Abstract: A tubular element can be expanded using an expander tool that includes a flexible sleeve having an outer diameter less than or equal to the inner diameter of the tubular element, a cone expander section on which the sleeve is mounted and an elongate mandrel. The cone expander section includes a first cone having a first narrow end that fits inside the sleeve and that increases in diameter from the first narrow end to a maximum at a base that is greater than the inner diameter of the sleeve but less than the inner diameter of the tubular element. The expander tool can be positioned at a predetermined location in the tubular element, fixed in place, and the expander section can be urged through the sleeve to expand the sleeve and thus the tubular element.