1. Scope and purpose
This technical manual covers maintenance procedures for closed and open circulating cooling systems of industrial enterprises in accordance with ISO 9001, EN 13445 and DSTU B V.2.5-35:2007 standards. It is intended for reliability engineers, mechanics and water treatment operators who are responsible for preventing corrosion, scale formation and biofouling on heat exchange equipment (shell and tube heat exchangers, cooling towers, condensers).
Maintenance is performed in the case of scheduled maintenance (weekly, monthly and quarterly), as well as unscheduled when the heat transfer coefficient decreases by more than 15% or when the pressure drop on the heat exchangers increases above 0.8 bar.
2. Safety measures
DANGER WARNING! - Chemical hazard: Biocides and corrosion inhibitors are toxic and irritating substances. Be sure to use an acid-resistant rubber apron, rubber gloves (nitrile or neoprene), safety glasses and a full face shield according to EN 166.
- Lockout/Tagout (LOTO): Prior to any work on metering pumps, purge lines, or removal of corrosion coupons, turn off power to actuators, close shut-off valves, and place "DO NOT OPERATE. People at Work" signs (ISO 3864 standard).
- Pressurization: Before disassembling sampling assemblies or coupon mounting cells, depressurize the system to 0 bar and check that there is no residual pressure on the pressure gauge.
3. Necessary tools and materials
| The name of the tool / material | Technical specification | Quantity |
|---|
| Digital photocolorimeter / pH meter | pH range 0-14, accuracy ±0.01 | 1 pc. |
| Laboratory scales | Weighing accuracy up to 0.1 mg | 1 pc. |
| Torque wrench | The range is 10-50 Nm | 1 pc. |
| A set of combination keys | Sizes 10-32 mm | 1 set |
| Digital multimeter | CAT III 600V (for testing metering pumps) | 1 pc. |
| Teflon tape (FUM) | Thickness 0.1 mm, width 12 mm | 2 rolls |
| Corrosive coupons | Steel St.3 / Stainless steel 1.4404 / Brass | By the number of points |
| Personal protective equipment | GOST EN 166, DSTU EN 374 | Set |
4. Checklist before maintenance
| Check element | What to check | Acceptance / rejection criteria | Notes |
|---|
| Dosing pumps | The integrity of the membranes, the absence of leakage | No chemical leaks, pressure in the line 3.5 - 5.0 bar | Check the tightness of the joints of PVC pipes |
| pH and conductivity sensors | Calibration and cleanliness of the glass | The calibration error is less than 2%. Absence of deposits | Use buffer solutions pH 4.01, 7.01 |
| A node of corrosion coupons | The integrity of the seals, the condition of the holder | The absence of thread corrosion, the presence of fluoroplastic gaskets | The flange tightening torque is no more than 25 Nm |
| Purge valve | Serviceability of the electric drive/pneumatic drive | Opening/closing time less than 5 seconds, airtight in the closed position | Check the signal from the conductometer |
5. Step-by-step service procedure
- Preparation of the system and dosing equipment
- Put the biocide and inhibitor dosing pumps into manual mode (Manual) on the control panel (PLC).
- Purge the dispenser suction line to remove air blockages. The working pressure in the reagent supply line should be 4.0 ± 0.5 bar.
- Typical error: Starting dosing with the outlet valve closed leads to water hammer and rupture of the membrane of the dosing pump.
- Control and optimization of biocide dosing
- Take a water sample from the point after the cooler for analysis for total microbial count (TBC) and the presence of sulfate-reducing bacteria (SRB).
- According to the results of the analysis, adjust the dosage of the shock biocide. The concentration of free active chlorine or isothiazolinones in the system should be maintained at the level of 0.5 - 1.5 mg/l for 4 hours.
- Check the operation of the cyclic dosing timer (recommended frequency: 2 times a week for open systems).
- Disassembly and Analysis of Corrosion Coupons
- Close the stop valves on the bypass line of the corrosion coupon stand. Completely release the residual pressure through the drain valve.
- Remove the coupon holder using a 19 mm combination wrench. Fix the moment of unscrewing.
- Remove the coupons, rinse them with distilled water, dry them with filter paper and pack them in vacuum bags with silica gel for further weighing on a laboratory balance with an accuracy of 0.1 mg.
