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One of the main benefits of Pressurfect XP seamless stainless tubing, according to Sandvik, is that it allows a thinner wall thickness using the same working pressure in GDI systems, thus reducing weight.

New Sandvik stainless tubing enables higher-pressure GDI

To assist the automotive industry in its quest to develop ever more fuel-efficient technologies, Sandvik Materials Technology is launching two grades of seamless stainless tubing—Pressurfect and Pressurfect XP—to handle higher fuel pressures in gasoline direct injection (GDI) engines. The products will be on display in Sandvik’s booth (209) at the SAE 2014 World Congress in Detroit April 8-10.

GDI systems facilitate the injection of fuel into the cylinders at considerably higher pressures, resulting in a more controlled and even burn. Rising fuel pressure in the combustion chamber is placing strains on fuel lines and fuel rails, the supplier notes. In addition, such products are often exposed to a highly corrosive environment, which can be exacerbated by the increasing use of different fuel blends, for example ethanol in regular petrol.

To counter these challenges, Sandvik has developed two tailored steel grades for fuel line and fuel rail production that it claims are highly corrosion resistant and perform well with “the pressures being used today and for the foreseeable future” in GDI systems.

Carbon steel tubing and welded carbon steel tubing exhibit less resistance to corrosion and stress corrosion cracking, according to Jari Ponsiluoma, Product Manager Automotive, Sandvik Material Technology. He believes high-quality stainless steel and duplex (austenitic-ferritic) stainless steel—i.e., Pressurfect XP—will become key enablers in the evolution of GDI technology and next-generation fuel systems.

“Due to the properties of high-quality seamless steel tubing, Pressurfect is capable of handling fuel pressures in today’s GDI systems with a healthy safety margin,” Ponsiluoma explained to SAE Magazines via email. “More importantly, however, it is ideal for coping with the rising pressures in the future generations of GDI systems, which are putting a strain on standard welded or other inferior-quality grades of stainless tubing.”

Due to the material composition of Pressurfect XP, Sandvik can offer lower total life-cycle cost, according to Ponsiluoma. “With this material, the engine designer can already now design more-efficient GDI systems to meet the tougher future legislations. One of the main benefits is that we can offer thinner wall thickness using the same working pressure in the GDI systems. This will give our customers a cost benefit due to lower weight on the tube/component.”

Wall thickness for the tubing ranges from 0.89 to 3.0 mm (0.035 to 0.118 in), with a tolerance of ±10%. At 20°C (68°F), Pressurfect has a proof strength of ≥210 MPa and tensile strength of 515 to 680 MPa, while Pressurfect XP’s proof strength is ≥450 MPa and its tensile strength 690 to 820 MPa.

The new grades are also highly machinable. Sandvik reports that it has received positive customer feedback on Pressurfect’s machinability and brazing properties.

“While the grades themselves are not new, the makers of GDI systems have very specific requirements when it comes to surface properties and other parameters,” Ponsiluoma shared. “Extensive efforts have been made to meet these specific industry requirements and to prove consistent quality and traceability for all batches.”

The material for the fuel rails is extruded, cold pilgered, and solution annealed seamless tubes. The fuel lines are extruded, cold pilgered, cold drawn, and solution annealed seamless tubes.

Ponsiluoma noted that Sandvik’s Automotive group is working with the R&D department and various customers to test the two new products for other future application areas beyond next-generation GDI systems.

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