ISO/EN 12944
This standard, which is both a
nev(/T~ternatiOrjiks'tandard
and, a European,/ Standard, has been given positivevot~'s"byboth
the International andEurope~~
committees and can now proceed to being ~!~,}b[ished standard. It is unlikely that this will be the case forru!
parts untiln;Jfd
, 1998~the earliest.~
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It should be noted, that because of the approval given by the European committee, this standard will replace existing national standards such as 8S5493 and DIN 55928.
The main problem I see at the moment is that it appears unlikely that the US based specifying houses will use the specification, but will continue to use SSPC and NACE guidelines.
ISO 12944 states that it is designed for use by engineers who have some technical knowledge in the area of corrosion protection. as well as knowledge of other relevant specifications.
Many will find the durability ranges to be extremely useful - this is the estimated time to first major maintenance. This needs to be agreed between the interested parties with reference to ISO 4628/1 to ISO 4628/5. It should always be realised that much less effort is required to maintain a coating which has broken down to Ri2 than one which has broken down to Ri3, for example.
considered are:
Low 2-5 Years
Medium 5-15 Years High >15 Years
and are assuming the coating has reached a breakdown level of Ri3.
(It is emphasised that the durability range is not a guarantee time. It is purely present to help the owner of the structure estimate sensible maintenance times. The guarantee time is generally shorter than the durability range, and there is no simple relationship between the two,)
IS 10":;;"1''''--'') ISO 1L O ... ... ISO 1 ISO 12944-6 ISO 12944-7 ISO 12944-8
SUMMARY SECTIONS
Covers the corrosivity of various environments and how these can be measured. Various anti-corrosive systems can then be specified for these environments.
Deals with best practices in structural steel design from a corrosion prevention viewpoint.
Covers surface preparation - reference to ISO 8501, ISO 8502, ISO 8503, ISO 8504.
Typical paint systems by generic type for a given durability in a given environment.
Laboratory testing of paint systems, particularly intended for those
,,---~~~~-" - - ""
where sufficient practical experience is not yet available. Does not cover power tool cleaned steel specifically.
Covers application at works or on site, inspection and follow up. Also deals with reference areas.
specifications for corrosion protection and ancillary issues.
ISO/EN 12944
~-~
PARt 2 )
~4_ _-~/CLASSIFICATION OF ENVIRONMENTS
Defined from weight loss of metallic (low carbon steel and zinc) specimens over a defined period of 1 year (not more and not less).
There are obvious differences in this approach because of change of climate on a yearly basis, but this certainly helps quantify the corrosivity of an environment.
Very low - low Medium High Very high industrial Very high marine Structures immersed Structures * Above thicknesses <10-200 g/m2 (1.3-25IJm) 200-400 g/m2 (25-50lJm) 40-650 g/m2 (50-80lJ m) 650-1500 g/m2 Exterior pollution, dry.
and industrial atmospheres Moderate S02 pollution
Moderate coastal CI) Industrial and coastal.
ndustry with high humidity atmosphere
Heated buildings/neutral 'atm~pl:!9fes:
Unheated buildings, possible condensation
Production rooms with high humidity and air pollution
Chemical processing plants
D.F.T* 75IJm 200IJm 200IJm 240IJm (Zinc) 280IJm (Non-zinc) 320IJm 650-1 320IJm
TABLE 1 -CORROSIVITY OF ENVIRONMENTS
(Refer to ISO 12944-2)
Where single coats are applied higher film thicknesses will be required (see recommendec specifications) .
MJM/19/07/97/GO Page No.4
ISOIEN 12944
PART 3
STRUCTURAL DESIGN
ISO 12944-3, which covers basic design criteria, is really outside the scope of protective coatings manufacturers. This can only really be fully implemented at the New Construction stage or by major modification at a later date. Coatings are often expected to alleviate, or help alleviate, corrosion problems due to design errors. In this instance, it could well be that different coating specifications would be required for these areas which could be thicker/more corrosion resistant than those used elsewhere. Typically, if a certain area was subjected to frequent ponding of rain water because of design, then either modification would be required to prevent this or a different coating system could be needed.
ISO 12944-5
PROTECTIVE PAINT SYSTEMS
This section, and that on testing, are those most likely to be argued over and to provide the greatest areas of contention.
In the areas of generic paint systems, almost every type which can be imagined has been covered, and what appears to me a series of quite complicated matrices have been put together. This is possibly why this part of the specification is not due for completion until 1998 and will be the last section finalised.
At this time there continues to be much discussion on this section. and modifications will certainly be made.
