COMPOSITE HOSE- Design, Construction and Failure

Unlike a conventional rubber hose a Composite Hose is more flexible, lightweight and is primarily used for transfer of aromatic chemicals and liquified gases with cryogenic properties, which may not be suitable for rubber hoses.?

The composite hoses are designed and manufactured as per the following international EN (European) standards:

• EN 13765:2018 - Thermoplastic multi-layer (non-vulcanized) hoses and hose assemblies?for the transfer of hydrocarbons, solvents, and chemicals.?
• EN 13766:2018 - Thermoplastic multi-layer (non-vulcanized) hoses and hose assemblies?for the transfer of liquid petroleum gas and liquefied natural gas.

Composite hose for the transfer of hydrocarbons, solvents, and chemicals

The standards are governed by EN 13765 which specifies requirements:?

• Applicable for bore sizes from 25 mm to 300 mm.
• Applicable for working pressures from 4 bar to 14 bar.
• Applicable for working temperatures from 30 ° C to 150° C.
• Four types of thermoplastic multi-layer (non-vulcanized) hoses and hose assemblies:

* Type 1 hose: suitable for vapor applications.

* Type 2, Type 3, Type 4 hose: suitable for liquid applications.

* Type 3, Type 4 hose: used for STS (Ship-to-Ship Transfers).

Composite hose for the transfer of liquid petroleum gas and liquefied natural gas

The standards are governed by EN 13766 which specifies requirements:?

• Applicable for bore sizes from 25 mm to 250 mm.
• Applicable for working pressures from 10.5 bar to 25 bar.?
• Applicable for working temperatures from - 196° C to + 45° C.
• Two types of thermoplastic multi-layer (non-vulcanized) hoses and hose assemblies:?

* Type 1, Type 2 hose: used based on their pressure and temperature ratings.?

* Type 1 and Type 2 hoses are subdivided into two classes: Class A for onshore duties and Class B for offshore duties (STS).

Construction of composite hose

A composite hose is manufactured in three sections, which primarily is the inner high-tensile inner wire helix, reinforcement and protective liquid-tight layers, and outer high-tensile wire helix.?

Figure 1: Cross sectional view of a typical composite hose

Inner helix wire:?The inner helix wire is made of cargo compatible metal and has pitch corresponding to the outer helix wire. It acts as inner support to prevent hose from collapsing under vacuum and it supports the inner liner and reinforcement fabric layers.??

Figure 2: Typical construction of a composite hose

Outer helix wire:?The outer helix wire has pitch corresponding to inner helix wire forming an interlocking pattern, which provides suitable external strength to the hose, allowing it to achieve the desired working pressure and structural integrity.?

In addition, it binds the various reinforcement layers within the outer and inner helix wires, and also acts as a protective external barrier to prevent the hose from mechanical abrasions during operation.?

Liner:?It is the innermost?protective layer in a composite hose which is in direct contact with the grade of product being transferred. The selection criteria of composite hose should always be verified based on the compatibility of the liner material with the grade of product.?

Reinforcement/Sealing layers:?For desired compatibility with various grades of chemicals/gases, the composite hoses are fabricated using various thermoplastic and reinforcement materials like polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polypropylene, polyamide, acrylic.?

End fittings:?Every composite hose is provided with end fittings, which is either epoxy wet-sealed or crimped dry-sealed. A typical composite hose in maritime use is provided with a fixed flange or a floating flange.?

Figure 3: Fixed flange?????????????????????????????????????????Figure 4: Floating flange

A floating type of flange of composite hose allows faster and easier connection to manifold without the necessity to turn the hose to align with the bolt holes.??

Flange standards and design

Composite hose flange(s) prevalent in marine industry are fabricated using stainless steel (like SUS 316L) or mild carbon steel, depending on their use, which is according to the?American Society of Mechanical Engineers (ASME) B16.5 standards published by the American National Standard Institute (ANSI) Class 150/Class 300.?

The selection criteria for type of pipe flange are dependent on:

• Diameter of the composite hose
• Designed pressure
• Temperature of operation

Typically, ANSI Class 150 composite hose is used for transfer of hydrocarbons, solvents, and chemicals, whereas ANSI Class 300 composite hose is used for transfer of liquid petroleum gas.

A composite hose flange typically has a raised face floating flange opposed to flat face fixed flange which is commonly found on the rubber hose flange face.?

Figure 5: Typical raised face flange???????????????????????Figure 6: Typical flat face flange

A typical raised face flange, as in Figure 5, has a raised surface above the bolting circle where the gasket is placed. Effective sealing on this type of flange face is accomplished by compressing a soft, flat, or semi-metallic gasket between mating flanges in the raised area of the flanges. A raised/flat face flange can be of floating type or fixed type.?

Identification markings on composite hose

As required, the operational detail of a composite hose is permanently marked by the manufacturer using a tape/band on its outer cover as per the standards. Although, composite hoses exposed to very low temperatures during transfer of liquid petroleum gas and liquefied natural gas can be permanently stamped/etched on the flange body.?

Figure 7: Typical composite hose with identification markings

Typical markings on a composite hose include:

• Maker’s details
• Hose material and diameter of hose
• Standard to construction (EN 13765/EN 13766)
• Type number of hose
• Maximum working pressure (MWP)
• Permissible working temperature??
• Quarter and year of manufacturing

An operator must ensure that every composite hose is operation is complying with the applicable design standards to meet the cargo grade requirements. Besides makers test certificate accompanying each composite hose, a hose shall also be type approved from the vessel’s classification society and shall also comply with the local regulations, if applicable.?

