Early investigations in the current NG-18 program (1) identified potassium chromate, sodium chromate, and sodium dichromate as strong inhibitors of stress-corrosion cracking (SCC) of pipe steel in 4.8 percent sodium carbonate-7.6 sodium bicarbonate, 31 percent sodium hydroxide, and 20 percent ammonium nitrate solutions, but further investigation of chromates was not pursued at that time because of the known toxicity of these compounds. In particular, large quantities of chromates could not be used to treat a right-of-way because of environmental considerations. Subsequently, the evaluation was...
Early investigations in the current NG-18 program (1) identified potassium chromate, sodium chromate, and sodium dichromate as strong inhibitors of stress-corrosion cracking (SCC) of pipe steel in 4.8 percent sodium carbonate-7.6 sodium bicarbonate, 31 percent sodium hydroxide, and 20 percent ammonium nitrate solutions, but further investigation of chromates was not pursued at that time because of the known toxicity of these compounds. In particular, large quantities of chromates could not be used to treat a right-of-way because of environmental considerations. Subsequently, the evaluation was continued, however, because chromates offered a high degree of inhibition, and they were being broadly applied for protection against general corrosion and pitting in coating systems in several industries. Similarly, chromates could be incorporated in primers or other line-pipe coatings to minimize SCC without undue pollution of the environment. This technical memorandum presents the results and conclusions of the further study on the effectiveness of chromate inhibitors.