ASTM_G_38_-_01_2013.pdf

Designation:G3801(Reapproved 2013)Standard Practice forMaking and Using C-Ring Stress-Corrosion Test Specimens1This standard is issued under the fixed designation G38;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This practice covers the essential features of the designand machining,and procedures for stressing,exposing,andinspecting C-ring type of stress-corrosion test specimens.Ananalysis is given of the state and distribution of stress in theC-ring.1.2 Specific considerations relating to the sampling processand to the selection of appropriate test environments areoutside the scope of this practice.1.3 The values stated in SI units are to be regarded asstandard.The values given in parentheses are for informationonly.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 to use.2.Referenced Documents2.1 NACE Document:NACE TM017796 Laboratory Testing of Metals for Resis-tance to Sulfide Stress Cracking and Stress CorrosionCracking in H2S Environments23.Summary of Practice3.1 This practice involves the preparation of and the quan-titative stressing of a C-ring stress-corrosion test specimen byapplication of a bending load.Characteristics of the stresssystem and the distribution of stresses are discussed.Guidanceis given for methods of exposure and inspection.4.Significance and Use4.1 The C-ring is a versatile,economical specimen forquantitatively determining the susceptibility to stress-corrosioncracking of all types of alloys in a wide variety of productforms.It is particularly suitable for making transverse tests oftubing and rod and for making short-transverse tests of variousproducts as illustrated for plate in Fig.1.5.Sampling5.1 Test specimens shall be taken from a location and withan orientation so that they adequately represent the material tobe tested.5.2 In testing thick sections that have a directional grainstructure,it is essential that the C-ring be oriented in thesection so that the direction of principal stress(parallel to thestressing bolt)is in the direction of minimum resistance tostress-corrosion cracking.For example,in the case of alumi-num alloys(1),3this is the short-transverse direction relative tothe grain structure.If the ring is not so oriented it will tend tocrack off-center at a location where the stress is unknown.6.Specimen Design6.1 Sizes for C-rings may be varied over a wide range,butC-rings with an outside diameter less than about 16 mm(58in.)are not recommended because of increased difficulties inmachining and decreased precision in stressing.The dimen-sions of the ring can affect the stress state,and these consid-erations are discussed in Section 7.A typical shop drawing forthe manufacture of a C-ring is shown in Fig.2.7.Stress Considerations7.1 The stress of principal interest in the C-ring specimen isthe circumferential stress.It should be recognized that thisstress is not uniform(2,3).First,there is a gradient through thethickness,varying from a maximum tension on one surface toa maximum compression on the opposite surface.Secondly,thestress varies around the circumference of the C-ring from zeroat each bolt hole to a maximum at the middle of the arcopposite the stressing bolt;the nominal stress is present onlyalong a line across the ring at the middle of the arc.Thus,whenthe specimen is stressed by measuring the strain on the tensionsurface of the C-ring,the strain gage should be positioned at1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-tally Assisted Cracking.Current edition approved May 1,2013.Published July 2013.Originally approvedin 1973.Last previous edition approved in 2007 as G38-01(2007).DOI:10.1520/G0038-01R13.2Available from NationalAssociation of Corrosion Engineers(NACE),P.O.Box218340,Houston,TX 772188340.3The boldface numbers in parentheses refer to the list of references at the end ofthis practice.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 the middle of the arc in order to indicate the maximum strain.Thirdly,the circumferential stress may vary across the width ofthe ring,the extent of the variation depending on the width-to-thickness and diameter-to-thickness ratios of the C-ring.Ingeneral,when loaded as shown in Fig.3(a,b),the tensile stresson the outer surface will be greater at the extreme edge than atthe center,while when loaded