Selection of Explosion-Proof Hoses for Metering Skids

Selection of Explosion-Proof Hoses for Metering Skids
The selection of explosion-proof hoses (explosion-proof flexible conduits) for metering skids focuses on compliance with explosion-proof requirements, material compatibility, pressure/temperature matching, dimensional and installation compatibility, as well as qualified protection and corrosion resistance, which must comply with standards such as GB 3836 and GB 50058.
I. Core Selection Criteria (Compliance First)
1. Explosion-Proof Rating and Certification (Critical)
Explosion-proof marking: Must match the hazardous area classification (Zone 0/1/2, gas/dust) where the metering skid is installed.
Gas atmosphere: Ex d IIB T4 Gb, Ex d IIC T6 Gb (common)
Dust atmosphere: Ex tD A21 IP65 T125℃ Db
Certification requirements: The hose and fittings assembly shall be certified by a national explosion-proof authority with a valid explosion-proof certificate.
Standards: GB 3836.1/2, GB 50058-2014, AQ 3009.
2. Material Selection (Based on Medium and Environment)
Main body material
304/316 stainless steel: corrosion-resistant, temperature range -40℃~300℃, suitable for natural gas, oil and gas, chemical media.
Carbon steel with galvanizing/chrome plating: low cost, for dry, non-corrosive environments.
Inner sealing: NBR, FKM (Viton), PTFE, compatible with media (oil, gas, water, corrosive fluids).
Outer protection: Stainless steel braided mesh (pressure and tensile resistance, rodent-proof), PVC/rubber sheath (waterproof, wear-resistant).
3. Pressure and Temperature Matching
Rated working pressure: ≥ maximum working pressure of the metering skid system (commonly 1.6/2.5/4.0/6.4 MPa).
Burst pressure: ≥ 3 times the rated working pressure.
Temperature range: Covers the on-site minimum and maximum temperatures (e.g., -40℃~+150℃).
4. Dimensions and Installation Parameters
Nominal diameter (DN): Match equipment connections (DN15/20/25/32/40/50).
Length: Based on actual on-site distance, with sufficient allowance to avoid stretching.
Bending radius: ≥ 5 times the outer diameter (mandatory by GB 50257, AQ 3009).
Connection type: Male/female threads (G, NPT, M), flanges, quick couplings, consistent with equipment ports.
5. Protection and Corrosion Resistance Grade
Ingress protection (IP rating): ≥ IP65 (dust-tight, splash-proof).
Corrosion resistance grade: WF1 for general environments, WF2 for coastal/chemical areas.
Anti-static: For flammable and explosive media, the hose shall be fully conductive with surface resistance ≤ 10⁶ Ω.
II. Selection Procedure (Directly Applicable)
Determine hazardous area: gas/dust, zone classification (Zone 1/2), medium group (IIA/IIB/IIC), temperature class (T4/T5/T6).
Clarify medium parameters: medium type, pressure, temperature, corrosiveness.
Match explosion-proof marking: select hoses with corresponding Ex marking and certification.
Confirm structure and material: stainless steel with compatible sealing and braided protection.
Determine dimensions: DN, length, connections, bending radius.
Verify protection / corrosion resistance / anti-static performance: IP rating, WF grade, conductivity.
Check standards and certificates: GB 3836, GB 50058, valid explosion-proof certificates.
III. Typical Selection Example (Natural Gas Metering Skid)
Explosion-proof marking: Ex d IIB T4 Gb
Material: 304 stainless steel bellows + 304 braided mesh + FKM seal
Pressure: Rated 2.5 MPa, burst 7.5 MPa
Temperature: -20℃~+80℃
Nominal diameter: DN20
Length: 500 mm
Connections: G3/4" female thread on both ends
Protection: IP65, WF2
IV. Selection Taboos
Using only the hose without a fully certified assembly (hose and fittings must be explosion-proof as a whole).
Bending radius less than 5 times the outer diameter (damages explosion-proof structure).
Material incompatibility with the medium (corrosion, swelling, leakage).
Pressure/temperature rating lower than system working conditions.
No explosion-proof certificate or expired certificate.