Currently, for example, it is indicated that both solvent based alkyds and water based acrylics will dry at DoC, certainly we would not recommend this type of condition for water based, and on conventional alkyds I would expect an extremely negative effect.
• Note, the proposed definition and rider regarding zinc rich coatings. This now becomes much closer to the SSPC SP20 definition than. for example, current British Standards.
• Minimum film thickness should be >80% specified d.f.t.
• Recommended that maximum d.f.t. is not greater than 3x nominal d.f.t. (this is much greater than we would specify and would certainly potentially create problems). Reference to paint manufacturer's technical data sheet.
ISO/EN 12944
THICKNESSES/LIFETIMES FOR VARIOUS ENVIRONMENTS
(Refer to ISO 12944-5)
C2 8Ol-lm - Low
150l-lm - Medium
2OOl-lm - High
C3 120l-lm Low
160l-lm Medium Medium corresponds to 5-15 years
200l-lm
-
High High corresponds to >15 yearsC4 16Ol-lm - Low
2OOl-lm - Medium
240l-lm High (Zinc) 280l-lm High (Non Zinc)
C51 200l-lm _ Low
C5M 280l-lm _ Medium
Low corresponds to 2-5 years
PAINT SYSTEMS
Those shown are examples for several environments:
• Other systems having the same performance are possible.
• All paints for all systems shall be suitable for the highest corrosion stress of the given corrosivity or immersion category.
• Documentation or guarantee stating suitability or the durability of a paint system in a given environment - experience or artificial ageing tests where necessary.
Standard arranges systems as follows:
A1 to AS According to binder in the topcoat Others According to binder in the primer coat
A1 All examples of systems for C2, C3 and C4.
A2 Systems for C2 (system not shown if it has high classification in A3, A4).
A3 Systems for C3 (system not shown if it has high classification in A4).
A4 Systems for C4.
Where a paint system cannot be allocated to one of the Tables A1 to A9, full information regarding:
Surface preparation Generic type
Number of coats
Nominal dry film thickness
ISO/EN 12944
There are an extremely wide range of generic coatings included in the specification, and really these can only be considered as examples. Basically, paint types used by all participating members have been included. No reference or allowance appears to have been made to recognise the effect of the introduction of legislation to reduce solvent emissions, and paint types whose use is being restricted for health and safety reasons are also included.
Also, as in almost all specifications, there is no allowance or mention of what are often perceived as key issues regarding coating systems, i.e.
• Drying times - handling times, overcoating times • Maximum overcoating times
• Effect of application conditions
In general, more problems are encountered due to poor interpretation, ignorance of the above, or by use of coatings which are not sufficiently tolerant over a wide range of conditions.
It is likely that most interest will be with the "high" durability systems, i.e. those with an expected life to first major maintenance of 15 years plus. With these it is also likely that the following environments will be most important:
C4 High Corrosivity C5-1 Very High Industrial C5-M Very High Marine
The C3 area of medium corrosivity will meet the 15 year requirements with most reasonable 2 or more coat schemes, giving minimum d.f.t's of 150-200 microns.
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When considering the actual schemes listed, the following points are worth noting:
1. All coating systems, with the exception of those designed for immersion, are very multi-coat in type. This would almost certainly lead to a request from any contractor to reduce the number of coats and utilise higher solids coatings with higher d.tfs.
2. Some of the mixtures of systems, for example, overcoating alkyds with chlorinated rubbers, are not normally utilised.
3. All specifications tend to be based on multiples of 40 microns, whereas in UK and many countries the multiples are of 25 microns, probably due to the influence of the US and 1 mil
=
25 microns.Hot dip Galvanized or Hot dip galvanized areas
BS EN ISO 1461: 1999 Hot Dip Galvanized coatings on fabricated iron & steel articles specifications & test methods! This standard specifies the thicknesses (minimum & average 80 Mic DFT zinc coat) that should be followed, sampling methods ,selection of reference areas for testing & renovation methods etc. Then use ISO 10747 to issue quality certificates when ever required by the customer.
Note The durability of the galvanized coating depends on the type of environment as classified under ISO 129441 ISO 9223 ,& according to that in a rural environment the corrosion rate of Zn is less than 1 micron. (suitable for environment category C 1, C2)
After galvanizing the total coating would be a combination of alloy layers (Fe & Zn) which is the maj ority & pure Zn.
Surface Cleaning: Free of zinc salts, dirt, contaminations and fresh water wash down and by dry
When viewed without magnification, the mild steel surfaces shall be free from visible Oil grease and dirt and from poorly adhering mill scales, rust paint coatings and foreign matter, moreover the metallic substrate shall give rise to a metallic sheen. Dampness with salty finger prints not Acceptable
