Change in chemical ('equivalent') service of an operating system requires an MOC. This is an opportunity to assess any adverse impact of chemical residues to the downstream process including the related product purity or contamination. Such operating system should include boiler system as well especially when live steam is mixed with process stream.
Besides, it is also a good practice to include MOC for the introduction of a new chemical ('non-equivalent'), or reintroduction of a chemical after an absence of two years or more. This is because there might have other process changes over the past years that warrant a re-visit to make sure.
I hope they are helpful.
You are absolutely correct. For Case of Boiler Material Safety Data Sheet must be known, Pressure/temperature boiler and how to work safely with the chemical product. The water quality required for your specific boiler/types of boiler is essential. As inadequate water treatment can lead to the scaling, corrosion, and fouling of the boiler and downstream equipment. Quality of BFW. HAZOP study, update the all accessory if required. If above condition not fulfill then changed the MOC. But nowadays advance treatment system is available. The most appropriate boiler feed water treatment system will help the facility avoid costly plant downtime, expensive maintenance fees, and boiler failure as a result of scaling, corrosion, and fouling of the boiler and downstream equipment.
Management of change. (1) The employer shall establish and implement written procedures to manage changes (except for "replacements in kind") to process chemicals, technology, equipment, and procedures; and, changes to facilities that affect a covered process.