IE Product Manufacture

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. σ_t /p > 6

According to thin cylindrical formula, wall thickness of pipe

                    

                         t = (P.D/2σ_t)                                     

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. σ_t) +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

σ_t= 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.

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.

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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