316L / Hastelloy Seamless Coil Tube for Online pH/ORP Electrode Housings
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd (Product No. 167) supplies precision-engineered seamless stainless steel coil tubes purpose-designed for online pH and ORP (Oxidation-Reduction Potential) electrode housings in industrial process analysis systems. These coil tubes serve as the critical protective sheath through which sensitive electrochemical sensors are deployed directly into corrosive acid-base media. The tubing must simultaneously provide chemical inertness, mechanical integrity, and a hermetic sealing interface to ensure accurate, rapid, and reliable analytical readings in demanding process environments.
Unlike general-purpose tubing, this product line is engineered around the stringent requirements of process instrumentation: minimal response time for real-time monitoring, resistance to aggressive chemical attack, and compatibility with precision sealing designs that prevent cross-contamination between the process fluid and the electrode assembly.
Unique Selling Points
- Chemical Excellence: Available in 316L and Hastelloy grades, providing superior resistance to acids, alkalis, and reducing/oxidizing environments that would degrade standard austenitic stainless steels.
- Seamless Construction: Eliminates internal weld seams that could create crevice corrosion sites, trap contaminants, or interfere with the uniform current distribution essential for accurate pH/ORP measurement.
- Coil Form Factor: Supplied in continuous coil form for efficient downstream forming, cutting, and assembly into electrode housing geometries without the need for butt welding or mechanical splicing.
- Sealing-Ready Tolerances: Manufactured to tight dimensional tolerances and surface finishes that accommodate O-ring grooves, threaded couplings, and press-fit sealing interfaces critical to process isolation.
- Minimal Response Latency: Thin-wall options available to reduce thermal and chemical diffusion lag, ensuring electrode response times meet the fast dynamic requirements of real-time process control loops.
Material & Properties
316L Seamless Stainless Steel
316L (UNS S31603) is the baseline grade for this application. The addition of molybdenum (2.0–3.0%) to the 304L matrix provides enhanced resistance to pitting and crevice corrosion in chloride-containing and acidic environments. The low-carbon designation (≤0.03% C) minimizes intergranular sensitization during any downstream heat treatment or welding operations. Typical properties include:
- Corrosion Resistance: Excellent resistance to dilute sulfuric, phosphoric, and acetic acids; good resistance to alkaline solutions up to pH 14.
- Mechanical Strength: Yield strength ≥ 170 MPa (24.7 ksi); ultimate tensile strength ≥ 485 MPa (70.3 ksi).
- Temperature Range: Serviceable from cryogenic temperatures up to 425°C (797°F) without loss of mechanical integrity.
- Non-Magnetic: Fully austenitic microstructure ensures non-magnetic behavior, avoiding interference with electromagnetic process instruments.
Hastelloy Seamless Stainless Steel
For applications involving highly aggressive media — concentrated acids, hot alkalis, or mixed oxidizing-reducing environments — Hastelloy grades (C-276, C-22, or B-3) are offered as the premium material option. Hastelloy provides exceptional resistance to nearly all chemical processing environments, including hydrofluoric acid solutions, concentrated sulfuric acid, and strong caustic media. This grade is recommended when the process medium presents a combination of high temperature, high chloride concentration, and aggressive redox conditions that exceed the limits of 316L.
- Corrosion Resistance: Outstanding resistance to reducing acids, hot caustics, and oxidizing-reducing mixtures; virtually immune to stress corrosion cracking in chloride environments.
- Mechanical Strength: Yield strength ≥ 205 MPa (29.7 ksi); ultimate tensile strength ≥ 550 MPa (79.8 ksi) (grade-dependent).
- Temperature Range: Serviceable up to 400–500°C (752–932°F) depending on specific Hastelloy grade.
- Weldability: Excellent weldability with minimal post-weld treatment required, facilitating field assembly of electrode housings.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Coil Tube — Online pH/ORP Electrode Housing |
| Product No. | 167 |
| Material Grades | 316L (UNS S31603) / Hastelloy C-276 / C-22 / B-3 |
| Manufacturing Method | Hot-rolled → Cold-drawn seamless tubing, coiled |
| Outer Diameter (OD) | 3.0 – 50.0 mm (0.118" – 1.969") |
| Wall Thickness | 0.3 – 3.0 mm (0.012" – 0.118") |
| OD Tolerance | ±0.05 mm (±0.002") |
| Wall Thickness Tolerance | ±0.03 mm (±0.001") |
| Straightness | ≤ 1.0 mm/m (≤ 0.039"/ft) |
| Surface Finish | Pickled & passivated; Ra ≤ 0.4 μm (16 μin) available on request |
| Coil Inner Diameter | 50 – 200 mm (1.97" – 7.87") |
| Coil Length | 5 – 50 m (16.4 – 164 ft) per coil; custom lengths available |
| Standards Compliance | ASTM A269 / ASME SA-269 / ASTM A213 / EN 10216-5 / GB/T 12771 |
| Application Environment | Direct contact with acid-base process media; online analytical instrumentation |
| Key Design Feature | Sealing-compatible geometry; precision tolerances for O-ring and thread interfaces |
Manufacturing Process
The production of seamless coil tubing for pH/ORP electrode housings follows a rigorous multi-stage process designed to ensure microstructural uniformity, dimensional precision, and surface integrity:
- Billet Preparation: Virgin ingots of certified 316L or Hastelloy alloy are reheated to controlled forging temperatures (1150–1250°C / 2092–2282°F) to achieve homogeneous austenitic microstructure.
