EHTT - Extremely High Temperature Tubing

Extremely High Temperature Tubing – Insulated tubing connected by welding

EHTT fabrication with P91 steel
EHTT fabrication with P91 steel

MAJUS developed with an oil major a solution to thermally insulate tubing for fluid up to 525°C. A first study confirmed no showstopper to install insulated pipe-in-pipe tubings in horizontal wells to circulate fluids at 525°C. In 2014, a prototype was fabricated and assembled over the wellhead by welding before insertion into a well for a pilot with molten salt. The testing are still ongoing.


The EHTT is a pipe-in-pipe technology using Izoflex as insulation material. Pre-fabricated sections are fabricated in Majus plant and sent on location where it is welded over the wellhead. EHTT can withstand high temperature up to 525°C.

Thanks to a dedicated sliding seal developed by a world class specialist, stresses induced by the thermal expansion between the inner pipe and the outer pipe are very low.


The EHTT was developed for oil shale production. The process involved is to heat the reservoir up by very high temperature fluid circulating through the EHTT, the kerogen is cracked in-situ and hydrocarbons (oil & gas) are produced by a standard production well.