Flanges and fatigue testing

Ramiz Selimbasic asks what do non-weld flange connections have to do with flight safety?

The statistics are clear: aircraft remain one of the safest modes of travel available nowadays. This is why aircraft manufacturers are working hard to maintain safety standards during the whole flight process. To test the wings of an aircraft and build up huge test stands, Parker high-performance flanges (HPF) & F37 flange systems are playing a key role.

For aircraft building it is essential to meet strict regulations and certifications to ensure aircraft security. One of the most outstanding components of an aircraft are the wings. These have a width of up to 36m and must withstand huge forces while taxying, takeoff, during flight and landing.

This is why at one of the world's biggest aircraft manufacturers based in UK, fatigue testing of the aircrafts’ wings is performed for various aircraft types. Within the extensive tests, the aircraft wings are mounted on a hydraulically operated test rig to simulate the forces acting on the wings during operation. Testing is then done continuously for several weeks or even months.

To increase capacity a new turnkey facility of approximately 10,000m2 in size was opened in 2018, with a total of four test areas. The construction of the hydraulic system used to power the test stands was completed by the Fluid Power Group, which specialises in the design, manufacture, installation and maintenance of hydraulic, compressed air, fuel and lubrication systems. The company has in-house design and build capabilities, combined with on-site installation and servicing and support for specialised industrial and mobile hydraulic OEMs and, additionally, a wide range of industrial end users.

The team was responsible for the design, manufacture, on-site assembly and commissioning of the hydraulic systems on this project which had some unique challenges and a tight schedule. The goal was to deliver a turnkey hydraulic system that would operate reliably for multiple decades. The 2.4MW power unit set out over two plant rooms needed to be able to intelligently distribute the flow rate of 4,200 litres a minute at 300 bars via four ring mains using pipework from 3in up to a 10in exterior diameter and a total length of 1.9km of large bore piping. Pipelines needed to withstand pressure peaks during operation without any leakages to not interrupt the test-cycles and have therefore been one of the key challenges.

The Fluidpower Group project team focused on reliability and innovation when choosing which companies to partner with for component supply. The team learned about the Parker F37 Parflange, the HPF and the Complete Piping Solutions (CPS) centre through the media. The team then learned about the technical details of both flange systems in-depth during a multi-day visit to the Parker CPS in Augustdorf, Germany and left feeling confident that the Parker solution and the team at the CPS would be the right choice to use and partner with for this project.

The decision taken to use the two Parker flange systems offered significant advantages over classic welding of hydraulic pipes. These included time-savings over traditional welding because heavy wall pipe connectors require several layers and must be made by qualified welders. All welds have to have an X-ray inspection and the pipe systems must be flushed through due to the high contamination from the welding process. Within the project of building the test stand for aircraft wings, the installation process using the Parker system was reduced from days to hours due to the high quality and cleanliness of the components from the outset. The HPF and F37 system was also more environmentally friendly as the flanging process does not cause noxious gases and eliminates fire hazards. This also reduced the need for hot work permits.

During the upcoming weeks many project meetings took place where Parker was able to take the idea to build a customised solution and design of the whole piping infrastructure for the Fluidpower Group. After some cycles of testing and reengineering, the ready-to-use products were delivered. Fluidpower Group was then able to install the whole piping infrastructure on its own.

Fluidpower Group completed the project ahead of schedule, without any issues and was able to comply with customer specifications. Today, the newly built test stands are used to simulate the loads and forces that will impact the wings for several million cycles, along with the other aircraft components that require rigorous testing. In total more than 2,500 HPF and F37 flanges run within the system reliably every day.

Beyond simply selecting its products, Fluidpower Group launched an intensive collaboration with the Parker CPS team and has become an official piping partner. In this partnership, Parker engineers have proven to be innovative designers, and are able to share their long-term experience from other projects to benefit Fluidpower Group.

The company also decided to have pipe and flange components for other projects to be produced in the Complete Piping Solution Centre in Augustdorf and have them delivered onsite. Fluidpower Group also purchased HPF and Parflange F37 machines for pipe finishing. For these, Parker provided extensive training including how to operate the machines, showing pipe manufacture and assembly techniques which allowed for final pipe manufacturing and safe assembly to be completed on-site.

Parker and Fluidpower Group are continuing to strengthen their relationship, working closely together for the benefit of the end customer with one goal: building win-win co-operation for all parties involved.

The HPF was designed as a system that resists tear-off, and that can withstand working pressures up to 500 bar for pipe diameters of 25 to 150mm and wall thicknesses up to 20mm. It is also designed for flange hole patterns in accordance with ISO 6162-1 (SAE J518, Code 61), ISO 6162-2 (SAE J518, Code 62) and ISO 6164.

The HPF design is based on templates from the natural world. The flanging on the pipe recalls the base of a branch where it meets the trunk of a tree: a hydraulic axial press is used to create the flared base of the pipe. The formed area of the pipe creates a parabola that runs from 10° to 37°. The flat start of the formed area creates additional protection against severe system vibrations.

The Parflange F37 system has a similar enlarged area in the pipe. After an F37-flange is pulled onto a seamless pipe, the pipe end to be connected is expanded using a specialised orbital flanging process that compresses the surface of the pipe end through roller-knurling. This gives the end of the pipe a funnel-like shape with an angle of 37°, which explains its name.

A steel or stainless-steel insert is then placed in the expanded end of the pipe with a geometry that matches the funnel-shaped end of the pipe itself. This insert has an O-ring on the funnel-shaped side that seals against the wall of the pipe. There is also a groove on the front of the insert, into which an F37 seal profile seal made of a material like polyurethane is placed. Alternatively, the insert can be designed with a flat front or a steel or stainless-steel compound gasket with an NBR or FKM elastomer sealing lip. There is a special insert shape for pipe-to-pipe connections that has funnel-shaped contours with O-ring seals on both sides.

The Parflange F37 system is licensed for pressure levels up to 420 bar. It can be used to connect pipes with an exterior diameter of 16 to 273 mm (1/2in to 10in flange size).

Ramiz Selimbasic is with Parker Hannifin HPCE