ASTM A896 A896M-2009 Standard Practice for Conducting Case Studies on Galvanized Structures《镀锌结构传导性的研究案例用标准规范》.pdf

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1、Designation: A 896/A 896M 09Standard Practice forConducting Case Studies on Galvanized Structures1This standard is issued under the fixed designationA 896/A 896M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last rev

2、ision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice sets forth the procedures for conductingcase studies of galvanized installations. It is intended forstructural

3、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 This specification is applicable

4、to orders in eitherinch-pound units (as A 896) or in SI units (as A 896M).Inch-pound units and SI units are not necessarily exactequivalents. Within the text of this specification and whereappropriate, SI units are shown in brackets. Each system shallbe used independently of the other without combin

5、ing values inany way.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 limitations prior t

6、o use.2. Referenced Documents2.1 ASTM Standards:2B 499 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsE 376 Practice for Measuring Coating Thickness byMagnetic-Field or Eddy-Current (Electromagnetic) Exami-nation Methods3. Sign

7、ificance 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.3.3 Meth

8、od 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 thicknes

9、s 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 MethodA, butis complementary and optional.4. Apparatus4.1 Surface Prepara

10、tion: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 use of

11、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 are to

12、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 tonnageand cos

13、t 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. Determine1This practice is under the jurisdiction of ASTM Committee A05 on Metallic-Coated Iron and Steel Products and is the direct re

14、sponsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specifications.Current edition approved May 1, 2009. Published June 2009. Originallyapproved in 1989. Last previous edition approved in 2004 as A 896 - 89 (2004).2For referenced ASTM standards, visit the ASTM website, www.astm.org,

15、 orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C70

16、0, West Conshohocken, PA 19428-2959, United States.if there are areas of the installation which were painted ratherthan galvanized, or painted over galvanizing.5.1.2 Determine if any problems were experienced duringfabrication, galvanizing, construction, and operation.5.2 Corrosive Environment Ident

17、ification:5.2.1 The galvanized installation should be divided 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 enviro

18、nments.5.2.2 Pertinent data relating to the corrosive environmentsshould 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

19、 of the galvanizedstructure, and the appearance of each type 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 p

20、resence of fumes orhigh humidity, and effects of orientation, 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 resp

21、ect to light versusheavy sections or handrails versus beams.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 membe

22、rs should be basedmainly on the section thickness. A minimum 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 measureme

23、nts is at the discre-tion of the inspector and may be based 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 pa

24、rts of bolt heads or nuts.5.4.1.3 Calibrate the coating thickness 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 salt

25、s.5.4.1.5 At each location, make a minimum of five measure-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 ofsuitabl

26、e locations is at the discretion of the inspector. Takemeasurements 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 a

27、nd again at the end of the survey.5.4.2.3 Clean the surface, 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

28、. By removing the basic zinc saltsfilm, corrosion can be accelerated.)5.4.2.4 Twenty-five measurements should be made at eachlocation within an area 2 by 2 in. 50 by 50 mm square, andthe mean (X) and the 90 % confidence limit on the mean (Sm90)should be determined (see Appendix X1). A different test

29、 areashould be surveyed if Sm90 is greater than 0.3 mil 6 m. Ifpossible, use a template with 25 small holes (approximately 0.2in. 4 mm diameter) ina5by5grid, with outside cornermeasurements 2 by 2 in. 50 by 50 mm. Holes should be 0.5in. 12 mm apart horizontally and vertically. The grid shouldbe cent

30、ered in a larger square measuring 3 by 3 in. 75 by 75mm with outside corners containing small holes (see Fig. 1).Put the template on the cleaned surface and mark the 29 holeswith a felt tip marker. Measurements are to be taken startingwith the top left and recorded on the report form in the sameorde

31、r as measured on the grid.5.4.2.5 To make test areas easier to locate for future surveys,center punch the outside corners of the 3 by 3 in. 75 by 75mm square so identification marks do not interfere withcoating measurements. If punching is not possible, use paint orother permanent marker (less desir

32、able). If possible, take aphotographic record to properly document the position of eachstructural member on which measurements were made inrelation to the plant layout.FIG. 1 Template (not to scale)A 896/A 896M 0925.4.2.6 Periodic surveys should be conducted. An initialtwo-year interval is recommend

33、ed for the first several years.Depending on the nature of the data 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 fo

34、r each survey.5.5 Photographs:5.5.1 Obtain an overall photographic 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

35、thatwould normally be present.5.5.3 Take close-up photographs where 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

36、, staining, etc., that is not typical of thegalvanized structure 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 X1.6.2 State the name of the company of installation and itslocation. Describe t

37、he type of structure if an industrial plant.6.3 The inspector should 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 versuso

38、ther coating systems.6.5 Visual Inspection:6.5.1 Report the general 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 sili

39、con steels within each type of environment, ifapplicable.6.5.2 Relate 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

40、. Make mention of differences in coatingthickness that may arise 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 n

41、umber of digits.6.6.3 Relate photographs to the corresponding areasmeasured.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 individ

42、ual reading,X = mean of group of 25 readings, andn = number of measurements.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

43、found intextbooks on statistics or in most engineering handbooks. 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

44、.X1.2.2 If some number other than 25 measurements is used,the value 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 the

45、re is a 90 %probability that the true value of the mean will lie 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 0.1 mil/year 2.5 m/year, it will bepossible to see a significant difference between a

46、verage coatingthicknesses resulting from surveys carried out ten years apart intime and based on 25 readings.X1.4 Example of Calculations:A 896/A 896M 093X1.4.1 Xi= 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, 6.1, 6.5, 6.7, 6.5, 5.8, 6.0, 6.4, 6.0, 6.4, 6.3 mil142, 165,

47、 170, 155, 168, 132, 163, 152, 179, 142, 157, 173,152, 135, 170, 155, 165, 170, 165, 147, 152, 163, 152, 163, 160m.X1.4.2 Mean, X = 6.2 mil 157 m.X1.4.3 Standard deviation, s = 0.5 mil 12 m.X1.4.4 90 % confidence interval, Sm90 = 0.2 mil 4 m.X2. CASE STUDY REPORT SHEETX2.1 Fig. X2.1 shows a case stu

48、dy report sheet.A 896/A 896M 094FIG. X2.1 Case Study Report SheetA 896/A 896M 095FIG. X2.1 Case Study Report Sheet (continued)A 896/A 896M 096FIG. X2.1 Case Study Report Sheet (continued)A 896/A 896M 097SUMMARY OF CHANGESCommittee A05 has identified the location of selected changes to this standard

49、since the last issue (A 896 - 89(2004) that may impact the use of this standard. (May 1, 2009)(1) Revised 1.3, 5.4, and Appendixes as well as changeddesignation to make standard applicable in both units.FIG. X2.1 Case Study Report Sheet (continued)A 896/A 896M 098ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infrin