{"id":1152,"date":"2025-02-14T20:22:41","date_gmt":"2025-02-14T20:22:41","guid":{"rendered":"https:\/\/hydrocarbon.sbs\/?p=1152"},"modified":"2026-03-24T23:26:30","modified_gmt":"2026-03-24T23:26:30","slug":"sea-cooling-water-corrosion","status":"publish","type":"post","link":"https:\/\/petrostreet.com\/main\/sea-cooling-water-corrosion\/","title":{"rendered":"Sea Cooling Water Corrosion"},"content":{"rendered":"\n

In petrochemical, oil & gas, refinery and other many industries, cooling water is the heart and soul of all operations. Without a cooling water system, there is no operation possible. Last to be down during shutdowns and first to be up during start-ups, the cooling water system is by far the most critical system, yet containing a non-toxic, non-flammable, non-hazardous fluid – water. However, any threat to the mechanical integrity of this system may lead to plant downtime, lost production and maintenance cost impact. Therefore, inspection, maintenance and operation of this system is as critical as the system itself, as it doesn\u2019t matter that the leaking fluid is only water, but it may put down the plant for days.<\/p>\n\n\n\n

There are different sources for cooling water systems, like the sea, canals, or wells. Facilities installed near the sea use sea water for cooling. Similarly, facilities away from sea but near big rivers or seasonal canals use these as water sources by digging wells to access this very important raw material to keep the plant running. Based upon the source, the corrosion of cooling water differs. Then comes its handling and treatment, which also has an impact on its corrosive nature. Operation is another factor, which directly affects the erosion issues related to cooling water, especially where valves are throttled and velocities are not maintained.<\/p>\n\n\n\n

In this article, sea cooling water corrosion is the topic of discussion. Sea cooling water corrosion and erosion issues affect almost all commonly used metallurgy, starting from carbon steel, low alloy steel, all grades of stainless steel, copper, aluminum, titanium and nickel based alloys. Metallurgical and material solutions to resist sea cooling water corrosion will be discussed in detail, however operational controls to mitigate sea cooling water corrosion are not addressed in this article.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Fig. 1:<\/strong> Sea water corrosion leak<\/p>\n\n\n\n

What causes corrosion in sea water?<\/strong><\/h3>\n\n\n\n

There are three factors that impact the corrosion of sea water heavily:<\/p>\n\n\n\n

    \n
  1. Chloride concentration<\/li>\n\n\n\n
  2. Oxygen<\/li>\n\n\n\n
  3. Temperature<\/li>\n<\/ol>\n\n\n\n

    Chloride concentration<\/strong><\/p>\n\n\n\n

    Chloride ions are present in sea water as the most aggressive agents and reacts with ferrous ions to form ferrous chloride, which eventually reacts with dissolved oxygen in sea water to form ferric oxide and ferric chloride. Ferric ions are considered agents that can cause severe corrosion.<\/p>\n\n\n\n

    Fe = Fe2+<\/sup> + 2e–<\/sup><\/p>\n\n\n\n

    Fe2+<\/sup> + 2Cl–<\/sup> = FeCl\u00ad2<\/sub><\/p>\n\n\n\n

    Oxygen<\/strong><\/p>\n\n\n\n

    Dissolved oxygen in sea water also plays an important role in the corrosion of sea water. The presence of chloride ions changes its dissolved oxygen concentration. At 3.5 weight percent of NaCl, maximum oxygen concentration is obtained. The below Chart A explains how the corrosion rate of steel is affected with the concentration of NaCl in sea water:<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Chart A<\/strong>: Effect of NaCl concentration on corrosion rate of steel<\/p>\n\n\n\n

    Temperature<\/strong><\/p>\n\n\n\n

    Corrosion of steel in water increases from 2% to 4% per degree (o<\/sup>C) rise in temperature. Based upon this, sea water corrosion is more aggressive in tropical areas compared to cold ones. Serious scaling occurs when the outlet temperature of sea water goes beyond 46 o<\/sup>C.<\/p>\n\n\n\n

    Other than these three factors, the velocity of sea cooling water directly affects the erosion-corrosion of material. The impact of velocity is different for different metallurgies. Table 1 represents insights to this:<\/p>\n\n\n\n

    Material<\/strong><\/td>Maximum Pit Depth
    (mm)<\/strong><\/td>    		Average Corrosion Rate
    (mm\/y)<\/strong><\/td><\/tr>
    Still Seawater<\/td>Flowing Seawater<\/td><\/tr>
    8.2 m\/s<\/td>35 – 42 m\/s<\/td><\/tr>
    Carbon Steel<\/strong><\/td>2<\/td>–<\/td>4.5<\/td><\/tr>
    Grey Cast Iron<\/strong><\/td>4.9<\/td>4.4<\/td>13.2<\/td><\/tr>
    Admiralty Gunmetal<\/strong><\/td>0.25<\/td>0.9<\/td>1.07<\/td><\/tr>
    85\/5\/5\/5 Cu Zn Pb Zn<\/strong><\/td>0.32<\/td>1.8<\/td>1.32<\/td><\/tr>
    Ni Resist Cast Iron Type 1B<\/strong><\/td>Nil<\/td>0.2<\/td>0.97<\/td><\/tr>
    Ni Al Bronze<\/strong><\/td>1.12<\/td>0.22<\/td>0.97<\/td><\/tr>
    70\/30 Cu Ni + Fe<\/strong><\/td>0.25<\/td>0.12<\/td>1.47<\/td><\/tr>
    Type 316 Stainless Steel<\/strong><\/td>1.8<\/td><0.02<\/td><0.01<\/td><\/tr>
    6% Mo Stainless Steel<\/strong><\/td>Nil<\/td><0.02<\/td><0.01<\/td><\/tr>
    Ni-Cu Alloy 40<\/strong><\/td>1.3<\/td><0.01<\/td>0.01<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Table 1:<\/strong> Pitting depths and corrosion rates in seawater service<\/p>\n\n\n\n

