La description

~Freet has manufactured six generations pre-stressed insulated  tubing(PIT) since ***9.
PIT as a high-tech product of Freet have applied two national patents, one patent of Supercritical insulated tubing manufacturing (***********9.9)has been awarded to Freet(Supercritical insulated tubing is the fifth generation of PIT).
The other patent of sulfate resistance pre-stressed insulated tubing welding has been accepted, and product have been applied in down-hole of PDO with great effect.
VIT (the four generation of PIT)is composed of host string, thermo-case, coupling, seal ring and liner pipe.
The insulated tubing adopts double-walled enclosed welded structure; the inner tube is treated with pre-stressing during welding.
 There are multi-layer insulation structure in the annulus space and getter in the thermo-case which can reduce heat transfer,  energy loss by convection and radiation,  and protect hydrogen explosion and  prolong the service life with special handicraft treatment.
VIT applies to such operating condition as the temperature of heat carrier is not over **0℃. It mainly applies to steam thermal recovery well with “huff and puff” and “steam drive” as well as heavy oil well with “integration of production and injection”.
Using VIT correctly can not only reduce the heat loss of steam injection and guarantee steam quality but also decrease casing deformation and protect cementing casing.
The thread type of VIT is API buttress modified.
With PTFE seal ring inside coupling and insulated liner in annulus space between inner and outer tube they can not only assure positive confinement among pipe strings and connection reliable but also insure the laminar flow state of steam injection and reduce the resistance of steam transport and heat loss in the coupling.

VIT is manufactured in accordance with the standard of SY/T******4   Pre-stressed insulated tubing .VIT with different performance grades can meet the needs of thermal recovery for heavy oil, super heavy oil with different depth and horizontal wells.
The thermal conductivity(λ) of VIT is less than 0.*2w/m*℃, which K value is less than 0.**2 BTU/(h-ft- °F)(,and equal to grade D and E in SY/T******4), is the fourth generation PIT for heavy oil thermal recovery leading in domestic market.
VIT both grade D and E applies to heavy oil well and super heavy oil well, and can improve the quality of injected steam and development effect after steaming; it also applies to production well with high water, and protects oil string, too. At the same time, VIT can not only save fuel and shorten steaming circle obviously but also have distinguished economic and social benefit.
Supercritical  insulation tubes (SIT) is a new product territory in which hasn’t been set foot in the world, and also the fifth generation product of pre-stressed insulated tubing .
The product can meet such well condition that temperature of steam injection is not more than **0℃, injection pressure is not more than *6MPa, and the well depth is less than ***0 meters.
It can meet the requirements of the steamed thermal recovery for both heavy oil well and super heavy oil well.