PURPOSE: To prevent the sticking of scale by using products made of reinforced plastics such as FRP as a storage tank, a reactor, etc. used in the manufacture of highly corrosive wet process phosphoric acid soln. or industrial chemicals from the soln. as starting material.

CONSTITUTION: Owing to its acidity and fluorine, sulfuric acid and other many impurities contained, a wet process phosphoric acid soln. is highly corrosive as compared to a pure phosphoric acid soln., and it forms scale of impurities. As a reactor, a storage tank, etc. used in the manufacture of such a wet process phosphoric acid soln. or industrial chemicals by adding alkali or the like to the soln., containers made of phenol resin, polyester resin or composite molding obtd. by adding a reinforcing material such as glass fiber to such resin, i.e. reinforced plastics are used. Containers covered with these materials may be used. No scale is stuck to the inner walls of the containers, so the number of times of cleaning work can be reduced.