• If applicable
Posted Monday, April 20th, 2020

All steel structures, facilities and installations, exposed to atmosphere, staying under water or in soil, suffer because of corrosion and require protection. Throughout this article you will find important information regarding paint technology, criteria for right paint selection and surface preparation requirements.

This article does tie in with the International Standard ISO 12944 “Paints and Varnishes – corrosion protection of steel structures by protective paint systems.”

There are different ways of protecting steel structures from corrosion. ISO 12944 (all parts) deals with protection by paint systems and covers, in the various parts, all features that are important in achieving adequate corrosion protection. Additional or other measures are possible but require particular agreement between customer and supplier.

The tanks that Fuelchief fabricate in New Zealand (ie the SuperVault, Praxis, Vanguard and Pyrotector) along with our stocked DC Series tanks are all supplied painted to our customer. Only our welded collection can be provided un-covered (if the customer is organising their own paint process), however we strongly recommend against this to ensure longevity in the field and for warranty validation.

The Fuelchief DC Series of tanks are supplied painted with an industrial grade paint (Hempel which is an ISO 12944 supplier) to withstand the elements for an elongated period of time. The selected paint aids against corrosion of your asset and ensures protection with its high-performance coatings.  The paint system has a C3 Grade and offers advanced optimised application for a durable finish that looks good for longer, in even the most challenging climates.  Below is a table showing the 5 atmospheric corrosivity categories:

 

Corrosivity Category Environment Examples Environment Examples
Exterior Interior
C1 – Very Low NA Heated buildings with a clean atmosphere such as offices, shops, schools, hotels.
C2 – Low Atmosphere contaminated to a small extent, mainly rural regions Buildings which are not heated, where condensation may occur e.g. storehouses, sports halls.
C3 – Medium Industrial and urban atmosphere with an average sulphur oxide (IV) contamination level.
Inshore areas of low salinity.
Production space of high humidity and certain air contamination e.g. foodstuff plants, laundries, breweries, dairies.
C4 – High Industrial areas and inshore areas of medium salinity. Chemical plants, swimming pools, ship repair yards
C5 – I – Very High (Industrial) Industrial areas of high humidity and aggressive atmosphere. Buildings and areas of almost constant condensation and high contamination.
C5-M – Very High (Marine Grade Inshore areas and offshore areas of high salinity. Buildings and areas of almost constant condensation and high contamination.

 

Our welded suite of tanks are custom painted, when thinking about what paint to use it is important to consider the following factors:

  • Environment
  • Type of protected surface
  • Durability required for the paint
  • Planning the paint application process

ENVIRONMENT

When selecting a paint system it is vitally important to work out the conditions in which the structure, facility or installation is to operate. To establish the effect of environmental corrosivity, the following factors must be taken into account:

• humidity and temperature (service temperature and temperature gradients)
• the presence of UV radiation
• chemical exposure (e.g. specific exposure in industrial plants)
• mechanical damage (impact, abrasion etc.)

In the case of buried structures their porosity must be considered and the ground conditions which they are subject to. The dampness and pH of the terrain and biological exposure to bacteria and micro-organisms are of critical importance. In the case of water, the type and chemical composition of the water present is also significant. The corrosive aggressiveness of the environment will influence:

• the type of paint used for protection
• the total thickness of a paint system
• the surface preparation required
• minimum and maximum re-coating intervals

TYPE OF PROTECTED SURFACE

Designing a coating system normally involves dealing with constructional materials such as steel, hot dipped galvanised steel, spray-metallised steel, aluminium or stainless steel. The surface preparation, the paint products used (particularly the primer) and the total system thickness will depend mainly on the constructional material to be protected.

DURABILITY REQUIRED FOR PAINT SYSTEM

The lifetime of a paint system is assumed to be the period of time which passes until maintenance is required for the first time after application. ISO 12944 specifies a range of three time frames to categorise durability:

Property  Standard
Low – L  2-5 Years
Medium – M  5-15 Years
High – H  More Than 15 Years

PLANNING THE PAINT APPLICATION PROCESS

The building schedule and the various stages of construction of any particular project determine how and when the paint system needs to be applied.

Consideration needs to be given to materials at their prefabrication stage, when components are being prefabricated both off and on site and when building stages are complete.

It is necessary to plan the job so that surface preparation and the drying/curing time of paint products in relation to temperature and humidity are considered. Also, if one stage of construction takes place in a protected workshop environment and the next stage then takes place on site, re-coating intervals must also be considered.

The paint options that Fuelchief use for their welded range are all C5-I with the option of C5-M (at an additional cost).

Preparation for such paint jobs take the following steps for our fabricated range of tanks:

  • All surfaces to be coated are clean, dry and free from contamination. Prior to paint application, all surfaces should be assessed and treated in accordance with ISO 8504:2000. Oil or grease should be removed in accordance with SSPC-SP1 solvent cleaning.
  • Abrasive blast clean to Sa2.5 (ISO 8501-1:1988) or SSPC-SP6. If oxidation has occurred between blasting and application, the surface should be reblasted to the specified visual standard. Surface defects revealed by the blast cleaning process, should be ground, filled, or treated in the appropriate manner.
  • Stripe coats should be applied to all welds, lap joints, plate edges, corners, sharp edges and any other areas where spray application of the overall coating system may prove difficult resulting in low dry film thickness.

The durability factor for the above for all our models combined is over 35 years protection.

To find out more about our products visit the link. To find out about maintenance on tanks check out our tips and maintenance section.

*All Fuelchief tanks fabricated in New Zealand are audited and carry a paint manufacturers warranty. Find out more by emailing [email protected]