After initial attempts with the Franco-Crosti boiler on the class 42 were unsuccessful due to corrosion damage, a new attempt was made in 1954 on a class 50 locomotive. Since this enabled a coal saving of 22 percent to be achieved, 30 other locomotives were converted in exactly the same way in 1958 and 1959. One problem was the smoke from the central chimney, which was improved with a wind deflector. As early as 1961, corrosion damage to the boiler was also found on these locomotives. Since the conversion measures now required were more expensive than the savings in coal, the locomotives were retired by 1967. 