1、STD.BS1 BS EN IS0 12944-2-ENGL 1998 LLi4bb 0738257 O49 BRITISH STANDARD Paints and varnishes - Corrosion protection of steel structures by protective paint systems - Part 2: Classification of environments The European Standard EN IS0 12944-2: 1998 has the status of a British Standard ICs 87.020; 91.
2、080.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN IS0 12944-2:1998 STD-BSI BS EN IS0 L29qq-Z-ENGL 1998 D Lb2qbbS 0738258 T85 D been prepared under the direction of the Sector Commime for Materials and Chemicals, was published under the authoriy of the Standards Comm
3、ittee and comes into effect on 15 November 1998 Amd. No. O BSI 1998 ISBN O 580 30348 4 BS EN Is0 12944-2:1998 Date Text affected National foreword This British Standard is the English language version of EN IS0 12944-2: 1998. It is identid with IS0 129442 1998. Together with the other seven parts of
4、 BS EN IS0 12944, it partialiy supersedes BS 5493 1977 which is declared obsolescent. The UK participation in its preparation was entsusted to Technical Committee S”b27, Paint systems for metallic substrates, which has the responsibility to: - aid enquirem to understand the te* - present to the resp
5、onsible intedo - describes different categories of environment for structures immersed in water or buried in soil; - gives information on some special corrosion stresses that may cause a significant increase in corrosion rate or place higher demands on the performance of the protective paint system.
6、 The corrosion stresses associated with a particular environment or corrosivity category represent one essential parameter governing the selection of protective paint systems. 1.2 This part of IS0 12944 does not deal with the classification of those environments that consist of special atmospheres (
7、for example those in and around chemical and metallurgical plants). 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this pari of IS0 12944. At the time of publication, the editions indicated were valid. All standards a
8、re subject to revision, and parties to agreements based on this part of IS0 12944 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 9223:1992,
9、Corrosion of metals and alloys - Corrosivity of atmospheres - Classification. IS0 9226:1992, Corrosion of metals and alloys - Corrosivity of atmospheres - Determination of corrosion rafe of standard specimens for the evaluation of corrosivity. IS0 12944-1:1998, Paints and varnishes - Corrosion prote
10、ction of steel Structures by protective paint systems - Part 1: General introduction. EN 12501 -1 :- 11, Protection of metallic materials against corrosion- Corrosion likelihood in soil - Part 7: General. 1) To be published. 1 EN IS0 12944-21998 3 Definitions For the purposes of this part of IS0 129
11、44, the following definitions apply in addition to those given in IS0 12944-1. NOTE - Some of the definitions have been taken from IS0 8044:1989, Corrosion of metals and alloys - Vocabulary, as indicated. 3.1 corrosivity: Ability of an environment to cause corrosion in a given corrosion system. IS0
12、80441 3.2 corrosion stresses: The environmental factors which promote corrosion. 3.3 corrosion system: System consisting of one or more metals and all parts of the environment which influence corrosion. IS0 8044) 3.4 climate: lhe weather prevailing at a given location or in a given area, as establis
13、hed statistically by meteorological parameters recorded over a prolonged period. 3.5 atmosphere: A mixture of gases, and normally also aerosols and particles, that surrounds a given object. 3.6 atmospheric corrosion: Corrosion with the Earths atmosphere at ambient temperature as the corrosive enviro
14、nment. IS0 80441 3.7 type of atmosphere: Characterization of the atmosphere on the basis of the corrosive agents present and their concentration. NOTE - The main corrosive agents are gases (especially sulfur dioxide) and salts (especially chlorides andor sulfates). 3.7.1 rural atmosphere: The atmosp
15、here prevailing in rural areas and small towns, without significant contamination by corrosive agents such as sulfur dioxide and/or chlorides. 3.7.2 urban atmosphere: The contaminated atmosphere prevailing in densely populated areas without significant industty. It has moderate concentrations of pol
16、lutants such as sulfur dioxide and/or chlorides. 3.7.3 industrial atmosphere: The atmosphere contaminated by corrosive pollutants from local and regional industry (mainly sulfur dioxide). 3.7.4 marine atmosphere: The atmosphere over and near the sea. NOTE - A manne atmosphere will extend a certain d
17、istance inland, depending on topography and prevailing wind direction. It is heavily polluted with sea-salt aerosols (mainly chlorides). 3.8 local environment: The atmospheric conditions prevailing around a constituent element of a structure. NOTE - These conditions determine the corrosivi category
18、and include both meteorological and pollution parameters. 3.9 micro-envlronment: The environment at the interface between a constituent element of a structure and its surroundings. The micro-environment is one of the decisive factors in the assessment of corrosion stresses. 3.10 time of wetness: The
19、 period during which a metal surface is covered by a film of electrolyte that is capable of causing atmospheric corrosion. Guidance values for time of wetness can be calculated from temperature and relative humidity by summing the hours during which the relative humidity is above 80 % and, at same t
