Keep heat-transfer-system repairs uneventful

A good plan is the key to avoiding risks in the maintenance of systems using high-temperature organic fluids.

By Conrad E. Gamble, Solutia Inc.

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corrosion

High moisture content

Provide better moisture removal by allowing full circulation through the expansion tank while venting to a safe location.

High acidity of fluid

Identify source of acidity and correct, then replace fluid. Consider system flush to avoid residual acidity. Fill systems with new fluid from the lowest point with the expansion tank vent open, to allow best removal of air. Then, consider a dry inert gas “blanket” in the expansion tank to protect the fluid during operation.



Develop the job plan: A job plan is formed by combining the primary repair item(s), selected items from the secondary list, and any corrective actions from root cause of failure assessments. All job plans should consider the basic facets of work place safety to protect against the hazards discussed earlier. The plans should list each task in sequence, along with materials and manpower requirements. Any unique needs for a specific site or process should be added to these basic considerations.
Prepare for work activities: Preparation involves four steps: shutdown, HTF management, lock out/tag out (LOTO) and isolation, and clean out.

Typically, it is the responsibility of operations personnel to safely shut down the process unit, including the HTF system, and properly prepare it for repair. The piping and equipment in the repair area should be emptied of process liquids and HTFs by pumping, draining, blowing with inert gas, or other means. Proper job planning can protect the fluid and even allow for its safe reuse. The two key factors that compromise fluid condition are oxidation and moisture contamination.

Hot fluid can oxidize when exposed to air. Draining the HTF when its temperature is below 250°F should adequately protect it from oxidation. Draining it into clean, dry containers for storage might allow it to be safely reused. Otherwise, the HTF should be properly disposed of. Check with your fluid supplier or site management about options.

When draining hot fluids, receiving containers must be free of moisture to prevent violent splattering and increased burn potential. Thermal burn prevention requires that fluids are cooled to at least 140°F. If the bulk of the HTF can be kept within the system and isolated from work activities, it should be suitable for reuse.

The job plan should include an approved list of those items requiring LOTO, including all rotating or energized equipment. The job coordinator should ensure the safe isolation of energy in the work area prior to initiating the process entry step and should always keep in mind that energy can be stored in various forms, including electrical, thermal, hydraulic or mechanical tension/compression.

Using the process and instrumentation diagrams (P&IDs), all valves must be identified for closure and securing with a lock/tag to prevent fluid flow into the work area. In a typical heat transfer system, this might include main pumps discharge valves, filter bypass loops, branch isolation valves, heat-tracing supply valves, fuel supply to heaters, and possibly the valves on the expansion tank piping. If vessel entry is required at the expansion tank, it might also be necessary to isolate the inert-gas supply.

All connecting branches of piping around the equipment where work is to be performed must be isolated. Electrical energy isolation requirements might include breakers for electrical heating elements or heat tracing, and starters for circulation and other pumps and motors. A good practice is to try starting equipment with start/stop switches to ensure each is de-energized, especially in older plants where power might come from more than one source.

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