Stainless Steel Coil Tube — Karl Fischer / Dew Point Moisture Testing Specification

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a precision-engineered tubing solution designed for the most demanding industrial and semiconductor applications. This product knowledge point focuses specifically on the moisture content testing methodology employed to ensure ppm-level (parts per million) water vapor control within the coil tube's internal bore. The adoption of the Karl Fischer Titration Method and Dew Point Meter instrumentation ensures that residual moisture is quantified and controlled to ultralow levels, thereby preventing hydrolysis reactions in electronic specialty gas (ESG) delivery systems.

In semiconductor fabrication, photolithography, and ultra-high-purity (UHP) gas distribution environments, even trace quantities of water vapor—measured in single-digit or double-digit ppm—can catalyze hydrolysis of reactive gases such as halogenated silanes, phosphorus hydrides, and boron compounds. The coil tube's internal surface cleanliness and moisture retention characteristics are therefore critical performance parameters, and the Karl Fischer / Dew Point testing protocol serves as the definitive quality gate.

2. Material & Properties

2.1 Base Material Composition

2.2 Surface Treatment & Passivation

2.3 Moisture-Related Material Properties

The 316L austenitic microstructure provides inherent resistance to pitting and intergranular corrosion, which is essential when trace moisture interacts with chlorides or acidic species in the gas stream. The low carbon content (≤ 0.030%) minimizes carbide precipitation at grain boundaries, ensuring that the material maintains its corrosion resistance even under prolonged exposure to humid or reactive gas environments. The molybdenum addition further enhances resistance to chloride-induced stress corrosion cracking (SCC), which can be accelerated by the presence of water vapor.

3. Specifications

Parameter Specification / Requirement Test Method
Product Type Stainless Steel Coil Tube (盘管 Coiltube) —
Material Grade SUS316L / TP316L (ASTM A269) Optical Emission Spectroscopy (OES)
Outer Diameter (OD) 1/16" – 1" (1.588 mm – 25.4 mm), custom sizes available Caliper / CMM
Wall Thickness 0.1 mm – 1.0 mm (0.004" – 0.040") Ultrasonic Thickness Gauge
Coil Length 50 m – 200 m per coil (customizable) Length Encoder
Internal Surface Roughness (Ra) ≤ 0.25 μm Surface Roughness Tester
Residual Moisture Content ≤ 1 ppm (ppm-level control) Karl Fischer Titration / Dew Point Meter
Helium Leak Rate ≤ 1 × 10⁻⁹ atm·cm³/s Helium Mass Spectrometer Leak Detector
Particle Count (Internal) ≤ 10 particles ≥ 0.3 μm per 100 mm Particle Counter (SEMI F57)
Hydrogen Outgassing Rate ≤ 5 × 10⁻⁸ cm³ H₂/s·cm² (after bake-out) TGA / Outgassing Chamber
Passivation Treatment ASTM A967 compliant Passivation Verification (ASTM A380)
Operating Temperature −196 °C (LN₂) to +540 °C Thermal Cycling Test
Maximum Operating Pressure Up to 6,000 psi (41.4 MPa) Hydrostatic Pressure Test

4. Moisture Testing Methodology

4.1 Karl Fischer Titration Method

The Karl Fischer (KF) Titration is the internationally recognized standard method for the quantitative determination of water content in materials, gases, and liquids. In the context of stainless steel coil tube quality assurance, the KF method is employed as follows:

  1. Sample Preparation: A representative sample of the coil tube is cut to a specified length (typically 100–300 mm). The internal bore is flushed with anhydrous carrier gas (e.g., dry nitrogen or helium) to displace any adsorbed moisture from the inner wall surface.
  2. Extraction: The carrier gas stream, now carrying any liberated water vapor, is directed through a coulometric Karl Fischer titrator. The titrator contains an anhydrous methanol-based reagent with iodine and a base.
  3. Titration Reaction: Water reacts stoichiometrically with iodine in the KF reagent according to the following reaction:
    H₂O + I₂ + S + 3CH₃OH → 2CH₃OH·HI + CH₃OH·SO₃ The coulometric variant generates iodine electrochemically, enabling detection limits down to 10⁻⁶ ppm (10 ppb).
  4. Quantification: The volume of iodine consumed is directly proportional to the water content. Results are reported in ppm (μg/g) or ppb (ng/g).

