Use of a heat transfer tube in a damp environment in air-conditioning equipment and exposed to corrosive action caused by a corrosive medium comprising at least one lower carboxylic acid, the heat transfer tube a copper tube comprising 0.10-1.0% by weight of P and the balance consisting of Cu and inevitable impurities. The corrosive action progresses in the form of an ants' nest from an outer surface of the heat transfer tube in a direction of its wall thickness, wherein. Also, use of a copper tube comprising 0.10-1.0% by weight of P and the balance consisting of Cu and inevitable impurities for improving corrosion-resistance against ant nest corrosion caused by a corrosive medium consisting of a lower carboxylic acid in a damp environment, method of inhibiting ants' nest corrosion in a heat transfer tube, and a method of positioning a tube in an air conditioning apparatus or a refrigeration apparatus.