NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING
PGDIE-42
Industrial Engineering
Assignment on Product Manufacture:-
Presented By: -
Saket
A. Wankhede
PGDIE
42
Roll
NO. 84
Jitendra Nayak
PGDIE 42
Roll No.118
STEEL PIPES
INTRODUCTION
The pipes are used for
transporting various fluids like water, steam, different types of gases, oil
and other chemicals with or without pressure from one place to another. Cast
iron, wrought iron, steel and brass are the materials generally used for pipes
in engineering practice. The use of cast iron pipes is limited to pressures of
about 0.7 N/mm2 because of its low resistance to shocks which may be created
due to the action of water hammer. These pipes are best suited for water and
sewage systems. The wrought iron and steel pipes are used chiefly for conveying
steam, air and oil. Brass pipes, in small sizes, finds use in pressure
lubrication systems on prime movers. These are made up and threaded to the same
standards as wrought iron and steel pipes. Brass pipe is not liable to
corrosion. The pipes used in petroleum industry are generally seamless pipes
made of heat-resistant chrome-molybdenum alloy steel. Such type of pipes can
resist pressures more than 4 N/mm2 and temperatures greater than 440°C.
DESIGN OF PIPES
1.
Inside diameter of the
pipe
The
inside diameter of the pipe depends upon the quantity of fluid to be delivered
Let
D = Inside diameter of the pipe,
v = Velocity of
fluid flowing per minute, and
Q =
Quantity of fluid carried per minute
We know that the quantity of fluid
flowing per minute
2. Wall thickness of the pipe
After deciding upon the
inside diameter of the pipe, the thickness of the wall (t) in order to
withstand the internal fluid pressure (p) may be obtained by using thin
cylindrical or thick cylindrical formula
a) Stress across the section of the pipe is uniform.
b) Internal
diameter of the pipe (D) is more than 20 times its wall thickness i.e.
D/t>20.
c) The allowable stress is 6 times more than the
pressure inside the tube i.e. σt /p > 6
According to thin cylindrical formula, wall thickness of pipe
t = (P.D/2σt)
A little consideration
will show that the thickness of wall as obtained by the above relation is too
small. Therefore for the design of pipes, a certain constant is added to the
above relation.
T= (P.D/2. σt) +C
C is a constant and its value changes
according to material.
DESIGN
OF PIPES
Assumptions:
Steam passing
through the tube:
Q=
2400 m3/h = 40 m3/min
p=
1.4 N/mm2
v=
30 m/s = 1800 m/min
σt= 40
MPa = 40 N/mm2
Solution:
Inside diameter of the pipe
We know that inside
diameter of the pipe,
MANUFACTURING PROCESS
The process consisted of
forging individual metal plates over a mandrel to produce an open-seam pipe, and then heating the mating edges of the
open seam and welding them by pressing them together mechanically in a draw bench.
Welded steel
tubes and pipes are manufactured with either a longitudinal or a spiral
(helical) seam. The diameters of these products range from approx. 6 to 2500
mm, with wall thicknesses from 0.5 to approx. 40 mm.
1. Fretz-Moon process:
In this process, named after its
inventors, steel strip in the form of a continuous skelp is heated to welding temperature in a forming and welding line
(Fig. 1). The stock is continuously formed by rollers into an open-seam
tube and then the mating edges are pressed together and welded by a process
related to the forge-welding technique of old. Tube and pipe from 40 to 114 mm
outside diameter can be manufactured in this way, with welding speeds ranging
from 200 to 100 m/min respectively.
Figure1. Fretz-Moon welding line viewed from
below
The hot-rolled steel strip coils
used as the starting material are uncoiled at high speed and stored in loop accumulators. These serve as a buffer during the
continuous production process, enabling the trailing end to be
butt-welded to the leading end of the strip provided by the next coil. This
continuous strip or “skelp” is taken through
a tunnel furnace where it is heated to a high temperature. Laterally arranged burners increase the temperature at the
skelp edges to a welding heat approx. 100 to 150 °C higher than the temperature prevailing at the skelp
centre. The forming roll stand shapes the continuously incoming skelp into an open-seam pipe, the circumference
of which is slightly reduced (by approx.
3 %) in the downstream squeeze roll welding stand, which is offset at 90° to
the preceding stand. The upsetting
pressure which this welding stand produces causes the edges to be pressed together and welded. The weld structure is further
compressed in the following, again 90° offset, and reducing roller stands which serve to size the tube. A flying hot
saw located downstream of the welding line cuts the endless tube into
individual lengths which are then conveyed via cooling beds to the tube
finishing department.
