| 摘要 |
<p>A tubular apparatus is assembled from inner and outer tubes or tubulars (14,12) which are connected at spaced locations (16,18) along their length. After heat treatment and other processing steps, either the inner or outer tube (14,12) is heated to reduce its yield strength and then stretched beyond its yield point but not beyond the yield point of the other tubular. The heat source is removed so that the stretched state is maintained. The tubular apparatus is thus prestressed with the inner tubular (14) under compressive prestressing when the inner tubular (14) has been heated and stretched, and the inner tubular (14) under tensile prestressing when the outer tubular (12) has been heated and stretched.</p> |
