FACT+FANCY   SM
engineering and rules consultants

Ammonia Refrigeration Maintenance Practices

The information in the table below is our attempt at assembling a list of ammonia-refrigeration maintenance practices based on what we have read, seen, and heard. It is probably not entirely applicable to many ammonia refrigeration systems.

This information is provided for free, as is. Use at your own risk. Absolutely no warranty. Electrical, fire-prevention, and building codes maintenance and inspections are outside the scope of this list.

To us, "maintenance" and "mechanical integrity" programs are best viewed as a combined effort, and the schedule below covers both. "Manufacturers' manuals" means all types of guidance documents provided by a manufacturer -- including installation, operation, and maintenance manuals, safety and technical bulletins, etc.

The table below is collated first by frequency (starting with yearly or more often) and then alphabetically by description.

Change Log:
2016.04.26 -- Added guards, noise, and vibration checks for rotating equipment. Added more detail for all fans. Added test of low-oil shutoff switch for pumps with mechanical seals. Added signs for refrigerating-machinery rooms. Add air-flow patterns to emergency-ventilation air-flow check. Added auto-purger maintenance. Added access-hatch bolts check and more detail on typical manufacturer recommendations for compressors. Added water leaks and ice checks for evaporative condensers. Added water-strainer cleaning to evaporative condenser water treatment. Added detail on addressing damaged insulation. Renamed and added detail to liquid-level shutoff testing (had been called high-level shutoff switches). Revised sight glasses. Clarified that internal erosion more likely from liquid and wet suction. Added seismic considerations and also adequacy and condition of pressure relief, guarding, and access to independent full inspection. Added replace if valve opens to pressure-relief valves. Terminology: changed shutoff valve to stop valve.
2017.12.29 -- added additional checks on pipe & component markers (labels) and valve tags. Clarified water-content analysis frequency.

