A Material for Tubing and Casing Applications in Deep, Sour Gas Wells
- Richard A. Heacox (Latrobe Steel Co.) | James P. Stroup (Latrobe Steel Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1976
- Document Type
- Journal Paper
- 705 - 707
- 1976. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 4.2.3 Materials and Corrosion
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- 135 since 2007
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Multiphase MP35N is a nickel-cobalt-base alloy containing 35-percent nickel, 35-percent cobalt, 20-percent chromium, and 10-percent molybdenum that is produced by double vacuum melting. MP35N exhibits a produced by double vacuum melting. MP35N exhibits a unique combination of ultrahigh strengths, good ductility, and excellent corrosion resistance.
Multiphase MP35N develops yield strengths of 150 to 250 ksi with 10- to 25-percent elongation by cold working and aging. Mechanical property data for large bars and tubing are presented. Corrosion test results show excellent resistance to cracking in H2S environments. Testing by a number of oil companies has resulted in very high interest in this alloy for such applications as down-hole tubing and casing in deep, sour well environments and for valve cores exposed to H2S. Presently, this alloy is being used successfully for Presently, this alloy is being used successfully for cables to suspend instrument packages in sour wells.
At high temperatures MP35N has an austenitic face-centered cubic (FCC) structure. Although a hexagonal close-packed (HCP) structure is stable below about 800 deg. F, this transformation is so sluggish that the FCC structure remains after cooling to room temperature. Subsequent cold working results in the formation of thin, coherent HCP platelets in the metastable FCC matrix. The coherency of the platelets strains the lattice and results in strengthening. The amount of strengthening (transformation) depends on the amount and, to a lesser degree, the temperature of deformation. Further strengthening can be achieved by aging, which results in precipitation of a Co3Mo compound at the interfaces between the FCC matrix and the HCP platelets.
In the annealed condition (Table 1) MP35N exhibits moderate strengths and very high ductilities. The effect of cold reduction (by drawing) and aging on the room-temperature tensile properties of MP35N is shown in Fig. 1. For fastener applications (bar sizes of 0.2 to 1.3 in.), cold reduction is designed to provide an ultimate minimum tensile strength of 260 ksi, a 0.2-percent minimum yield strength of 240 ksi, and ductility minimums of 8-percent elongation and 35-percent reduction of area after aging at 1,100 deg. F. Note also that the properties of MP35N can be controlled over a wide range by adjusting the amount of cold reduction.
Properties obtained from large-diameter bars are shown in Table 2. The two larger bars were produced by cold Pilgering rather than by cold drawing. Note that, after equivalent amounts of cold work, the material reduced by drawing exhibits higher strengths than the Pilgered material.
TABLE 1 -- TYPICAL ANNEALED PROPERTIES OF MP35N
Tensile strength, ksi 135 0.2-percent yield strength, ksi 60 Elongation in four dimensions, percent 70 Reduction of area, percent 70 Hardness 90 to 100 Rb Charpy V-notch impact, ft lb 2,001
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