4.2 Dew Point Meter Measurement

A Dew Point Meter provides a complementary, real-time measurement of water vapor concentration in the gas stream flowing through the coil tube. The instrument operates on the principle of capacitance change or chilled mirror condensation:

4.3 Acceptance Criteria for Moisture Content

Application Category Maximum Permitted Moisture (ppm) Test Method
General Industrial Gas Delivery ≤ 10 ppm Dew Point Meter
Electronic Specialty Gas (ESG) Piping ≤ 1 ppm Karl Fischer Titration
UHP / Semiconductor-grade Gas Distribution ≤ 0.1 ppm (100 ppb) Coulometric Karl Fischer
Ultra-High Vacuum (UHV) Applications ≤ 0.01 ppm (10 ppb) Coulometric Karl Fischer / TGA

5. Manufacturing Process

5.1 Coil Tube Production Workflow

  1. Coil Winding: Precision-drawn stainless steel tubing is wound into a helical coil configuration on a mandrel to achieve the required pitch, diameter, and length. The coiling process is performed under controlled tension to prevent deformation or ovality.
  2. Internal Surface Finishing: The coil tube bore undergoes electrolytic passivation or electropolishing to achieve Ra ≤ 0.25 μm. This removes surface contamination, deoxidized layers, and any residual metal particles that could serve as moisture adsorption sites.
  3. Acid Passivation: The coil is immersed in a citric acid or nitric acid solution (per ASTM A967) to form a uniform chromium oxide passive film. This film is hydrophobic and resistant to moisture adsorption.
  4. Purging & Drying: The coil is flushed with high-purity, anhydrous nitrogen or helium gas at controlled flow rates to remove any residual moisture from the internal bore. For semiconductor-grade applications, the coil may be subjected to a hydrogen bake-out at 400–500 °C under vacuum to drive off adsorbed water.
  5. Moisture Verification: Post-bake-out, the coil is tested using the Karl Fischer titration method and/or dew point meter to confirm that the residual moisture content meets the specified ppm-level requirement.
  6. End Sealing & Packaging: Each coil is sealed at both ends with hermetic caps (typically stainless steel or fluoropolymer plug seals) to prevent atmospheric moisture re-adsorption. The sealed coil is then packaged in a moisture-barrier foil bag with desiccant, or stored in a dry nitrogen cabinet.

5.2 Critical Process Controls for Moisture

6. Applications

6.1 Electronic Specialty Gas (ESG) Delivery Systems

This is the primary application domain for moisture-controlled coil tubes. In semiconductor fabrication facilities, reactive gases such as silane (SiH₄), dichlorosilane (SiH₂Cl₂), phosphine (PH₃), arsine (AsH₃), boron trichloride (BCl₃), and hydrogen chloride (HCl) are delivered through tubing networks to process chambers. These gases are highly susceptible to hydrolysis when exposed to water vapor:

Example — Silane Hydrolysis:
SiH₄ + 2H₂O → SiO₂ + 4H₂

Example — Phosphine Hydrolysis:
PH₃ + H₂O → H₃PO₃ + 2H₂ (in presence of oxidants)

Hydrolysis products such as silicon dioxide (SiO₂) and phosphoric acid (H₃PO₄) can deposit on wafer surfaces, causing particle contamination, film thickness non-uniformity, and yield loss. The ppm-level moisture control achieved through Karl Fischer / Dew Point testing ensures that the coil tube does not contribute moisture to the gas stream.

6.2 Additional Applications