- Piercing & Hot Rolling: The heated billet is pierced to produce a hollow tube blank, which is then hot-rolled through a series of reduction stands to achieve the target outer diameter and wall thickness. Hot rolling refines the grain structure and eliminates internal voids.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1150°C (1922–2092°F) followed by rapid water quenching to dissolve carbide precipitates and restore full solution-hardened corrosion resistance.
- Pickling & Passivation: Tubes are pickled in a mixed acid bath (nitric/hydrofluoric acid blend) to remove scale and oxide films, followed by passivation to establish a stable chromium oxide protective layer on the surface.
- Cold Drawing: Tubes are cold-drawn through precision dies to achieve final dimensions within tight tolerances. Cold working introduces beneficial work hardening and improves surface finish quality (Ra ≤ 0.4 μm achievable).
- Intermediate Annealing: Periodic solution annealing cycles are performed between cold-drawing passes to relieve accumulated cold-work stresses and prevent cracking in thin-wall configurations.
- Final Straightening & Coiling: Tubes are straightened to specification and wound onto precision coils of the required inner diameter. Coil ends are sealed to prevent moisture ingress and surface contamination during storage and transport.
- Quality Inspection: Every batch undergoes 100% visual inspection, dimensional verification, and batch sampling for chemical composition analysis, mechanical testing, and hydrostatic pressure testing.
Applications
This coil tube product is specifically engineered for the following instrumentation and process analysis applications:
- Online pH Electrode Housings: The primary application — providing a chemically inert, hermetically sealed protective sheath for pH electrodes deployed in acid-base process streams. The seamless construction ensures no crevice corrosion sites that could contaminate the measurement.
- ORP (Redox Potential) Sensor Shields: Protecting ORP reference and indicator electrodes in highly oxidizing or reducing environments where material compatibility is critical to measurement accuracy.
- Process Water Treatment: Electrode housings in water treatment plants handling acid dosing, chlorine residual monitoring, and pH control of treatment chemicals.
- Chemical Processing: pH/ORP monitoring in sulfuric acid, hydrochloric acid, caustic soda, and mixed acid processing streams in the chemical, petrochemical, and pharmaceutical industries.
- Food & Beverage Processing: Sanitary-grade pH monitoring housings in food, dairy, and beverage production where CIP (Clean-In-Place) compatibility and material purity are essential.
- Power Generation: Monitoring of boiler feedwater, cooling water, and flue gas desulfurization (FGD) systems where aggressive acid-base conditions prevail.
- Environmental Monitoring: pH/ORP measurement in wastewater treatment, acid mine drainage, and industrial effluent monitoring applications.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management systems and holds the following certifications and compliance standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control throughout the manufacturing chain.
- ISO 14001 — Environmental Management System certification demonstrating commitment to environmentally responsible manufacturing practices.
- CE Marking — Compliance with European Union directives for machinery and industrial equipment components.
- Mill Test Certificates (MTC / EN 10204 3.1): Every shipment is accompanied by a detailed mill test certificate documenting chemical composition, mechanical properties, heat treatment status, and test results for each heat/batch.
- Material Traceability: Full heat-number traceability from raw material mill through final product delivery, enabling complete quality documentation for customer audits and regulatory compliance.
- Third-Party Testing: Available upon request — independent laboratory verification of chemical analysis, mechanical properties, and corrosion resistance testing by accredited third-party organizations.
Technical Notes & Ordering Guidance
Sealing Design Considerations: When specifying coil tubing for electrode housing applications, customers should define the required sealing interface type (O-ring groove, threaded coupling, press-fit, or ferrule connection) to ensure the tubing is manufactured with appropriate end conditions, surface finishes, and dimensional tolerances. Wenzhou Jixing Metal Materials offers pre-machined end treatments, including chamfering, threading, and groove milling, to reduce downstream processing requirements.
Response Time Optimization: For applications requiring fast electrode response (≤ 5 seconds), thinner wall thickness options (0.3–0.5 mm / 0.012"–0.020") are recommended. These reduce the diffusion path length for the process medium to reach the electrode membrane, minimizing measurement lag. However, thinner walls require careful handling to avoid deformation during assembly.
Material Selection Guide: 316L is suitable for most acid-base applications with moderate chloride concentrations (≤ 1,000 ppm) and temperatures below 60°C (140°F). Hastelloy C-276 is recommended for aggressive environments including hot concentrated acids, mixed oxidizing-reducing media, and high-chloride conditions exceeding 316L limits. Hastelloy B-3 is preferred for highly reducing acid environments such as hydrochloric and sulfuric acid at elevated temperatures.