[0001] This invention relates to the continuous finishing of pipe.
[0002] In the production of steel pipe, pipes are rolled or formed and finally processed
in finishing facilities which are usually composed of a straightener, nondestructive
inspection equipment and an end cutter.
[0003] Conventionally, pipes are cooled on a cooling bed, and the ends of the pipes are
cut by an end cutter to a predetermined length. The cut pipes are straightened and
inspected for quality by nondestructive inspection facilities.
[0004] The conventional finishing method has the following problems:
1) the pipes have to be straightened after having been cut to the required length.
However, the end parts of the pipes are difficult to straighten using a rotary straightener.
Therefore, after cutting, another straightening step is required, as an off-line operation;
2) when the ends of the pipes are seized by the rolls of the rotary straightener,
they are prone to deformation or crushing. Any crushed ends have to be cut off by
an end cutter, which is another off-line operation, and which lowers the yield;
3) the length of the pipes can change with straightening. Where there is a severe
dimensional requirement, the pipe may have to be re-cut, which is another off-line
operation.
4) the pipes have to be inspected after cutting. However the end parts of the pipes
are difficult to inspect by nondestructive inspection facilities. This lowers the
inspection accuracy which thus threatens the guarantee of quality of the products.
Therefore the cut pipe ends have to be re-inspected, which is another off-line operation.
Sometimes, the end parts have to be re-cut after re-inspection, which lowers the yield
of the products.
[0005] Generally a conventional rotary straightener is composed of three or four pairs of
skewed concave rolls accommodated in stands.
[0006] Japanese laid-open Patent Publication No.123419/1986 discloses a method of straightening
wherein the offset, or the deviation of the path line of bent pipes, and the crush,
or the difference between the pipe diameter and the roll clearance of the straightener,
are predetermined by a set of equations. However the ends of the pipe cannot be straightened
by the method according to this publication.
[0007] Japanese laid-open Patent Publication No.18244/1985 discloses a method wherein the
pressure of the rolls is dynamically adjusted to avoid crushing of pipe ends. However,
it is very difficult to avoid crushing when the pipes are straightened at high speed.
[0008] It is an object of the invention to provide a method of continuous finishing of pipe.
It is an object of the invention to provide a method which continuously finishes the
pipe without re-straightening and re-inspecting.
[0009] The invention provides a method of continuous finishing of pipe comprising the steps
of:
straightening rolled pipes which have been cooled on a cooling bed;
inspecting said straightened pipes by nondestructive inspection; and
cutting the inspected pipes, to a predetermined length.
[0010] In this method, a high speed straightener having at least five roll pair stands can
be utilized for the straightening step. The number of the stands is preferably five
but may be six or seven. The plural pairs of the rolls of the stands adjacent to each
other can co-operate to achieve the maximum offset. As a rule the distance between
adjacent ones of the stands is 750 to 850mm. The skew angle of said pair of rolls
is normally set in a range of from 35° to 50°. The outer diameter of the pipe should
be from 25.4mm to 153.7mm. As a rule, the speed of advance of the pipes is less than
4.0 m/sec. A cutter is utilized for the cutting, which cuts plural pipes in one cycle.
[0011] For a better understanding of the invention, and to show more clearly how the same
may be carried into effect, reference will now be made, by way of example, to the
accompanying drawings, in which:
FIGURE 1 is a flow chart of an embodiment of the invention;
FIGURE 2 is an explanatory illustration of an embodiment of the invention;
FIGURE 3 is an explanatory illustration wherein is shown a previous proposal not in
accordance with the present invention; and
FIGURE 4 is an explanatory illustration wherein an embodiment of the invention is
shown.
[0012] A problem encountered in the conventional finishing of rolled pipes is that straightening
and inspection in on-line operation is not sufficient to achieve the required quality.
Therefore off-line operation is required, wherein additional operations have to be
carried out. Moreover, pipes with a length of from 6 to 45m and with comparatively
small diameter are straightened at a maximum speed of only 120 m/min, which is not
sufficient for on-line operation. Hence the rolled pipes are cut, straightened and
inspected by off-line operation.
[0013] To solve these problems, it is proposed to straighten and inspect the rolled pipes
before they are cut to the required length.
[0014] The main obstacle in this on-line operation is the capacity, that is, the line speed
of the straightener.
[0015] As shown in Figure 1, a rotary straightener 20 is arranged downstream of a rolled
pipe cooling bed 10 and a nondestructive inspection device 30 is arranged downstream
of the rotary straightener 20. A pipe cutter 40 is arranged downstream of the nondestructive
inspection device 30.
[0016] The nondestructive inspection device 30 is composed of a leakage flux detector; a
thickness meter which may be an electromagnetic supersonic thickness meter or a supersonic
thickness meter; and a meter which measures the outside diameter of the pipe. The
detecting capacity of the device is 192 m/min. The cutter having a cutting grinder
can cut the plural pipes in one cutting cycle which promotes cutting efficiency and
cutting accuracy, and minimises burring.
[0017] This is an on-line operation. By this operation the bent parts and collapsed ends
of pipes are cut off as crop ends, or removed in the cutting operation.
[0018] Also the uninspected ends of the pipes are included in the crop ends.
