ASME B31.3 edition introduced a new design factor ,Wled joint strength reduction factor (W)in section 302.3.5(e). Will appreciate any information on historical background for the factor. Was this based on any PVRC/WRC studies or any other published papers?

Susheer

I believe you mean "B31.3" added this factor, not B31.4.

For background on this, try Journal of Pressure Vessel Technology -- February 2006 -- Volume 128, Issue 1, pp. 46-48 . The article is New Weld Joint Strength Reduction Factors in the Creep Regime in ASME B31.3 Piping, by Charles Becht.

The 2004 edition of ASME B31.3, Process Piping Code, includes strength-reduction factors that apply to welds operating in the creep regime for the material. These factors apply to allowable stresses for sustained loads, such as weight and pressure. This paper describes the background for the rules. ©2006 American Society of Mechanical Engineers.