What’s New in ASME B31.3, 2004 Edition

Charles Becht IV, PE, PhD

Becht Engineering Co., Inc.22 Church Street, P.O. Box 300

Liberty Corner, NJ 07938Tel: 908-580-1119Fax: 908-580-9260

www.becht.com

Some Significant Changes

Weld joint strength reduction factorsf factorsAlternative flexibility analysis methodAlternative allowable for occasional loadsNew Appendix with flexibility analysis exampleExpanded use of thermoplasticsAdditional misc changes

Weld Joint Strength Reduction Factor

Applies in the creep regime, at temperatures above 950oFRecognizes that many weldments have creep strength less than the base materialFactor, W, applies in pressure design, and design for sustained stressFactor, W, does not apply for occasional loads and thermal expansion type stress

Weld Joint Factor

May be developed by creep testsIn the absence of more applicable data, the factor linearly varies from 1.0 and 950oF to 0.5 at 1500oF

f Factorsf factors greater than 1.0, as high as 1.2, now permitted.

Permits design for fewer than 7,000 cyclesRestrictions for high strength steels, material in the creep regime, and material other than steel (e.g. aluminum)

Endurance limit f factor now provided, minimum f is 0.15

Permits design for high cycle conditions such as vibration

Cycles, N- - - - - Ferrous materials, specified minimum tensile strength <=517 MPa (75 ksi), and at

design metal temperatures <=371 C (700 F)_____ All other materials

Alternative Flexibility Analysis Rules

New Appendix P provides alternative rules for flexibility analysisDesigned, considering current computer analysis capabilitiesMore comprehensiveCalculates stress range by taking differences in operation conditions, considering all loads

Alternative Flexibility Rules

Includes stress due to axial loads, and consideration of axial stress intensification factorsInherently, correctly includes the effect of nonlinear restraints

Alternative Allowable for Occasional Loads

For temperatures above 800ºF (427ºC), the sum of the longitudinal stresses due to pressure, weight, other sustained loadings, and stresses produced by occasional loads, SL, must not exceed 90% of the yield strength at temperature times a strength reduction factor.

SL ≤ 0.90 Syt X (Ec)Where the strength reduction factor X = 1.0 for austenitic

stainless steels and 0.8 for other materialsThis alternative may not be used for cast irons or other

materials with non-ductile behavior.

Flexibility Analysis Example

Appendix S addedContains one example problem in the 2004 editionMore examples to be added in the future

Expanded Use of Thermoplastics

Now permitted for above ground flammable fluid service provided

Size not to exceed DN 25 (NPS 1)Owner approvesSafeguarding providedPrecautions listed in Appendix F are considered

Additional Misc Changes

Revised examination requirements for non-metallic piping in Category M fluid serviceUT now a permitted option for alternative leak testCode wording that stated material selection was the responsibility of the designer was eliminated

Interesting Interpretations

Intent interpretation that states structural attachment welds are included in the joints that must be visually examined during leak testing of the pipingInterpretation that clearly states that the design temperature is not required to be used as the maximum metal temperature in the flexibility analysis

Upcoming Code Case

Provides an equation for calculating sustained stressIncludes sustained stress index = 0.75i, in the absence of more applicable dataIncludes stress due to axial, bending, and torsion loads