The reliability of plant components made of polymers makes a significant contribution in the steel industry to the efficiency of pickling lines, as well as to occupational safety and environmental protection. Owing to their stability against the highly aggressive pickling acids, polymers have been employed successfully for decades as material for tanks, pipes, valves and acid regeneration technology. Most commonly plastics as well as composite materials are used. But, when in contact with pickling acids, even these supposedly acid-resistant materials show phenomena such as degradation, swelling, stress cracking or acid diffusion, which can be also called "Plastic corrosion". Therefore, there is a strong need in the steel industry for increased knowledge on the use of polymers in pickling plants.