A Plastic Fracture Mechanics Prediction of Fracture Instability in a Circumferentially Cracked Pipe in Bending—Part II: Experimental Verification on a Type 304 Stainless Steel Pipe

Abstract

The possibility of a pipe fracture emanating from a stress corrosion crack in the heat-affected zones of girth-welds in Type 304 stainless steel pipes was investigated. The J-resistance curve—tearing modulus parameter for the prediction of crack initiation, stable growth and fracture instability—was employed. To evaluate the analysis, a pipe fracture experiment was performed using a spring-loaded four-point bending system that simulated an 8.8-m (29-ft) long section of unsupported 102-mm- (4-in-) dia pipe. An initial through-wall crack of length equal to 104 mm (4.1 in.) was used. Fracture instability was predicted to occur between 15.2 and 22.1 mm (0.60 and 0.87 in.) of stable crack growth at each tip. In the actual experiment, the onset of fracture instability occurred beyond maximum load at an average stable crack growth of 11.7 to 19 mm (0.463 to 0.750 in.) at each tip.

Investigations of fracture instability in crack growth for several metals-Part I: Experimental results

“…If the crack extension is determined, the crack-opening angle can be obtained from (12). In [21 ] the crack extension was determined by the following equation…”

“…The J-integral tearing modulus approach [1], although limited to small amounts of crack growth [7] has been shown to be successful in predicting stable crack growth and ductile fracture instability [8][9][10][11][12][13]. The engineering applications have also been developed by EPRI [14][15][16].…”

“…The engineering applications have also been developed by EPRI [14][15][16]. The experimental verification in 3PB specimen and CT specimen geometries and circumferentially cracked pipe in bending were usually made in test machines with large linear compliance of the system (spring+testing machine+uncracked specimen) [8][9][10][11][12]. The lack of experiments in test machines with small linear compliance of the system (large stiffness of test system) means the experiment verifiations lack integrity.…”

Some recent developments on integrity assessment of pipes and elbows. Part I: Theoretical investigations

“…A ÔcÕ term was proposed by Hutchinson and Paris (1979) and later generalized by Ernst et al (1979) and Ernst and Paris (1980) to correct the J-integral to account for the crack growth. The Ôg pl Õ and ÔcÕ functions are available for limited geometry under specified loading conditions Ernst et al, 1979;Ernst and Paris, 1980;Zahoor and Kanninen, 1981;Wilkowski et al, 1981;Ernst et al, 1981;Zahoor and Norris, 1984;Rajab and Zahoor, 1990;Zhou et al, 1991). These functions have been derived from dimensional analyses that are specific to the geometry and loading conditions.…”

Investigations on the effect of shape of traction separation law on the results of cohesive zone model

“…In these types of materials, the resistance to crack growth is also so large that the design of the structures becomes conservative if the crack initiation criterion is adopted as the failure condition of structures in the assessment of the structural integrity [1]. It is known, however, that even in such materials unstable fracture occurs after some amount of stable crack growth when the loading system has some amount of compliance [2,3]. In order to study such phenomenon, the analysis of stable crack growth is necessary and the finite element method is considered to be useful for this purpose.…”