20、ime, the temperature is above O OC. 2 4 Corrosion stresses due to the atmosphere, water and soil 4.1 Atmospheric corrosion Atmospheric corrosion is a process that takes place in a film of moisture on the metal surface. The moisture film may be so thin that it is invisible to the naked eye. The corro
21、sion rate is increased by the following factors: - an increase in relative humidity; - the occurrence of condensation (when the surface temperature is at or below the dew point); - an increase in the amount of pollution in the atmosphere (the corrosive pollutants can react with the steel and may for
22、m deposits on the surface). Experience has shown that significant corrosion is likely to take place if the relative humidity is above 80 Oh and the temperature above O 9C. However, if pollutants and/or hygroscopic salts are present, corrosion occurs at much lower humidity levels. The atmospheric hum
23、idity and air temperature in a particular region of the world will depend on the climate prevailing in that pari of the world. A brief description of the most important climates is given in annex A. The location of the constituent element of a structure also influences corrosion. Where structures ar
24、e exposed to the open air, climatic parameters such as rain and sunshine and pollutants in the form of gases or aerosols affect corrosion. Under cover, the climatic influences are reduced. Indoors, the effect of atmospheric pollutants is reduced, although a locally high corrosion rate caused by poor
25、 ventilation, high humidity or condensation is possible. For the estimation of the corrosion stresses, an appreciation of the local environment and the micro-environment is essential. Examples of decisive micro-environments are the underside of a bridge (particularly over water), the roof of an indo
26、or swimming pool, and the sunny and shady sides of a building. 4.2 Corrosion in water and soil Special care shall be taken when considering structures that are partly immersed in water or partly buried in soil. Corrosion under such conditions is often restricted to a small part of the structure wher
27、e the corrosion rate can be high. Exposure tests for estimating the corrosivity of water or soil environments are not recommended. However, different immersion/burial conditions can be described. 4.2.1 Structures immersed in water The type of water - fresh, brackish or salt - has a significant influ
28、ence on the corrosion of steel. Corrosivity is also influenced by the oxygen content of the water, the type and quantity of dissolved substances and the water temperature. Animal or vegetable growth can accelerate corrosion. Three different zones for immersion in water can be defined: - the underwat
29、er zone is the area which is permanently exposed to water; - the intermediate (fluctuating level) zone is the area in which the water level changes due to natural or artificial effects, thus giving rise to increased corrosion due to the combined impact of water and the atmosphere; - the splash zone
30、is the area wetted by wave and spray action which can give rise to exceptionally high corrosion stresses, especially with sea water. 3 EN IS0 12944-2:1998 4.2.2 Structures buried in soil Corrosion in soil is dependent on the mineral content of the soil and the nature of these minerals, and on the or
31、ganic matter present, the water content and the oxygen content. The corrosivity of soil is strongly influenced by the degree of aeration. The oxygen content will vary and corrosion cells may be formed. Where major steel structures such as pipelines, tunnels, tank installations, etc., pass through di
32、fferent types of soil, soils with differing oxygen contents, soils with differing ground water levels, etc., increased local corrosion (pitting) may occur due to formation of corrosion cells. For further details, see EN 12501 -1. Different types of soil and differences in soil parameters are not con
33、sidered as classification criteria in this pari of IS0 12944. 4.3 Special cases For the selection of a protective paint system, special stresses to which a structure is subjected and special situations in which a structure is located shall also be taken into account. Both the design as well as the u
34、se of the structure may lead to corrosion stresses not taken into consideration in the classification system given in clause 5. Examples of such special cases are given in annex B. 5 Classification of environments 5.1 Atmospherlc-corrosivity categories 5.1.1 For the purposes of IS0 12944, atmospheri
35、c environments are classified into six atmospheric-corrosivity categories: C1 verylow c2 low C3 medium C4 high C5-I very high (industrial) C5-M very high (marine) 5.1.2 To determine corrosivity categories, the exposure of standard specimens is strongly recommended. Table 1 defines the corrosivity ca
36、tegories in terms of the mass or thickness loss of such standard specimens made of low- carbon steel andor zinc after the first year of exposure. For details of standard specimens and the treatment of the specimens prior to and after exposure, see IS0 9226. Extrapolation of the mass or thickness los
37、ses to one year from shorter exposure times, or back-extrapolation from longer times, will not give reliable results and is therefore not permitted. The mass or thickness losses obtained for steel and zinc specimens may sometimes give different categories. In such cases, the higher corrosivity categ
38、ory shall be taken. If it is not possible to expose standard specimens in the actual environment of interest, the corrosivity category may be estimated by simply considering the examples of typical environments given in table 1. The examples listed are informative and may occasionally be misleading.