The manufacturer of a composite hose shall provide cargo grade compatibility chart for the hose. A user must verify the chemical properties of the product and suitability of the composite hose prior to use.?

Operational concerns of a composite hose

Whereas a composite hose is more flexible and lightweight, the structural integrity of a composite hose is affected/limited by following factors:

1. Operating temperature range:?The minimum and maximum permissible temperature range for a composite hose is provided by the maker. Using a composite hose beyond recommended temperature range can severely affect the structural integrity of the compatible liner grade. Due to properties of thermoplastics material used in composite hose, elevated temperatures are always a disadvantage. Operations at temperatures typically above 60°C can cause elongation of composite hose, which then requires suitable support. Improperly supported composite hose under elevated temperature elongation can undergo plastic deformation and possible displacement of helical wire support from their pitch leading to catastrophic failure of hose.?
2. Operating pressure range:?The hose is certified for MWP by the maker. Simultaneous operation at elevated pressure and temperature is not recommended to prevent damage to composite hose. A sudden pressure surge in composite hose can lead to elongation of hose, which could displace the internal helical wire support from their pitch.?
3. Minimum Bend Radius (MBR):?A composite hose manufacturer provides the MBR. Bending a composite hose beyond the recommended MBR can permanently displace the helical wire from its pitch leading to rupture of hose. A composite hose hence shall be properly supported throughout the length and especially towards the end fittings while in use. The composite hose shall never be stowed, coiled, secured by kinking/bending/coiling beyond recommended MBR.?
4. Flow rate:?The composite hose manufacturer provides the permissible flow rate of a hose, which is dependent on:

* Length of hose

* Diameter of hose

* Viscosity of cargo?

A composite hose due to their internal helical wire design is subjected to higher frictional and pressure losses in comparison to smooth bored rubber hoses. Product with higher viscosity as well as higher flow rate will experience notable drop in pressure across the composite hose, which could eventually displace the inner helical wire support and collapse the hose.?

During operations any abnormal and/or unexplained increase in pressure or reduction of flow rate across the composite hose shall be treated with concerns, with immediate stopping cargo operations and thorough internal inspection of the hose.?

Typical recommended velocities for a composite hose are 7 ~ 9 m/s.?

Figure 8: Max. flow rate for given velocities and bore size (ISGOTT 18.2.5)

Figure 9: An example of good composite hose rupturing catastrophically when loading high density and viscous cargo at agreed low loading rate but exceeding recommended velocity?

Continuity test of composite hose

Composite hose shall be tested for electrical continuity (as per procedures in ISGOTT) and records shall be maintained onboard. The composite hoses are electrically continuous and should have a resistance of less than 100?W, measured between end flange to end flange.?

Electrically discontinuous hoses should have a resistance of not less that 25,000?W, measured between end flange to end flange.?

Pressure testing of composite hoses

Composite hoses are tested as per procedures in ISGOTT 18.2.6.3. Unlike rubber hose, composite hoses elongate more during pressure testing. The testing interval of composite hoses shall never exceed twelve (12) months period. If temporary elongation is in excess of 10% during pressure testing, then the composite hose shall be withdrawn from the service.?

Electrical continuity shall always be tested before and after the pressure testing of composite hose.?

Terms commonly used in pressure testing of hose:

Maximum Working Pressure (MWP):?The MWP is the maximum hose pressure capability. This pressure rating is expected to account for dynamic surge pressures and is used by BS and EN Standards for designing hoses.?

Rated Working Pressure (RWP):?The Rated Working Pressure (RWP) does not take into account dynamic surge pressures and is not to be confused with MWP. It is the working pressure expected during normal working conditions.?

Factory test pressure:?This is referenced in BS EN 1765 and is defined as equal to the MWP.?

Maximum Allowable Working Pressure (MAWP):?The MAWP is used as a reference by the United States Coast Guard (USCG) and is commonly used by terminals to define their system equipment limitations.

Hydrostatic test pressure:?This is the pressure at which the hose is tested at least annually.?

Proof pressure:?This is a one-time pressure that is applied to production hoses to ensure integrity following manufacture and is equal to 1.5 times the MWP.?

Burst test pressure:?This is a test requirement for a single prototype hose to confirm the hose design and manufacture of each specific hose type. The pressure is equal to a minimum of four times the factory test pressure and must be applied in a specific manner and held for 15 minutes without hose failure.

Burst pressure:?This is the actual pressure at which a prototype hose fails. For a successful prototype hose, the burst pressure would exceed the burst test pressure.

Visual and routine inspection of composite hose?

An operator/user must select suitable and cargo grade compatible composite hose, and shall operate, and routinely inspect the composite hose as per the maker’s directives.?

A thorough visual inspection with following findings/damages shall immediately withdraw the composite hose from service:

Figure 10: Damaged external protective cover

Figure 11: Outer helix displaced from pitch, damaged with bulging protective cover?

Figure 12:Inner helix wire collapsed from pitch & protective liner found ruptured

Figure 13:Damaged outer helix wire???Figure 14:Compressive damage to hose body

Fig.15:Corroded flange & retracted ferrule??Fig.18: End flange dislodged from hose

Records of operations (product/grade), handling, routine inspection and pressure testing details of composite hose shall be maintained onboard for effective handling and service life of composite hoses.?