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ISO 27127:2021 – Thermoplastic Multi-Layer Hoses for LPG and LNG Transfer
Specifications, classification, and testing requirements for cryogenic and liquefied gas hose assemblies
Introduction to ISO 27127:2021
ISO 27127:2021 is the second edition of an international standard that specifies requirements for thermoplastic multi-layer (non-vulcanized) hoses and hose assemblies used for transferring liquefied petroleum gas (LPG) and liquefied natural gas (LNG). Developed by ISO/TC 45 Subcommittee SC 1, this standard replaces ISO 27127:2014 and represents a significant technical revision that aligns with current industry practices for safe gas transfer.
These specialized hoses are engineered for the unique challenges of liquefied gas handling, including extreme low-temperature service, high-pressure operation, and stringent safety requirements related to flammability and static discharge. The standard covers multiple hose types with bore sizes ranging from 25 mm to 300 mm and working pressures up to 1.4 MPa (14 bar).
ISO 27127 specifically applies to LPG and LNG transfer hoses. For general hydrocarbon, solvent, and chemical transfer applications, refer to ISO 27126. The two standards share a common hose construction philosophy but differ in performance requirements reflecting the distinct hazards of liquefied gases.
Classification and Performance Characteristics
ISO 27127 defines four hose types tailored to different liquefied gas transfer scenarios. Each type is characterized by its pressure rating, temperature capability, and intended service conditions.
| Parameter | Type A | Type B | Type C | Type D |
|---|---|---|---|---|
| Max working pressure | 0.4 MPa (4 bar) | 1.0 MPa (10 bar) | 1.4 MPa (14 bar) | 1.4 MPa (14 bar) |
| Proof pressure | 0.6 MPa (6 bar) | 1.5 MPa (15 bar) | 2.1 MPa (21 bar) | 2.1 MPa (21 bar) |
| Min burst pressure | 1.6 MPa (16 bar) | 4.0 MPa (40 bar) | 5.6 MPa (56 bar) | 5.6 MPa (56 bar) |
| Vacuum rating | 0.05 MPa | 0.09 MPa | 0.09 MPa | 0.09 MPa |
| Bore size range | 25-200 mm | 25-200 mm | 25-200 mm | 25-300 mm |
| Key feature | Basic LPG service | Medium-pressure LPG | High-pressure LPG/LNG | Large-bore LNG transfer |
The 2021 revision introduced several important changes including the addition of flammability testing (new Annex G), burst pressure requirements (new Table 4), and multi-component adhesive specifications for hose assemblies. The temperature tolerance for minimum temperature was also removed, providing greater flexibility in cold-service applications.
LPG and LNG hoses operate in potentially explosive atmospheres. The electrical continuity requirement between end fittings is a critical safety feature. The 2021 revision modified these resistance requirements — always verify that your hose assemblies meet the latest specifications before putting them into service.
Materials, Construction, and Dimensional Standards
The hose construction for ISO 27127 follows a multi-layer thermoplastic design with internal and external wire reinforcement. The material selection is critical for low-temperature performance, as thermoplastics can become brittle below their glass transition temperature.
Key Construction Elements
| Component | Material Options | Critical Properties |
|---|---|---|
| Inner liner | Polyamide, Polyethylene, PVDF | Chemical resistance, low-temperature flexibility, permeation resistance |
| Reinforcement layers | Polyester fabric, Aramid fabric | Tensile strength, pressure containment, dimensional stability |
| Internal wire helix | Galvanized steel, Stainless steel | Collapse resistance, vacuum stability, corrosion resistance |
| External wire helix | Galvanized steel, Stainless steel | Pressure containment, abrasion resistance, static dissipation |
| Outer cover | Thermoplastic polyurethane (TPU), PVC | Weather resistance, abrasion protection, UV stability |
| End fittings | Carbon steel, Stainless steel, Brass | Leak tightness, pull-off resistance, corrosion compatibility |
The addition of multi-component adhesive requirements for hose assemblies in the 2021 revision addresses a longstanding industry challenge: ensuring reliable bonding between different layers and fitting components in cryogenic service. This is particularly important for LNG applications where thermal cycling can stress adhesive bonds.
Performance Testing Regime
ISO 27127 mandates an extensive testing program to verify hose safety and performance. The standard distinguishes between type tests (design qualification) and routine tests (production quality control), with batch tests providing additional statistical process control.
