Nuclear-Grade 304NG/316NG Seamless Coil Tube — Primary Loop Main Pump Seal Cooling System

Product Overview

This product is a precision-engineered stainless steel coil tube (盘管 / Coil Tube) specifically designed for the Primary Loop Main Pump Seal Cooling System in pressurized water reactor (PWR) nuclear power plants. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube serves as a critical component within the primary coolant circuit, responsible for dissipating heat generated at the mechanical seals of the reactor coolant pumps (RCPs). The tube must operate continuously under demanding conditions including borrowed acid water (boric acid water) coolant at 300 °C and 15 MPa, within a high-neutron-flux irradiation environment. Any failure in this component can compromise the integrity of the primary containment boundary, making material purity, metallurgical quality, and dimensional accuracy of paramount importance.

This product falls under the application classification of Nuclear Power (核电) within the broader Power & Energy (电力能源) sector, and is catalogued as item No. 125 in the manufacturer's product registry.

Material & Properties

The coil tube is fabricated from two nuclear-grade austenitic stainless steel grades, both of which are specifically qualified for use in nuclear reactor primary circuits:

304NG (UNS S30400 / EN 1.4301) — Nuclear Grade

Full English Name: Type 304 Nuclear Grade Austenitic Stainless Steel
Composition Highlights: Cr 18–20%, Ni 8–10.5%, C ≤ 0.08%, with stringent limits on residual elements (Nb, Ta, Ti, Sn, Sb, P, S) to ensure resistance to stress corrosion cracking (SCC) and irradiation-induced sensitization.
Key Advantage: Excellent general corrosion resistance in boric acid water; cost-effective for moderate irradiation environments.

316NG (UNS S31600 / EN 1.4401) — Nuclear Grade

Full English Name: Type 316 Nuclear Grade Austenitic Stainless Steel (Molybdenum-Enhanced)
Composition Highlights: Cr 16–18%, Ni 10–14%, Mo 2–3%, C ≤ 0.08%, with similarly strict impurity controls.
Key Advantage: Superior resistance to intergranular stress corrosion cracking (IGSCC) and pitting corrosion in chloride-containing or boric acid environments; preferred for higher-irradiation zones.

Mechanical Properties (Typical, Annealed Condition)

Property	304NG	316NG	Test Standard
Tensile Strength (R_m)	≥ 520 MPa	≥ 520 MPa	ASTM A240 / EN 10204
Yield Strength (R_p0.2)	≥ 205 MPa	≥ 205 MPa	ASTM A240 / EN 10204
Elongation (A)	≥ 40%	≥ 40%	ASTM A240
Hardness (HBW)	≤ 217	≤ 217	ASTM E10
Operating Temperature Range	−196 °C to +800 °C	−196 °C to +800 °C	—
Design Operating Temperature	300 °C		—
Design Operating Pressure	15 MPa		—

Specifications

Parameter	Specification
Product Name	Primary Loop Main Pump Seal Cooling Coil Tube
Product Category	Coil Tube (盘管 / Coiltube)
Application Classification	Power & Energy → Nuclear Power
Material Grades	304NG / 316NG (Nuclear Grade Austenitic Stainless Steel)
Tube Type	Seamless (无缝管 / Seamless Tube)
Melting Process	VIM (Vacuum Induction Melting) + VAR (Vacuum Arc Remelting)
Coil Form	Continuous Coil / Helical Coil (盘管)
Operating Coolant	Boric Acid Water (硼酸水 / Boric Acid Water)
Operating Temperature	300 °C
Operating Pressure	15 MPa
Environment	High-Neutron-Flux Irradiation Environment
Surface Finish	Machined / Polished Internal Surface (as required for heat transfer efficiency)
Heat Treatment	Solution Annealing (1050–1100 °C) + Water Quench
Quality Documentation	Full Traceability Warranty Certificate + EN 10204 3.2 Inspection Certificate
Manufacturer	Wenzhou Jixing Metal Materials Co., Ltd.
Catalogue No.	125

Manufacturing Process

The production of this nuclear-grade coil tube follows a rigorously controlled, multi-stage manufacturing workflow designed to ensure metallurgical homogeneity, freedom from inclusions, and dimensional precision:

