asme sec viii d3 part kd-12.pdf

ARTICLE KD-12EXPERIMENTAL DESIGN VERIFICATION

KD-1200 GENERAL REQUIREMENTS

KD-1201 When Experimental Stress Analysis IsRequired

The critical or governing stresses in parts for whichtheoretical stress analysis is inadequate or for whichdesign values are unavailable shall be substantiated byexperimental stress analysis.

KD-1202 When Reevaluation Is Not Required

Reevaluation is not required for configurations forwhich detailed experimental results, that are consistentwith the requirements of this Article, are available.

KD-1203 Discounting of Corrosion Allowance,Etcetera

The test procedures followed and the interpretationof the results shall be such as to discount the effectsof material added to the thickness of members, suchas corrosion allowance or other material that cannotbe considered as contributing to the strength of the part.

KD-1204 Inspection and Reports

Tests conducted in accordance with this Article neednot be witnessed by the Inspector. However, a detailedreport of the test procedure and the results obtained shallbe included with the Manufacturer’s Design Report.

KD-1210 TYPES OF TESTS

Tests may be run in order to determine governingstresses, the collapse pressure, or the adequacy of apart for cyclic loading. For determining governingstresses and the collapse pressure, a single test isnormally adequate.

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KD-1211 Tests for Determination of GoverningStresses

Permissible types of tests for the determination ofgoverning stresses are strain measurement tests andphotoelastic tests. Brittle coating tests may be usedonly for the purpose described in KD-1241. Results ofdisplacement measurement tests and tests to destructionare not acceptable for governing stress determination.

KD-1212 Tests for Determination of CollapsePressure CP

Strain measurement tests may be used for the determi-nation of the collapse pressureCP. Distortion measure-ment tests may be used for the determination of theCP if it can be clearly shown that the test setup andthe instrumentation used will give valid results for theconfiguration on which the measurements are made.Brittle coating tests and tests to destruction shall notbe used to determine theCP.

KD-1213 Fatigue Tests

Fatigue tests may be used to evaluate the adequacyof a part for cyclic loading, as described in KD-1260.

KD-1220 STRAIN MEASUREMENT TESTPROCEDURE

KD-1221 Requirements for Strain Gages

Strain gages of any type capable of indicating strainsto an accuracy of 0.00005 in. /in. (0.005%) or bettermay be used. It is recommended that the gage lengthbe such that the maximum strain within the gage lengthdoes not exceed the average strain within the gagelength by more than 10%. Instrumentation shall be suchthat both surface principal stresses may be determined ateach gage location in the elastic range of materialbehavior at that gage location. A similar number andorientation of gages at each gage location are requiredto be used in tests beyond the elastic range of material

COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling ServicesCOPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services

KD-1221 PART KD — DESIGN REQUIREMENTS KD-1251

behavior. The strain gages and cements that are usedshall be shown to be reliable for use on the materialsurface finish and configuration considered to strainvalues at least 50% higher than those expected.

KD-1222 Use of Models for Strain orDistortion Measurements

Except in tests made for the measurement of theCP, strain gage data may be obtained from the actualcomponent or from a model component of any scalethat meets the gage length requirements of KD-1221.The model material need not be the same as thecomponent material, but shall have an elastic modulusthat is either known or has been measured at the testconditions. The requirements of dimensional similitudeshall be met.

In the case ofCP tests, only full-scale models,prototypical in all respects, are permitted unless thetester can clearly demonstrate the validity of the scalinglaws used. The test vessel or component used to deter-mine CP shall be made from material of the sametype, grade, and class as the production vessel.

KD-1230 PHOTOELASTIC TESTPROCEDURE

Either two-dimensional or three-dimensional tech-niques may be used as long as the model representsthe structural effects of the loading.

KD-1240 TEST PROCEDURES

KD-1241 Location of Test Gages

(a) In tests for determination of governing stresses,sufficient locations on the vessel shall be investigatedto ensure that measurements are taken at the mostcritical areas. The location of the critical areas and theoptimum orientation of test gages may be determinedby a brittle coating test.

