METHOD OF FORMING PROTECTIVE DIFFUSION COAT ON EXTERNAL AND INTERNAL SURFACES OF TUBE AND ITS THREADED PARTS AND OIL WELL TUBING Russian patent published in 2006 - IPC C23C10/52 F16L58/08 

FIELD: manufacture and construction of oil tubes used in construction of oil and gas wells, namely oil well tubing, 64-114 mm in diameter, casing pipes, 114-508 mm in diameter and other pipes.

SUBSTANCE: proposed method includes treatment of threaded parts and adjoining area by isothermal holding in diffusion mixture followed by cooling in air. Diffusion mixture contains metal powder consisting of mixture of zinc, copper and aluminum powders at graininess of 0.1-0.5 mm at the following ratio of components, mass-%: zinc, 25-40; copper, 0.045-0.075; aluminum, 0.175-0.225; the remainder being inert filler. Isothermal holding continues for 1.0-3.0 h at temperature of 440±10°C, thus obtaining protective coat, 30-80 mcm thick. Protective coat includes the following components, mass-%: iron, 6-15; zinc, 84.1-93.4; copper, 0.4-0.6; aluminum, 0.2-0.3. Micro-hardness of protective coat ranges from 4500 to 5250 Mpa determined by method of reduced print of tetrahedral pyramid. Proposed oil well tubing has body with at least one section of thread provided with protective coat made by said method.

EFFECT: enhanced corrosion resistance and tightness of threaded sections of tubes.

3 cl, 2 tbl