Bundles and towed installation

Bundles and towed installation

39

COMPARISON OF MATERIALS

Material

Maximum temper- ature

K-value W/m/K (BTU in/hr/ft/F°) 0.021 to 0.024 (0.147 to 0.168)

Needs P-I-P

Installation method and comments

Low density polyurethane foam (LDPUF)

160 °C (320 °F)

Yes Injected

Compliant

Microporous silica

1000 °C (1832 °F)

0.019 to 0.033 (0. 133 to 0.231)

Yes Requires spacers

Alumina silicate microspheres

Mineral or glass wool (Fiberglass)

400 °C (752 °F)

0.040 (0.280)

Yes High thermal conductivity Must be kept dry Requires spacers

Syntactic polyurethene (SPU) and polypropylene (PP)

150 °C (302 °F)

0.200 to 0.400 (1.400 to 2.800)

No Water resistant

Strong but high cost | £2000/m³ ($100/ft³)

Silica aerogel

500 °C (932 °F)

0.012 (0.084)

Yes Novel at present – LNG and LPG lines Very good insulation

LDPUF is injected into the annulus between the flowline and the steel sleeve pipe and is able to transfer thermal expansion loading from flowline to sleeve pipe (compliant structure). Microporous silica is laid around the flowline in moulded tile or fabric quilt form and encased in steel sleeve pipe (pipe-in-pipe). Concentric spacers are required to accommodate the loose- fitting flowline within a sleeve pipe. To reduce cost, it is used in conjunction with alumina silicate microspheres to give a compliant structure. Mineral or glass wool is applied to flowlines in half shell assemblies and then encased in steel sleeve pipe (pipe-in-pipe). Its thermal conductivity is higher than LDPUF and it must be kept dry in a sleeve pipe with concentric spacers. SPU and PP are water-resistant materials that can resist high compressive loads (induced by the hydrostatic head) with minimal creep. They can be used in deep-water applications without a sleeve pipe but have a high material cost. Aerogels are currently being evaluated for cryogenic LNG and LPG lines. They have extremely good insulation properties (0.012 W/m/K (0.084 BTU in/hr/ft/ q F) and can be applied either as a helically-wound strip (see www.cabot-corp.com) or half-shells (see www.aerogel.com). Aspen aerogel, ‘Spaceloft AR5103’ is extremely hydrophobic, and will not absorb water. Since it is not brittle, water paths will not open up through the material. It maintains its flexibility, even at cryogenic temperatures, and lines do not become rigid.

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