NB/T 31006-2011 PDF English
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Technical Code for Anticorrosion of Offshore Wind Farm Steel Structures
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NB/T 31006-2011: PDF in English (NBT 31006-2011) NB/T 31006-2011
NB
ENERGY INDUSTRY STANDARD OF
THE PEOPLE’S REPUBLIC OF CHINA
ICS 27.180
F 11
Record No.: 33242-2011
Technical Code for Anticorrosion of Offshore Wind
Farm Steel Structures
ISSUED ON: AUGUST 06, 2011
IMPLEMENTED ON: NOVEMBER 01, 2011
Issued by: National Energy Administration
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative References ... 4
3 Terms and Definitions ... 6
4 General ... 8
5 Anti-Corrosion Measures ... 10
6 Anti-Corrosion Requirements ... 11
7 Test and Acceptance ... 24
Appendix A (Informative) Calculation of Dew Point ... 29
Appendix B (Informative) Calculation of the Common Protection Current
Density Value of the Uncoated Steel and the Protection Current Density of
Coated Steel ... 30
Appendix C (Informative) Calculation Formula of Cathodic Protection Design
... 31
Appendix D (Informative) Test Method for the Adhesive Strength of the Thermal
Spraying Coating ... 36
Technical Code for Anticorrosion of Offshore Wind
Farm Steel Structures
1 Scope
This Standard specifies the surface pretreatment and coating protection, thermal
spraying metal protection, cathodic protection common anti-corrosion methods and
related technical requirements of offshore wind farm steel structures (mainly including
fixed steel support structures of wind turbine generator system and substations).
This Standard is applicable to the anti-corrosion design, construction, acceptance and
operation and maintenance of offshore wind farm steel structures.
2 Normative References
The following documents are essential to the application of this document. For the
dated documents, only the versions with the dates indicated are applicable to this
document; for the undated documents, only the latest version (including all the
amendments) are applicable to this document.
GB/T 1740 Methods of Test for Resistance to Heat and Humidity of Paint Films
GB/T 1771 Paints and Varnishes－Determination of Resistance to Neutral Salt
Spray
GB/T 1865 Paints and Varnishes - Artificial Weathering and Exposure to Artificial
Radiation-Filtered Xenon-Arc Radiation
GB/T 4948 Sacrificial Anode of Al-Zn-In Series Alloy
GB/T 4949 Chemical Analysis Methods for Sacrificial Anodes of Al-Zn-In System
Alloy
GB/T 4950 Sacrificial Anode of Zn-Al-Cd Alloy
GB/T 4951 Chemical Analysis Methods for Sacrificial Anodes of Zn-Al-Cd Alloy
GB/T 4956 Non-Magnetic Coatings on Magnetic Substrates – Measurement of
Coating Thickness - Magnetic Method
GB/T 5210 Paints and Varnishes - Pull-off Test for Adhesion
GB/T 6462 Metallic and Oxide Coatings - Measurement of Coating Thickness -
Microscopical Method
GB 6514 Safety Code for Painting - Safety, Ventilation and Air Clean-up for
Painting Process
GB/T 7387 Requirements for Marine Reference Electrode
GB/T 7388 Requirements for Marine Auxiliary Anode
GB/T 7788 General Specification for Anodic Shield Coating of Ship and Marine
Engineering
GB 8923 Rust grades and Preparation Grades of Steel Surfaces before
Application
GB/T 9274 Paints and Varnishes - Determination of Resistance to Liquids
GB/T 10610 Geometrical Product Specifications (GPS) - Surface Texture: Profile
Method - Rules and Procedures for the Assessment of Surface Texture
GB 11375 Metallic and Other Inorganic Coatings - Thermal Spraying - Safe
Practices
GB/T 12608 Thermal Spraying - Wires, Rods and Cords for Flame and Arc
Spraying -Classification and Technical Supply Condition
GB 12942 Safety Code for Painting - Technical Requirements of Safety for
Working in Confined Spaces
GB/T 13288 The Assessment of Profile Grades of Steel Surface before Application
of Paint and Related Products－Comparator
GB/T 13748 Chemical Analysis Methods of Magnesium and Magnesium Alloys
GB/T 17731 Magnesium Alloy Sacrificial Anode
GB/T 17848 Test Methods for Electrochemical Properties of Sacrificial Anodes
GB/T 17850.1 Preparation of Steel Substrates before Application of Paints and
Related Products - Specifications for Non-Metallic Blast-Cleaning Abrasives -
General Introduction and Classification
GB/T 18570.3 Preparation of Steel Substrates before Application of Paints and
Related Products - Tests for the Assessment of Surface Cleanliness - Part3:
Assessment of Dust on Steel Surface Prepared for Painting (Pressure-Sensitive
Tape Method)
A method of using a heat source to melt, semi-melt or soften metallic materials and
spray them on the surface of the substrate at a certain speed to form a coating.