39、 Only the actual measurement of mass or thickness loss will give the correct classification. 8 NOTE- Corrosiviiy categories can also be estimated by considering the combined effect of the following environmental factors: yearly time of wetness, yearly mean concentration of sulfur dioxide and yearly
40、mean deposition of chloride (see IS0 9223). 4 STD-BSI BS EN IS0 L2744-2-ENGL L778 E Lb24bb7 07382b7 Bb = Mass loss per unit surfadthickness loss (after first year of exposure) EN IS0 12944-2:1998 - Examples of typical environments in a temperate climate (informative only) Table 1 - Atmospheric-corro
41、sivity categories and examples of typical environments Cim s 1,3 9/m2 Cim s 0,7 ?z 0,l - Heated buildings with clean atmospheres, e. offices, shops, sckools, hotels. Low-cari Mass loss iery low 0,l to 0,7 0,7 to 2,l 2,l to 4,2 10 to 200 200 to 400 Atmospheres with low Unheated buildings level of pol
42、lution. where condensation Mostly rural areas. Urban and industrial Production rooms atmospheres, with high humidity and moderate sulfur some air pollution, ag. dioxide pollution. food- rocessing plants Coastal areas with low Iaunges, breweries, salinity. dairies. Industrial areas and Chemical plant
43、s, coastal areas with swimmin pools, moderate salinity. coastal shp- and may occur, e.g. depots sports halls. boatvards. medium Industrial areas with Buildings or areas high humidity and with almost permaneni aggressive condensation and with atmosphere. high pollution. Coastal and offshore Buildings
44、 or areas areas with high with almost permanen salinity. condensation and with high pollution. c4 high C5-I ve high (in7ustfiai) 400 to 650 650 to 1 500 C5-M very high (marine) 650 to 1 SOC n steel Zinc Exterior Thickness 1 Massloss I ThiLcless 1 loss Category Iml lm2 lm3 Interior Environment Exampl
45、es of environments and structures Fresh water Sea or brackish water Harbour areas with structures like sluice gates, locks, jetties; Soil River installations, hydro-electric power plants offshore structures Buried tanks, steel piles, steel pipes 1.3 to 25 25 to 50 50 to 80 0,7 to 5 5to15 15 to 30 80
46、 to 200 30 to 60 80 to 200 30 to 60 -I- 4,2 to 8,4 4,2 to 8,4 I NOTES 1 The loss values used for the corrosivity categories are identical to those given in IS0 9223. 2 In coastal areas in hot, humid zones, the mass or thickness losses can exceed the limits of category C5-M. Special precautions mu th
47、erefore be taken when selecting protective paint systems for structures in such areas. 5.2 Categories for water and soil For structures immersed in water or buried in soil, corrosion is normally local in nature and corrosivity categories are difficult to define, However, for the purpose of this Inte
48、rnational Standard, various environments can be described. In table 2, three different environments are given together with their designations. See 4.2 for more detail. NOTE - In many such situations, cathodic protection is involved and this should be borne in mind. 5 - STD-BSI BS EN IS0 L2744-2-ENG
49、L 1998 Lb24bb7 0738270 582 W Type of climate EN IS0 12944-21998 Mean value of the annual extreme values Highest Calculated time of Low temperature High temperature temperature with wetness at RH 80X RH95% and temperature O C Annex A (informative) Cold - 50 + 32 + 20 150 to 2 500 Cold temperate - 33 +34 + 23 Warm temperate - 20 + 35 + 25 Warm dry - 20 + 40 + 27 Mild warm dry -5 +40 + 27 10 to 1 600 I Extremely warm dtv +3 + 55 + 28 2 500 to 4 200 Climatic conditions Usually, only general conclusions as to the likely corrosion behaviour can be drawn from the type of c
