The key role and technical requirements of steel pipes in nuclear power plant construction

With the continuous optimization of the global energy structure,nuclear energy,as a clean,efficient and stable energy form,is being listed as the focus of future energy development by more and more countries.In the construction of nuclear power plants,steel pipes,as the core component of the pipeline system,are responsible for transmitting cooling water,steam,exhaust gas and other media.Their quality and performance are directly related to the operational safety and service life of nuclear power plants.

In such a demanding industrial scenario,steel pipes not only need to have extremely strong mechanical properties and high and low temperature resistance,but also must cope with the harsh corrosive environment during long-term service.Therefore,pipeline anti-corrosion coating technology has become one of the key means to ensure the stable operation of nuclear power plant steel pipe systems.

1.Application background of steel pipes for nuclear power plants

The piping system inside a nuclear power plant is distributed in multiple functional areas such as the reactor building,auxiliary building,cooling system,steam turbine power generation system,etc.There are many types of steel pipes involved and the use environment is also extremely complex.Common steel pipe applications include:

Main steam pipe

Reactor cooling circuit

Condenser water inlet and outlet system

Polluted wastewater treatment system

High pressure water spray system

The steel pipes in these systems have to withstand multiple tests such as high temperature,high pressure,radiation,chemical corrosion,erosion,etc.for a long time during operation,so they must have excellent corrosion resistance,wear resistance,pressure resistance and structural stability.

2.Technical requirements for steel pipes for nuclear power plants

Under the guidance of"ASME,ISO,GB and other international nuclear power standards",steel pipes used in nuclear power projects usually need to meet the following key technical requirements:

Material standards:such as ASTM A106,A335,API 5L,EN 10216,etc.

High dimensional accuracy:including outer diameter,tolerance,and wall thickness must be strictly controlled;

Excellent mechanical properties:yield strength,tensile strength,impact toughness,etc.must meet nuclear power standards;

High corrosion resistance:especially chloride ion stress corrosion cracking(SCC)and hot corrosion;

Good welding performance:Pipelines are extensively welded during installation,so the weld performance must be guaranteed;

No radioactive pollution:Raw materials and processing procedures must meet nuclear safety environment requirements.

3.Corrosion Challenges Faced by Nuclear Power Steel Pipes

The operating environment of nuclear power plants is rather special,and the types of corrosion are diverse,mainly including:

Uniform corrosion:Oxidation occurs due to long-term contact of the pipeline with cooling water,waste liquid,etc.;

Pitting and crevice corrosion:small corrosion holes are formed at the connection parts or deposition areas;

Stress corrosion cracking(SCC):It is more likely to occur in high temperature and high pressure environments where chloride ions exist;

Microbiologically Influenced Corrosion(MIC):Common in cooling systems or shutdown systems;

Irradiation corrosion:changes in metal structure and intensified corrosion caused by neutron radiation.

Therefore,in order to prevent the occurrence of the above-mentioned types of corrosion,it is imperative to adopt effective anti-corrosion coating technology.

4.Solutions for anti-corrosion coating technology

In response to the stringent anti-corrosion requirements of nuclear power plants for steel pipes,the following coating technologies are currently available:

●Inorganic Zinc Coating

Advantages:

Has excellent cathodic protection performance;

Strong temperature resistance,can withstand up to 400°C;

It can be used in high temperature areas such as flue gas ducts and steam systems.

Applicable scenarios:main steam pipe,exhaust pipe outer wall.

●Polyurethane Coating

Advantages:

Strong wear resistance and aging resistance;

Good adhesion,suitable for complex curved surfaces;

The construction is simple and the curing time is short.

Applicable scenarios:cooling water system,circulating water pipe.

●Epoxy coating(Fusion Bonded Epoxy,FBE)

Advantages:

Excellent resistance to chemical corrosion;

The construction is mature and the process is controllable;

Suitable for buried or underwater pipelines.

Applicable scenarios:nuclear power plant external water pipes,buried water supply pipelines.

●Glass Flake Coating

Advantages:

High corrosion resistance,especially suitable for acid and alkali media;

Form a dense barrier layer to prevent medium penetration;

Long service life and low maintenance cost.

Applicable scenarios:wastewater treatment system,sewage pool steel liner.

●Thermal Spray Coating

Advantages:

High temperature metal zinc aluminum or stainless steel powder spraying;

Strong adhesion and good radiation resistance;

Excellent resistance to salt spray,acid and alkali environments.

Applicable scenarios:areas affected by radiation and areas in special contact with chemical media.

5.Anti-corrosion process and quality control

The construction of anti-corrosion coatings for steel pipes used in nuclear power plants must meet strict process specifications.The main processes include:

Surface treatment:sandblasting to remove rust,reaching Sa2.5 or Sa3 standard;

Primer coating:Use inorganic zinc or epoxy primer;

Intermediate layer and topcoat construction:Use polyurethane or glass flakes;

Coating thickness control:multiple tests are carried out according to design requirements;

Adhesion test:Use the cross-hatch method or pull-off method to test the adhesion of the coating;

Curing and maintenance:Control the ambient temperature and humidity to avoid coating cracking,bubbles and other problems.

VI.International quality system and certification requirements

The anti-corrosion coating of nuclear power steel pipes must not only meet technical standards,but also comply with international quality standards and certification requirements of third-party organizations:

ISO 12944:Design standard for industrial anti-corrosion coatings;

ASME NQA-1:Nuclear power equipment quality assurance system;

ISO 9001/ISO 14001/OHSAS 18001:Management,environment and occupational safety system certification;

PED/EN 10204 3.2:EU Pressure Equipment Directive,inspection report requirements;

Third-party certification and audits such as NQA,Lloyd's,SGS,and TÜV.

7.Future Development Trends

With the development of the fourth-generation nuclear power plants and the promotion of small modular reactors(SMRs),the requirements for steel pipe anti-corrosion technology are also increasing.The future anti-corrosion coating technology will develop in the following directions:

Nano coating materials:improve anti-permeability and anti-corrosion performance;

Self-repairing coating:once damaged,it can repair itself and extend the service life;

Environmentally friendly solvent-free coating:reduces VOCs emissions and complies with the green manufacturing concept;

Intelligent monitoring system:real-time monitoring of pipeline coating health status and assisting operation and maintenance decision-making.

Conclusion:#Anti-corrosion steel pipe#

In a highly demanding engineering system such as a nuclear power plant,steel pipe anti-corrosion coating technology has been upgraded from an"option"to a"necessary configuration".Through the scientific selection of anti-corrosion materials,standardized construction processes,strict quality control and continuous technological innovation,the service life of steel pipes in harsh environments can be greatly improved,providing a solid guarantee for the safe operation of nuclear power plants.

Selecting high-quality steel pipes and reliable anti-corrosion solutions is the key behind the success of every nuclear power project.

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