What are Induction Bends ? Induction Bending is a controlled means of bending pipes through the application of local heating using high frequency induced electrical power. Originally used for the purpose of surface hardening steels, induction technology when used in pipe bending consists basically of an induction coil placed around the pipe to be bent. The induction coil heats a narrow, circumferential section of the pipe to a temperature of between 850 and 1100 degrees Celsius (dependant on the material to be formed). As the correct bending temperature range is reached, the pipe is moved slowly through the induction coil whilst the bending force is applied by a fixed radius arm arrangement. Induction Bends/Spools and air/steam rings Tube Bending are manufactured by the process of induction heating in meeting diverse high quality requirements in accordance with ASTM, API, DIN, BS, ANSI, ASME PFI and other international technical specifications.

Manufacture of Induction Bends

Induction bends are formed in a factory by passing a length of straight pipe through an induction bending machine. This machine uses an induction coil to heat a narrow band of the pipe material. The leading end of the pipe is clamped to a pivot arm.
As the pipe is pushed through the machine, a bend with the desired radius of curvature is produced. The heated material just beyond the induction coil is quenched with a water spray on the outside surface of the pipe. Thermal expansion of the narrow heated section of pipe is restrained due to the unheated pipe on either side, which causes diameter shrinkage upon cooling.
The induction bending process also causes wall thickening on the intrados and thinning on the extrados. The severity of thickening/thinning is dependant on the bending temperature, the speed at which the pipe is pushed through the induction coil, the placement of the induction coil relative to the pipe (closer to the intrados or extrados), and other factors.
Most induction bends are manufactured with tangent ends (straight sections) that are not affected by the induction bending process. Field welds are made or pipe pup sections are attached to the unaffected tangent ends, allowing for fitup similar to that found when welding straight sections of pipe together.
Induction bends come in standard bend angles (e.g. 45°, 90°, etc.) or can be custom made to specific bend angles. Compound bends (out-of-plane) bends in a single joint of pipe can also be produced. The bend radius is specified as a function of the diameter. For example, common bend radii for induction bends are 3D, 5D and 7D, where D is the nominal pipe diameter.

Applications

• Oil & Gas Sector – Onshore and Offshore Sub-Sea applications

• Refineries

• Petrochemicals

• Power Plants

• Fertilizers

• Metallurgical Industries

• Shipping and other Infrastructure Projects

Bending Capablities

Advantages

• Large radii for smooth flow of fluid.
• Cost efficiency, straight material is less costly than standard components (e.g. elbows) and bends can be produced faster than standard components can be welded.
  
• Elbows can be replaced by larger radius bends where applicable and subsequently friction, wear and pump energy can be reduced.
  
• Induction bending reduces the number of welds in a system. It removes welds at the critical points (the tangents) and improves the ability to absorb pressure and stress.
  
• Induction bends are stronger than elbows with uniform wall thickness.
  
• Less non-destructive testing of welds, such as X-ray examination will save cost.
  
• Stock of elbows and standard bends can be greatly reduced.
  
• Faster access to base materials. Straight pipes are more readily available than elbows or standard components and bends can almost always be produced cheaper and faster.
  
• A limited amount of tools is needed (no use of thorns or mandrels as required in cold bending).
  
• Induction bending is a clean process. No lubrication is needed for the process and water needed for the cooling is recycled.
  
• Minimum wall thinning rate and ovality.
  
• Precise bending radius and angle.
  
• No pipe wrinkles.
  
• Reduced oxidation or de-carbonization due to instantaneous heating.
  
• Lesser impurities or scratches on the inner surface.
  
• Diverse bendings: square pipe, flat bar, I-beam, H-beam, channel sash, etc.
  
• Three-dimensional bendings without any welding.
  
• Special heat treatment for stainless steel not required due to prompt heating and water-cooling.
  
• Uniform hardness.
  

Major advantages of induction bending are:

• Elbows can often be replaced by larger radius bends, reducing friction, wear and required pump capacity.
• Induction bending reduces the number of welds in a system.

• No welds at the critical points thanks to the tangents. 
• Less non-destructive testing,  saving cost.

• Induction bends are stronger than elbows with uniform wall thickness
• Stock of elbows and standard bends can be greatly reduced.
• Straight pipe is more readily available than elbows, reducing time to market
• Bends can be made from the same base material as the straight pipe.
• Induction bending does not need  bend dies or mandrels. A simple clamping/ inductor set covers  a wide range of radii and wall thicknesses
• Induction bending is a clean process. No lubricants necessary.

ASME B16.49

Bending Process

The pre-inspected pipe having positive thickness is kept on the pipe carriage and clamped hydraulically on the rear carriage. The induction coil and cooling coils are mounted around the pipe.

The concentricity of induction coil is adjusted with 3-plane movement to assure the uniform heating by induction. The radius of bend is fixed by adjusting the radius arm and front clamp. The pointer is also set to the correct degree. The pipe is pushed forward slowly so as to clamp rigidly with front clamp. The pipe is marked for arc length and initial thickness / hardness measurements.

Before starting the bending operations the hydraulic pressure / water level / flow switches etc. are checked. The pipe is now heated by induction to the temp of 815 - 995 C. By pushing the pipe by push clamp the bending of the pipe is started slowly and carried out at speed of 10 - 40 mm/min.

The bending operation is stopped at the specified angle of bend and predetermined arc length. The bend is removed from the machine and kept on an inspection platform for measurement of tolerances.

Potential Material for Induction Bend

• Carbon Steel (Seamless/Weld Seam) - (API 5L X42-52-60-65-70, P265GH, P295GH...)
  
• Alloy Steel - ASTM A 335 Gr P11, P22, P5, P9, P9.1, P9.2, X20, 15CD205, 15Mo3, 15NiCuMo
  
• Stainless Steel - TP 316, 316L, 304, 304L
  
• High Chrome Steel
  
• High Nickle High Chrome Steel
  
• Inconel
  
• Monel Metal
  
• Copper Alloy
  
• Titanium (Grade 1, Grade 2, Grade 3, Grade 4, Grade 5)
• Line Pipe - API 5L X52 / X65 / X70 / X80 – X100, A106 Grade.B / Grade.C / P1/ P9, A312TP304, TP316
• Inconel 625
• Incolloy 600H
  

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