(b) In tests made for the measurement ofCP, suffi-cient measurements shall be taken so that all areaswhich have any reasonable probability of indicating aminimum CP are adequately covered. It is noted, how-ever, that the intent of the measurements is to recordmotion in the vessel due to primary loading effects.Care shall be taken to avoid making measurements atareas of concentrated stress due to secondary or peakingeffects. If strain gages are used to determine theCP,particular care should be given to ensuring that strains(either membrane, bending, or a combination) are being

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measured which are actually indicative of the load-carrying capacity of the structure. If distortion measure-ment devices are used, care should be given to ensurethat it is the change in significant dimensions or deflec-tions that is measured, such as diameter or lengthextension, or beam or plate deflections that are indicativeof the tendency of the structure to reach theCP.

KD-1242 Requirements for Pressure Gages andTransducers

Pressure gages and transducers shall meet the require-ments of Article KT-4.

KD-1243 Application of Pressure or Load

(a) In tests for determining governing stresses, theinternal pressure or mechanical load shall be appliedin such increments that the variation of strain withload can be plotted so as to establish the ratio of stressto load in the elastic range. If the first loading resultsin strains that are not linearly proportional to the load,it is permissible to unload and reload successively untilthe linear proportionality has been established.

(b) When frozen stress photoelastic techniques areused, only one load value can be applied, in whichcase the load shall not be so high as to result indeformations that invalidate the test results.

(c) In tests made for the measurement of theCP,the proportional load shall be applied in sufficientlysmall increments so that an adequate number of datapoints for each gage are available for statistical analysisin the linear elastic range of behavior. All gages shallbe evaluated prior to increasing the load beyond thisvalue. A least square fit (regression) analysis shall beused to obtain the best-fit straight line and the confidenceinterval shall be compared to preset values for accept-ance or rejection of the strain gage or other instrumenta-tion. Unacceptable instrumentation shall be replacedand the replacement instrumentation tested in the samemanner.

(d) After all instrumentation has been deemed accept-able, the test shall be continued on a strain- or displace-ment-controlled basis, with adequate time permittedbetween load changes for all metal flow to be completed.

KD-1250 INTERPRETATION OF RESULTS

KD-1251 Interpretation to Be on Elastic Basis

The experimental results obtained shall be interpretedon an elastic basis to determine the stresses correspond-


KD-1251 2001 SECTION VIII — DIVISION 3 KD-1254

ing to the design loads; that is, in the evaluation ofstresses from strain gage data, the calculations shallbe performed under the assumption that the materialis elastic. The elastic constants used in the evaluationof experimental data shall be those applicable to thetest material at the test temperature.

KD-1252 Required Extent of Stress Analysis

The extent of experimental stress analysis performedshall be sufficient to determine the governing stressesfor which design values are unavailable, as describedin KD-1201. When possible, combined analytical andexperimental methods shall be used to distinguish be-tween primary, secondary, and local stresses so thateach combination of categories can be controlled bythe applicable stress limit.

KD-1253 Determination of Collapse PressureCP

(a) For distortion measurement tests, the loads areplotted as the ordinate and the measured deflectionsare plotted as the abscissa. For strain gage tests, theloads are plotted as the ordinate and the maximumprincipal strains on the surface as the abscissa. ThetestCP is taken as the pressure that produces a measuredstrain of no more than 2%. This strain limit shall bebased on the actual strain in the test vessel due toprimary loading effects. Therefore, strain gages ordistortion measuring devices shall be located to obtainresults due to primary loading, and to avoid resultsdue to secondary and peak effects (see KD-1241).

(b) If the vessel is destroyed or fails to maintain itspressure boundary before theCP can be determined,the vessel shall be redesigned and retested. The processis repeated until the vessel can sustain pressures thatare large enough to obtain theCP in the prescribedmanner.

(c) The CP used for design purposes shall be thetestCP multiplied by the ratio of the specified materialyield strength at design temperature to the actual mea-sured test material yield strength at the test temperature.When the design pressure is based on theCP test,the maximum design pressure shall be determined inaccordance with KD-1254. Careful attention shall begiven to assuring that proper consideration is given tothe actual as-built dimensions of the test model whencorrelating theCP of the test model to that expectedfor the actual structure being designed.

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KD-1254 Determination of Maximum DesignPressure at Room Temperature

The maximum design pressureP when based on theCP testing as described in this paragraph shall becomputed by one of the following equations using theactual material yield strength.

(a) If the actual measured yield strength is determinedonly by the testing required by the material specification,

P p 0.4CP 1 Sy

Syms2

whereSyp specified minimum yield strength at room tem-

perature, psiSymsp actual yield strength based on the testing re-

quired by the material specification, psi, but notless thanSy

(b) If the actual yield strength is determined inaccordance with the additional testing prescribed below,

P p 0.5CP 1 Sy

Syact2

whereSyactp actual average yield strength from test speci-

mens at room temperature, psi, but not lessthanSy

(c) The yield strength of the material in the parttested shall be determined in accordance with ASMESA-370 with the following additional requirements.

