Avoid Instrument Issues During Revamps

The main intent of revamp and debottlenecking projects is to safely use the existing facility, equipment and installation as much as possible -- to reduce capital expenditures on material, installation, commissioning and spares. The same objective holds for in-place control and safety valves and instruments.

So, assessing whether you can retain existing devices is a critical activity. Adequacy checks include verifying plant and component safety, e.g., via Process Hazard Analysis (PHA) and Safety Integrity Level (SIL) assessment, and confirming suitability for the new process conditions.

Decision Tree

Figure 1. Assessing the adequacy of a control valve demands a structured approach that considers numerous issues. Download a PDF of this Decision Tree.

THE STARTING POINT
Once the process diagrams and the new design conditions for the revamp are available, the immediate task is to identify the existing valves and instruments that must undergo adequacy checks. You must assess all units subject to new process conditions. These include control valves, flow instruments, safety relief valves, thermowells, pressure and temperature transmitters and gauges, analytical instruments and equipment-mounted instruments like level gauges and transmitters.

After you've pinpointed all units requiring adequacy checks, then you must gather as-built details (like datasheets, make, model, serial number, calculation sheets, catalog cut sheets, and inspection and test records) for each. The quality of documents gathered will directly bear on the quality of adequacy checks and, eventually, the success or failure of the revamp project.

Each plant handles documentation in its own way; more often than not, it's hard to get the latest information for instruments. Although use of data management packages is improving the quality of documentation and data archiving, some old plants may lack the procedures to manage the day-to-day changes and, so, documents may not be up-to-date.

Gathering details on existing instruments commonly poses a number of challenges:
• lack of instrument datasheets;
• mismatches between instrument datasheets and instruments in the field;
• missing name and tag plates (serial number information) on field devices;
• lack of instrument make or series details;
• obsolete instrument make or series;
• incomplete process data in existing datasheet or calculation sheet; and
• unavailability of functionality and operation-related issues for the existing instruments.

You thoroughly must check information gathered from the plant for correctness and update it to as-built status (if it isn't already) before using it to carry out the adequacy checks. This activity requires close interaction with plant operation and maintenance personnel so that all "known" changes are captured efficiently.

THE NEXT STEP
Once the as-built information is available, you should conduct the tough process of performing adequacy checks.

Control valves. These need the most attention and time. It's prudent to use sizing software from the manufacturer of the installed valves, to ensure the adequacy check is accurate. Figure 1 shows a decision tree for checking control valves.

Most valve manufacturers keep records of the serial number and valve details in their archives for a considerable length of time. It's important to have adequacy checks carried out or reviewed by the original manufacturer and to carefully analyze its recommendations. Adequacy check reports should record the recommendation for each valve, clearly indicating if the valve is suitable for reuse as is, requires modifications or needs replacement.

The process designer and the end user also should review the adequacy reports and confirm that the process requirements are clearly understood and the decisions made are accurate.

If you're replacing valve internals (trim), the trim material must suit the new process conditions. The method (at vendor's workshop or in-situ) and the timing of the trim replacement need careful planning with the vendor, the owner and the construction team. Inform piping and process disciplines if the new valve has a bigger or a smaller body size valve than the current one.