Double wall pipe
The present invention relates to a double wall pipe with an inner high pressure pipe ( 1 ) having an inner flow space for harmful and/or flammable liquids, particularly fuel to be infected or hydraulic oil, and with an outer protection pipe ( 2 ) coaxially arranged around the inner pipe, having an enter flow space between inner pipe and outer pipe, for possibly leaking or spilling liquid from the inner pipe, wherein the protection pipe ( 2 ) has several substantially longitudinal arranged grooves ( 23 ) throughout its inner surface ( 21 ); the inner high pressure pipe ( 1 ) is fitted tightly into the protection pipe ( 2 ); and after bending the double wall pipe ( 100 ), the double wall pipe ( 100 ) is unified by surface pressure due to deformation of bending process.
1. 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 ).
2. The double wall pipe according to claim 1 , wherein a clearance between the inner high pressure pipe ( 1 ) and the outer protection pipe ( 2 ) in areas not unified by bending is smaller than 0.5 mm.
3. The double wall pipe according to claim 1 , wherein the grooves ( 23 ) are circumferentially regularly spaced on the inner surface ( 21 ) of the outer protection pipe ( 2 ).
4. The double wall pipe according to claim 1 , wherein three to twelve axially orientated grooves ( 23 ) are provided in the inner surface ( 21 ) of the outer protection pipe ( 2 ).
5. The double wall pipe according to claim 1 , wherein each groove ( 23 ) has a sectional width w of approximately
w =(π/2 n )·ID2,
wherein: n is the number of grooves ( 23 ) in the outer protection pipe ( 2 ); and ID 2 is the inner diameter of the outer protection pipe ( 2 ).
6. The double wall pipe according to claim 1 , wherein the cross sectional area of the outer flow space is greater than the cross sectional area of the inner flow space.
7. The double wall pipe according to claim 1 , wherein the material of the inner high pressure pipe ( 1 ) has substantially the same thermal expansion coefficient as the material of the outer protection pipe ( 2 ).
8. The double wall pipe according to claim 1 , wherein the harmful and/or flammable liquids are fuel or hydraulic oil.
9. The double wall pipe according to claim 2 , wherein the clearance between the inner high pressure pipe ( 1 ) and the outer protection pipe ( 2 ) is 0.2 mm.
10. The double wall pipe according to claim 4 , wherein six axially orientated grooves ( 23 ) are provided in the inner surface ( 21 ) of the outer protection pipe ( 2 ).
11. The double wall pipe according to claim 1 , wherein the inner high pressure pipe ( 1 ) is of the material St 52.4 and contains C, Si, Mn, P, S and/or Al.
12. The double wall pipe according to claim 1 , wherein the outer pipe ( 2 ) is of the material St 35.
13. The double wall pipe according to claim 1 , wherein the double wall pipe is a fuel injection pipe for a two stroke diesel engine.