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The Welding Research Council's Bulletin 330, "Accuracy of Code Stress Intensification Factors for Branch Connections" documented a major attempt to re-assess the existing code requirements for the intensification of stresses at tees and other branch connections. The difficulty of this task was summed up in the bulletin by author E. C. Rodabaugh, who stated: "We would rate the relative complexity of i-factors for pipe, elbows and branch connections by the ratios 1:5:500. Thes

As noted previously, Markl's fatigue tests generated endurance curves for various fitting configurations, such as straight pipe, butt welded pipe, elbows, miters, welding tees, unreinforced and reinforced fabricated tees, mostly using 4" nominal diameter, size-on-size fittings. Markl noticed that the fatigue failures occurred not in the middle of his test spans, but primarily in the vicinity of the fittings, and in those cases, they also occurred at lower stress/cycle combina

In almost all cases the material fatigue curves are generated using a completely alternating stress; i.e., the average stress component is zero. Research has shown that the magnitude of the mean stress can have an effect on the endurance strength of a material, the trend of which is shown below: Note that as the mean stress increases the maximum permissible absolute stress (Sa + Sm) increases, while the permissible alternating stress decreases. The relationship between the al

At some point, in the vicinity of 7,000 cycles, the (Syc + Syh) limitation intersects the fatigue curve for carbon and low alloy steel. The allowable stress range must therefore be reduced to fit the fatigue curve for cyclic applications with 7,000 cycles or more: SE <= F f (SYC + Syh) Where: f = cyclic reduction factor, as shown in the accompanying table Read More: Introduction to Pipe Stress Analysis To get our piping engineering services, please contact our engineering con

A. R. C. Markl investigated the phenomenon of fatigue failure of piping during the 1940's and 1950's, and published his results in papers such as "Piping Flexibility Analysis", published in 1955. He tested a number of configurations (straight pipe, and various fittings, such as pipe elbow, miter bend, unreinforced fabricated tee, welding tee, etc.) by using cyclic displacements to apply alternating bending stresses. Plotting the cycles to failure for each applied displacement