Electrifying tube bending

A CNC (computer numerical control) tube bending machine with advanced programmability is helping Siemens Subsea Products to improve the precision and production efficiency of subsea hydraulic components and systems. Steve Hadrell explains.

Bennex Anguila cobra heads can contain up to 13 precision-bent hydraulic tubes. Photos from Unison.

Hydraulic distribution, connection and control systems, for subsea use with equipment such as wellhead trees, have very demanding tube fabrication requirements, not dissimilar to those of the aerospace industry.

Much of this equipment is intended for operation at depths to 3000m and beyond, which means the tubes can be subjected to extreme internal and external pressures, and has a design life of 30 years or more. Common requirements include use of costly corrosion resistant alloys, the need to form complex precision bends with tight process control, to prevent mechanical stresses that would seriously impair the tubing’s strength, and very small production batch sizes – which demand considerable tooling changeover flexibility and exceptionally high standard manufacturing.

Such demands can lead manufacturers to outsource tube production to specialist third-party tube bending companies.

Siemens Subsea Products recently chose a different strategy for small bore tube manufacturing. The firm produces a diverse range of electrical and hydraulic power and control systems, as well as fiber-optic communications connectors, for subsea applications. Many of these products reply on small-bore metal tubing to convey hydraulic fluid for power and control purposes. Typical examples include hydraulic flying leads with multiple quick connections, subsea distribution units and the Bennex Anguila range of cobra heads, used to terminate hydraulic and electrical umbilicals on subsea equipment.

Until last year, Siemens Subsea Products fabricated some of the tubes for these products in-house, using manual bending techniques, but met about 50-60% of its needs using bought-in preformed parts. The tubes’ dimensions and properties depend on the application, but they are typically 1-3m-long, with outside diameters from 3/8in. to 5/8in. and have a 3mm wall thickness. Many are manufactured from extremely hard alloys, such as Inconel and Duplex/Super Duplex stainless steel – materials which are extremely difficult or even impossible to bend by hand.

Siemens Subsea Products’ hydraulic workshop in Norway uses this Unison tube bender for all small-bore tube fabrication.

In 2013, to improve production efficiency, the company equipped its hydraulic workshop at Kongsberg in Norway with a Unison all-electric tube bending machine. It chose all-electric servomotor-based movement instead of traditional hydraulically powered technology because this offered more accurate and repeatable results, lower energy consumption and lower noise. Fast tool changeover was also important – many of the tubes are produced in very small batch sizes. Unison was able to develop a machine configuration specifically for Siemens.

The tube bending machine undergoing final commissioning checks at Unison’s UK manufacturing facility, prior to shipment.

The tube bender is a 25mm model based on Unison’s Breeze platform of all-electric machines, with “rise and fall” pressure dies, which allows it to perform right- and left-handed bending. This increases manufacturing efficiency by allowing tubes up to 6m in length with multiple complex precision bends to be produced in one continuous machine cycle. Previously, manual bending required repeatedly inserting each tube into various forming dies and required a minimum space between bends of 20mm to allow for clamping; this is reduced to just 5mm on the bending machine, allowing Siemens to create parts that are optimized for space-constrained applications much more easily.

Storm Trosdahl, Product Specialist for hydraulic distribution systems at Siemens Subsea Products, says: “For applications such as our cobra heads, where we are packing up to 13 hydraulic lines in a very confined space, we necessarily have to use some small radii tube bends, with precision control over the bending process to avoid stressing the material. This was difficult to achieve manually, but the Unison machine allows us to apply constant torque throughout the bending process, while also controlling the rate of bending. This makes it easy to control the resultant changes in the material. Also, of course, it has sufficient torque to handle all our requirements, including bending tubes made from Inconel (a type of alloy) – which we previously always had to contract out.”

The first project to use the machine was the production of 800 tubes for hydraulic flying leads intended for deployment in Indonesia’s South Belut gas field in the South Natuna Sea, involving an eight-well subsea tieback to a central processing platform in the North Belut gas field. Each tube is manufactured from 316 stainless steel and required as many as six complex bends, followed by orbital welding at both ends. There were eight different tube configurations, and all 800 were produced to exactly the right dimensions, with no wastage. The next major use of the bending machine was producing tubes for cobra heads destined for the Greater Plutonio project in offshore Angola, where the equipment will be used at depths of 1600m.

All critical movement axes on the Unison tube bender are driven by software-controlled servomotors, providing fully automated set-up, that allows fast and repeatable fabrication of parts with accuracies to within fractions of a millimeter. This programmability and repeatability are key to Siemens Subsea Products’ manufacturing strategy. Instead of using drawings to convey requirements for manual tube bending, the company now designs every tube on an Inventor 3D computer aided design system that is networked to the bending machine. After producing a prototype and verifying its accuracy, any necessary corrections are fed back into the process to ensure that all subsequent parts are manufactured to the same consistent quality. This has resulted in a significant reduction in expensive material scrap; with manual bending, the company was losing about 6m of tube per week to trial parts and production errors – the figure is now typically about 0.5m per week.

Siemens Subsea Products now produces all its tube parts in-house. Instead of requiring five people with specialist fabrication skills to produce 40% of the tubes that it needs, it now takes just one machine operator to satisfy all production requirements. Automating the bending process has also reduced production costs. Siemens originally estimated a machine payback period of slightly less than two years – in itself a good figure – based on a typical £100/part cost for third-party bending. The machine has paid for itself in half this time.

Over the past year, Siemens Subsea Products has also produced hydraulic flying leads for a number of smaller projects, such as Ithaca Energy’s Stella oil field in the North Sea, which is currently under development, as well as undertaking specialist tube bending work for several third-party subsea equipment manufacturers.

Steve Haddrell has served as key accounts manager for Unison since 2009. Prior to that, he was UK branch manager for the Optonics division of machine tool manufacturer Yamazaki Mazak. Hadrell has also worked in senior sales management and technical support roles for a number of other machine tool manufacturers, including Kerf Developments and the 600 Group.