#### DMCA

## W. B. Bradley The Effect of Casing Wear on the Burst Strength of Casing Part 1 Joint Leakage

### BibTeX

@MISC{Asme_w.b.,

author = {Mem Asme},

title = {W. B. Bradley The Effect of Casing Wear on the Burst Strength of Casing Part 1 Joint Leakage},

year = {}

}

### OpenURL

### Abstract

A theoretical analysis has been performed to determine the effects of wear on the burst strength of casing. Burst failure occurs either by a leakage at the casing joint or by rupturing of the casing wall. Joint leakage and the effect of casing wear on joint leakage are discussed in this paper. Rupturing of the casing wall is treated in a companion paper [1J. 1 The results of the analysis presented in this paper show that, for practical purposes, joint leakage under internal pressure is unaffected by casing wear. Introduction Failure of casing under internal pressure, "burst," will occur either by rupturing of the casing wall or by leakage at the casing joints. The occurrence of either of these failures can cause serious problems during drilling and during subsequent completion and production operations. If the casing has become worn during the drilling operation, these problems can be further aggravated. For serious wear, loss of the well may result. This paper describes the effects of casing wear on leakage of casing joints under internal and external pressure and casing failure by thread jumpout. The statistical nature of burst failure of worn and unworn casing strings is treated in a companion paper Leakage of Casing Joints The equations for joint leakage under a combination of internal and external pressure are as follows (see Appendix A for derivation). For the conditions that the internal pressure is greater than the external pressure (i.e., P; > Po): 1 Numbers in brackets designate References at end of paper. Contributed by the Petroleum Division and presented at the Thirtieth Annual Petroleum Mechanical Engineering Conference, Tulsa, Okla., September 21-25, 1975, of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. Manuscript received at ASME Headquarters June 13, 1975. Paper No. 75-Pet-ll. For the external pressure greater than the internal pressure, Po > Pi: where Pi = internal casing pressure Po = external casing pressure Pieak internal = internal pressure at which joint leakage first occurs Pleak external = external pressure at which joint leakage first occurs UD = diametral interference (from the point of hand-tight makeup) E = elastic modulus W = outside diameter of the coupling di = the first sealing point when P; > Po, diameter at the root of the coupling thread at the end of the pipe (tip of pin) in the powertight position di = the first sealing point when Po > Pi, diameter at the root of the pipe thread at the end of the coupling in the power-tight position Di = internal diameter of the pin. The given equations apply to any made-up casing joint which can be approximated by the interference fit of two concentric cylinders or cones. As a result, the given equations apply to the tapered API joint. The equations describe the elastic response to internal and external pressure loadings and do not include the effects of axial and bending loads. Specific results presented are for API eight-round joints as follows from their particular dimensions and specifications for makeup. These equations predict the point at which the combined contact stress across the joint interface due Journal of Engineering for Industry MAY 1976 / 681 Copyright © 1976 by ASME to the initial interference makeup stress and the radial internal and external pressure stress at the interface equals the internal pressure or the external pressure; i.e., where (TINT = normal stress across the joint interface due to the interference at makeup in the power-tight position o> = radial stress at the joint interface at the first sealing point in the made-up joint due to the internal and external pressures. At pressures equal to or exceeding Pi ea k, the internal pressure (or external pressure) is of sufficient magnitude to carry the contact load between the pin and the coupling so that physical contact between them is not required and the joint will separate. Examination of equations Current internal pressure design calculations [7] are based on thin-wall cylinder analysis for both the casing and the coupling. The minimum value of internal pressure to produce yielding in the casing or in the coupling is used as the burst pressure rating. -Nomenclature,* A = hand-tight standoff a = internal radius b = outside radius D = nominal outside casing diameter D; = inside diameter of the pin di = diameter at the root of the coupling thread at the end of the pipe (tip of pin) in the power-tight position dz = diameter at the root of the pipe thread at the end of the coupling in the power-tight position E = elastic modulus E\ = pitch diameter at the hand-tight plane H = thread height Li = length, from end of pipe to hand-tight plane Pi = internal casing pressure Po = external casing pressure Pburst = internal pressure at failure -Pieak internal = internal pressure at which joint leakage first occurs r = radial coordinate S rn -thread root radius reduction in thread height T = thread taper t = casing wall thickness UD = diametral interference Uhon -total radial deformation of the box t/int = total radial interference at makeup f/pin = total radial deformation of the pin W = outside diameter of the coupling W = reduced outside diameter of the coupling w = remaining casing wall thickness Y p = yield strength Y c = minimum yield strength of coupling M = Poisson's ratio aINT = normal stress across the joint interface due to the interference at makeup o> = radial stress at the joint interface in the made-up joint due to the internal and external pressure / MAY 1976 Transactions of the ASME 5.18 makeup turns, the joint begins to leak at the pressure at which the coupling just begins to yield. The leakage pressure for 7-in.-dia S-95 casing is shown in As casing diameters become larger, the theoretical internal pressure at which a joint leaks becomes less and less. As a result, this pressure becomes the controlling factor in casing burst for more and more casing weights. External joint leakage pressures calculated from this analysis are above the collapse pressure ratings for API casing. Nonstandard joint connections should be checked to make sure that the external leakage pressure does not fall below the collapse rating of the casing. Effects of machining tolerances on leak pressure can be calculated using equation Calculations of leak pressure on two-inch tubing were made to compare with experimental results of Mayberry In equation Leakage of Worn Joints In equation In addition,