Is ‘PUR’ or ‘PIR’ better for cryogenic supports for LNG terminals?

PUR (polyurethane) and PIR (polyisocyanurate) are both cellular insulation materials produced from a catalytic self-polymeric reaction of isocyanate. They are widely used in chemical, alkene cracking plants and LNG storage and transportation where excellent cold insulation capability is required.

The difference between PUR & PIR is that PUR is a much stronger material able to absorb impact. PIR is a very brittle material that is normally used as low density line insulation but it is not suitable for use at pipe support locations where high loading has to be absorbed.

PUR is moulded by Bergen Pipes Supports to the required shape & so has no residual stress. PIR is generally cut from bun stock which can have high residual stress & can cause cut pieces to distort. Their operating temperatures are similar (PUR’s range is -196 ~ 140oC and PIR’s is -196 ~ 160oC).

PIR has better fire resistance than PUR, but PUR is acceptable for LNG applications.

Vapour stops are applied to the end of the low-density insulation by the installation contractor to prevent vapour from spreading along the pipe. It is standard practice to apply  vapour stops each side of pipe supports, valves & flanged joints as it is usually accepted these items will need maintenance at some time in the life of the plant. Vapour stops consist of a short section of ‘sacrificial’ insulation each side of the support or valve. This can be removed easily without causing damage to the main insulation. A coat of sealant is applied to the exposed surfaces of our cryogenic supports during manufacture to prevent moisture damaging the insulation.

We use proprietary adhesives for both processes and we apply these adhesives according to the manufacturers’ recommendations, so there should be no reason to do any testing on either process, apart from visual inspection. We have in the past tested the bond strength of the PUF to PUF joints, and, if the client wishes, we can test the joint strength and arrange for third-party testing of the foil to PUF bond. With regard to water-vapour permeability – the foil we use is fully tested and rated so we do not consider it necessary to perform independent testing. It is vitally important that all joints are made correctly and thoroughly on site by the installation contractor otherwise moisture will be drawn into the insulation and cause major icing problems. Joints can also be reinforced using products such as Foster’s Mastafab or Temati’s Scrimtex in combination with Foster’s 90-66.