3.6 cathodic protection
Technology to control the electrochemical corrosion of metals through cathodic
polarization. Cathodic protection has sacrificial anode method and impressed current
method.
3.7 Surface preparation
In order to improve the bonding force between the coating and the substrate and the
anti-corrosion effect, the surface of the substrate is treated by mechanical or chemical
methods before application to achieve measures that meet the application
requirements.
3.8 Adhesion
The firmness of the bond between the paint film and the coated surface (through
physical and chemical action).
3.9 Coat sealant
A material that is used to penetrate and seal the pores of thermal sprayed metal
coatings.
3.10 Flame spraying
A thermal spraying method that uses the flame to combust after mixing combustible
gas and combustion-supporting gas as the heat source.
3.11 Arc spraying; electric spraying
A thermal spraying method in which the arc generated between two consumable
electrode wires forming coating materials is used as a heat source, and the melting
consumable electrode wires is added, and sprayed onto the substrate by compressed
gas to form a coating.
3.12 Minimum local thickness
The minimum value of the local thickness of the thermal spray coating that is measured
on the main surface of a workpiece.
3.13 Adhesive strength
The strength of the bond between the thermal spraying metal coating and the substrate.
3.14 Impressed current
U2 – highest astronomical tide, in m;
U3 – foundation settlement, in m.
Where:
L1 – 0.4H1/3, H1/3 is the 1/3 effective wave height with return period of 100 years,
in m;
L2 – lowest astronomical tide, in m.
c) The area below the splash zone is the full-immersion zone, including two parts in
the water and in the sea mud.
d) The internal area is a closed part that is not in contact with the outside seawater.
4.3 The offshore wind farm steel structures shall be simple in structural design, and
corrosion-resistant materials shall be selected reasonably.
4.4 The offshore wind farm steel structures may adopt but not limited to anti-corrosion
measures such as increased corrosion allowance, coating protection, thermal spraying
metal coating protection, cathodic protection, and combined cathodic protection and
coating protection, etc.
4.5 The design working life of the anti-corrosion system shall consider the design
working life of the wind turbine generator system, and generally it should not be less
than 15 years.
4.6 Instruments, equipment, and measuring tools for testing shall be certified by
metrology and within the validity period of the verification.
4.7 The corrosion status and anti-corrosion effect of the offshore wind farm steel
structures shall be regularly patrolled for inspection and tested. The patrolling-
inspection cycle shall be three months; and the content mainly includes the aging
damage of the coating in the atmosphere area, the splash area and the structural
corrosion, and the cathodic protection potential in the full-immersion area. The regular
test cycle is generally 5 years; and the test cycle may be shortened appropriately on
the basis of the corrosion status obtained from the patrolling-inspection result. The test
shall find out the degree of structural corrosion, evaluate the effect of the anti-corrosion
system, estimate the working life of the anti-corrosion system, and put forward
treatment measures and opinions.
a) Use a scraper or a grinder to remove welding spatter, and rough welds need to
be polished to smooth;
b) The sharp edges shall be polished by a grinding wheel into a rounded corner with
a radius of curvature greater than 2mm;
c) Surface stacking, cracks, inclusions, etc. need to be polished and conducted
repairing welding if necessary.
6.2.4 The degreasing requirements include: the oil stains on the surface shall adopt
low-pressure spray cleaning or soft brush scrubbing; and use the clean fresh water to
wash away all residues. Flame treatment or lye cleaning may also be used; and lye
cleaning shall be rinsed with fresh water to neutrality. Small area of oily dirt may be
scrubbed with solvent.
6.2.5 The desalination requirements include: the soluble chloride content on the steel
surface before rust removal shall be no greater than 70mg/m2; when it exceeds the
standard value, use the high-pressure clean fresh water to wash. When the steel is
confirmed not to be exposed to the chloride ion environment, the surface soluble salt
test may not be performed; when it is not completely confirmed, the first-time test shall
be performed.
