How do we make... pipes?

Posted on November 02, 2015 by Caren-Malina Butscher, Images by Robert Hack

A glimpse into the mtu pipe-making shop reveals that it involves more than just pipe-bending.
Friedrichshafen, Germany

Whether they carry water, oil, fuel or air, dozens of pipes provide life-giving sustenance to mtu engines. Pipes deliver liquids and gases to where they are needed for combustion, cooling, aspiration and power transmission. Because of the many different engine models and applications, mtu not only buy pipes from suppliers but also manufactures them in-house. And a glimpse into the mtu pipe-making shop reveals that it involves more than just pipe-bending. mtu staff produce between 350,000 and 500,000 pipes a year.

The pipes for all models are stored in a twelve-metre-high racking system.

At first sight, it looks like a self-service area at an IKEA store, but there are no sofas or lamps on the high-rise racking in the pipe store. The twelve-metre-high racks contain piping with diameters from four to 159 cm and a standard length of six metres. There is a choice of steel, stainless steel, copper, brass and a sea-water resistant alloy of copper, nickel and iron (CuNiFe). The material used depends on the engine model and its application. Pipes intended for a Series 396 submarine engine for example must not have magnetic properties, so chrome-nickel pipes are fitted. The total number of possible different piping variations is 16,500 – a figure that illustrates the vast extent of the product range.

After processing on the CNC machine, the pipe comes out with multiple bends.

CNC machine bends used for pipe-bending

In the cutting shop, production worker Bernhard Bentele fetches a pipe from the high-rise rack and cuts the bar stock to the required length on the two circular cold saws. The lengths used vary between one and three metres. Before further processing, the pipes are deburred and washed. To shape the pipe to fit so that it closely follows the engine contours, it is processed by a CNC (computerised numerical control) machine. The CNC machine bends pipes with a diameter ranging from five to 70 mm according to precisely defined programs, so that every pipe is identical. The process is computer-controlled and so has a lower reject rate than a manually operated work process would have. Pipe-machinist Thomas Günthör places the pipe in the bending machine. The machine draws in the straight length of pipe, and after a few seconds feeds it out again with a complicated series of bends.

Pipes with smaller diameters are joined to the fitting by soldering.

Soldering: gas or flame?

A washing machine cleans the pipes at a temperature of roughly 70°. Once all dirt has been removed, the pipe and fitting are either soldered on the inductive soldering stations or, in the case of large diameters, welded. With soldering, there is a choice of inductive soldering using inert gas or flame-soldering with flux. With both processes, the pipe is heated evenly from all sides and joined to the connecting part in that way. In the case of larger pipes, high-precision work is required: The welding machine current has to be set so that it produces a melt, the pipe material becomes fluid and can be joined to the fitting with the aid of a welding rod. Finally, the pipe surface is pickled and given a corrosion-proof coating. To make sure the joint does not leak, it is pressure-tested under water with compressed air at 0.5 bar. Pipes that are subjected to higher pressures on the engine are tested for leaks on a special test bench by pressurising with oil to 80 bar.

Large pipes are welded. The welding machine produces a melt so the pipe can be joined to the fitting with the aid of a welding rod.

Point of contact

Klaus Jäger
+49 7541 90 3316

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