(1) Yield strength so determined (Syact) shall bethe average of at least three specimens cut from thepart tested after the test is completed. The specimensshall be cut from a location where the stress duringthe test has not exceeded the yield strength. The speci-mens shall not be flame cut because this might affectthe strength of the material.

(2) When excess stock from the same piece ofwrought material is available and has been given thesame heat treatment as the pressure part, the testspecimens may be cut from this excess stock. Thespecimen shall not be removed by flame cutting orany other method involving sufficient heat to affectthe properties of the specimen.



KD-1260 EXPERIMENTALDETERMINATION OFALLOWABLE NUMBER OFOPERATING CYCLES

Experimental methods may be used to determine theallowable number of operating cycles of componentsand vessels as an alternative to the requirements ofArticle KD-3. This approach shall only be used forvessels or components that have been shown to demon-strate a leak-before-burst mode of failure.

KD-1261 Test Description

When a fatigue test is used to demonstrate theadequacy of a component or a portion thereof towithstand cyclic loading, a description of the test shallbe included in the Design Report. This description shallcontain sufficient detail to show compliance with therequirements stated herein.

KD-1262 Test Procedure

(a) The test component or portion thereof shall beconstructed of material having the same compositionand subjected to the same mechanical working andheat treating so as to produce mechanical propertiesequivalent to those of the material in the prototypecomponent. Structural similitude shall be maintained,at least in those portions whose ability to withstandcyclic loading is being investigated and in those adjacentareas that affect the stresses in the portion under test.

(b) The test component or portion thereof shall with-stand the number of cycles as set forth in KD-1262(c)before failure occurs.Failure is herein defined as apropagation of a crack through the entire thicknesssuch as would produce a measurable leak in a pressureretaining member.

(c) The minimum number of test cyclesNT that thecomponent shall withstand, and the magnitude of theloading PT [see Eqs. (1), (2), and (3)] to be appliedto the component during test, shall be determined bymultiplying the design service cyclesND by a specifiedfactor KTN, and the design service loadsPD by KTS.Values of these factors shall be determined by meansof the test parameter ratio diagram, the constructionof which is as follows and is illustrated in Fig. KD-1260.1.

(1) Project a vertical line from the design servicecyclesND on the abscissa of theSa versusN diagram,to intersect the fatigue design curveSa of the appropriatefigure in Article KD-3, to an ordinate value ofKs

times SaD. Label this point A. Ks is a factor that

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accounts for the effect of several test parameters [seeKD-1262(g)].

(2) Extend a horizontal line through the pointDuntil its length corresponds to an abscissa value ofKn

times ND. Label this pointB. Note thatKn is a factorthat accounts for the effect of several test parameters[see KD-1262(g)].

(3) Connect pointsA and B. The segmentsABembrace all the allowable combinations ofKTS andKTN

[see KD-1262(e) for accelerated testing]. Any pointCon this segment may be chosen at the convenience ofthe tester. Referring to Fig. KD-1260.1, the factorsKTS

and KTN are defined by:

KTS pvalue of ordinate at pointCvalue of ordinate at pointD

KTN pvalue of abscissa at pointCvalue of abscissa at pointD

Thus

PT (test loading)p KTSPD (1)

NT (test cycles)p KTNND (2)

(d) It should be noted that if the test component isnot full size but a geometrically similar model, thevalue PT would have to be adjusted by the appropriatescale factor, to be determined from structural similitudeprinciples, if the loading is other than pressure. Thenumber of cycles that the component shall withstandduring this test without failure must not be less thanNT, while subjected to a cyclic test loadingPT whichshall be adjusted, if required, using model similitudeprinciples if the component is not full size.

(e) Accelerated fatigue testing (test cyclesND) maybe conducted if the design cyclesND are greater than104 and the testing conditions are determined by thefollowing procedures, which are illustrated in Fig. KD-1260.2. In this Figure, the pointsA, B,andD correspondto similar labeled points in Fig. KD-1260.1.

(1) The minimum number of test cyclesNT min

shall be:

NT min p 102!ND

Project a vertical line throughNT min on the abscissaof the Sa versusN diagram such that it intersects andextends beyond the fatigue design curve.

