Thin wall permeator tubes have been produced by diffusion welding of Pd-Ag foils. These dense metal membranes are proposed for separating and producing ultra-pure hydrogen as a result of their complete hydrogen selectivity. Furthermore, they present high hydrogen permeation fluxes as well as reduced costs on account of their reduced metal thickness. The reliability of these membrane tubes has been continuously tested during over 12 months of experimental campaign in presence of thermal and hydrogenation cycles. The permeability tests have been carried out measuring the hydrogen fluxes under controlled conditions of temperature and trans-membrane differential pressure. In particular, the behaviour of the membrane tube has been investigated in a wide range of temperatures (150-400 degrees C) and pressures (100-200 kPa) in order to simulate the use within permeators and membrane reactors where processes for producing hydrogen from hydrocarbons takes place. At temperature of 350-400 degrees C hydrogen permeability values around 1.0 x 10(-8) mol m(-1) s(-1) Pa-0.5 have been measured and they are comparable with the literature data. A new mechanical design (finger-like configuration) of the membrane module has ensured the long life of the Pd-Ag permeator. The complete hydrogen selectivity of the membrane has been demonstrated by the tests. (c) 2006 Elsevier B.V. All rights reserved.