Internally profiled tubes
The present invention relates to internally profiled variable pitch tubes or pipes made of steel. The terms tube and pipe are used synonymously in the context of this invention. These tubes are used in the petrochemical industry to crack oil, gas and shale feedstocks into simple hydrocarbons such as ethylene and similar products.
1 . A steel tube for use in cracking hydrocarbons at high temperature, wherein the steel tube has a fin formed on the inner wall of the tube, the fin extending continuously in a helical direction across at least a portion of an axial length of the tube, wherein the fin comprises:
an initial region of constant helical pitch,
an intermediary region of varying helical pitch that extends for at least three helical rotations of the fin, wherein a pitch of the fin in the intermediary region of varying helical pitch increases from its beginning to its end, and
a final region of constant helical pitch.
2 . The steel tube of claim 1 , wherein the fin extends for an entire axial length of the tube.
3 . The steel tube of claim 1 , wherein the initial region of constant helical pitch is between 1 D and 40 D in length (where D is an internal diameter of the tube).
4 . The steel tube of claim 1 , wherein the final region of constant helical pitch is between 1 D and 40 D in length (where D is an internal diameter of the tube).
5 . The steel tube of claim 1 , wherein the intermediary region of variable helical pitch is a length that is at least 80% of the axial length of the tube.
6 . The steel tube of claim 1 , wherein the intermediary region of variable helical pitch is a length that is at least 50% of the axial length of the tube.
7 . The steel tube of claim 1 , wherein the pitch increases at a constant rate along the axial length of the intermediary region of varying helical pitch.
8 . The steel tube of claim 1 , wherein a cross-sectional profile of the inner wall of the tube is circular in shape.
9 . The steel tube of claim 1 , wherein a height of the fin is approximately constant along its axial length.
10 . The steel tube of claim 1 , wherein the tube has an internal diameter in the range of 20 mm to 100 mm.
11 . The steel tube of claim 1 , wherein the tube has an internal diameter in the range of 20 mm to 70 mm.
12 . The steel tube of claim 1 , wherein a cross-section of the fin is semi-circular.
13 . The steel tube of claim 1 , wherein the overall change in helical pitch from the beginning of the intermediary region to the end of the intermediary region is greater than 0.2 D, where D is the internal diameter of the tube.
14 . The steel tube of claim 1 , wherein the fin is a first fin, and wherein the steel tube includes a second fin that at least partially overlaps with the first fin.