Water Chillers and Maintenance parti 4 Extended (long-term) maintenance checks

Water Chillers and Maintenance

 parti 4

Extended (long-term) maintenance checks

Extended (long-term) maintenance checks

Extended (long-term) maintenance checks:

1. Every 5 years (or more frequently as the chiller ages), perform eddy current

(electromagnetic) testing of heat exchanger tubes. [This testing will

typically detect tube pits, cracks, and tube wear (thinning).] If only 1–5

tubes are found defective, plug tubes. If more than 5 are found defective,

replace tubes. (Any tube that is replaced as a result of this testing should

be examined and cross-sections cut so the cause of the defects can be

evaluated.)

2. Other components must be serviced, inspected, and/or replaced at the

intervals recommended by the chiller manufacturer.

Recommended maintenance procedures for water-cooled electric-drive rotary

compressor water chillers are as follows:

Daily monitoring/visual inspection: The majority of chiller operating problems

and maintenance needs are discovered by visual inspection and

frequent monitoring of equipment operating parameters.

Monthly, quarterly, and annual preventative maintenance:

1. Clean the evaporator tubes every 2–4 years (annually for chillers serving

air washers or other “open” cooling loads).

2. Clean the condenser tubes every year.

3. Quarterly, calibrate pressure, temperature, and flow controls.

4. Annually, inspect starter wiring connections, contacts, and action. Tighten

and adjust as required. Perform thermographic survey every 5 years.

5. Annually, test the operation of safety interlocks devices, such as flow

switches, pump starter auxiliary contracts, phase-loss protection, and so

on. Repair or replace as required.

6. Annually, perform dielectric motor testing to identify failures in motor

winding insulation. For large chillers (100 tons or larger), additional

annual motor tests are required to test for the imbalance of electrical

resistance among windings, imbalance of total inductance with phase

inductances, power factor, capacitance imbalance, and running amperage

versus nameplate amperage.

7. Annually, check the tightness of the hot-gas valve (as applicable). If the

valve does not provide tight shutoff, replace it.

8. Annually, replace lubricant (oil) filter and drier.

9. Laboratory analysis of the lubricant should be performed annually during

the first 10 years of chiller life and every 6 months thereafter. Analysis

must address oil moisture content, acidity, and chiller wear as follows:

a. Maximum moisture content of 50 ppm. Higher levels may indicate

air leaks in low-pressure chillers or heat exchanger tube leaks.

b. Maximum acidity of 1 ppm is normal for a new or reclaimed refrigerant.

Higher levels may be caused by oxidation of oil during aging

and/or degradation of refrigerant. If higher levels are found, contact

the chiller manufacturer.

c.Trace amounts of metals could be metal oxides formed from moisture

in the oil or may indicate excess wear conditions. Due to variations

in metals used by different chiller manufacturers, there are no

standard limits. However, if metal content increases from year to

year, one or more of the following excess wear conditions may be

responsible:

Aluminum: impellor or bearing wear

Chromium: wear on rechromed shafts

Copper: corrosion

Iron: corrosion and/or gear wear

Tin: bearing wear

Silicon: leakage of silica gel from dehydrator cartridge or dirt

in system

Zinc: zinc left over from the manufacturing process or loss

of galvanizing from some parts

10. Valve and bearing inspection in accordance with manufacturer’s

recommendation.

11. Relief valves (both refrigerant and water) should be checked annually.

Disconnect the vent piping at the valve outlet and visually inspect the

valve body and mechanism for corrosion, dirt, or leakage. If there are

problems, replace the valve; do not attempt to clean or repair it.

12. Annually, inspect gearbox for wear and repair or replace it as needed.

13. Perform chemical testing of system water at least quarterly. Treat as

needed to ensure proper water chemistry.

Extended (long-term) maintenance checks:

1. Every 5 years (or more frequently as the chiller ages), perform eddy current

(electromagnetic) testing of heat exchanger tubes. [This testing will

typically detect tube pits, cracks, and tube wear (thinning).] If only a

limited number of tubes are found defective, plug tubes. If more than few

are found defective, replace tubes. (Any tube that is replaced as a result

of this testing should be examined and cross-sections should be cut so

that the cause of the defects can be evaluated.)

2. Every 3–5 years, perform vibration test and analysis to evaluate motor

and rotor balance, bearing and gear alignment, and bearing and gear

wear. Use accelerometer-type sensors for gears and bearings (high frequency)

and piezoelectric velocity sensors for compressor motors, rotors,

and bearings (low velocity).

3. Every 5 years, perform an acoustic emission test to identify potential

stress cracks in pressure vessels, tubes, and tube sheets.

4. Other components must be serviced, inspected, and/or replaced at the

intervals recommended by the chiller manufacturer.

 
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