(2) Construct a curve through the pointA andintersect the vertical projection ofNT min [see KD-


Fig. KD-1260.1 2001 SECTION VIII — DIVISION 3

FIG. KD-1260.1 CONSTRUCTION OF TESTING PARAMETER RATIO DIAGRAM

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PART KD — DESIGN REQUIREMENTS Fig. KD-1260.2

FIG. KD-1260.2 CONSTRUCTION OF TESTING PARAMETER RATIO DIAGRAM FOR ACCELERATED TESTS

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KD-1262 2001 SECTION VIII — DIVISION 3 KD-1270

1262(e)(1)] by multiplying every point on the fatiguedesign curve by the factorKs [see KD-1262(c)(1)].Label the intersection of this curve and the verticalprojection of NTmin as A′.

(3) Any pointC on the segmentA, A′, B determinesthe allowable combinations ofKTS andKTN. The factorsKTS and KTN are obtained in the same manner as inKD-1262(c).

(f) In certain instances, it may be desirable (orpossible) in performing the test to increase only theloading or number of cycles, but not both, in whichevent two special cases of interest result from the abovegeneral case.

(1) Case 1(factor applied to cycles only). In thiscase,KTS p 1 and

KTN pvalue of abscissa at pointBvalue of abscissa at pointD

The number of test cycles that the component shallwithstand during this test must, therefore, not beless than

NT p KTNND

while subjected to the cyclic design service loading,adjusted as required, if a model is used.

(2) Case 2 (factor applied to loading only). Inthis case,KTN p 1 and

KTS pvalue of ordinate at pointAvalue of ordinate at pointD

The component must, therefore, withstand a numberof cycles at least equal to the number of design servicecycles, while subjected to a cyclic test loading

PT p KTSPD (3)

again adjusted as required, if a model is used.(g) The values ofKs and Kn are the multiples of

factors that account for the effects of size, surfacefinish, cyclic rate, temperature, and the number ofreplicate tests performed. They shall be determined asfollows:

Knp greater of (Ks)4.3 or 2.6

Ksp greater ofKsaKsfKscKstKss or 1.25Ksap factor for the effect of size of the highly stressed

surface area on fatigue lifep greater of (Ap/AT)

1/30 or 1.0, whereAp is thesize of the highly stressed surface area of theprototype component andAT is the size of the

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highly stressed surface area of the test com-ponent

Kscp factor for differences in design fatigue curvesat various temperatures

p greater of(SaN at Tc) (Sa10n at Tt)(SaN at TD) (Sa10n at Tc)

or 1.0

Ksfp factor for the effect of surface finishp greater ofKr(P) /Kr(T) or 1.0, whereKr(P) is

the surface roughness factor of the prototypeandKr(T) is the surface roughness factor of thetest component. TheKr(P) andKr(T) factors arebased on the surface finish and shall be takenfrom Fig. KD-320.3.

Kssp factor for the statistical variation in test resultsp greater of 1.470 − (0.044 × number of replicate

tests) or 1.0Kstp factor for the effect of test temperature

p greater of (E at Tt) /(E at TD) or 1.0, whereE isthe elastic modulus of the component material

Sa10np Sa from the applicable fatigue design curve atthe maximum number of cycles defined onthe curve

Tcp 700°F for carbon and low alloy steels, and800°F for austenitic stainless steels and nickel–chromium–iron alloys

TDp design temperatureTtp test temperature

KD-1270 DETERMINATION OF FATIGUESTRENGTH REDUCTION FACTORS

(a) Experimental determination of fatigue strengthreduction factors shall be in accordance with the follow-ing procedures.

(1) The test part shall be fabricated from a materialwith the same nominal chemistry, mechanical properties,and heat treatment as the component.

(2) The stress level in the specimen shall besuch that the linearized primary-plus-secondary stressintensity (PL + Pb + Q) does not exceed the limitprescribed in Fig. KD-230 so that failure does notoccur in less than 1,000 cycles.

(3) The configuration, surface finish, and stressstate of the specimen shall closely simulate those ex-pected in the components. In particular, the stressgradient shall not be more abrupt than that expectedin the component.



(4) The cyclic rate shall be such that appreciableheating of the specimen does not occur.

(b) It is recommended that the fatigue strength reduc-tion factor be determined by performing tests on notchedand unnotched specimens and calculated as the ratioof the unnotched stress to the notched stress for failure.

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asme sec viii d3 part kd-12.pdf

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