[0019] Therefore in this on-line operation, there is no off-line operation and no lowering
of the yield by re-cutting of the pipes.
[0020] As an example of this improvement the number of persons in an operating crew was
cut by 30. The yield increases were almost 1%. A guarantee of quality was established.
[0021] All these improvements depend upon the capacity of the high speed straightener.
[0022] In the illustrated embodiment of Figure 2 a high speed straightener having five stands
and five pairs of rolls is utilized in the straightening. As shown in Figure 2, the
rotary straightener is composed of five stands each of which incorporates two concave
rolls skewed as for the pass line. The top and bottom rolls are skewed at the same
absolute value of angle as for the pass line but in the positive and negative direction.
As the rolls are rotated at the same speed, the pipe is spirally moved towards the
delivery side.
[0023] The clearances between the top and the bottom rolls are set smaller than the outside
diameter of the pipe to apply a plastic deformation. The middle points of the clearances
of the rolls at No.1, No.4 and No.5 are on the pass line. The middle points of the
clearances of the rolls at No.2 and No.3 are off the pass line which is called the
offset of the rotary straightener.
[0024] To increase the speed of the rotary straightener the rate of rotation of the motor
which drives the roll may be increased. However as the result of the increase of the
rotational speed of the rolls, the rotational speed of the pipe increases, which gives
rise to vibration of the pipe and may break the pipe. To increase the translational
speed of the pipe without increasing the rotational speed of the rolls, it is desirable
to set the skew angle in a range of from 35 to 50° instead of the conventional range
of from 25 to 35°. However, with such a high skew angle, the area of contact of the
pipe with the rolls is decreased, which reduces the plastic deformation of the pipe,
which is needed to straighten the pipe. This problem, met in high speed straightening,
is solved by adopting a five-stand rotary straightener.
[0025] As shown in Figure 3, in an earlier method, the rolls of No.1, No.3 and No.4 stands
are on the line, or the middle point of the clearance between the top and the bottom
roll of a stand on the pass line. The rolls of No.2 stand are in an offset position.
the straightening deformation is carried out be a single bending with the maximum
offset of d
max.
[0026] As shown in Figure 4 in the present method, the rolls of No.1, No.4 and No.5 are
on the line and the rolls of No.2 and No.3 are in offset positions. As shown in this
embodiment, when the plural sets of the rolls adjacent to each other co-operate to
achieve the maximum offset of d
max, the quantity of the maximum offset can be increased without applying an excessive
offset on a single stand which may cause a spirally shaped defect on the surface of
the pipes.
[0027] The number of the stands of the rotary straightener is not limited to five but may
be more than five. However when the number is increased, the chance of defect generation
and the investment and the maintenance cost are increased. Therefore the number is
limited to seven.
[0028] The distance between adjacent stands is preferably from 750 to 850 mm. When the distance
is more than 850 mm, the leading end of the pipe is seized only with difficulty by
the rolls. When the distance is less than 750 mm, a severe enough bending is difficult
to impose on the pipes. Therefore the distance is determined to be from 750 to 850
mm.
[0029] As a rule, range of outer diameters of the pipe wherein the invention is practicable,
is from 25.4 to 153.7 mm.
[0030] It is desirable to set the angle of the rolls in a range of from 35° to 50°. are
on the skew angle is less than 35°, the rotational speed of the roll is excessive
and the pipe wall may be cut through during its straightening. When the skew angle
is more than 50°, the area of contact of the pipe with the rolls is so low that a
reasonable plastic deformation cannot be achieved.
[0031] The translational speed of advance of the pipes is preferably no more than 4.0 m/sec.,
since when the rotational speed of the pipe at the rotary straightener is over 3000
rpm, it may cause the breakage of the pipe even when the skew angle of the rolls is
set as 50°.
[0032] As for the length of the pipes, there is no limitation. In this example, the upper
limit of the length of the pipes is 45 m. However it may be 100 m or more. It depends
on the overall capacity of the rolling mills.
1. A method of continuous finishing of pipe, characterized by the steps of:
straightening rolled pipes already cooled on a cooling bed;
inspecting the straightened pipes by nondestructive inspection; and
cutting the inspected pipes to a predetermined length.
2. A method according to claim 1, characterized in that a cutter is utilized for the
cutting, which cuts a plurality of pipes in one cycle.
3. A method according to claim 1 or 2, characterized in that the translational speed
of advance of the pipes is below 4.0 m/sec.
4. A method according to claim 1, 2 or 3, characterized in that a high speed straightener
comprising five stands, each having a pair of rolls therein, is selected for performing
said straightening step.
5. A method according to claim 4 characterized in that the skew angle of each said
pair of rolls is set in a range of from 35° to 50°.
6. A method according to claim 4 or 5, characterized in that the number of the stands
is six.
7. A method according to claim 4 or 5, characterized in that the number of the stands
is seven.
8. A method according to any one of the claims 4, 5, 6 or 7 characterized by the step
of causing two adjacent plural pairs of the rolls to co-operate with each other to
achieve the maximum offset.
9. A method according to any one of claims 4 to 8, characterized in that the distance
between adjacent ones of said stands is from 750 to 850 mm.
10. The use of a high speed straightener comprising five stands of roll pairs, in
an on-line method of continuous finishing of pipe.