6.2.6 The rust removal requirements include:
a) Abrasive blast cleaning method shall be used to remove rust; and the parts that
are not easy to spray rust may be removed by hand or power tools.
b) Rust removal shall be performed under environmental conditions where the
relative humidity of the air is no higher than 85% and the surface temperature of
the steel is at least 3°C higher than the dew point. Refer to Appendix A for dew
point calculation. The temperature and humidity of the construction environment
shall be measured by a temperature and humidity meter; and the number of
measurements per work shift shall be no less than 3.
c) Abrasive requirements include:
1) The metallic abrasive used for blast cleaning shall meet the requirements of
GB/T 18838.1;
2) Non-metallic abrasives for blast cleaning shall meet the requirements of GB/T
17850.1;
3) According to the requirements of surface roughness, select the abrasive with
appropriate particle size.
d) Uncoated steel surface and steel surface preparation level requirements after
6.3.4 Application requirements
6.3.4.1 Application environment
a) No application is allowed when the relative humidity is greater than 85% and the
surface temperature of the coated substrate is 3°C lower than the dew point. If
the paint technical requirements are otherwise specified, the construction shall
be carried out according to the specified requirements. Refer to Appendix A for
dew point calculation;
b) The temperature and humidity of the construction environment shall be measured
by a temperature and humidity meter, and the number of measurements per work
shift shall be no less than 3;
c) The application operation shall ensure the cleanliness of the surrounding
environment, and avoid the unseasoned coating from being polluted by dust.
6.3.4.2 Paint preparation and use time
a) The Paint shall be fully stirred and evenly mixed before construction; and electric
or pneumatic devices may be used for stirring. For two-component or multi-
component paint, the components should be stirred evenly first, and then mixed
evenly after being prepared in proportion;
b) The mixed paint shall be cured in the time specified by the product technical
requirements;
c) The use time of the paint shall be implemented according to the applicable period
specified in the product technical requirements;
d) The working environment temperature shall be higher than 5°C.
6.3.4.3 Coating process
a) High-pressure airless spraying shall be used for large-area spraying; and air
spraying or brushing may be used for slender, small-area and complex-shaped
components;
b) The safety of the application process and its ventilation and purification shall
comply with the relevant provisions of GB 6514. The safety protection during
application operations in a limited space shall comply with the provisions of GB
12942.
6.3.4.4 Coating interval time
The interval time of each coating shall meet the technical requirements of the material
supplier. When the maximum recoating interval time is exceeded, it needs to be applied
6.4.2.4 The coat sealant should use an active paint or other suitable paint with low
viscosity, easy penetration, high solid content in the film, and capable of phosphating
the surface of the thermal spraying coating.
6.4.2.5 For the application paint on the surface of the thermal spraying coating, the
intermediate layer and the surface layer paint may be selected according to Table 2.
The thickness of the paint coating should be 240μm~320μm.
6.4.3 Construction requirements
6.4.3.1 The working environment temperature of thermal spraying shall be higher than
5°C or the substrate surface temperature shall be at least 3°C higher than the dew
point. Refer to Appendix A for dew point calculation. The temperature and humidity of
the construction environment shall be measured by a temperature and humidity meter;
and the number of measurements per work shift shall be no less than 3.
6.4.3.2 The thickness of the thermal spraying coating shall be uniform. Two or more
coatings shall be covered by perpendicular and crossing methods. The thickness of a
single layer should not exceed 100μm.
6.4.3.3 Flame spraying or arc spraying may be used for thermal spraying of zinc and
zinc alloy; and arc spraying should be used for thermal spraying of aluminum and
aluminum alloy.
6.4.3.4 After the thermal spraying metal, it shall be sealed or applied; and the longest
should not exceed 4h.
6.4.3.5 Thermal spraying operators shall be assessed in accordance with the
provisions of GB/T 19824; and the operational safety of thermal spraying shall meet
the requirements of GB 11375.
6.4.3.6 Refer to 6.3.4 for the construction requirements for surface paint application of
thermal spraying coating.
6.4.3.7 After transportation and installation, the damaged part of the coating shall be
repaired according to the original process. When conditions are not available, thermal
spraying zinc and zinc alloy coatings may be repaired by zinc-rich primer; and thermal
spraying aluminum and aluminum alloy coatings may be repaired by aluminum powder
primer. The paint coating is repaired by the same paint.
6.4.4 Coating quality
6.4.4.1 Appearance
The surface of the thermal spraying coating shall be uniform, free of pores or exposed
spots on the substrate; there are no weakly attached molten metal particles or defects
6.5.3 Sacrificial anode system
6.5.3.1 Sacrificial anode material
a) Commonly-used sacrificial anode materials are aluminum-based, zinc-based and
magnesium-based alloys. Aluminum alloy is suitable for sea water and brackish
water environment; zinc alloy is suitable for sea water, brackish water and sea
mud environment; and magnesium alloy is suitable for fresh water and brackish
sea environment with high resistivity;
b) The properties of aluminum alloy, zinc alloy and magnesium alloy shall meet the
requirements of GB/T 4948, GB/T 4950, and GB/T 17731, respectively.
6.5.3.2 Sacrificial anode calculation
Refer to Appendix C for the calculation method of sacrificial anode design.
