Fatigue behavior of welded stainless steel circular tubular T-joints

Stainless steel tubular joints are increasingly used in offshore and coastal engineering for structural efficiency and corrosion resistance, but remain vulnerable to fatigue failure under cyclic marine loads from waves, currents, and wind. This study investigated the fatigue behavior of typical stainless steel circular tubular T-joints by static test, fatigue test and numerical analysis, considering the effects of the brace-to-chord diameter ratio ( β ), brace-to-chord thickness ratio ( τ ), and chord diameter-to-thickness ratio (2 γ ). Static test results indicated the strain along the weld decreased from the saddle to the crown, with the highest values closer to the weld, and the most pronounced strain gradients occurring between 45° and 67.5°. The stress concentration factor (SCF) conversion coefficient ( ω ) for stainless steel tubular joints differed from that of carbon steel counterparts, with LR providing more suitable predictions than CIDECT or API guidelines. Fatigue test results exhibited crack initiated at the chord saddle near the weld toe, coinciding with the location of the maximum hot spot stress (HSS), and propagated along the weld towards the crown, with growth rate slowing as crack width increased until final fracture. Stainless steel tubular joints demonstrated inherently high fatigue resistance, with no cracking observed within two million cycles at low stress amplitudes, whereas higher amplitudes or fabrication variability led to earlier initiation, occasional asymmetry, and multiple initiation sites. CIDECT provided conservative fatigue life predictions in close agreement with the test results, whereas DNV and API (AWS) were overly conservative with marked deviation. Finite element (FE) analysis was conducted to examine the effects of parameters β , τ and 2 γ on the SCF of stainless steel tubular T-joints. Fatigue behavior was further analyzed using FE-SAFE to predict crack initiation and fatigue life, showing good agreement with experiments. The S _r,hs - N curves obtained from regression analysis exhibited higher fatigue strength than those specified in CIDECT, API/AWS, and DNV codes.