A flexible tubular device that includes a metal wall in which are formed corrugated convolutions that define corrugated outside and inside surfaces of the device. The convolutions are perpendicular to a longitudinal axis of the device, and each convolution has oppositely-disposed rounded top and bottom portions. The outside surface of the device has first and second sections with change positions therebetween. Each first section extends from one of the change positions to another via one of the top portions. Each second section extends from one of the change positions to another via one of the bottom portions. The length of each first section is at least 10% longer than the length of each second section. The outside surface has a curvature that is numerically smaller at the top portions than at the bottom portions, and changes sign only once at each change position.
