Abstract: Anti-vibration spacer elements are located between adjacent elongated heat exchanger tubes for operation at temperatures above ambient in a tubular type heat exchanger. The spacer elements are formed of metal alloys having a shape-memory characteristic and are placed between adjacent rows of elongated tubes in the heat exchanger, such as a steam generator or feed water heater, and are supported from a girth ring in the casing of the heat exchanger. When the heat exchanger operating temperature is increased above a transition temperature (TT) for the spacer metal, such as a temperature between -100.degree. F. and 1000.degree. F., the spacer element increases in its overall effective thickness dimension so as to provide a lateral loading force against the adjacent tube pairs, and thereby dampen and prevent undesired vibrations of the elongated tubes. The invention also provides a method for providing vibration dampening for elongated tubes in heat exchangers operating at -100.degree. to 1000.degree. F.