The two major categories of chemical cleaning are pre-operational chemical cleaning—part of pre-commissioning or commissioning activities—and post-operational or maintenance chemical cleaning—part of regular shut down work.
Pre-operational chemical cleaning is performed to remove any foreign material remaining from the construction activities either on the pipe or system fabrication. Major considerations in the pre-operational phase include mill scale, corrosion products, weld scale, oil, grease, sand, dirt, temporary protective coatings, and other construction debris.
Post-operational cleaning is performed for a number of reasons, including reduced heat transfer, reduced flow, safety (e.g., H2S, pyrophoric iron, LELs, ammonia, etc.), reduced surface area (e.g., catalyst), access to full inspection, and more. The type and frequency of post-operational cleaning varies with system design, operating requirements, and history of operation and fluid/water treatment.
TO CHOOSE A PROPER CHEMICAL CLEANING METHOD, SEVERAL FACTORS SHOULD BE CONSIDERED, INCLUDING:
- System design
- Operational conditions of the fluid (flow, temperature, pressure, etc.)
- Characteristics and quantity of deposits
- Compatibility of the cleaning solvent with metallurgy of the system
- Deposit solubility in the cleaning fluid
- HSE issues