New alloy for oil & gas applications

Longitudinally-welded and redrawn tubes made of VDM® Alloy 825 CTP are now available on the market.

Text & image by Schoeller Werk

The German manufacturer of longitudinally welded stainless-steel tubes, Schoeller Werk, has introduced an innovative product: tubes made of Alloy 825 CTP/2.4861. The new VDM® material Alloy 825 CTP/2.4861 is a fully austenitic nickel-iron-chromium alloy with additions of molybdenum and copper.
Werner Hannig, Director of Product Management and Development, proudly announced: “With longitudinally welded tubes made of the new material Alloy 825 CTP, we are adding a product to our portfolio that stands out as a high quality and application-optimised material alternative.”
The material VDM® Alloy 825 CTP is a further development of the alloy VDM® Alloy 825, which has been used as a standard in the offshore sector for many years. CTP stands for Corrosion, Temperature, Pressure and denotes material types that were specially designed to meet the requirements of the oil and gas industry.

Higher corrosion resistance, better weldability

Alloy 825 CTP/2.4861 tubes offer higher corrosion resistance and better weldability. Schoeller has increased the percentage of molybendum from 2.5 to at least 4.5 percent, resulting in higher corrosion resistance. With an accompanying increase of chromium from 19.5 to at least 21 percent, Schoeller was also able to improve the Pitting Resistance Equivalent Number (PREN) significantly. This ensures that the tubes are less susceptible to chloride-induced pitting and crevice corrosion in seawater.
Unlike Alloy 825, the new material Alloy 825 CTP is melted without the addition of the stabilising element titanium. Due to this change, the quality of the weld seam during a fusion welding process was improved, as it is not possible for titanium carbonitride to melt out in the weld seam area.

Test samples available

Because the Schoeller team recognise that customers need to convince themselves of the effectiveness of the new Alloy 825 CTP/2.4861, test samples of the dimensions 6.35 x 1.24 mm can now be ordered. They also supply customers with the longitudinally welded tubes made of VDM® Alloy 825 CTP in calibrated or redrawn and solution annealed conditions. Additionally, calibrated fabrication lengths are available in the dimensional ranges outside diameter 3 to 127 mm and wall thickness 0.20 to 3.00 mm, as well as redrawn coiled tubes in the dimensional ranges outside diameter 0.80 to 15.88 mm and wall thickness 0.20 to 2.11 mm. On request, the dimension and the specific tube designs can be individualised to fit the respective applications.
Hannig comments: “The longitudinally welded tube made of Alloy 825 CTP is manufactured using the TIG welding process, which is generally carried out at Schoeller Werk without the use of a filler metal. Further heat treatment and cross-section-reducing drawing steps can be used to meet different condition and dimensional requirements. This technological diversity allows us to respond flexibly to specific customer requirements.”

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