39、 from such factors as section thickness,orientation, etc.6.6.2 Method BProvide details about each location atwhich thickness measurements were made and state the meanand the 90 % confidence interval, rounding to the least signifi-cant number of digits.6.6.3 Relate photographs to the corresponding ar

40、easmeasured.APPENDIXES(Nonmandatory Information)X1. CALCULATION OF 90 % CONFIDENCE INTERVALX1.1 The standard deviation, s, of a series of measurementscan be calculated using the following equation:s 5(Xi2 X!2#n 2 1where:Xi= each individual reading,X = mean of group of 25 readings, andn = number of m

41、easurements.X1.2 The 90 % confidence interval on the mean, Sm90, canbe expressed as follows:Sm90 5ts=nwhere:s = standard deviation, andt = the t distribution value for n 1 degrees of freedom.X1.2.1 Tables containing values for t can be found intextbooks on statistics or in most engineering handbooks

42、. Forthe number of measurements ( n = 25) prescribed in 5.4.2.4, t= 1.711 for n-1 degrees of freedom and the value oft/=n5 1.711/5 5 0.34.The 90 % confidence interval on the mean for 25 measure-ments can then be written as Sm90 = 0.34 s.X1.2.2 If some number other than 25 measurements is used,the va

43、lue of t for n-1 degrees of freedom must be determinedfrom statistical tables.X1.2.2.1 Calculation of X, s, and Sm90 values can betedious, and the use of an electronic calculator is recom-mended.X1.3 The significance of Sm90 is that there is a 90 %probability that the true value of the mean will lie

44、 within therange X 6 Sm90, the most probable value being X. A testprogram involving field measurements has shown that consid-ering a corrosion rate of 2.5 m/year 0.1 mil/year, it will bepossible to see a significant difference between average coatingthicknesses resulting from surveys carried out ten

45、 years apart intime and based on 25 readings.X1.4 Example of Calculations:A 896 89 (2004)3X1.4.1 Xi= 142, 165, 170, 155, 168, 132, 163, 152, 179,142, 157, 173, 152, 135, 170, 155, 165, 170, 165, 147, 152,163, 152, 163, 160 m 5.6, 6.5, 6.7, 6.1, 6.6, 5.2, 6.4, 6.0, 7.0,5.6, 6.2, 6.8, 6.0, 5.3, 6.7, 6

46、.1, 6.5, 6.7, 6.5, 5.8, 6.0, 6.4, 6.0,6.4, 6.3 mil.X1.4.2 Mean, X = 157 m 6.2 mil.X1.4.3 Standard deviation, s = 12 m 0.5 mil.X1.4.4 90 % confidence interval, Sm90=4m0.2 mil.X2. CASE STUDY REPORT SHEETX2.1 Fig. X2.1 shows a case study report sheet.A 896 89 (2004)4FIG. X2.1 Case Study Report SheetA 8

47、96 89 (2004)5FIG. X2.1 Case Study Report Sheet (continued)A 896 89 (2004)6FIG. X2.1 Case Study Report Sheet (continued)A 896 89 (2004)7ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this stand

48、ard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andi

49、f not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Har