What is the Advantage and Disadvantage of welded pipe manufacturing machine

In conversation, it’s sometimes difficult to tell whether the word “welder” refers to a machine or its operator. However, it’s obvious whether a weld bead was laid down by a human or a machine. Automated welding has a level of consistency that even master manual welders can’t match. With machine welds, it’s often impossible to discern individual weld beads. This is especially true in pipe welding, where the nature of the material means that a manual welder must start and stop to change positions. Automated TIG orbital welding has the advantage of being continuous, and given the skill and quality challenges of manual pipe and tube welding, it’s clear that orbital welding is underutilized. Still, there are advantages and disadvantages to orbital welding, and it’s a good idea for any project manager in the development phase of a pipe or tube welding project to consider both before making a decision. 

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Key Advantages of Orbital Welding

In order to understand the advantages of orbital welding, it is necessary to understand how manual pipe welding is usually performed. It is close to impossible for a manual welder to weld the entire circumference of a pipe in a single uninterrupted pass. Instead, the circumference of a pipe is divided up into quarters, and each pass is completed one quarter at a time. This creates inconsistencies as the arc is stopped and started again. Changing the temperature of the fill material and pipe from hot to cold to hot again multiple times affects the degree of penetration and fusion. The welder must also change position for each quarter of the circumference. Two of those quarters will be in the overhead position, which is widely known as a tiring and difficult welding position.

In orbital welding, the operator mounts the weld head by clamping it to the pipe directly (like a set of vice grips) or by using a guide ring fitted to the pipe. With both methods, the weld head moves around a typically stationary pipe. The operator monitors the weld in case an intervention is needed. Orbital welding offers the following advantages compared to traditional manual pipe welding:

• Consistent Weld Bead Results: Since the weld head moves smoothly and automatically around the pipe, there is no need to stop and restart the weld during the course of normal operation. This improves weld quality by ensuring consistent penetration and fusion.
• Consistent Weld Quality Results: Besides not needing to stop and restart, another significant impact on quality is the consistency of the output of the automated orbital welding equipment, which closely monitors and very precisely controls all the process parameters. As long as the joint preparation and the base material properties are consistent, the orbital solution will precisely execute the pre programmed welding procedure which will lead to consistent results.
• Greater Efficiency: A weld head only needs to be set up one time per weld joint, unlike a manual weld, which requires a change in “setup” on every quadrant for each and every pass. Variations in travel speed, weld current, arc voltage, and the feed rate of fill material are accounted for in the weld schedule entered into the machine. Only minor adjustments to electrode angle may have to be made from pass to pass. This speeds up the welding process, and removes fatigue and discomfort as a factor that can lead to inconsistent welds.
• Ease of Use: Orbital welding machines require the trained operator to understand and be familiar with the machine and know how to set it up. Manual welding, in contrast, requires the operator to be practiced in the particular welding process being used, have experience with the properties of the metals and alloys being welded, and be able to maintain efforts for ten- to 12-hour shifts. It is much easier to obtain a consistent and reliable weld from an orbital system with a properly trained operator.

The result of these advantages is the precision, predictability, quality, and consistency that makes a machine weld so immediately identifiable. And this is true of more than just the visual aspect of a weld. Once a weld procedure from an automated orbital system has been qualified for the structural and mechanical characteristics required by the project, the system will be able to reproduce that quality consistently and be able maintain the tolerances specified in the weld schedule. Any application involving high pressures, corrosive substances, or the need to withstand constant vibrations would see major benefits using an automated orbital welding system.

The advantages of orbital welding and other automated welding processes are so manifest and  apply to so many applications that from an engineering standpoint it is surprising that manual welding is still widespread. However, there are some disadvantages to the purchasing, setup, maintenance, and operation of orbital and other automated welding machines.

The Disadvantages of Orbital Welding 

The disadvantages of orbital welding have little to do with the welds produced by an orbital welding machine, which are precise and repeatable as long as all variables are taken into consideration. Instead, they have to do with orbital welding being a relatively rare and niche process. As a result, barriers to adopting orbital welding may arise in the following areas:

• Equipment Costs and Service: The power supplies and weld heads required for an orbital welding setup aren’t common. They are built in limited numbers and often for specific purposes, and are therefore more expensive than typical manual welding setups. Specific orbital welding equipment also isn’t available at local building and hardware stores like manual welding equipment is. If a weld head becomes damaged or a controller becomes unusable, it can be more difficult to replace or fix in a timely manner.
• Training: Countless welding programs and vocational schools teach manual welding processes and industry standards. However, few intensive training programs for orbital welding exist, so training on specific equipment is generally offered only by vendors in certain locations.
• Setup Time: Due to the precise nature of orbital welding, setup time is required. In some applications, this setup time may be more than that required for manual welding.
• Consistent and High-Quality Joint Preparation: On most piping welding applications, consistent weld joint preparation is required. Thus, joint preparation equipment and consumables have to be considered and included in the cost of the solution.  

