Abstract: A bent pipe to which external force, such as an internal pressure and a bending moment, is applied singly or in combination, characterized in that the relationship among the outside diameter D.sub.0 of the bent part, the radius of curvature R of the bent part, the outside diameter D.sub.0 of the straight part, the wall thickness T.sub.0 of the straight part, the central cross section angle .phi. of the bent part and the wall thickness t of the pipe, is in the range defined by the following equations (1) and (2): ##EQU1## whereby the bent pipe has a sectional form of high strength.

Abstract: A threaded joint with high gas-leak-tightness for oil and gas well pipe comprises a box having an internal female thread and a pin having an external male thread, the box and pin being screwed together in use. On a non-threaded tip portion of the pin, a front shoulder formed stepwisely and a tip shoulder are provided, and between these shoulders, a conical face tapered convergently toward the tip side of the pin is provided. On a non-threaded portion of the box corresponding to the non-threaded portion of the pin, there are provided two shoulders respectively corresponding to said front step shoulder and said tip shoulder and, between these two shoulders, there is provided a conical face corresponding to said conical face on the pin.