A pickling installation for applying a pickling treatment to a metal strip in continuous movement, said pickling treatment using an acid solution, said pickling installation comprising: - a plurality of cascading treatment tanks (1A, 1B, 1C, 1D, 1E, 1F, 11, 12, 13, etc.) among which at least one treatment tank (1A, 1B, 1C) comprising a spray/injection section (3, 4, 7) for spraying/injecting the acid solution on the metal strip, and - collection means (8, 9) for retrieving the sprayed acid solution after use and redirect the same to each spray/injection section (3, 4, 7); the at least one treatment tank (1A, 1B, 1C) comprising a first header in use in front of a first face of the metal strip and a second header in use in front of a second face of the metal strip, wherein - in a first treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of metal strip, and at a distance thereof, defining a first gap and a second gap respectively, said first header and said second header comprising each a plurality of holes drilled through the internal flat surface according to a defined 2D-pattern, for spraying the acid solution to the metal strip in straight jets, under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid cushion, or alternately - in a second treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of the metal strip, and at a distance thereof, defining a first gap and a second gap respectively, acid solution injection means being provided at an edge injection opening of each respective gap (5A, 5B), under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid zone occupying the whole respective gap (5A, 5B) volume, or alternately - a third treatment tank configuration combines the first treatment tank configuration and the second treatment tank configuration; and wherein, either in the first treatment tank configuration or in the second treatment tank configuration, said internal flat surface, except at the locations of the holes drilled therein in case of the first treatment tank configuration, is continuous. - a plurality of cascading treatment tanks (1A, 1B, 1C, 1D, 1E, 1F, 11, 12, 13, etc.) among which at least one treatment tank (1A, 1B, 1C) comprising a spray/injection section (3, 4, 7) for spraying/injecting the acid solution on the metal strip, and - collection means (8, 9) for retrieving the sprayed acid solution after use and redirect the same to each spray/injection section (3, 4, 7); - in a first treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of metal strip, and at a distance thereof, defining a first gap and a second gap respectively, said first header and said second header comprising each a plurality of holes drilled through the internal flat surface according to a defined 2D-pattern, for spraying the acid solution to the metal strip in straight jets, under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid cushion, or alternately - in a second treatment tank configuration, each of the first header and the second header have an internal flat surface intended to be parallel respectively to the first and second faces of the metal strip, and at a distance thereof, defining a first gap and a second gap respectively, acid solution injection means being provided at an edge injection opening of each respective gap (5A, 5B), under conditions suitable to create in use at the surface of the metal strip a highly turbulent liquid zone occupying the whole respective gap (5A, 5B) volume, or alternately - a third treatment tank configuration combines the first treatment tank configuration and the second treatment tank configuration;