In modern Fretz-Moon facilities, the endless tube is directly charged to a stretch-reducing mill. This is provided in the run out line for rolling the stock in the same heat to various diameters down to approx. 13 mm. The tube string is then cut into individual lengths for placement on the cooling beds. This combination of facilities has the advantage that the Fretz-Moon plant can be used for a single, constant tube diameter, so eliminating costly roll changing and resetting work.
In modern Fretz-Moon facilities, the endless tube is directly charged to a stretch-reducing mill. This is provided in the run out line for rolling the stock in the same heat to various diameters down to approx. 13 mm. The tube string is then cut into individual lengths for placement on the cooling beds. This combination of facilities has the advantage that the Fretz-Moon plant can be used for a single, constant tube diameter, so eliminating costly roll changing and resetting work.
2. Electric resistance welding
DC processes
The processes which operate with
direct current or employ the quasi-direct current effect were
developed for the longitudinal welding of small tube up to 20 mm, and in special
cases up to 30 mm OD, with small wall thicknesses from 0.5 to approx. 2.0 mm.
The advantages of DC welding compared with low-frequency and
high-frequency methods are derived in particular
from the relatively smooth finish of the inside pass with no more than minimal ridging (reinforcement). This advantage is important in
tubes in which a smooth inside weld is required and where inside
flash removal is not possible, such as in the case of tubes for heat exchangers
or for subsequent drawing.
The range of applications of the DC process is limited by the electrical
power which can be transmitted by the disc electrodes employed.
The welding speeds attained range from 50 to 100 m/min. The
tubes produced are, without exception, subsequently cold stretch-reduced, in
which process the thickness of the main body is increased slightly more than
that of the weld zone, as a result of which these tubes exhibit virtually no
internal weld protrusion at all. For tolerance reasons, cold-rolled strip is employed as the starting material.
Low-frequency process
In this process, welding is performed with alternating current frequencies from 50 to 400 Hz. An electrode comprising two insulated discs of a copper alloy serves not only as the power supply but also as the forming tool and the element which generates the necessary welding pressure.
Figure 2. Low Frequency pressure resistance
welding
The electrodes constitute the critical components of the plant, because
not only must they be provided with a groove which matches the
diameter of the tube being manufactured, but also this radius has to be
constantly monitored for wear during production operations.
The material extruded during the pressure welding process forms an inner
and outer flash along the weld zone which has
to be removed inline just downstream of the welding point by internal and
external trimmers.
Provided that the process is carefully monitored in line with these
various requirements, the low frequency welding method can produce welds of a
high degree of perfection. This process is used
to manufacture longitudinally welded tube from 10 to 114 mm in diameter at
welding speeds of up to approx. 90 m/min, depending on the wall thickness.
High Frequency Welding (Electric Resistance Welding)
The Electric Resistance Welding
(E.R.W) is also known as high frequency contract welding. The world most
sophisticated and efficient method of tube welding. The H.R.Steel Strip cut to
specified width with a very close tolerance and with edges that are in the
ideal condition for perfect welding will be made to pass through various rolls,
will be formed as open seem pipes, then through the connection from plant the
edges of open seem pipe will be heated and welded (at this point the welding
unit plant delivers current at a frequency of 4,50,000 cycles per second .) the
welded edges joint together under forcing pressure by roles . The result is a
strong welded pipe /tube like any other metal but without change in its
chemical composition. Soon after welding the special cutting tool completely
removes the weld flash on the outer surface of all welded tubes. The weld flash
in the bore of the tube is also trimmed when specified. At this stage an
arrangement of roles size and straighten to the tube to the close tolerance as
required. Once this is done the tube automatically cut into specific pre
determined lengths.
Figure 3. Complete Manufacturing process of ERW
Finally the emphasis is laid on
precision. When specification or application demand grater dimensional
accuracy, enhanced physical properties and a super fine finished is performed
without any trace of the inner and outer weld flash. The tubes are then finally
checked thoroughly for dimensional accuracy and surface quality as required by
various specifications.