Many of these disadvantages are more apparent in smaller projects, where the costs of equipment, training, and setup time may not be worth it. However, in large, repetitive pipe welding projects, orbital welding’s advantages quickly outweigh its disadvantages. The key to getting the most out of an orbital welding setup is to choose an experienced orbital welding vendor that offers training classes on specific equipment as well as reliable repair, replacement, and maintenance services.

The Advantages and Disadvantages of Orbital Welding: Maximizing the Advantages

Arc Machines, Inc. (AMI) allows companies to maximize the benefits of orbital welding by offering training classes at their California headquarters and in several other locations in the U.S. as well as in Europe. Thorough documentation of the company’s equipment is available online so users can ensure AMI welding machines are correctly set up every time. Arc Machines also supports its customers with extended warranties and field service that sends trained service specialists to remote job sites to bring machinery back into operation as quickly as possible. AMI’s trained staff of experienced welding experts understand the advantages and disadvantages of orbital welding, and are ready to help your company make the most of automated welding’s many benefits.                           

• Fundamentals and Principles of HF Welding
• Advantages and Disadvantages
• Induction Seam Welding of Pipe and Tubing
• Contact Seam Welding of Pipe and Tubing

Fundamentals and Principles of HF Welding

High Frequency (HF) welding processes rely on the properties of HF electricity and thermal conduction, which determine the distribution of heat in the workpieces. HF contact welding and high-frequency induction welding are used to weld products made from coil, flat, or tubular stock with a constant joint symmetry throughout the length of the weld. Figure 1 illustrates basic joint designs used in HF welding. Figures 1 (A) and (B) are butt seam welds; Figure 1 (C) is a mash seam weld produced with a mandrel, or backside/inside bar. Figure 1 (D) is a butt joint design in strip metal; and Figure 1 (E) shows a T-joint. Figures 1 (F) and (G) are examples of helical pipe and spiral-fin tube joint designs. Figure 1 (J) illustrates a butt illustrates a butt joint in pipe, showing the placement of the coil. Figure 4.L-6 (K) shows a butt joint in bar stock.

HF current in metal conductors tends to flow at the surface of the metal at a relatively shallow depth, which becomes shallower as the electrical frequency of the power source is increased. This commonly is called the skin effect. The depth of electrical current penetration into the surface of the conductor also is a function of electrical resistivity, and magnetic permeability, the values of which depend on temperature. Thus, the depth of penetration also is a function of the temperature of the material. In most metals, the electrical resistivity increases with temperature; as the temperature of the weld area increases, so does the depth of penetration. For example, the resistivity of low-carbon steel increases by a factor of five between room temperature to welding temperature. Metals that are magnetic at room temperature lose the magnetic properties above the Curie temperature. When this happens, the depth of penetration increases drastically in the portion of metal that is above the Curie temperature while remaining much shallower in the metal that is below the Curie temperature. When these effects are combined in steel heated at a frequency of 400 kHz, the depth of current penetration is 0.05 mm (0.002 in.) at room temperature, while it is 0.8 mm (0.03 in.) at 800°C (°F). The depth of current penetration for several metals as a function of frequency is shown in Figure 2.

The second important physical effect governing the HF welding process is thermal conduction of the heat generated by the electric currents in the workpiece. Control of the thermal conduction and of the penetration depth provides control of the depth of heating in the metal. Because thermal conduction is a time-dependent process, the depth to which the heat will conduct depends on the welding speed and the length of the electrical current path in the workpiece. If the current path is shortened or the welding speed is increased, the heat generated by the electric current in the workpiece will be more concentrated and intense. However, if the current path is lengthened or the welding speed is reduced, the heat generated by the electric current will be dispersed and less intense. The effect of thermal conduction is especially important when welding metals with high thermal conductivity, such as Cu or Al. It is not possible to weld these materials if the current path is too long or the welding speed is too slow. Changing the electrical frequency of the HF current can compensate for changes in welding speed or the length of the weld path, and the choice of frequency, welding speed, and path length can adapt the shape of the HAZ to optimize the properties of the weld metal for a particular application.A-11, A-15

Advantages/Disadvantages of HF Welding

A wide range of commonly used metals can be welded, including low-carbon and alloy steels, ferritic and austenitic stainless steels, and many Al, Cu, Ti, and Ni alloys.