AMMONIA REFRIGERATION MAINTENANCE PRACTICES
Description Frequency
Manufacturer Recommendations. Perform all inspections and maintenance listed in manufacturers' manuals or more recent guidance. These may be modified based on operating experience or industry guidance; in this case, consult with the manufacturer, if possible, and document the reason for the change. Per manufacturers' recommendations.
All rotating equipment. Check for excessive noise or vibrations. At least daily for compressors and pumps and at least weekly for all others, including condenser and evaporator fans.
Air-cooling Units (Evaporators). Keep coils clean. Keep free of excessive frost buildup. Monitor for shocks or excessive vibration during defrost. Inspect, lubricate, and maintain motors, any belts, tension-adjusting screws, fans, bearings and shafts (lubrication, end play, etc.), and guards. Check fan blades, fastenings, and any balancing weights for cracks, other damage, and proper attachment. See also IIAR Bulletin 110, Sections 6.4.2.2 and 6.4.3.2 (February 4, 2004 revision). Per manufacturer's recommendation, for example yearly.
Ammonia Hoses. Visually examine and check expiration date before each use. Additional inspection and replacement per manufacturer's recommendations. Before each use and per manufacturer's recommendations
Ammonia Pumps with Mechanical Seals. Monitor oil use daily and promptly replace seals as soon as oil consumption increases or any ammonia leak starts. At least yearly, test any low-oil shutoff switch and check any guards. As needed and per manufacturer's recommendations.
Ammonia Sensors, Emergency Ventilation Fans and Louvers, Emergency-Stop Buttons, Shutoffs, and Alarms -- the refrigerating-machinery room safety systems and signs: Per manufacturer's recommendations, for example:
    Perform response test of ammonia sensor, emergency ventilation operation, any valve or equipment shutoff functions, and audio/visual alarm function. (Expose sensor to higher than set-point concentration and check proper response.) Every 3 months
    Calibrate ammonia sensor with certified calibration gas. Every six months
    Response test of ventilation turn-on switches and emergency-stop switches. Every year
    Ventilation fan maintenance and, if applicable, louver maintenance. Verify adequate air flow and flow patterns. Inspect, lubricate, and maintain motors, any belts, tension-adjusting screws, fans, bearings and shafts (lubrication, end play, etc.), and guards. Check fan blades, fastenings, and any balancing weights for cracks, other damage, and proper attachment. Every year
    Check adequacy and condition of refrigerating-machinery room signs. See any state codes, IIAR 2-2014, Section 6.15 and Appendix J, and ASHRAE 15-2013, Sections 11.2 and 11.7. Every year
Auto-Purger:
- Daily Record purge counts: check for air leaks into refrigeration system if these increase, check for proper auto-purger operation if these decrease. Opening piping for maintenance can also affect purge counts.
- Confirm that each purge point is working by manually cycling through each purge point and checking for lower than condensing pressure in the auto-purger condenser.
- Clean water bubbler, inspect metering orifice on inlet pipe, and inspect air outlet orifice from water bubbler.
- Drain oil if needed (after isolating and pumping-out).
- Completely inspect auto-purger and verify proper operation.
- Clean strainers.
- Check for proper operation of all lights.
- Test or replace internal differential pressure check valves.
Per manufacturer's recommendations, typically at least yearly, or based on operating experience.
Compressors.
- Promptly replace seals if any ammonia leak starts.
- Daily monitor oil level and shaft-seal leakage. Replace seals per manufacturer recommendations.
- Monthly check tightness of oil-separator and other access-hatch bolts.
- Perform other maintenance per manufacturers' recommendations, which typically include, as applicable:
    > quarterly to yearly safety-shutoff calibration and testing, such as high discharge pressure, low suction pressure, low oil pressure, high oil-filter differential pressure, high oil temperature, etc., as applicable,
    > oil-analysis methods and frequencies and also oil-replacement, bearing service, etc. criteria for screw compressors,
    > oil-changing frequencies for reciprocating compressors,
    > vibration-analysis methods and frequencies for twin-screw compressors,
    > cleaning strainers, changing filters, and changing oil-separator coalescers,
    > operating any compressor capacity and volume ratio controls through their range,
    > corrosion checks on any water-jackets,
    > checking compressor-to-motor alignment, coupling, and bearing float or end play,
    > checking any belts or sheaves,
    > checking guards,
    > checking any oil regulators, pumps, and valves,
    > motor lubricating or maintenance as needed,
    > motor current draw, motor starter, oil heater, and controls checks, and
    > rebuild or parts-replacement schedules.
- See also recommendations in IIAR Bulletin 110, Section 6.3.
As needed and per manufacturer's recommendations.
Evaporative Condensers. Check for proper water-spray pattern, mist eliminator function, plugged nozzles, and other signs of wear or damage. Visually examine for blemishes, "white powdery cells" (white rust), or excessive scale on the accessible/viewable portions of the galvanized steel tubes. Inspect, lubricate, and maintain motors, belts, tension-adjusting screws, fans, bearings and shafts (lubrication, end play, etc.), and guards. Check fan blades, fastenings, and any balancing weights for cracks, other damage, and proper attachment. Check for water leaks and excessive ice buildup if water is run in winter. See also IIAR Bulletin 110, Section 6.4.2.3 (February 4, 2004 revision). Per manufacturer's recommendation, for example at least yearly.
