Nuclear-Grade Stainless Steel Coil Tube for Main Pump High-Pressure Coolers

Product Overview

The Nuclear Main Pump High-Pressure Cooler Coil Tube (hereinafter referred to as "HPCC Coil Tube") is a precision-engineered austenitic stainless steel coil tube designed specifically for the thermal management subsystem of nuclear reactor main coolant pumps. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product represents the culmination of advanced metallurgical research and process engineering, developed through the systematic study documented in the technical white paper "Development of Manufacturing Process for Nuclear Main Pump High-Pressure Cooler Coil Tube."

The HPCC Coil Tube serves as the critical heat exchange element within the main pump's high-pressure cooler assembly, where it must operate continuously under extreme conditions—high differential pressures (up to 15 MPa), elevated temperatures (ranging from 30°C to 320°C), and sustained exposure to radioactive coolant media. The product is engineered to withstand the full spectrum of nuclear-grade mechanical, thermal, and corrosion challenges while maintaining dimensional integrity over design lifetimes exceeding 60 years.

This coil tube product is classified under the nuclear component supply chain and is manufactured in accordance with the stringent requirements of ASME Boiler and Pressure Vessel Code Section III (Nuclear Power Plant Components), the European PED (Pressure Equipment Directive 2014/68/EU), and applicable national nuclear regulatory standards.

Material & Properties

Base Alloy Selection

The HPCC Coil Tube is fabricated from high-purity austenitic stainless steel grades, with the primary material being SAE 316L (UNS S31603) and SAE 316H (UNS S31609), selected for their exceptional resistance to stress corrosion cracking (SCC), intergranular corrosion, and general aqueous corrosion in nuclear-grade cooling water environments. The "L" suffix denotes low carbon content (≤0.03% C), which significantly reduces the susceptibility to sensitization during welding and high-temperature service. The "H" grade provides enhanced high-temperature creep strength for components operating at elevated temperatures.

Alternative material options include SAE 304L (UNS S30403) for lower-clad environments and SAE 321 (UNS S32100) (stabilized with titanium) where elevated-temperature oxidation resistance is paramount.

Mechanical Properties

• Tensile Strength (UTS): ≥ 485 MPa (316L), ≥ 515 MPa (316H) at room temperature
• Yield Strength (0.2% offset): ≥ 170 MPa (316L), ≥ 205 MPa (316H) at room temperature
• Elongation (% Elongation at Break): ≥ 40% (minimum), typically 55–65% achieved
• Impact Energy (Charpy V-Notch): ≥ 47 J at −40°C, ensuring adequate ductility under cryogenic and low-temperature transients
• Creep Strength (100,000 hours at 650°C): ≥ 100 MPa (316H)

Corrosion Resistance

• Pitting Resistance (PREN): ≥ 25 (316L), ≥ 26 (316H), calculated as %Cr + 3.3×%Mo + 16×%N
• Intergranular Corrosion Resistance: Verified per ASTM A262 Practice No. 1E and Practice No. 4E; no intergranular attack detected
• Stress Corrosion Cracking Resistance: Evaluated per ASTM G102 in chloride-containing solutions at 60°C; no cracking observed over 1000-hour exposure
• Crevice Corrosion Resistance: Confirmed per ASTM G115 in 6% FeCl₃ solution at 60°C

Chemical Composition (Typical, wt%)

Element	316L (UNS S31603)	316H (UNS S31609)
C (Carbon)	≤ 0.030	0.040 – 0.100
Si (Silicon)	≤ 1.00	≤ 1.00
Mn (Manganese)	≤ 2.00	≤ 2.00
P (Phosphorus)	≤ 0.035	≤ 0.045
S (Sulfur)	≤ 0.030	≤ 0.030
Cr (Chromium)	16.00 – 18.00	16.00 – 18.00
Ni (Nickel)	10.00 – 14.00	10.00 – 14.00
Mo (Molybdenum)	2.00 – 3.00	2.00 – 3.00
N (Nitrogen)	—	0.020 – 0.100
Fe (Iron)	Balance	Balance

Specifications

Parameter	Specification / Range	Standard Reference
Product Name	Nuclear Main Pump High-Pressure Cooler Coil Tube (盘管 / Coiltube)	—
Catalog No.	455	—
Material Grade	SAE 316L / 316H / 304L / 321 (austenitic stainless steel)	ASTM A213 / A269 / ASME SA-213 / SA-269
Outer Diameter (OD)	Φ 8.0 mm – Φ 25.4 mm (customizable)	ASTM A269
Wall Thickness	0.5 mm – 3.0 mm (tolerance ±10%)	ASTM A269
Coil Bend Radius	≥ 5× OD (minimum); typical 8× – 12× OD	Manufacturer's Process Specification
Coil Diameter (Mean)	Φ 100 mm – Φ 500 mm (customizable per design)	Customer Drawing / Design Specification
Number of Turns	10 – 500 turns (configurable)	Customer Drawing
Surface Finish	Electro-polished (Ra ≤ 0.4 μm) or pickled & passivated (Ra ≤ 0.8 μm)	ASTM A967 / ASME BPE
Welding Method	TIG (GTAW) / Orbital TIG / Laser Welding; filler wire matching base alloy	ASME BPV Code Section IX, QW-451
Heat Treatment	Solution Annealing at 1050°C – 1150°C followed by water quench; optional stabilization anneal for 321 grade	ASTM A213 / ASME SA-213
Non-Destructive Testing (NDT)	100% Eddy Current (EC) per ASTM E309; 100% Radiographic Testing (RT) of welds per ASME Section V Article 2; 100% Hydrostatic Pressure Test at 1.5× design pressure	ASME BPV Code Section V / ASTM E309
Design Pressure Rating	Up to 15.0 MPa (2175 psi) at maximum operating temperature	ASME BPV Code Section III, NB-3200
Operating Temperature Range	−40°C to +320°C (continuous); transient up to +400°C	Customer Design Specification
Design Lifetime	≥ 60 years (aligned with nuclear plant design life)	IAEA / National Nuclear Regulatory Authority
Applicable Codes & Standards	ASME BPV Code Section III (Subsections NB, NC, ND); ASME NQA-1; ISO 9001:2015; ISO 2859-1; PED 2014/68/EU (Category III/IV); GB/T 12771 (Chinese National Standard for Welded Stainless Steel Tubes); NB/T 20001 (Nuclear Industry Standard)	—

