Abstract: The process is suitable for detecting leaks in a heat exchanger for heat exchange between two gaseous fluids, for instance for super heating steam. The heat exchanger has a lower pressure fluid circuit and a higher pressure fluid circuit. A predetermined amount of a tracer gas, typically helium, is injected into the higher pressure fluid at the inlet of the heat exchanger and the presence of tracer gas within the lower pressure fluid is determined at the outlet of the heat exchanger. If the lower pressure gas is steam to be super heated, a minor amount of super heated steam is sampled at the outlet of the exchanger and is condensed. Then the uncondensable products are examined for presence of tracer gas.