Evaporative-Condenser Water Treatment. Perform and document all tests, chemical additions, water-strainer cleaning, and water sump clean-outs specified by the evaporative condenser water-treatment chemical supplier. Use water treatment methods that meet the condenser manufacturer's recommendations. Improper water treatment can damage the galvanized finish on tubes or decrease efficiency due to scaling. Per condenser manufacturer's and water-treatment chemical supplier's recommendations.
Gauges and sensors. Check that all gauges and sensors are working and accurate. Replace as needed. Use Teflon tape or a pipe-thread compound that is recommended by its manufacturer for use on ammonia-refrigeration systems when replacing items in threaded sockets. If a gauge or sensor is failing often, investigate the cause. Oil filled and spring mounted gauges are less prone to vibration damage. Per manufacturer's recommendation, for example yearly. Replace promptly after noticing failure.
Heat-Transfer Liquids (Water, Glycol Solutions, Brines, etc.) Determine appropriate testing schedules based on chemical supplier and equipment manufacturer recommendations as well as operating experience. This may include visual checks for oil or discoloration as well as or testing pH, glycol concentration, coupons kept in the heat-transfer liquid, or periodically sending samples for lab analysis of biocides and inhibitors, etc. Per manufacturers' recommendations and operating experience, typically at least yearly.
Liquid-Level Shutoffs. Test all liquid-level sensors and switches that shutoff compressors or perform other safety functions. For float switches that shutoff compressors or pumps, trip the switch with a magnet at least yearly and test the float at least every five years. For example, to test at high level, close the stop valve at the top of a level column and bleed out gas through a nipple to raise the liquid level in the level column. Or, close the stop valve at the bottom of a level column and fill the column with liquid ammonia refrigerant from a cylinder. Either way, develop a written procedure to safely and effectively complete this. Compressors may be off, if so observe the response at motor controllers. Level probes that are redundant to another method for shutting off compressors, such as a high-level float, or that shutoff pumps may be calibrated against bullseyes and then tested in simulation mode. Per manufacturer's recommendation, for example yearly.
Oil Draining and Oil Log. Drain oil as needed, for example when frost melts off an oil pot. Drain oil either via an oil pot, a spring-closing valve, or both. Common option: maintain an oil added and drained log (date and amount). As needed.
Paint and Insulation (including Markers and Tags):
     Paint. Visually examine for damage (blisters, pealing, rust stains, etc.) on all painted vessels, equipment, piping, and valves as well as on painted supports and hangers for vessels, equipment, and piping. Pay particular attention to support structures and piping exposed to condenser-water over-spray.
     Insulation. Visually examine for damage (dents, cracks, frost buildups, ammonia leaks, etc.) Thermal/infrared cameras help with insulation inspection. If the vapor retarder is visibly broken or fails (sometimes observed as frost buildup on the outside of insulation), remove insulation until dry insulation is found. Check lower or colder areas where water may have migrated along piping and around vessels. Visually examine the steel under wet or damaged insulation for corrosion. Also, when installing or replacing insulation, seal the vapor retarder to the steel periodically to create barriers to water migration away from a vapor-retarder breach. In other words, create vapor-retarder cells around vessels and within piping runs.
     Both. Complete additional testing, such as ultrasonic, if the steel protected by paint or insulation has moderately or severely corroded. Replace or repair the steel as needed. If there is only slight rusting with no significant pitting (or if testing indicates adequate steel thickness remains), properly clean and prepare the steel surface and apply a corrosion-inhibiting coating before re-painting or re-insulating any steel that has rusted.
     Both. Ensure all required or needed pipe & component markers and valve tags are present, legible, and consistent with the P&ID and other Process Safety Information.
Yearly or promptly after noticing failure.
Relief Vent (RV) Piping. Check for and drain water from any drip legs (water traps) in RV piping, which is the piping that carries the discharge from pressure-relief valves. Check for obstructions near outlets, such as insect nests, etc. If water is routinely found in a drip leg, improve the RV-piping discharge-to-atmosphere so that moisture is less likely to enter, and increase the frequency of checks until resolved.
     Precautions should be taken and proper personnel-protective equipment should be worn when checking for water in drip legs in case a pressure-relief valve opens while the RV piping is open.
     For easier water checks, often a drain valve is installed on the main drip legs below each RV-piping discharge-to-atmosphere stack.
     For backup drip legs, which are not below a discharge-to-atmosphere and which are located in warm areas, a reduction to a 5-year frequency may be acceptable. Typically these backup drip legs are located next to the pressure-relief valves. Typically, they do not have drain valves, so a threaded cap must be removed and properly reinstalled to check these, which can be done when the pressure-relief valves are being replaced.
Initially every six months. Reduce to yearly if water is not found for 24 months.
Sight glasses (bull's eyes, tubular, or flat plate). Visually examine glass, any retaining ring or other fasteners, and -- if visible -- gaskets and housing for damage, misalignment, or corrosion. On glass, look for nicks, scratches, or other imperfections using illumination to provide back or oblique lighting. Check adequacy and condition of guards, for example, complete -- full length and 360-degree -- coverage for tubular sight glasses. Per manufacturer's recommendation, for example yearly.
