Product information

The product can be used for corrosion inhibition in many types of closed recirculation systems such as:

  • Diesel engine cooling water systems
  • Compressor cooling water systems
  • Centralised cooling systems
  • Hot water heating systems
  • Auxiliary machinery cooling systems


  • Liquid product, easy to use
  • By forming an oxide film on the metal surfaces electrolytic corrosion is prevented
  • Effective against cavitation and erosion
  • Compatible with hoses, gaskets and seals
  • Compatible with glycols for frost protection


  • Approved by major diesel engine manufacturers
  • Simple control test



  • Approved by all major engine manufacturers

Safety Data Sheet (SDS)


Directions for use

NALFLEET™ Rocor NB Liquid is a highly effective corrosion inhibitor for the common ferrous and non-ferrous metals in cooling water systems. The stable oxide film that is formed prevents corrosion caused by electrolytic action between dissimilar metals used in the system. NALFLEET™ Rocor NB Liquid has been field tested and found to have no detrimental effects on non metallic substances such as seals, glands, packing, hoses, gaskets etc., normally used in these systems. The compound is alkaline and so will suppress acid corrosion, which would otherwise result in corrosion damage such as pitting. However, the alkalinity control is such that even if the product is accidentally overdosed, the pH of the water will remain within limits. The metals which would be affected by extremes of alkalinity or acidity are protected. In cases where systems are contaminated with oil and/or scale they should be cleaned before starting to apply NALFLEET™ Rocor NB Liquid. There are suitable WSS products to carry out the cleaning. Degreasing should be carried out using UNITOR™ Seaclean Plus and descaling by using UNITOR™ Descalex. Refer to Water Treatment handbook. Freeze protection can be required if the vessel is to be laid up in cold areas. NALFLEET™ Rocor NB Liquid can be used in conjunction with glycols to provide suitable freeze protection. If the system contains zinc galvanized parts, it is advisory to clean the system with Descalex prior to commencing the treatment.

NALFLEET™ Rocor NB is not suitable for use in cooling systems containing aluminium components.

For general guidance where aluminium is present:

No aluminium present - Use Engine Water Treatment 9-108 or Rocor NB Liquid

<10% Aluminium - Use NALFLEET 2000 or Cooltreat AL

>10% Aluminium - Use Cooltreat AL

Dosing method

NALFLEET™ Rocor NB Liquid should be dosed to a suitable point in the system. If the expansion tank is used then adequate circulation must be assured.

Sampling and testing

The Spectrapak Test Kit provides the necessary equipment to carry out the control tests. Obtain a representative sample of the cooling water. Carry out the tests immediately after sampling (following the instructions given in the Test Kit) and log the results in Waterproof. The results should be sent to WSS as stated in the Waterproof instructions. Use the dosage chart overleaf to adjust treatment to obtain the optimum level. It is important that testing is carried out at least once per week, to ensure levels of treatment are correct.

Dosage and Control

Initial dosage for an untreated system is 9 litres of NALFLEET™ Rocor NB Liquid/1000 litres of untreated distilled/technical water. This will bring the treatment up to the minimum level of 1000 ppm nitrite. The dosage chart given below is for convenience in calculating the amount of NALFLEET™ Rocor NB Liquid required to bring the treatment level to the suitable point between the minimum and maximum - this being 1440 ppm nitrite.

Normal nitrite limits: 1000-2400 ppm nitrite (NO2)

Measured Nitrite (as ppm NO2)  









  1440 - 2400

Rocor NB Liquid Lit/m3










N.B.Buffering agents in NALFLEET™ Rocor NB Liquid maintain pH values within suitable limits when the product is dosed as recommended. Normal pH should be maintained between 8.3 and 10 by the treatment. The engine manufacturer's recommendations for water quality should always be complied with.

Chloride levels should always be as low as possible. Most engine manufacturers recommend a maximum of 50 ppm chlorides. For this reason, Wilhelmsen Ships Service recommends the use of distilled water as make-up.