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GB/T 30790.2-2014 PDF in English


GB/T 30790.2-2014 (GB/T30790.2-2014, GBT 30790.2-2014, GBT30790.2-2014)
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GB/T 30790.2-2014: PDF in English (GBT 30790.2-2014)

GB/T 30790.2-2014
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 87.020
G 50
Paints and varnishes – Corrosion protection of
steel structures by protective paint systems -
Part 1. Classification of environments
(ISO 12944-2.1998, MOD)
ISSUED ON. JULY 8, 2014
IMPLEMENTED ON. DECEMBER 1, 2014
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine of the People's Republic of China;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Corrosion stresses due to the atmosphere, water and soil ... 8
5 Classification of environments ... 10
Annex A (Informative) Climatic conditions ... 13
Annex B (Informative) Special cases ... 14
Annex C (Informative) Technical differences between this Part and ISO
12944-2.1998 and their reasons ... 17
Bibliography ... 18
Foreword
GB/T 30790, Paints and varnishes – Corrosion protection of steel structures by
protective paint systems, comprises 8 parts.
-- Part 1. General introduction;
-- Part 2. Classification of environments;
-- Part 3. Design considerations;
-- Part 4. Types of surface and surface preparation;
-- Part 5. Protective paint systems;
-- Part 6. Laboratory performance test methods;
-- Part 7. Execution and supervision of paint work;
-- Part 8. Development of specification for new work and maintenance.
This Part is Part 2 of GB/T 30790.
This Part was drafted in accordance with the rules given in GB/T 1.1-2009.
This Part was redrafted by adopting ISO 12944-2.1998, Paints and varnishes –
Corrosion protection of steel structures by protective paint systems – Part 2.
Classification of environments.
This Part has technical differences from ISO 12944-2.1998. The clauses concerning
these differences are marked with vertical single lines (|) in the page margins. Annex
C gives the list of corresponding technical differences and their reasons.
This Part was proposed by China Petroleum and Chemical Industry Federation.
This Part shall be under the jurisdiction of National Technical Committee 5 on Paints
and Pigments of Standardization Administration of China (SAC/TC 5).
The drafting organizations of this Part. CNOOC Changzhou Paint and Chemicals
Research Institute, AkzoNobel Protective Paint (Suzhou) Co., Ltd., Beijing Hongshi
Paint Co., Ltd., Jotun Paint (Zhangjiagang) Co., Ltd., Zhejiang Yu Tong New Materials
Co., Ltd., Hempel (China) Co., Ltd., COSCO Kansai Paint and Chemicals Co., Ltd.,
Zhejiang Feijing Paint Co., Ltd., Beijing BIAM New Materials and Technological
Engineering Co., Ltd., Shandong Puntium Paint Co., Ltd., Yejian New Material Co.,
Ltd., Shenzhen Grandland Decoration Group Co., Ltd.
The main drafters of this Part. Huang Ning, Liu Jinwei, Li Yunde, Yang Yaliang, Wang
Paints and varnishes - Corrosion protection of
steel structures by protective paint systems -
Part 2. Classification of environments
1 Scope
1.1 This Part of GB/T 30790 deals with the classification of the principal environments
to which steel structures are exposed, and the corrosivity of these environments. It
-- defines atmosphere-corrosivity categories, based on mass loss (or thickness loss)
by standard specimens, and describes typical natural atmospheric environments
to which steel structures are exposed, giving advice on the estimation of the
corrosivity;
-- 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.
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 does not deal with the classification of those environments that consist
of special atmospheres (for example those in and around chemical and metallurgical
plants).
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition dated applies to this document. For
undated references, the latest edition of the referenced documents (including all
amendments) applies to this document.
GB/T 19292.1, Corrosion of metals and alloys – Corrosivity of atmospheres –
Classification (GB/T 19292.1-2003, ISO 9223.1992, IDT)
dew point);
-- an increase in the amount of pollution in the atmosphere (the corrosive pollutants
can react with the steel and may form deposits on the surface).
Experience has shown that significant corrosion is likely to take place if the relative
humidity is above 80% and around the temperature above 0°C. However, if pollutants
and/or hygroscopic salts are present, corrosion occurs at much lower humidity levels.
The atmospheric humidity and air temperature in a particular region of the world will
depend on the climate prevailing in that part 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 are 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 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 indoor 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 where 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 influence 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 underwater 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
Annex B
(Informative)
Special cases
B.1 Special situations
B.1.1 Corrosion inside buildings
Corrosion stresses on steel structures located inside buildings sheltered from the
outside environment are generally insignificant.
If the interior of the building is only partly sheltered from the outside environment, the
corrosion stresses may be assumed to be the same as those associated with the type
of atmosphere surrounding the building.
The effect of corrosion stresses dur to the climate inside the building can be
considerably intensified by the use to which the building is put, and these stresses
should be dealt with as special stresses (see Clause B.2). Such stresses may occur in
indoor swimming pools with chlorinated water, livestock buildings and other special-
purpose buildings.
Cooler areas on structures can be subjected to higher corrosion stresses as a result
of seasonal formation of condensation.
In cases where surfaces are wetted by electrolytes, even if such wetting is only
temporary (for example in the case of saturated building materials), particularly
stringent corrosion requirements are necessary.
B.1.2 Corrosion in box members and hollow components
Hollow components that are hermitically sealed and thus inaccessible are not
subjected to any internal corrosion, whereas tightly sealed casings which are opened
occasionally are subject to small corrosion stressed.
The design of sealed hollow components and box members should ensure their
airtightness (e.g. no discontinuous welds, tightly bolted joints). Otherwise – depending
on the outside temperature – moisture from precipitation or condensation may be
drawn in and retained. If this is likely to happen, the internal surfaces have to be
protected. Note that condensation is often observed even in boxes which have been
designed with tightly sealed casings.
Corrosion must be expected inside box members and hollow components that are not
c) severe. high mechanical stresses due, for example, to
-- solid debris, sand, gravel, shingle or ice entrained in large quantities by fast-
flowing water over horizontal or inclined surfaces,
-- dense growth (animal or vegetable), particularly if, for operational reasons, it
must be removed mechanically from time to time.
B.2.3 Stresses due to condensation
If the temperature at the surface of a structure remains below the dew point for several
days, the condensation produced will represent a particularly high corrosion stress,
especially if such condensation may be expected to recur at regular intervals (for
example in water works, on cooling-water pipes).
B.2.4 Stresses due to medium or high temperatures
In this Part, medium temperatures are those between + 60°C and + 150°C, and high
temperatures those between + 150°C and + 400°C. Temperatures of this magnitude
only occur under special conditions during construction or operation (for example
medium temperatures occur during the laying of asphalt on roads, and high
temperatures occur in chimneys made of sheet steel, flue gas ducts, or gas off-take
mains in coking works).
B.2.5 Increased corrosion due to combination of stresses
Corrosion may develop more quickly on surfaces exposed simultaneously to
mechanical and chemical stresses. This applies particularly to steel structures near
roads on which grit and salt have been spread. Passing vehicles will splash salty water
and throw up grit on to parts of such structures. The surface is then exposed to
corrosion stresses from the salt and at the same time to mechanical stresses due to
the impact of grit.
Other parts of the structure will be wetted by salt spray. This affects, for example, the
underside of flyovers above roads that have been salted. The spray zone is generally
assumed to extend to a distance of 15 m from the road concerned.
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.