Longitudinal cracks

A routine inspection of the tube bundle during a plant outage revealed fine cracks of the type shown in Fig. 9.11. Scattered longitudinal cracks were observed along the lengths of most tubes. The external surface was covered with a thin film of black copper oxide and deposits. The bundle had been exposed to ammonia levels that produced 14 ppm of ammonia in the accumulated condensate. 

Figure 9.11 A network of longitudinal cracks along the external surface. (Magnification 7.5x.)...

Longitudinal cracks of the type illustrated in Fig. 10.10 affected numerous tubes in the exchanger. Cracking ivas a recurrent problem. 

The longitudinal crack apparent in Fig. 12.21 resulted from stresses from internal pressure that exceeded the tensile strength of the metal in the greatly thinned tube wall. 

Figure 12.21 Cavitation damage on the internal surface of the condenser tube. Note longitudinal crack. The surfaces are covered with orange, air-formed iron oxides that formed subsequently to the removal of the condenser tube.

Figure 14.6 shows the straight, unbranched, longitudinal cracks typical of tubes removed from the unit. The cracked tubes had been located by eddy-current inspection. 

Figure 16. Reverse osmosis membrane exhibiting three types of macrovoids large (a), medium (b), and small (c). (A) Before testing and (B) after exposure to 13, atm hydraulic pressure. A longitudinal crack in the skin is designated by the per-...

Features Very thin bark, greyish-brown outside with corky growths (lenticels), slight longitudinal crackings, laminate, light brown internally. Fracture forms flat splinters. 

Figure 1. Longitudinal crack near the weld of an AISI 316 vessel after exercise.

Longitudinal cracks Circumferential cracks Mixed orientation... 

The postcorrosion structural responses of corroded RC beams containing ordinary concrete and HPFRCC materials have also been reported by few researchers. Maalej et al. (2003) evaluated the influence of DFRCC on the structural response of corroded FGC beams. Figure 6.27a shows the load-deflection curves of the corroded and uncorroded ordinary Portland cement (OPC) concrete beams. As the figure shows, the corroded beam (OPCC-2) lost about 13% of its ultimate loadcarrying capacity and 9% of its deflection capacity at failure in comparison with those of the uncorroded one (OPCC-1). In the corroded specimen, after reaching the yield load, a longitudinal crack. 

In the interior of a cross-ply laminate, local delaminations develop at intersections of longitudinal and transverse cracks [23], Local tensile stresses are provided by the longitudinal cracks. The tensile nature of the stress produces an out-of-plane tensile stress component at the interface. In addition, an out-of-plane tensile stress component is provided by the trans-... 

Final failure of a composite laminate is preceded by a sudden and rapid drop in stiffness. Formation of longitudinal cracks and coalescence of delaminations between adjacent longitudinal cracks leads to the isolation of strands of 0° fibres from the remaining material. This total separation occurs occasionally. The strand failure now leads to a sudden, rapid and stepwise drop in stiffness. 

During fatigue stage II, longitudinal cracks along the fill threads develop and increase both in length and density. A similar mechanism to that already described for cross-ply laminates causes this longitudinal crack... 

At the undulation of warp and fill threads, delaminations develop in the interior, being initiated at intersections of the transverse and longitudinal cracks, where local tensile stresses are provided by the transverse warp threads. As soon as delaminations occur, the stiffness of a test coupon decreases considerably and enters stage III, that is, the last 50% of fatigue life, producing final failure. 

ABSTRACT Eddy current sensors are well-established in industrial appheations, such as in hot testing of rolled rods. However, the eddy current sensors currently in use are not able to detect longitudinal cracks in hod rolled rods. This paper introduces a 3D eddy current model which allows an investigation of this particular problem. Generally, 3D eddy current Finite Element Analysis (FEA) are time consuming due to the fine mesh as a result of the small penetration depth of the currents. The introduced 3D FEA model calculates the complex coil impedance of a detection coil affected by a rod with cracks using the current sheet approximation with additional correction formulas. 

Figure 33. Bending test the longitudinal crack in the beam indicates premature failure of the adhesive layer 009-05 (left). The right picture shows the slip between top and bottom members of the bipartite beam and the adhesive layer is tom.

Figure A7-6 shows Ki for the case of a longitudinal crack of various depths in a cylinder wall (such as, for example, in a pipe or the reactor vessel).

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