Vacuum Induction Melting (VIM — Vacuum Induction Melting):
The initial melting of the 304NG or 316NG steel is conducted under high vacuum conditions (≤ 10⁻² Pa) in a VIM furnace. This process ensures extremely low levels of oxygen, nitrogen, and other gaseous impurities, while enabling precise alloy composition control. The resulting ingot exhibits superior purity and reduced non-metallic inclusion content compared to conventional open-hearth or electric arc furnace (EAF) melting.
Vacuum Arc Remelting (VAR — Vacuum Arc Remelting):
The VIM-consumable ingot is subsequently remelted in a VAR furnace under vacuum. This secondary melting process further refines the microstructure by eliminating residual inclusions, homogenizing the grain structure, and achieving a near-zero porosity cast. The combination of VIM + VAR (dual vacuum melting) is a hallmark of nuclear-grade steel production and is essential for ensuring the tube's resistance to irradiation-induced defects and stress corrosion cracking.
Hot Rolling / Hot Extrusion:
The VAR-consumable billet is heated to the appropriate austenitization temperature and subjected to hot rolling or hot extrusion to produce a seamless tube blank (seamless tube / 无缝管). The seamless construction eliminates the weld seam that would otherwise represent a potential failure initiation site under irradiation and cyclic thermal loading.
Cold Drawing / Cold Reduction:
The hot-rolled tube undergoes cold drawing to achieve the final dimensional tolerances, surface finish, and mechanical properties required for nuclear service. Multiple passes of cold reduction are performed with intermediate annealing to maintain ductility and prevent cracking.
Solution Annealing:
The cold-worked tube is solution annealed at 1050–1100 °C followed by rapid water quenching. This heat treatment dissolves any carbide precipitation, restores full austenitic microstructure, and maximizes corrosion resistance — a critical requirement for long-term exposure to boric acid water at elevated temperatures.
Coil Forming:
The straight seamless tube is coiled into the required helical coil configuration (盘管 / Coil Tube) using precision bending equipment. The coil geometry is designed to maximize heat transfer surface area within the compact volume of the pump seal cooling system while maintaining structural integrity under 15 MPa internal pressure.
Non-Destructive Testing (NDT):
Each coil tube assembly undergoes comprehensive NDT including:
— Eddy Current Testing (ECT): for detection of surface and near-surface defects
— Ultrasonic Testing (UT): for volumetric flaw detection
— Helium Leak Testing: for verification of pressure containment integrity
— Dimensional Inspection: using CMM (Coordinate Measuring Machine) for geometric accuracy

Applications

This coil tube is purpose-engineered for the following specific nuclear power plant application:

Primary Loop Main Pump Seal Cooling (一回路主泵密封冷却):
In a PWR nuclear power plant, the Reactor Coolant Pumps (RCPs) circulate the primary coolant water through the reactor vessel. The mechanical seals on these pumps generate significant frictional heat that must be continuously removed to prevent seal degradation and potential leakage of radioactive primary coolant. The coil tube functions as the heat exchange element within the seal cooling loop, absorbing heat from the seal flush water and dissipating it through a secondary cooling circuit.
Operating Environment Characteristics:
- Coolant: Boric acid water — used as a neutron absorber in the primary coolant loop; the boric acid introduces a mildly corrosive chemical environment requiring high-grade austenitic stainless steel.
- Temperature: 300 °C — sustained high-temperature operation demands excellent thermal stability and resistance to thermal fatigue.
- Pressure: 15 MPa — high internal pressure requires robust wall thickness and superior fatigue resistance.
- Irradiation: The component is located within or adjacent to the reactor containment boundary, exposing it to a high neutron flux environment. The VIM/VAR metallurgy ensures resistance to irradiation-induced swelling, void swelling, and irradiation-assisted stress corrosion cracking (IASCC).
Reactor Types: Compatible with PWR (Pressurized Water Reactor) designs including CANDU, Westinghouse, and Chinese Hualong One (华龙一号) reactor platforms, subject to specific design qualification.

Quality Certifications

Given the safety-critical nature of nuclear power applications, this product is accompanied by the most comprehensive quality documentation available in the metallurgical industry:

Full Traceability Warranty Certificate (全程质保书):
A complete, end-to-end quality assurance documentation package that provides full traceability from raw material origin through every manufacturing stage to the final product. This includes:
— Raw material mill certificates (including VIM and VAR furnace records)
— Chemical analysis reports (spectrographic and wet chemistry)
— Mechanical test results (tensile, hardness, impact)
— Heat treatment records and furnace load charts
— NDT reports with calibrated equipment traceability
— Dimensional inspection certificates
— Visual inspection and surface finish verification reports
EN 10204 3.2 Inspection Certificate:
Also known as a "Specific Third-Party Inspection Certificate," EN 10204 3.2 represents the highest level of product certification under the European standard EN 10204 (formerly BS EN 10204). This certificate is issued by an independent third-party inspection body (such as SGS, TÜV, or Lloyd's Register) and certifies that:
— The product conforms to the specified material grade and technical requirements
— All manufacturing and testing operations have been independently witnessed and verified
— The product is suitable for nuclear-grade service applications
— Full traceability from chemical composition to final dimensional inspection is documented and verified

Important Note: EN 10204 3.2 certification is a prerequisite for the acceptance of materials and components in most nuclear power plant construction and maintenance programs worldwide. It provides the regulatory bodies and plant operators with the assurance that every aspect of the product's quality has been independently verified, meeting the stringent requirements of nuclear safety culture.

Unique Selling Points

Dual Vacuum Melting (VIM + VAR): The combination of Vacuum Induction Melting and Vacuum Arc Remelting provides unmatched metallurgical purity, essential for resisting irradiation-induced degradation and stress corrosion cracking in the nuclear primary loop environment.