iso12944大气腐蚀环境

I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 1 7/31/98 This standard, which is both a new International Standard and a European Standard, has been given positive votes by both the International and European committees and can now proceed to being a full published standard. It is unlikely that this will be the case for all parts until mid 1998 at the earliest. It should be noted, that because of the approval given by the European committee, this standard will replace existing national standards such as BS5493 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. The ‘durability’ ranges 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.) I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 2 SUMMARY SECTIONS ISO 12944-2 Covers the corrosivity of various environments and how these can be measured. Various anti-corrosive systems can then be specified for these environments. IS 19244-3 Deals with best practices in structural steel design from a corrosion prevention viewpoint. ISO 12944-4 Covers surface preparation - reference to ISO 8501, IS0 8502, IS0 8503, ISO 8504. ISO 12944-5 Typical paint systems by generic type for a given durability in a given environment. ISO 12944-6 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. ISO 12944-7 Covers application at works or on site, inspection and follow up. Also deals with reference areas. ISO 12944-8 Describes how to prepare specifications for corrosion protection and ancillary issues. I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 3 PART 2 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. I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 4 07 May 1997 TABLE 1 - CORROSIVITY OF ENVIRONMENTS Exterior Interior D.F.T* C1, C2 Very low - low <10-200 g/m2 (1.3-25µm) Heated buildings/neutral atmospheres. 75µm Rural areas, low pollution, dry. Unheated buildings, possible condensation 200µm C3 Medium 200-400 g/m2 (25-50µm) Urban and industrial atmospheres Moderate SO2 pollution Moderate coastal Cl) Production rooms with high humidity and air pollution 200µm C4 High 40-650 g/m2 (50-80µm) Industrial and coastal. Chemical processing plants 240µm (Zinc) 280µm (Non-zinc) C5-I Very high industrial 650-1500 g/m2 Industry with high humidity and aggressive atmosphere 320µm C5-M Very high marine 650-1500 g/m2 Marine coastal, offshore High salinity 320µm I1 Structures immersed in fresh water I2 Structures immersed in sea or brackish water I3 Structures immersed in soil (Refer to ISO 12944-2) * Above thicknesses refer to multi-coat systems. Where single coats are applied higher film thicknesses will be required (see recommended specifications). I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 5 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. I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 6 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 0ºC, 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. · Note, all references are to airless spray application. I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 7 THICKNESSES/LIFETIMES FOR VARIOUS ENVIRONMENTS (Refer to ISO 12944-5) C2 80µm º Low 150µm º Medium 200µm º High C3 120µm º Low Low corresponds to 2-5 years 160µm º Medium Medium corresponds to 5-15 years 200µm º High High corresponds to >15 years C4 160µm º Low 200µm º Medium 240µm º High (Zinc) 280µm º High (Non Zinc) C5I 200µm º Low C5M 280µm º Medium 320 º High I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 8 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 A5 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 shall be given in the same way as indicated in the tables. I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 9 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-I 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. I S O / E N 1 2 9 4 4 MJM/19/07/97/GD Page No. 10 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.f.t’s. 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.