Abstract: A leak detector sleeve allows performing leak detection at a flanged joint. The leak detector sleeve is made of elastomeric material that allows achieving a gas-tight seal when the leak detector sleeve encircles a flanged joint. The leak detector sleeve includes a hole that communicates with a gap in the flanged joint, thereby allowing the tip of a sniffer probe to be placed in or near the hole to detect whether the flanged joint is leaking. The leak detector sleeve is made of material that will withstand the operating temperature of the flanged joint without becoming hardened or brittle. A method for detecting a leak using the leak detector sleeve allows for efficiently and conveniently detecting leaks. In addition, the sleeve may be easily used and reused without the adverse effects or intensive manual labor required in the prior art.