Three-layer SST Optical Cable - Fiber In Metal Tube (FIMT) - Oil Well Sensing Optical Cable - High Temperature Optical Cable

Alias: Triple-Layer Downhole Fiber Cable, Triple-Wall SST Fiber Cable, 1/4" Triple-Tube Optical Cable, Tube-in-Tube-in-Tube Fiber, Kevlar Reinforced Downhole Fiber, Triple Hydrogen Barrier Cable, Alloy 825 Triple-Wall Fiber, Permanent Downhole Monitoring (PDM) Cable, HPHT Triple Armored Sensing Unit.

1. Product Overview of OFSCN® Triple-Layer Downhole High-Temperature Fiber Optic Cable

The OFSCN® Triple-Layer Downhole High-Temperature Fiber Optic Cable is the flagship solution for extreme sensing environments. Featuring a "Tube-in-Tube-in-Tube" nested structure, it utilizes three layers of seamless stainless steel or alloy tubing to provide unprecedented physical protection. This design creates a triple-stage barrier against hydrogen ingress and mechanical stress. It is specifically engineered for ultra-deep wells, high-$H_2S$ environments, and permanent subsea installations where a service life of over 20 years is required.

2. Mechanical Structure & Physical Parameters of OFSCN® Triple-Layer Downhole High-Temperature Fiber Optic Cable

Parameter	Technical Specification (Standard)	Advanced Options
Brand	OFSCN®	-
Encapsulation	Triple-Wall Seamless Nested Tubes	High-integrity metallic seal
Tube Material	316L Stainless Steel (Default)	Alloy 825 (Enhanced corrosion resistance)
Outer Tube (OD/Wall)	6.35 mm (1/4") / 0.9 mm	Primary load & crush resistance layer
Middle Tube (OD/Wall)	4.0 mm / 0.3 mm	Intermediate buffer & hydrogen shield
Inner Tube (OD/Wall)	3.0 mm / 0.3 mm	Precision fiber housing layer
Product Weight	~171 kg/km	Calculated for 316L density
Tensile Strength	> 11,000 N	Superior vertical suspension capacity
Crush Resistance	> 180 MPa	Resists extreme formation/hydrostatic pressure
Min. Bending Radius	25 times Cable OD	Static installation
Min. Order Qty (MOQ)	1,000 Meters	Standard engineering batch

3. Internal Fiber & Packaging Options of OFSCN® Triple-Layer Downhole High-Temperature Fiber Optic Cable

3.1 200°C Grade (Enhanced Tensile/Cushioning)

• Optical Fiber: OFSCN® 200°C Polyimide Optical Fiber
• Internal Packaging Option: Kevlar (Aramid Yarn). For the 200°C version, high-strength Kevlar fibers can be added inside the inner tube to provide additional tensile reinforcement and vibration damping for the fiber cores.
• Fiber Type: Single-mode (SM), Multi-mode (MM), or Pure Silica Core (PSC).

3.2 300°C Grade (Ultra-High Temp)

• Optical Fiber:

OFSCN® 300°C SM/MM Polyimide Optical Fiber

OFSCN® 300°C MM PI Fiber

• Fiber Type: Single-mode (SM) or Multi-mode (MM) combinations.
• Note: Kevlar is not recommended for 300°C as it exceeds the material's thermal stability limit; 300°C models utilize all-metal/fiber configurations.

4. Technical Calculations & Strategic Advantages of OFSCN® Triple-Layer Downhole High-Temperature Fiber Optic Cable

4.1 Physical Calculations (Based on 316L)

• Weight: Total metal cross-sectional area is approx. 21.44 mm2. At a 316L density of 7.98 g/cm3, the weight is approx. 171 kg/km.
• Tensile: The 0.9 mm heavy-duty outer wall contributes the majority of the tensile strength, with a theoretical breaking force exceeding 11,000 N, allowing safe deployment in wells several kilometers deep.
• Crush: The triple-concentric geometry provides exceptional radial stability, maintaining integrity under pressures exceeding 180 MPa (approx. 26,000 psi).

4.2 Why Triple-Layer?

1. Exponential Hydrogen Shielding: Hydrogen diffusion is drastically reduced through three independent seamless metallic walls, protecting against "hydrogen darkening" in high-H2S wells.
2. Mechanical Decoupling: The nested structure ensures that external impacts or tube deformations are absorbed by the outer layers, keeping the innermost fiber in a "zero-stress" environment for precise sensing.

5. Connectivity & Applications of OFSCN® Triple-Layer Downhole High-Temperature Fiber Optic Cable

• Connection Method: Field Fusion Splicing is the primary method. Specialized triple-stage high-pressure compression fittings or orbital welding are used for sealing.
• Pre-termination: High-temperature FC/APC connectors can be pre-installed for easy interface with DTS (Temperature) or DAS (Acoustic) interrogators at the surface.