Ship Maintenance: Descaling is Critical for Effective Heat Transfer

Water scale on any heat transfer surface reduces the effectiveness of that heat transfer. In turn, this results in reduced equipment efficiency while increasing energy consumption, increasing costs and even increasing plant operational downtime. Often this “buildup” problem is either ignored or relegated to “fixing it at the last minute or upon mechanical failure” status because of downtime costs. This is historically based on the premise that descaling takes a great deal of time.

As a marine engineer, this brings focus to one very important concern – every cruise and merchant ship must be self-sustaining as far as the production of fresh water is concerned.

The large quantities of fresh water required aboard ship for boiler feed, drinking, cooking, bathing, recreation, and washing make it impracticable to provide storage tanks large enough for more than a few days’ supply. Therefore, all ships depend upon water generating plants to meet the requirements for large quantities of fresh water.

Since shipboard cooling consists of a number of heat exchangers, each serving one or more specified purposes, the operation as a whole provides an excellent illustration of many thermodynamic processes and concepts. Practical manifestations of heat transfer – including heating, cooling, and change of phase – abound in the distilling plant, boilers, chillers, AC&R units. The significance of the pressure-temperature relationships of liquids and their vapors is clearly evident.

Cleaning can be done either mechanically or through the use of chemicals. Mechanical cleaning obviously takes a great deal of downtime because it requires that you dismantle equipment. Another consideration is the replacement of gaskets and seals which adds to overall maintenance cost. In addition, mechanical cleaning may not consistently get all the scale out.

Having said the above, there are some good descaler products available. A good descaler:

  • Has low corrosion rates – it removes a good amount of scale with verifiably low corrosion rates and does not harm seals and gaskets in a system.
  • Is easily rinsed out – being free rinsing, it does not need to be neutralized in the system after use. A quick flush with water will get the product out, leaving no residual. Be sure the system is tested after descaler use to make sure PH levels meet disposal standards prior to disposal.
  • Provides good cleaning efficiency of more than just scale – there should be other ingredients to remove oil, rust, loosened silica and other undesirable materials that often is mixed with the scale deposits.
  • Is simple to use and accomplishes the task quickly – the major criteria for many marine engineers is to minimize downtime — speed is important! Any descaler must have the right mix of acids and detergents to clean scale and other impurities quickly.

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Vince DaSilva
Goodway Blogging Team

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