Manufacturing Process

The manufacturing process for the Nuclear Main Pump High-Pressure Cooler Coil Tube is a highly controlled, multi-stage process that has been developed and validated through systematic experimental study as documented in the technical literature. The process flow is outlined below:

1. Raw Material Procurement and Incoming Inspection
   • Stainless steel strip or seamless tube stock is procured from certified suppliers with full mill test certificates (MTC) traceable to heat number.
   • Incoming inspection includes chemical composition verification (OES / Spark Spectroscopy), mechanical property testing (tensile, hardness), grain size evaluation, and surface quality assessment.
   • Material traceability is maintained through a unique heat lot number assigned to each coil tube assembly.
2. Dimensional Preparation and Pre-Forming
   • Raw tube stock is cut to specified lengths using precision plasma or laser cutting, followed by deburring and chamfering to ensure uniform wall thickness.
   • For welded coil tubes, strip material is cold-rolled to precise thickness and width, with edge preparation (beveling) for TIG welding.
3. Coil Forming (Cold Bending)
   • The tube is cold-formed into the specified coil geometry using a CNC-controlled coil bending machine equipped with precision hydraulic forming dies.
   • The bending radius is maintained at ≥ 5× OD to prevent ovality distortion (≤ 3% of OD) and wall thinning (≤ 10%).
   • During forming, the material undergoes plastic deformation and work hardening; strain distribution is monitored using strain gauges and FEA (Finite Element Analysis) simulation to ensure no localized necking or cracking occurs.
   • Post-forming dimensional inspection verifies coil diameter tolerance (±2 mm), turn-to-turn spacing (±0.5 mm), and overall helix accuracy.
4. Welding (for welded coil tubes or end connections)
   • Orbital TIG (GTAW) welding is employed for circumferential seams, ensuring full-penetration welds with controlled heat input (≤ 1.0 kJ/mm) to minimize the sensitization zone.
   • For end connections and headers, manual TIG welding is performed by ASME-certified welders (qualified per ASME Section IX QW-451).
   • Weld parameters are documented and maintained under a Welding Procedure Specification (WPS) qualified by a Procedure Qualification Record (PQR).
   • Filler wire composition is matched to the base metal grade (e.g., ER316L for 316L base, ER316H for 316H base).
5. Heat Treatment (Solution Annealing)
   • All coil tubes undergo solution annealing at 1050°C – 1150°C in a continuous or batch furnace with controlled atmosphere (argon or vacuum) to dissolve carbides and restore full austenitic structure.
   • Water quenching follows immediately to freeze the solution-treated microstructure and prevent re-precipitation of chromium carbides at grain boundaries.
   • Post-annealing hardness verification confirms values ≤ 220 HV (consistent with fully solution-annealed condition).
   • For 321 grade, a stabilization anneal at 870°C – 900°C may be applied to promote TiC precipitation and prevent sensitization.
6. Surface Treatment
   • Electro-polishing (per ASTM A967) is performed to achieve a surface roughness of Ra ≤ 0.4 μm, removing surface contamination, decarburization layers, and micro-roughness that could serve as corrosion initiation sites.
   • Alternative: pickling and passivation using a controlled citric acid or nitric acid-hydrofluoric acid solution, followed by thorough rinsing with deionized water.
   • Surface integrity is verified using surface roughness measurement (contact profilometry) and visual inspection under controlled lighting.
7. Non-Destructive Testing (NDT) and Quality Assurance
   • Eddy Current Testing (EC): 100% coverage of the coil tube length per ASTM E309 to detect surface and near-surface defects (cracks, inclusions, wall thinning). The EC probe is calibrated using standard reference samples (Type A, B, C, D per ASTM E309).
   • Radiographic Testing (RT): 100% of welds inspected per ASME BPV Code Section V Article 2, using X-ray or gamma-ray sources, with film or digital radiography. Acceptance criteria per ASME Section III NB-2300 (no cracks, no undercut, no incomplete fusion; porosity and slag inclusions limited per Table NB-2310).
   • Hydrostatic Pressure Test: Each coil tube assembly is pressure-tested at 1.5× the maximum