    Affected metallurgies<\/strong><\/h3>\n\n\n\n

    Carbon steel<\/strong><\/p>\n\n\n\n

    Bare carbon steel cannot withstand sea cooling water, as it corrodes and erodes at the same time in presence of high velocities. And in case of still water, pitting starts, which affects the steel and eventually leads to leakages.<\/p>\n\n\n\n

    Stainless steel<\/strong><\/p>\n\n\n\n

    300 series stainless steel suffers from stress corrosion cracking, crevice corrosion or pitting corrosion, depending upon the operating parameters in sea water service. This makes this material vulnerable and it therefore is not recommended to be used.<\/p>\n\n\n\n

    Copper alloys<\/strong><\/p>\n\n\n\n

    Copper alloys have also been used as one of the combatant materials against sea cooling water corrosion since many years. They offer good resistance when compared to steels. The presence of oxide film plays an important role. Studies have shown that with time passing, the oxide film on copper alloys improve. The initial corrosion rate is higher compared to the long term corrosion rate. Chart B shows the corrosion rate of most commonly used Cu-Ni alloy in flowing sea water.<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Chart B:<\/strong> Corrosion rate of Alloy 70600 in flowing sea water<\/p>\n\n\n\n

    Copper-zinc alloys can suffer dezincification in sea water service.<\/p>\n\n\n\n

    Concrete<\/strong><\/p>\n\n\n\n

    Chlorides penetrate into concrete through its flaws and may affect the carbon steel substrate, which would eventually corrode to leak.<\/p>\n\n\n\n

    Recommended solutions<\/strong><\/h3>\n\n\n\n

    Isolation of steel through coating<\/strong><\/p>\n\n\n\n

    Bare steel is not resistant to sea water corrosion and erosion-corrosion damages. However, the solution, which is being commonly used in industries to resist sea water corrosion is coated steel. Just isolate the steel from sea water by applying an appropriate coating system. However, the question is which coating is effective considering cost and the life of the coating material. There are cement lining materials, glass flake reinforced polyester, fusion-bonded epoxy, and rubber lining to choose from.<\/p>\n\n\n\n

    Cement lining<\/strong><\/p>\n\n\n\n

    Cement lining is cost effective and easily available, however quality control practices shall ensure the entire process of cement lining. Cementous material containing pores may lead to leaks in a very short time. Field joints stand as a challenge and must be done with utmost care. Cement lining itself is a thick layer and difficult to apply in small bore piping. Also, bigger pipe diameters are required when considering to apply cement lining inside in order to have an effective required diameter.<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Fig. 2:<\/strong> Cement mortar lining in progress<\/p>\n\n\n\n

    Glass flake reinforced polyester<\/strong><\/p>\n\n\n\n

    Glass flake reinforced polyester is another coating material being used in sea water applications. An easy to apply coating system has its own drawbacks, where its ability to resist erosion is challenged especially in the presence of marine growth, sea shells and other substances causing erosion at higher velocities.<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Fig. 3:<\/strong> Glass flake polyester lining<\/p>\n\n\n\n

    Fusion-bonded epoxy<\/strong><\/p>\n\n\n\n

    Fusion-bonded epoxy is another internal coating system, which is used to resist cooling water corrosion agents\u2019 permeation to steel substrate. Defect free epoxy coatings resist the diffusion of chloride and oxygen, however they are not impermeable to moisture. This property benefits in saving the carbon steel base metal to come in contact with corrosive agents.<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Fig. 4:<\/strong> FBE coating in progress<\/p>\n\n\n\n

    Cupronickels<\/strong><\/p>\n\n\n\n

    Cupronickels where 10%-30% nickel is added, is the number one choice for sea water services since many years. Alloy C70600 provides better long term corrosion resistance. However, the application of cupronickels is mostly within exchangers as tube materials. It is seldom used as piping material for sea cooling water service.<\/p>\n\n\n\n

    Titanium<\/strong><\/p>\n\n\n\n

    Using titanium is a very costly affair but effective for long term applications and maintenance free operations. However its application is also limited to exchangers\u2019 tube material.<\/p>\n\n\n\n

    Conclusion<\/strong><\/h3>\n\n\n\n

    Based on the experience of different sea water cooling industrial sectors, the following conclusion is drawn:<\/p>\n\n\n\n

    For piping applications, coated steel with fusion bonded epoxy serves best in sea water operation. Fusion-bonded epoxy is one part, heat curable, thermosetting epoxy resin powder utilizing heat to melt and adhere to a metal substrate. With excellent adhesion, tough, smooth finish resistant to abrasion and chemicals FBE coatings are combating corrosion since 1960.<\/p>\n\n\n\n

    For best performance, the thickness is normally in the four hundred microns range.<\/p>\n\n\n\n

    FBE is currently in use in oil & gas, refining, petrochemicals and other industrial sectors all over the world. Specifically, for sea water corrosion, it is well tested and provides excellent results for many years.<\/p>\n\n\n\n

    <\/a><\/p>\n\n\n\n

    <\/p>\n","protected":false},"excerpt":{"rendered":"

    In petrochemical, oil & gas, refinery and other many industries, cooling water is the heart and soul of all operations. 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