Thermowells. Usually existing thermowells are replaced. However, if it's decided to carry out an adequacy check on them, then you usually must assess their wake frequency as well as pressure and temperature data for the new process conditions. All reused thermowells should have calculations done per ASME PTC 19.3 for both process and personnel safety reasons.
Transmitters. Pressure transmitters must undergo adequacy checks to verify that pressure and temperature limits are suitable for the new condition. Diaphragm and capillary material, where applicable, must be compatible with the new process conditions and service.
Gauges. Usually the existing temperature and pressure gauges are replaced, as they aren't expensive. However if you must perform adequacy checks, assess instrument range, pressure and temperature. It's important to determine the suitability of the existing instrument's diaphragm material for the revamp conditions and service.
Instruments on equipment. Temperature, pressure and level instruments on vessels and equipment also must undergo adequacy checks. If the vessel or equipment is reused without much modification or many process changes, existing instruments likely will suffice. However, it's absolutely necessary to carry out a thorough adequacy check to ensure the existing instruments are good enough to meet the new process conditions.
Analytical instruments. Carefully review existing devices against the new process stream contents and check whether or not the existing sample gathering and conditioning units can handle them. Reverify transport time and fast loop components for adequacy.
Installation. Assess existing instruments' installations (above tap point, below tap point, etc.) for new process conditions and fluid states. Transmitters may be good for re-use but you may need to modify their installation to suit the revamp conditions.
Standards. One critical decision that you must make when reusing existing instruments is the extent to which you'll apply international standards for the revamp project -- because in-place instruments may not comply with the latest rules. Also, in some instances, the existing instruments may not even meet client or project standards. For instance, some materials that were okay in the past for sour service no longer are acceptable.
Project management must consciously decide how far to apply the latest standards. You must notify the owner of instances where existing instruments violate safety requirements of the latest standards.
AN ESSENTIAL ELEMENT
By reusing existing instruments, stakeholders can control project cost. However, reusing them for the revamp conditions can pose risks and requires careful review to mitigate potential safety or operability problems. So, adequacy checks, while time consuming, are crucial. You must allow sufficient time in the project schedule to carry out reasonable checks to ensure safe and reliable service from the existing devices under the new process conditions.
GIRISH SATHYANARAYANA is technical professional leader, instrumentation, for KBR Hydrocarbons, Singapore. Email him at email@example.com.