Main Problems

Scale

Some closed systems, such as chilled water systems, operate at relatively low temperatures and require very little makeup water. Because no concentration of dissolved solids occurs, fairly hard makeup water may be used with little danger of scale formation. However, in diesel and gas engines, the high temperature of the jacket water significantly increases its tendency to deposit scale. Over a long period, the addition of even small amounts of hard makeup water causes a gradual buildup of scale in cylinders and cylinder heads.

Corrosion

Untreated systems can suffer serious corrosion damage from oxygen pitting, galvanic action, and crevice attack. Closed cooling systems that are shut down, oxygen can enter the water until its saturation limit is reached. When the system is returned to high-temperature operation, oxygen solubility drops and the released oxygen attacks metal surfaces. The metallurgy used in constructing modern engines, compressors, and cooling systems includes cast iron, steel, copper, copper alloys, and aluminum as well as solders. If bimetallic couples are present, galvanic corrosion may develop.

Microbiological fouling

Some times when nitrite base treatments programs used, nitrites are oxidized by microorganisms. This can lead to sever biological fouling.

Solutions

The three most reliable corrosion inhibitors for closed cooling water systems are :

• Chromate
• molybdate and
• nitrite materials

Generally, the chromate or molybdate types have proven to be superior treatments. For mixed metallurgy systems, the molybdate inhibitors provide the best corrosion protection.

Molybdate treatments provide effective corrosion protection and an environmentally acceptable alternative to chromate inhibitors. Molybdates are thermally stable and can provide excellent corrosion protection in both soft and hard water. Molybdate inhibitors should not be used with calcium levels greater than 500 ppm.

Nitrite- molybdate-azole blends inhibit corrosion in steel, copper, aluminum, and mixed-metallurgy systems. System pH is normally controlled between 7.0 and 9.0. Recommended treatment control limits are 200-300 ppm molybdate as MoO4.

Nitrite is another widely accepted nonchromate closed cooling water inhibitor. Nitrite concentrations in the range of 600-1200 ppm as NO2- will suitably inhibit iron and steel corrosion when the pH is maintained above 7.0. If aluminum is also present, the corrosion problem is intensified, and a treatment level of 10,000 ppm may be required. In all cases, the pH of the circulating water should be maintained in the alkaline range, but below 9.0 when aluminum is present.

One drawback to nitrite treatments is the fact that nitrites are oxidized by microorganisms. This can lead to low inhibitor levels and biological fouling. The feed of nonoxidizing antimicrobial may be necessary to control nitrite reversion and biological fouling.

Corrosion Inhibitors

• Molybdate/Phosphonate Corrosion Inhibitor, Closed Systems – is a superior molybdate /phosphonate based corrosion inhibitor developed to prevents corrosion and deposits in closed and aerated cooling water systems. It contains inhibitors for steel, copper and copper alloys in combination with dispersants.
• Nitrite Inhibitor for Closed/Chiller – multi-functional, nitrite-based chemical treatment used for the control of corrosion in closed cooling systems and chilled water
• Corrosion Inhibitor & Antifoulant for Closed Circuits containing Aluminium – is a superior corrosion inhibitor developed for use in closed water circulating systems containing aluminium. It is based on a novel blend of organic and inorganic corrosion inhibitors, including molybdate, intended to protect steel, copper and other nonferrous metals like aluminium.
• Copper Corrosion Inhibitor – is an innovative corrosion inhibitor for closed cooling systems. It creates an insoluble polymeric surface complex on copper and its alloys.

Combined Scale and Corrosion Inhibitors

• All Organic Scale & Corrosion Inhibitor – all organic scale and corrosion inhibitor for steel, aluminium and other non ferrous metals.
• Nitrite Inhibitor for Closed/Chilled Systems with Phosphonate – multi-functional, nitrite-based chemical treatment used for the control of corrosion in closed cooling systems and chilled water .
• Multifunctional Scale Inhibitor – multi-functional, nitrite-based chemical treatment used for the control deposits in closed cooling & heating systems.

Microbiocides

• Non-oxidising Biocide – is a non-oxidising non-foaming product ideally suited for use in cooling waters to control algae and aerobic and anaerobic bacteria over a wide pH range.
• Biodegradable Biocide – is an advanced, biodegradable non-oxidising micro-biocide developed specifically for the control of microbiological growths in cooling water systems.

Cleaners

• Pre-Commission Cleaner – an effective NTA/HEDP based cleaner for closed cooling or heating systems, developed specifically to remove iron and scale deposits from within a closed cooling or heating system.
• Bio-Dispersant (Oil Fouling) – is a highly effective bio-dispersant against organic fouling (oil, slime etc). Is designed to improve the performance of cooling and heating water systems, where fouling by organic slimes is reducing efficiency, by removing and dispersing the oil fouling.
  

Monitoring and Testing

Effective corrosion control monitoring is essential to ensure closed system reliability. ADTEC Chemicals provides well planned monitoring program which include the following:

• proper sampling and monitoring at critical points in the system
• completely representative sampling
• use of correct test procedures
• checking of test results against established limits
• a plan of action to be carried out promptly when test results are not within established limits
• a contingency plan for major upset conditions
• a quality improvement system and assessment of results based on testing and inspections