6.5.3.3 Sacrificial anode arrangement
The arrangement of the sacrificial anode shall make the surface potential distribution
of the protected steel structure uniform; and the installation position shall meet the
following requirements.
a) The sacrificial anode shall not be installed in the high stress and high fatigue area
of the steel structure;
b) The top elevation of the sacrificial anode shall be at least 1.0m below the lowest
water level; and the bottom elevation shall be at least 1.0m above the mud
surface.
6.5.3.4 Sacrificial anode construction
a) The sacrificial anode shall be short-circuited with the steel structure through the
iron core. The iron core structure shall be able to ensure electrical connection
with the anode body during the entire service life, and be able to withstand the
load imposed by its own weight and the environment;
b) The connection method shall adopt welding, or cable connection and mechanical
connection. When mechanical connection is adopted, it shall be ensured that the
connection resistance between the sacrificial anode and the protected steel
structure during the service life is no greater than 0.01Ω;
c) When the welding method is adopted for connection, the welding shall be firm,
the weld seam is full, and there is no false welding. When the sacrificial anode is
used for underwater welding, it shall be carried out by an underwater electric
welder who has obtained a qualified certificate;
environmental media, etc. The technical conditions of the reference electrode
shall comply with the provisions of GB/T 7387;
b) When using constant potential control, each power supply device shall be
equipped with at least one reference electrode for control. When using constant
current control, each power supply device shall be equipped with at least one
reference electrode for measurement;
c) The reference electrode shall be installed on the surface of the steel structure
closer and farther away from the auxiliary anode.
6.5.4.4 Cable
a) All cables shall be suitable for the use environment, and corresponding protection
measures shall be taken to meet the requirements of long-term use;
b) Copper core cables shall be used for auxiliary anode cables and cathode cables,
and shielded cables shall be used for control reference electrode cables;
c) The cross-sectional area of the cable is determined according to the allowable
voltage drop and mechanical strength of the cable;
d) The auxiliary anode, reference electrode and cable joints, as well as the steel
structure and cable joints shall be sealed and waterproof; and the joints between
the cables shall be sealed, waterproof and not be used in water;
e) The cathode cable and measurement cable must not be shared.
6.5.4.5 Anode shielding layer
In order to improve the potential distribution of the steel structure, an anode shielding
layer may be provided; and the performance of the anode shielding layer shall meet
the requirements of GB/T 7788.
6.5.4.6 Monitoring equipment
a) The monitoring equipment shall be able to adapt to the environment. When
outdoor arrangement is adopted, its protective casing shall be able to resist the
erosion of sea water splash, salt spray, rain water, ultraviolet rays and marine
corrosive media; and the connection point of measuring lead and instrument
shall be insulated and sealed.
b) The monitoring equipment shall have basic functions such as measuring and
displaying the protection potential of the steel structure, the output current and
output voltage of the power supply equipment; and if possible, it shall have the
functions of long-distance telemetry, remote control, analysis and evaluation.
Figure 1 – Distribution of Measuring Points in the 10cm2 Reference Area
7.3.3.3 In order to determine the minimum local thickness of the thermal spraying
coating, the coating thickness may be measured at the possible thinnest part.
7.3.3.4 The number of reference surfaces shall be determined so that the total area of
the reference surface is no less than 5% of the effective surface area; and the
reference surface shall be evenly distributed on the entire effective surface.
7.3.4 Adhesive strength of thermal spraying coating
The adhesive strength of the thermal spray coating may be tested qualitatively in
accordance with Appendix D, or quantitatively tested in accordance with ISO 16276-1.
7.4 Cathodic protection
7.4.1 Electrical connection
Visually inspect the appearance of all the electrical connection points of the cathodic
protection; and conduct sampling test against the electrical connection resistance.
7.4.2 Cathodic protection potential
Test the cathodic protection potential of each unit component; and the distribution of
test points shall be representative.
7.4.3 Sacrificial anode system
7.4.3.1 Sacrificial anode performance
a) The chemical composition of aluminum alloy, zinc alloy and magnesium alloy
sacrificial anodes may be carried out according to the provisions of GB/T 4949,
GB/T 4951 and GB/T 13748, respectively;
b) The electrochemical performance of zinc alloy, aluminum alloy and magnesium
alloy sacrificial anodes shall be carried out in accordance with GB/T 17848;
c) The contact resistance of the sacrificial anode shall be carried out in accordance
with the provisions of GB/T 4948 or GB/T 4950;
d) The surface quality, shapes, dimensions and weight of aluminum alloy, zinc alloy
and magnesium alloy sacrificial anodes shall be carried out in accordance with
GB/T 4948, GB/T 4950 and GB/T 17731, respectively.
7.4.3.2 Sacrificial anode construction
a) When the sacrificial anodes are constructed on the water, the construction quality
of all sacrificial anodes shall be visually inspected;
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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