NB/T 31006-2011 English PDF (NB/T31006-2011)

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NB/T 31006-2011: Technical code for anticorrosion of offshore wind farm steel structures
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...