Hollow plug for blocking a heat exchanger tube

摘要

A hollow plug for blocking a heat exchanger tube includes an expansion zone expanded into a frictional connection with the heat exchanger tube. An outer surface in the expansion zone has a first part with a relatively greater surface hardness and a second part with a relatively lesser surface hardness. The first part has a greater surface hardness than the heat exchanger tube. The second part has a lesser surface hardness than the heat exchanger tube. The first part also has a relief pattern.