ASTM-B614:16(R2021) pdf free download – Standard Practice for Descaling and Cleaning Zirconium and Zirconium Alloy Surfaces.
5.2.5.1 For example, the use of 30 % HNO3 with HF at 100°F increases the pickle rate compared to the use of an 80% HNO1 solution with the same HF concentration. Also, an increase in temperature from 110 to 160°F more than doubles the pickle rate (5.0 to 11.0 mg/dm2 in 7 mm.).
5.3 Following mechanical abrading or chemical conditioning, the material may be further treated to clean the surface completely using the following solution:
5.3.1 Material that has been mechanically abraded in accordance with 4. I, or chemically conditioned in accordance with 5.2. 1 and 5.2.2, may he finish-cleaned by immersion in an acid solution composed of 25 to 50 volume % (350 to 700 gIL) of nitric acid (70 %) and 3 to 7 volume % (36 to 84 gIL) of hydrofluoric acid (60 %) at 120°F (50°C) maintaining a ratio of 10 parts nitric acid to I part hydrofluoric acid. Hydrofluoric acid at 48 % concentration can be used in place of the 60 % concentration. If this is done, the ratio of nitric to hydrofluoric should be 8 to 1.
NOTE 2—Most of the acid pickling following molten salt bath conditioning is accomplished in the sulfuric or nitric-hydrofluoric acid solution.
The material is cycled through the salt bath, water rinse, and acid until all of the scale has been completely removed. Final brightening is obtained by a brief cycle in the nitric-hydrolluoric solution, in accordance with 5.3.
NOTE 3—In the nitric-hydrofluoric pickling solution, the ratio of nitric acid to hydrofluoric acid is more important than the concentration of either of these two acids. When this ratio is maintained at 10 to 1. hydrogen absorption during pickling is minimized. Hydrofluoric acid at 48 % concentration can be used in place of the 60 % concentration. If this is done, the ratio of nitric to hydrofluoric should be 8 to I.
NOTE 4—The components should be rinsed immediately and thoroughly in cold tap water following pickling to avoid staining of the surfaces with residual fluorides or chlorides which niay he detrimental in some services.
NOTE 5—In the processing of zirconium mill products and fabrications. an oxygen-rich layer is unavoidable where there is a combined exposure to high temperatures and an oxidizing atmosphere. In the removal of this oxygen-rich layer by pickling in strong solutions of nitric and hydrofluoric acids, it is extremely important that all residual oxide and scale have been removed to prevent preferential etching of the linished product.
6.2 Hydrogen absorption during the cleaning process should be minimized and well within tolerable limits if the procedures outlined are followed. Periodic monitoring of the cleaning system can be accomplished by processing samples of known hydrogen content through the complete system followed by chemical analyses. A hydrogen increase greater than 2 to 5 ppm over the original product analyses may be cause for replacing the acids or adjusting the composition to reduce the extent of hydrogen pickup.
6.3 Additional evaluation of product cleanliness may be obtained by chemical milling of an expendable sample test piece. It is recommended that approximately 0.001 to 0.002 in. (0.025 to 0.05 mm) shall be removed from each surface. After chemical milling, the surface should be uniformly smooth and bright with the absence of peaks indicative of residual scale or contarni nation.
7. Hazards
7.1 Cleaning using this practice involves the use of hazardous chemicals. These chemicals are as follows: acetone, nitric acid. hydrofluoric acid, molten cleaning salts, and alkaline cleaning solutions. Before using any of these materials consult a standard reference on safe use of chemicals or the man ufacturer’s recommendations for safe handling.