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Evaluation of crack growth during fracture and fatigue-crack-growth test using unloading compliance technique is well established for standard homogeneous fracture specimens. Three Point Bend specimens are widely used to measure fracture toughness and fatigue-crack-growth rates in metallic materials. A compliance functions is given in ASTM E1820-09 [5] to find out the in-situ crack length based on crack mouth opening displacement (CMOD). One of the inpute required in compliance function is the young's modulus of elasticity of the specimens material. To quantify the fracture toughness of weld joints, specimens are machined from weldments. Such specimens comprises of both weld and base materials. In general, base and weld materials have different young's modulus of elasticity ( E ). ASTM (E-1820) method doesn’t account for the influence of mismatch in “ E ” values of base and weld material on the compliance function. In this work, an effective modulus of elasticity is proposed for TPB specimens having weld center crack to account for the influence of mismatch in “ E ” values of base and weld material and geometry of weld on the measurement of crack length using ASTM compliance function. Numerical studies were carried out on TPB specimens. Compliances were calculated by linear elastic 3D Finite Element analysis. Wide range of relative crack length (a/w) varying from 0.3 to 0.7 and practical range of weld width were considered. Crack lengths calculated based on proposed effective modulus of elasticity were compared with the results obtained from ASTM (E-1820) technique (applicable to homogeneous specimens). Our studies revealed that, in comparison to ASTM technique, the proposed scheme for the TPB specimens having weld centre crack allows a very accurate evaluation of actual crack size.

The objective of the present study is to understand the fatigue crack growth behavior and validate analytical procedures for austenitic stainless steel and carbon steel pipes, pipe welds and elbows. The study involved fatigue tests on actual components and specimens. The Paris law has been used for the prediction of fatigue crack growth life. Paris constants have been determined for pipe (base), pipe weld and pipe elbow materials by using Compact Tension (CT)/Three Point Bend (TPB) specimens machined from the actual pipe, pipe weld and pipe elbow. Analyses have been carried out to predict the fatigue crack growth life of these piping components having part through cracks on the outer surface. In the analyses, Stress Intensity Factor ( K ) has been evaluated through two different schemes. The first scheme considers the ‘ K’ evaluations at two points of the crack front i.e. maximum crack depth and crack tip end at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (KRMS) at deepest and surface points. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipes, pipe welds with part through circumferential crack. The tests have also been conducted on the full scale carbon steel elbows having part-through circumferential notch at intrados location and axial notch at crown location on the outer surface. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (KRMS) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme.

With an objective of understanding the cyclic fracture, fatigue crack growth and ratcheting behaviour of Type 304LN stainless steel piping components used in primary heat transport system of nuclear power plants, subjected to various operational, loading and environmental conditions, experimental studies were carried out on totally 36 straight pipes and eight elbows. The pipe dimensions were in two categories: 170 mm OD and 15 mm thickness or 324 mm OD and 25 mm thickness. These studies on actual size piping components of power plants have resulted in very valuable fatigue behaviour related data, which would form important inputs in assuring safety and damage tolerant design of power plants. An overview of the studies is presented in this paper.

Almost every pipeline in power and process industries experiences vibration during its life time either during steady-state or due to dynamic transients like relief valve discharge, earthquake etc. Excessive piping vibrations are the major cause of machinery downtime, leaks, fatigue failure, high noise, fires and explosions in refineries and other process industries. It is important that piping vibration amplitudes should be quantified in order to check if the vibration levels are acceptable. If it is found beyond acceptable limit, the piping layout, piping supports or unsupported span needs to be modified. Flow-induced vibration is the most probable and widely observed mechanism of piping steady-state vibrations. Vibration in large diameter piping can produce excessive noise and can cause failures of attached small-bore piping or in severe cases pipe itself can rupture. In present paper quantification and required remedial action for mitigation of vibration from H 2 S booster discharge pipeline has been presented and also the codal qualification of piping with new support conditions have also been done as per applicable ASME B31.3 code.