Critical Test Methods
| Test | Annex | Significance for LPG/LNG Service |
|---|---|---|
| Crush recovery | Annex A | Essential for hose deployed on ship-to-shore transfer arms where crushing loads occur |
| Thermal ageing | Annex B | Evaluates degradation at elevated temperatures that can occur in solar-exposed installations |
| Low-temperature fitting test | Annex C | Critical for LNG service — verifies fitting integrity at cryogenic temperatures |
| Hydrostatic testing sequence | Annex D | Validates the complete pressure containment system including end fittings |
| Fitting security | Annex E | Measures pull-off force — a key safety parameter for personnel protection |
| Leak tightness | Annex F | Essential for preventing gas escape in hazardous area installations |
| Flammability | Annex G (NEW) | New in 2021 — addresses fire risk in LPG/LNG handling environments |
The flammability test added in the 2021 revision (Annex G) is a critical safety enhancement. LPG and LNG are highly flammable, and hose materials must not propagate flame or contribute to fire spread. Always specify hoses that have passed the flammability test for applications where fire risk exists.
Engineering Design Insights
When designing LPG and LNG transfer systems with ISO 27127 hoses, several engineering considerations come to the forefront. The minimum bend radius at low temperatures is particularly important — thermoplastics become stiffer as temperature decreases, and the standard’s bending tests at sub-ambient temperatures (referencing ISO 10619-2) provide essential design data.
The change-in-length requirement at proof pressure (modified in the 2021 revision from working pressure to proof pressure) affects system layout and stress calculations. Hose elongation under pressure must be accommodated in the piping design to prevent excessive loads on end connections and support structures.
For large-bore LNG transfer (Type D, up to 300 mm), the hose weight and bending stiffness become significant design factors. Proper hose handling equipment and bend restrictors are typically required to prevent over-bending and to manage the substantial forces involved in ship-to-shore transfer operations.
For LPG/LNG hose assemblies in cyclic temperature service, consider implementing a periodic proof pressure test program. The thermal cycling between ambient temperature and cryogenic conditions can gradually degrade the bond between hose layers and end fittings, making regular verification of fitting security (Annex E) a prudent maintenance practice.
Frequently Asked Questions
Q1: Can ISO 27127 hoses be used for both LPG and LNG?
A: Yes, but the specific hose type must be selected based on the operating temperature and pressure. LNG service typically requires Type C or D hoses due to the lower temperatures (-162 °C for LNG vs -42 °C for LPG at atmospheric pressure). The end fitting material compatibility must also be verified.
A: Yes, but the specific hose type must be selected based on the operating temperature and pressure. LNG service typically requires Type C or D hoses due to the lower temperatures (-162 °C for LNG vs -42 °C for LPG at atmospheric pressure). The end fitting material compatibility must also be verified.
Q2: What is the key difference between ISO 27127 and EN 1474-2?
A: ISO 27127 covers the hose specification itself, while EN 1474-2 addresses offshore LNG transfer systems including the complete hose handling and connection system. Both may apply to offshore LNG transfer applications.
A: ISO 27127 covers the hose specification itself, while EN 1474-2 addresses offshore LNG transfer systems including the complete hose handling and connection system. Both may apply to offshore LNG transfer applications.
Q3: How often should ISO 27127 hose assemblies be tested?
A: The standard specifies test frequencies for different test types in Clause 8. Routine tests are performed on production batches, while type tests are conducted for design qualification. In-service inspection intervals should follow applicable regulations and manufacturer recommendations.
A: The standard specifies test frequencies for different test types in Clause 8. Routine tests are performed on production batches, while type tests are conducted for design qualification. In-service inspection intervals should follow applicable regulations and manufacturer recommendations.
Q4: What does the low-temperature fitting test (Annex C) involve?
A: Annex C specifies a method for testing fittings subjected to low temperatures. The hose assembly is conditioned at the minimum rated temperature and then subjected to pressure and bending loads while cold. This verifies that the end fittings remain secure and leak-tight under cryogenic conditions.
A: Annex C specifies a method for testing fittings subjected to low temperatures. The hose assembly is conditioned at the minimum rated temperature and then subjected to pressure and bending loads while cold. This verifies that the end fittings remain secure and leak-tight under cryogenic conditions.
