Casing collapse load

Collapse load originates from the hydrostatic pressure of drilling fluid, cement slurry outside the casing and later on by moving formations e.g. salt... 

In establishing the model used to represent a structure, the usual approach is to first assume the locations of piastic hinges and then carry out the analysis. This approach is essentially an upper bound analysis which by definition provides a predicted collapse load that is either correct or too high. In most cases, fairly simple structural models are developed and it is obvious that the assumed mechanism is correct. For those cases involving irregular structural configurations and loading, a separate check should be made to confirm that no other possible failure mechanisms exist which may result in lower predicted collapse loads. 

A simple case where this can be done is that of three-point bending, shown in Figure 18. If the ligament is fully plastic with a stress distribution as shown, the collapse load is given by... 

During DST operations, the drill pipe may be affected by a combined effect of collapse pressure and tensile load. For such a case,... 

Collapse Assumed external fluid pressure gradient of 0.52 psi/ft and casing empty inside. Safety factor for collapse = 1.0. Reduction of collapse pressure resistance due to the axial load is considered. 

Shaped charge for perforating oil well casing) 55) Cook (1958), Chapter 10, "Principles of Shaped Charges , which includes History (pp 226-28) Explosive factors in cavity effect (228-29) Application to mass loading in different geometries (229-35) Detonation pressure in nonideal explosives (235-44) Mechanism of linear collapse and jet formation (244-47) Metal-... 

Fig. 5 Synaptic vesicle recycling in the synapse. For synaptic vesicle recycling, several endocytic mechanisms appear to co-exist in synaptic nerve terminals. In the case of fast kiss-and-ran exo-cytosis/endocytosis, the fused vesicle does not collapse into the membrane but is retrieved directly by a fast process. The molecular machinery underlying this pathway is unknown. Vesicles that have fully collapsed into the membrane are recycled by clathrin-mediated endocytosis. Clathrin, along with other proteins, is involved in membrane invagination (see figure and text) and leads finally to the formation of a constricted pit. The GTPase dynamin (black ring) mediates membrane scission of the constricted pit. After removal of the clathrin coat, two pathways are possible (direct recycling and recycling via the early endosome). In all cases, before fusion the recycled vesicles have to be loaded with neurotransmitters (NT).

For isotropic or one-dimensional conditions. Figure 4 shows the two stress spaces mentioned before. Also indicated are the assumed positions of the yield locus which mark the initiation of irreversible strains The Loading -Collapse (LC) curve in the case of the macrostructure and the Suction-Decrease (SD) curve in the case of microstructural changes. More details of the model may be found in Alonso (1998) and Alonso et al (1999)... 

It is useful to observe that, although the causes of corrosion can be trivial, the consequences may be catastrophic. For instance, cases are reported where collapses of structures were caused by changes in the cross section of load-bearing elements, introduced for aesthetic reasons (analogous to that shown... 

Code Case 2286 assumes that shells are axisym-metric, that for unstiffened vessels the shells are the same thickness, and that for stiffened cylinders and cones the thickness between stiffeners is uniform. Additionally, capacity reduction factors (or knockdown factors) are provided for general use, but are incorporated in the allowable stress equations. Stress reduction factors (FS) must be found for each direction of loading so that the values of FS are determined independently for both the longitudinal and circumferential directions. The stress reduction factors cover elastic and inelastic buckling, and plastic collapse behavior for elements in compression. 

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