Strainers for Ammonia. Clean ammonia-refrigerant strainers at least once after start-up or major maintenance upstream of the strainer. Clean strainers when clogging starts to cause reduced flow (poor cooling). IIAR Bulletin 110, Appendix G, suggests yearly strainer cleaning, but this is not typical for ammonia-refrigerant strainers. As needed.
Supports for Vessels, Equipment, and Piping (Yearly). Visually examine supports and related structures, foundations, hangers, and anchors for corrosion, wear, cracking, loose fasteners (bolts, etc), or other signs of damage or excessive loads. This yearly examination is often done by the maintenance technicians that routinely maintain the refrigeration system. Yearly. See IIAR Bulletins 109 and 110.
Water-Content of Ammonia Refrigerant Analysis. This is rarely done, so our suggested frequency is optional. See IIAR 2-2008, Appendix J, IIAR 2-2014, Appendix H, and IIAR Bulletin 110, Appendix E, which suggest that ensuring a minimum water content can help prevent stress-corrosion cracking. They also indicate that if vessels operated above 23-degrees Fahrenheit are post-weld heat treated, concerns about stress-corrosion cracking are greatly reduced, reducing the need for water-content analysis. If done, perform periodic ammonia water-content analysis in the high-pressure receiver (lower water) and the lowest temperature liquid recirculator or suction trap (higher water). Ensure the water content exceeds 0.2% to prevent stress-corrosion cracking, but otherwise remains as low as possible to ensure refrigerant performance. IIAR Bulletin 108 contains a water-content test method. Optional yearly. Less often if consistent results for three years.
Valves, Control (Expansion, Regulators, Solenoid, etc.) Typically reactive maintenance is used: repair or replace after an operational failure (fail shut, fail open, or leak by). Consult manufacturers' manuals for any routine inspections and maintenance. See also paint, valve, and flange visual examinations below. As needed and per manufacturer's recommendations.
Valves, Stop (Emergency). Visually examine and exercise stop valves (also called shutoff or block valves) that may be important in emergencies, that are not redundant with other stop or solenoid valves, and that are not likely to be routinely used, for example and if applicable, the King valve, ammonia pump suction valves, level column valves, thermosiphon supply and return valves, condenser inlet and outlet valves, receiver inlet and equalization valves, transfer system inlet valves, and possibly other valves.
     Typical valve examination and exercising procedure: visually examine valve exterior -- including stem, packing nut, bonnet, any flanges, etc. -- for loose, bent or stretched bolts, misalignment, or other damage. Clean and lubricate the valve stem (use anti-seize suitable for ammonia refrigeration, for example it should not contain copper or another material that could promote corrosion or damage the refrigeration system), slightly loosen packing nut, close valve, check for leak-by/poor seat seal where possible, fully open valve, and slightly re-tighten packing nut. Check that all required or needed valve tags are present, legible, and consistent with P&ID.
Every 1 to 2 years. More frequently for older valves prone to sticking, such as valves that do not have stainless-steel stems.
Valves, Stop (Operational) and Miscellaneous Flanges. Visually examine and exercise all stop valves. Visually examine any flanges not associated with valves. Follow the typical valve examination and exercising procedure described above. Every 5 years. More frequently if packing leaks or stuck stems occur at a five-year exercising frequency.
Erosion, Internal. Either have a qualified engineer determine that the refrigeration system is safe from erosion, for example, based on velocities in liquid and wet suction piping, how this piping discharges into vessels, etc. Or, measure wall thicknesses at approximately 1% to 2% of locations with the potential for erosion, such as at liquid and wet suction elbows or where internal vessel nozzles discharge against vessel walls, if any. Every 5 years unless otherwise recommended by a qualified engineer.
Independent Full Inspection of Pressure Vessels and All: Pressure Relief, Supports, Guarding, and Access. The inspector, who should be independent from the people who routinely operate and maintain the refrigeration system, determines methods per industry standards and practices. Thorough visual examination may be adequate. Include adequacy and condition of all pressure-relief systems, including at ammonia-pump discharges. Include supports and foundations for vessels, equipment, and piping, and include any applicable seismic requirements. Include adequacy and condition of guarding from traffic and other impact hazards (forklifts, trucks, snow removal, etc.) Include adequacy and condition of access, for example, ability to view vessels for inspection, aisles, egress, ladders, catwalks and their stairs, platforms, railings, fall-protection anchor points, and access under (or over via step-over ladders) roof piping runs. Avoid damage to insulation following the February 4, 2004, revision to IIAR Bulletin 110, Section 6.4.4.3. On stress-corrosion cracking, see IIAR 2-2008, Appendix J, or IIAR 2-2014, Appendix H. Every 5 years unless otherwise recommended by the most recent inspector.
Pressure-Relief Valves. Replace. Also, maintain any three-way valves following the typical valve examination and exercising procedure described above. The May 24, 2007 revision to IIAR Bulletin 110, Section 6.6.3 and the editions of Wisconsin's mechanical refrigeration code since August 2010 (Comm 45 and now SPS 345, Wisconsin Administrative Code) except pressure-relief valves that relieve back into the refrigeration system from the 5-year replacement requirement; for these valves, consult their manufacturer to determine if periodic replacement is still needed less often than every five years. If valve opens or every 5 years. See exception under description.


We place no restriction on the use, modification, or redistribution of the information above.

Originally Posted: 2012.02.07
Last Modified: 2017.12.29
Fact Fancy, LLC