1.1 This standard practice establishes guidelines to avoid caustic SCC of CS refinery equipment and piping. It addresses applications that use “fresh” caustic. Caustic SCC has been observed in the presence of contaminated caustic (especially contaminated with sulfide) in services that otherwise fall within area “A”of the Caustic Soda Service Chart shown in Figure 1.
1.2 The practices detailed below are specifically intended for handling aqueous solutions containing sodium hydroxide (NaOH). However, several companies extend these practices to include aqueous solutions of other strong alkali compounds such as potassium hydroxide (KOH) and lithium hydroxide (LiOH).
1.3 Some proprietary caustic solutions used in the industry (e.g., for carbon dioxide removal in hydrogen manufacturing units) contain inhibitors that may mitigate caustic SCC. In these cases, the practices included herein may be conservative. The effectiveness of any inhibitors added to industrial caustic solutions should be evaluated before the guidelines set forth in this standard practice are implemented.
