Patent ID: 7770602

Claim:
A double wall pipe, comprising: an inner high pressure steel pipe ( 1 ) having an inner flow space for harmful and/or flammable liquids; and an outer protection steel pipe ( 2 ) coaxially arranged around the inner high pressure steel pipe ( 1 ) and having an inner surface ( 21 ), the outer protection pipe ( 2 ) being formed with a plurality of substantially longitudinally arranged grooves ( 23 ) throughout the inner surface ( 21 ); wherein the inner high pressure pipe ( 1 ) is fitted tightly into the outer protection pipe ( 2 ), the inner high pressure pipe ( 1 ) and the outer protection pipe ( 2 ) are united into one component ( 100 ) by a bending process by surface pressure due to deformation of the bending process such that the grooves ( 23 ) form an outer flow space between the inner high pressure steel pipe ( 1 ) and the outer protection steel pipe ( 2 ), for containing any liquid leaking or spilling from the inner high pressure steel pipe ( 1 ), and wherein the inner high pressure pipe ( 1 ) has a hardness degree greater than that of the outer protection pipe ( 2 ).