- Calculate the corrosion rate ($CR$) using the formula: $CR = (87.6 imes W) / (D imes A imes T)$, where $W$ is the mass loss (mg), $D$ is the metal density (g/cm³), $A$ is the surface area (cm²), $T$ is the exposure time (h). Permissible corrosion rate for carbon steel: less than 0.1 mm/year.
- Typical mistake: Touching the cleaned coupons with bare hands before weighing leaves greasy marks that distort the results of the weight loss analysis.
- Blowdown system optimization and adjustment
- Measure the electrical conductivity of circulating water using a portable conductometer. The maximum permissible value of electrical conductivity (evaporation coefficient $K = 3 - 4$) is usually 2500 - 3500 μS/cm depending on the quality of the feed water.
- Program the purge controller to maintain a given salinity threshold.
- Check the flow capacity of the purge solenoid valve. The valve opening time is regulated according to the laboratory analysis of chlorine ions ($Cl^-$).
- Tighten the bolts of the flange connections of the purge line with a torque wrench to a value of 22 Nm. Visually check for leaks at an operating pressure of 3.0 bar.
6. Checklist after completion of work
| Test / Check | Expected result | Actual result | Status (Passed / Failed) |
|---|
| Checking the tightness of mains | No leaks of water and chemicals at 5.0 bar | | |
| Dispensers work in automatic mode | A signal from the feed flow meter activates the dispensers | | |
| Stability of pH indicators | The pH value is within 7.5 - 8.5 | | |
| Purge level | Electrical conductivity below 3000 μS/cm | | |
7. Search and troubleshooting
| Symptom | Probable nature of the malfunction | Corrective action |
|---|
| High corrosion rate (> 0.12 mm/year) | Low corrosion inhibitor concentration or low pH (< 7.0) | Check the inhibitor supply, increase the dosage of caustic soda to stabilize the pH |
| Intensive biofouling (slime in the cooling tower) | Insufficient efficiency of the biocide, resistance of bacteria | Change the type of biocide (alternation of oxidizing and non-oxidizing reagents), carry out shock biocidal treatment |
| Scale formation on heat exchangers | Excessive evaporation of water, malfunction of the purge valve | Reduce the evaporation cycle, calibrate the conductivity sensor, unlock the purge valve |
| The dosing pump does not pump the reagent | Aeration of the pump head or clogging of the check valve | Open the air deaeration valve on the pump head, rinse the non-return valve in a weak solution of hydrochloric acid |
8. Recommended maintenance schedule
| Task | Frequency | Estimated duration | Qualification level |
|---|
| Measurement of pH, conductivity, residual chlorine | Every day | 15 minutes | Installation operator |
| Checking the consumption of reagents and the presence of sediment | Every week | 30 minutes | Service technician |
| Analysis of corrosion coupons and replacement of reagents | Every month | 2 hours | Mechanical engineer |
| Complete flushing of the system and disinfection with a biocide | Every 6 months | 8 hours | Maintenance team |
9. Directory of spare parts
| Description of the part | Typical specification | Category UNITEC |
|---|
| Membrane metering pump | Q = 10 l/h, P = 10 bar, PVDF/PTFE | Pumping equipment and dispensers |
| Electromagnetic solenoid valve | Du 25, PN 16, 230V AC, FKM seal | Shut-off and regulating fittings |
| Conductivity sensor (conductivity meter) | 0 - 20,000 μS/cm, output 4-20 mA | Control and measuring devices (KVP) |
| A set of corrosion coupons | Art.3 / 1.4404, size 75x12.5x1.5 mm | Consumables for laboratories |
| Dispenser check valve | PVC body, Hastelloy spring | Pipeline components |
To order the necessary spare parts and consumables for cooling systems, visit the electronic catalog UNITEC-D.
10. Links
- ISO 9001: Quality management systems. Requirements
- EN 13445: Pressure vessels are not welded.
- DSTU B V.2.5-35:2007: Water supply and sewerage. External networks and structures.
- ISO 3864: Graphic symbols. Safety colors and safety signs.
- OEM Technical Manuals for Industrial Cooling Towers and Heat Exchangers.
