API Recommended Practice 551, Process Measurement, covers design and installation guidance for pressure, temperature, level, and flow measurement technologies. The 3rd edition is expected to be published toward the end of 2025. Melissa Westbrook, Senior Consultant and SIS-TECH's representative on the API 551 committee, provides an overview of the upcoming changes.
The 3rd edition includes changes to the level technology and temperature measurement sections, such as expanded technical coverage of nuclear level systems, design requirements for protection tubes, testing recommendations for thermowell, and multipoint temperature measurement system design features.
The instrument installation section has been updated to expand guidance for pressure measurement mounting practices and provides installation strategies to minimize vibration and thermal effects.
The updated document will include a new section that discusses instrument inspection before system commissioning. This new section will include general instrument infrastructure inspection - such as tubing inspection and leak testing procedures - and recommended inspection scope for the different types of level, temperature, pressure, and flow instrumentation technologies.