Because the concentrated HF current heats only a small volume of metal at the weld interface, the process can produce welds at very high welding speeds and with high energy efficiency. HF can be accomplished with a much lower current and less power than is required for low-frequency or direct-current resistance welding. Welds are produced with a very narrow and controllable HAZ and with no superfluous cast structures. This often eliminates the need for Post-Weld Heat Treatment (PWHT).

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Oxidation and discoloration of the metal and distortion of the workpiece are minimal. Discoloration may be further reduced by the choice of welding frequency. Maximum speeds normally are limited by mechanical considerations of material handling, forming and cutting. Minimum speeds are limited by material properties, excessive thermal conduction such that the heat dissipates from the weld area before bringing it to sufficient temperature, and weld quality requirements. The high process speed may also become a disadvantage if process settings are incorrect, as scrap can be generated at very high rates.

Considering the high processing speeds, with the high equipment cost required for HF welding, it is important to understand the amount of product needs for economic justification.

The fit-up of the surfaces to be joined and the way they are brought together are important if high-quality welds are to be produced. However, HF welding is far more tolerant in this regard than some other processes.

Flux is almost never used but can be introduced into the weld area in an inert gas stream. Inert gas shielding of the weld area generally is needed only for joining highly reactive metals such as Ti or for certain grades of stainless steel.A-11, A-15

Induction Seam Welding of Pipe and Tubing

The welding of continuous-seam pipe and tubing is the predominant application of HF induction welding. The pipe or tube is formed from metal strip in a continuous-roll forming mill and enters the welding area with the edges to be welded slightly separated. In the weld area, the open edges of the pipe or tube are brought together by a set of forge pressure rolls in a vee shape until the edges touch at the apex of the vee, where the weld is formed. The weld point occurs at the center of the mill forge rolls, which apply the pressure necessary to achieve a forged weld.

An induction coil, typically made of Cu tubing or Cu sheet with attached water- cooling tubes, encircles the tube (the workpiece) at a distance equal to one to two tube diameters ahead of the weld point. This distance, measured from the weld point to the edge of the nearest induction coil, is called the vee length. The induction coil induces a circumferential current in the tube strip that closes by traveling down the edge of the vee through the weld point and back to the portion of the tube under the induction coil. This is illustrated in Figure 3.

The HF current flows along the edge of the weld vee due to the proximity effect (see Fundamentals), and the edges are resistance-heated to a shallow depth due to the skin effect.

The geometry of the weld vee is such that its length usually is between one and one half to two tube diameters long. The included angle of the vee generally is between 3 and 7 degrees. If this angle is too small, arcing between the edges may occur, and it will be difficult to maintain the weld point at a fixed location. If the vee angle is too wide, the proximity effect will be weakened causing dispersed heating of the vee edges, and the edges may tend to buckle. The best vee angle depends on the characteristics of the tooling design and the metal to be welded. Variations in vee length and vee angle will cause variations in weld quality.

The welding speed and power source level are adjusted so that the two edges are at the welding or forge temperature when they reach the weld point. The forge rolls press the hot edges together, applying an upset force to complete the weld. Hot metal containing impurities from the faying surfaces of the joint is squeezed out of the weld in both directions, inside and outside the tube. The upset metal normally is trimmed off flush with the BM on the outside of the tube, and sometimes is trimmed from the inside, depending on the application for the tube being produced.A-11, A-15

The HF contact welding process provides another means of welding continuous seams in pipe and tubing. The process essentially is the same as that described above for induction welding and is illustrated in Figure 4. The major difference is that sliding contacts are placed on the tube adjacent to the unwelded edges at the vee length. With the contact process, the vee length generally is shorter than that used with the induction process. This is because the contact tips normally can be placed within the confines of the forge rolls where the induction coil must be placed sufficiently behind the forge rolls, so that the forge rolls are not inductively heated by the magnetic field of the induction coil. Because of the shorter vee lengths achievable with the contact process, an impeder often is not necessary, particularly for large-diameter tubes where the impedance of the current path inside the tube has significant inductive reactance.

An impeder, which is made from a magnetic material such as ferrite, generally is required to be placed inside the tube. The impeder is positioned so that it extends about 1.5 to 3 mm (1/16 to 1/8 in.) beyond the apex of the vee and the equivalent of one to two workpiece diameters upstream of the induction coil. The purpose of the impeder is to increase the inductive reactance of the current path around the inside wall of the workpiece. This reduces the current that would otherwise flow around the inside of the tube and cause an unacceptable loss of efficiency. The impeder also decreases the magnetic path length between the induction coil and the tube, further improving the efficiency of power transfer to the weld point. The impeder must be cooled to prevent its temperature from rising above its Curie temperature, where it becomes nonmagnetic. For ferrite, the Curie temperature typically is between 170 and 340°C (340 and 650°F).A-11, A-15

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