Fatigue Testing and Life Estimates of Welded Flat Head Pressure Vessel Joints

Abstract

Experimental results for the cyclic pressure fatigue of several pressure vessels with flat heads are reported and compared against various fatigue design methods. The geometry is based on a welded joint presented in a recent paper by Kalnins, Bergsten, and Rana (2005). Weld designs between the head and shell include full penetration welds completed from a single side and both sides of the shell. Unique characteristics of this test include thin plate design, a large D/t ratio, and a low membrane-to-bending ratio. These are aspects of flat head geometries which have not been widely reported in the literature. Allowable fatigue cycles for ASME Section VIII, Division 2, IIW, PD 5500, EN 13445, API 579, and the Master S-N method (proposed for the ASME Section VIII, Division 2 rewrite project) are presented. Results show that several of these design method produce non-conservative fatigue life predictions. In addition, the fatigue results demonstrate that size effects and plate thickness effects have diminishing influence for thin plates failing at less than 100,000 cycles. Finally, the fatigue strength of stainless steel is compared to carbon steel and the lack of a unified approach to stainless steel fatigue design is discussed.

Methods for Structural Stress Determination according to EN 13445-3 Annex NA – Comparison with other Codes for Unfired Pressure Vessels

“…The calculation example 1, flat head with cylindrical shell, refers to the fatigue tests described in [11]. Figure 5 shows the essential dimensions and cyclic loads for this calculation example 1.…”