Poor Performance of LT Cooler in a Centralized Cooling Water System – Rectification and Improvement Measures

If the Low Temperature (LT) cooler of the centralized cooling water system shows poor performance, a systematic and methodical approach should be followed to identify the cause and restore efficiency. The problem may be due to fouling, air binding, low flow, bypassing, or mechanical defects. The following measures should be initiated:

1. Immediate Operational Checks

Before opening the cooler, first determine whether the problem is due to a temporary operating condition or an actual defect.

• Compare the seawater inlet and outlet temperatures and the freshwater inlet and outlet temperatures with the design values given in the ship’s manual.
• A low temperature drop on the freshwater side indicates either:
  • poor heat transfer, or
  • insufficient water flow through the cooler.
  Part (b)

  Check for Air Venting

  • Inspect and vent the high-point air vents on the LT cooler freshwater side.
  • Air pockets trapped inside the cooler reduce the effective heat transfer area and lower cooling efficiency.
  Part (c)

  Check Pressures

  • Observe the pressure gauges on both the seawater side and freshwater side.
  • Low differential pressure may indicate:
    • pump malfunction, or
    • bypass valve stuck open.
  • High differential pressure may indicate:
    • fouling,
    • blockage due to marine growth on the seawater side, or
    • scale deposits on the freshwater side.

    2. Investigate Flow and Bypass Problems

    Part (a)

    Temperature Control Valve (TCV)

    • Check whether the automatic temperature control valve is operating correctly.
    • If the valve is stuck in a position that allows water to bypass the cooler, the cooling medium will not pass effectively through the cooler.
    • Verify actuator operation, control signal, and air supply pressure if pneumatically operated.
    Part (b)

    Seawater Strainer Inspection

    • Inspect the seawater inlet strainer, as clogging of the strainer is one of the most common causes of reduced seawater flow.
    • Clean and refit the strainer if fouled with mud, marine growth, or debris.
    Part (c)

    Check Valve Line-Up and Flow Balancing

    • Confirm that all valves in the LT cooling circuit are correctly lined up.
    • Ensure that no suction, discharge, or cooler isolation valve has been accidentally throttled or left partly closed.

    3. Rectification by Physical Inspection and Maintenance

    If the problem is not resolved by operational checks, the cooler should be isolated and inspected.

    Before carrying out maintenance, perform a risk assessment and follow Lock-Out/Tag-Out (LOTO) procedures.

    Part (a)

    Seawater Side Cleaning

    For a plate type LT cooler:

    • Drain the cooler and open the covers.
    • Inspect the plates for:
      • marine growth,
      • mud,
      • silt,
      • slime, or
      • other deposits.
    • Clean the plates using a soft brush and approved cleaning chemicals.
    • Do not use steel wire brushes, as they may damage the protective oxide layer of the stainless steel plates.
    Part (b)

    Freshwater Side Cleaning / Descaling

    • If scale formation is suspected on the freshwater side, carry out chemical cleaning / CIP (Cleaning in Place) using an approved mild descaling chemical suitable for plate heat exchangers.
    • Ensure the chemical used does not damage the plates or gaskets.
    Part (c)

    Plate Condition and Integrity Check

    • Inspect all plates for:
      • corrosion,
      • pitting,
      • erosion, and
      • physical damage.
    • Check for signs of inter-plate leakage or cross-contamination between seawater and freshwater.
    • If pinhole leakage is suspected, a dye penetrant test may be carried out.
    Part (d)

    Gasket Inspection

    • Check the condition of the plate gaskets for:
      • hardening,
      • cracking,
      • deformation, or
      • loss of elasticity.
    • If the cooler has been opened, it is good practice to replace or rejuvenate the gaskets before reassembly to prevent leakage.

    4. Long-Term Preventive Measures to Improve Performance

    Part (a)

    Maintain Correct Water Treatment

    • Ensure proper chemical treatment of the freshwater circuit using the recommended inhibitors such as nitrites / borates.
    • This helps prevent:
      • scaling,
      • corrosion, and
      • internal fouling.
      Part (b)

      Proper Sea Chest Management

      • In shallow, muddy, or silty waters, use the high sea chest where appropriate to reduce the entry of mud and silt into the seawater system.
      Part (c)

      Routine Back-Flushing and Strainer Maintenance

      • If fitted, ensure the automatic back-flushing system for seawater strainers is working properly.
      • Regular cleaning of strainers and seawater lines should be carried out to maintain good flow.
      Part (d)

      Maintain Performance Records

      • Keep a regular log of:
        • pressure drop across the cooler, and
        • temperature differential across the cooler.
      • This helps in identifying performance trends:
        • gradual deterioration usually indicates fouling,
        • sudden performance drop usually indicates obstruction, valve malfunction, or mechanical failure.