TPi May 2019

fitting must have sufficient strength and hardness to be able to deform the material.

About Sandvik Sandvik is a developer and manufacturer of products in advanced stainless steels and special alloys for the most demanding environments, as well as products and systems for industrial heating applications.

Field tests investigating different grades for H&I tubing Tests were conducted in two different marine environments: the west coast of Sweden (temperate climate), and Florida (tropical climate). The investigations examined tubes made of 316L, Alloy 825, 904L and SD 2507, and samples were exposed to sea spray at both sites. The tests were performed for a duration of 12 or 13 months, and included both tubes with fittings (not Alloy 825) and bent tubes in 316L, to investigate whether stress corrosion cracking could be promoted in cold- formed material. All fittings were made of 316L. Firstly, the results indicated that both 316L and Alloy 825 were unsuitable material choices for marine H&I installations in both test environments: both saw large amounts of pitting corrosion. The 316L components also displayed crevice corrosion of the tube material under the fitting ferrule, as well as corrosion on the coupling threads. In the temperate conditions of Sweden, samples made from 904L developed minor pitting corrosion but no crevice corrosion inside the fittings. In the higher humidity, higher temperature conditions of Florida, all grades suffered both pitting and crevice corrosion, with the exception of SD 2507. Alloy 904L provides a level of minimal corrosion resistance that may be sufficient for coastal H&I installations in temperate

zones, but warmer or more tropical environments call for higher alloyed grades, such as super-austenitic 6Mo, Alloy 625 or SD 2507. The super duplex (SD 2507) offers the greatest cost benefits as well as higher yield strength, which allows for thinner tube walls, resulting in a more lightweight system overall. As the field investigations demonstrated, SD 2507 is also highly resistant to corrosion under marine and coastal conditions. This, in combination with its high material strength and mechanical properties, makes it a robust and recommended material solution for marine H&I systems, where higher initial investment is rewarded with prolonged service lifetime and reduced maintenance costs.

Sandvik Materials Technology – Sweden www.materials.sandvik

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TUBE PRODUCTS INTERNATIONAL May 2019

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