The
same process is described in phases here under:
a) The strips will be available is
60/80 feet folded lengths. The folded raw materials will be available in
bundles. The bundles will be open and straightened to facilitate welding for
joining the strips to have a continuous feeding to the machine.
b) Then the joined strip will be feeded to
machine in the first stage the machine will remove the bends and straighten the
strip for the correct formation of pipe. The pipe making mill will be connected
to a slippering motor to have movement to the various rolls and to the raw
material feeded to the machine. The speed of the movement will depend upon the
feeded Raw Materials width the thickness. Because of this movement there will
be friction between the rolls and strip. Because of the friction the Rolls and
some parts of the machine gets heated. Hence the mill will be connected by an
efficient and continuous water circulation system to cool the rolls and machine
parts.
c) The next phase in the passage of
raw materials through slitting zone to remove the excess and uneven edges.
d) The next phase is the passages of
raw materials through various rolls to convert into open seem pipe.
e) The next phase is the passage of
open seem pipe through welding rolls where the mill will be connected to an
automatic electrical welding unit which releases required heat to melt the
edges of the open seem pipe and through the pressure from rolls the edges and
gap will be closed and becomes closed pipe. Then by using a special cutting
tool the weld flash will be removed.
f) The welded pipe will be made to
pass through cooling zone where there will be a continuous cool water supply to
control the heat caused by automatic electrical welding. The manufacturing process
requires continuous cool water supply to control the heat arises due to
manufacturing process.
g) The next phase will be the sizing
and straightening of the Pipes. Here the pipes and tubes will be made to pass
through rolls to control the bends of pipes.
h) The next phase will be the
passage of pipes through cutting machine where the pipes will be cut into
required sizes and removing the pipes from machine bed with the finished goods.
INSPECTION
PROCEDURE
Stainless steel, nickel and
titanium alloy tubes are manufactured on most modern production equipment,
whereby the applied production methods assure the highest possible standard of
quality. Moreover, for continuous quality assurance and -control testing
department is equipped with most modern testing facilities, i.e. tensile test
machinery, hardness measuring apparatus, ultrasonic and eddy-current testing
line, coldwater-pressure test equipment and many other modern destructive and
non-destructive test instruments. All tests carried out on material or finished
products can be split into major categories: Mechanical and technological
tests, microstructure examination, Non-Destructive tests and Corrosion tests.
The tests mentioned below will be carried out according to the relevant
material specification or on special request to be agreed upon in the purchase
order.
Manufacturing Flowchart:
Figure 4. Electric Resistance
Welding process flowchart
In the above figure intermediate and
product inspection steps are taken at each steel pipe mill. There are various
facilities for eddy current detection, magnetic particle detection, ultrasonic
detection, amalog sonoscope inspection, fluoroscopic inspection, spark tests,
etc. These non-destructive inspections are conducted from time to time on specifications
and dimensions of steel pipe, or in compliance with requests from the user,
therefore making quality assurance guaranteed.
Various Testing Methods:
1.
Ultrasonic Testing Method:-
This test involves ultrasonic
sound waves being aimed, via a coupling medium, at the material to be tested. A
proportion sound is bounced back at the coupling medium/material interface but
the remainder enters the material and is bounced back from the internal
surface, to the external surface, where a transducer converts the sound into
electrical energy. This is then monitored on a cathode ray tube. If a
calibrated standard is shown on the tube, any deviation from the standard will
be immediately visible, thus indicating cracks or internal defects.
The below is the ultrasonic
testing machine employed in the manufacturing facility of the pipe. It measures
the outside diameter and wall thickness automatically and indicates any
deviations from the specified dimensions.
Figure
5. Ultrasonic Tester
2.
Hydrostatic testing:-
This is
used to test the manufactured items under a test pressure equivalent or greater
than pressure encountered in operation. It involves filling the tube with
demineralised water, which cannot be compressed, and increasing the pressure,
to that specified, inside the tube. The pressure is transmitted to the tube by
the water and therefore a pressure to which the tube has been tested is
obtained.
3.
Amalog
Sonoscope Tester:-
Amalog-Sonoscope
is an inspection system that combines non-destructive techniques of EMI
(electro-magnetic induction) and UT (ultrasonic) principles. This technology is
used to detect, evaluate and classify transverse and longitudinal, internal and
external flaws, together with wall thickness variations and laminations. This
is undertaken in a single pass of the pipe through the system.
The inspection system is composed of two
main sections – the inspection platform and the computerized inspection
electronics. Placed within a pipe conveyor line, the pipes are advanced to the
inspection platform. Mounted on this platform are pinch rolls that contain the
pipe and provide the driving power to move it at a constant speed though the
three individual inspection heads, or positioners.
.
REFERENCES
[1] A Textbook on Machine Design by R.S.
Khurmi and J.K.Gupta.
[2]
Speciality Pipe and Tube by JFE Steel Corporation.
[3]
Steel Tube and Pipe Manufacturing Processes by Dr.-Ing. Karl-Heinz
Brensing, Dusseldorf.
[4]
www.tradekey.com/brochure/...3/manufacturers-process-india.pdf