WRC - BULLETIN 433
FATIGUE OF BUTT-WELDED PIPE AND EFFECT OF TESTING METHODS: FATIGUE OF BUTT-WELDED PIPE ; EFFECT OF TESTING METHODS ON STRESS INTENSIFICATION FACTORS
|Publication Date:||1 July 1998|
Report No. 1 combines the results of two bending fatigue studies on butt-welded pipe: one on 12 " schedule 80 pipe and the other on 4" schedule 40 pipe. The main objectives of these two investigations are to extend the fatigue database of butt-welded pipe from Markl's tests into the low cycle range (100 to 2,000) and to compare the measured fatigue strength with formulas developed by Markl of stress amplitude versus cycles to failure. Secondary objectives are to investigate the effects of pipe size and field welds on the fatigue strength of butt-welded pipe. Butt-welded pipe specimens were tested using two different four point bending test fixtures designed and fabricated for these test programs: fourteen 12 " schedule 80 A53 carbon steel specimens, seven 12 " schedule 80, A312, Type 304 SS specimens, fifteen 4" schedule 40 A106 carbon steel specimens, and three 4" schedule 40 Type 304 SS specimens. All testing was conducted by prescribing constant cyclic alternating displacement amplitudes about a zero mean value. Force deflection data were taken so that results could be compared with Markl's stress data. Strain amplitudes were also measured so those strain-cycle curves could be developed for butt-welded pipes. Report No. 2 investigates the "difference" between cantilever testing and 4-point testing. A simple theory for elastic-plastic bending of pipe is developed and described. This theory does no represent and local discontinuity such as a girth butt weld. Test data is described and theory is compared with the test data. The major uncertainty in these comparisons is the choice of Ep/E. Cantilever and 4-point testing theoretically give the same results in the elastic regime. However, in the plastic regime, the theory indicates that there is a "difference" in the i-factors developed by different testing methods. The appropriateness of testing methods is discussed, leading to the opinion that, for elastic analysis of piping systems, cantilever testing is preferred because this method provides the most "elastic follow-up."
Publication of this document - WRC Bulletin No. 433 was sponsored by the Pressure Vessel Research Council of the Welding Research Council.