The paper presents some of the most recent results obtained in the Corrosion Study Centre "A. Daccò" in studying the corrosion inhibition of engineering metal alloys in various acid environments. The subjects investigated were: -) Inhibition of low-alloyed chromium steels in HF solutions used in acid cleaning treatments of industrial apparatus; -) Inhibition of sensitized austenitic s.s. in sulphuric and sulphamic acid solutions adopted in pre-service cleaning of heat-exchangers;-) Inhibition of intergranular corrosion and stress corrosion cracking of extra-low interstitial ferritic stainless steels. The influenced exerted on the mechanical behaviour of the metallic alloys by hydrogen penetration, intergranular attack, stress-corrosion cracking were considered. Some considerations about the action mechanism of the organic inhibitors were formulated.