valve component

valve component

An autogenous CO2 laser weld joining a cap fitting to a valve body was analyzed using the ANSYS code. This stress analysis evaluated various weld penetration conditions from 0.02 to 0.04 in. The evaluation criteria included fracture, fatigue and general yielding of weld at three load conditions: maximum operating pressure (500 lb/in.2), proof pressure (750 lb/in.2) and burst pressure (1250 lb/in.2). It is concluded that, without considering welding-induced residual stresses, weld penetration of 0.02 in. is adequate for normal use of the investigated valve component. The factor of safety for 0.02 in. weld penetration is greater than 4 for the valve fitting. The residual stresses is found to affect the plastic zone size and shape. Weld shrinkage causes compressive radial stress at the weld root. The midsection of the weld penetration is in tension at radial, circumferential and longitudinal directions. The Von Mises equivalent stress in the weld is increased due to residual stresses, which reduces the safety factor by a range around 40%. However, the factors of safety for all cases are still greater than 3 at rupture pressure. The root openings of the weld fitting with penetration greater than 0.02 in. are nonpropagating and fracture stable under the proof pressure due to the compressive residual stress surrounding the root opening. For a conservative design to relax the postweld inspection requirement or to prevent failure from unexpected overloading situation, a minimum of 0.03-in. weld penetration is recommended for the cap fitting.

Introduction

The construction of the valve component includes joining the cap, the outlet and the inlet fittings to the valve body using the laser welding process. This valve component is made of 316L stainless steel and designed for 500 lb/in.2 (3.4 MPa) maximum operating pressure. Autogenous CO2 welds are made along the circumference of the fitting edges. During the proof tests, this valve component must sustain 750 lb/in.2 (5.2 MPa) proof pressure and 1250 lb/in.2 (8.6 MPa) burst pressure. Sufficient weld penetration is required to resist these pressures. The weld penetration ranging from 0.02 to 0.04 in. (0.50 to 1.0 mm) is recommended by the current design specifications. http://www.qtvalve.com/product/2/other-valve-component.html