Easy, Flexible and Accurate Ferrite Content Measurement Offshore

In the oil and gas industry it is common to transport the liquid or gaseous goods from high technology to offshore platforms, through undersea pipelines, often under extremely hazardous conditions. These modern production techniques require the use of the most advanced alloys, which offer excellent material properties such as strength, corrosion resistance, and resistance to chloride stress cracking, while still offering the advantages of low maintenance. Two major groups of alloys meeting these requirements are the austenitic and duplex stainless steels. Whilst offering the properties required, these alloys can be significantly affected by the ferrite content. Low ferrite content can result in welded zones becoming subject to hot cracking, while high ferrite content can affect ductility, toughness and corrosion resistance. Fischer have long recognised the need for flexible le measurement systems and the Feritscope® FMP30 addresses all current measurement requirements including on screen statistics, data storage, and easy transfer to PC, and also a special continuous measurement mode. The instrument uses the principle of magnetic induction for ferrite measurement. The FMP30 measures all the magnetic components in the otherwise non-magnetic structure. Thus in addition to delta ferrite, transformation martensite and sigma ferrite phase are also detected. Master Calibration can be performed using Fischer Calibration Standard Set (traceable to The Welding Institute, UK) or for customer specific requirements, a company’s own standards can be incorporated into user specific applications. Cross reference calibration with in-house standards This flexibility was demonstrated by the measurement requirements at OneSubSea Ltd (Leeds). The company required calibration using their own in house generated standards, with the ability to verify calibration to expected ferrite content to their typical duplex stainless steel and on samples with similar curvatures. The OneSubSea Standards contain base mild steel and two samples of typical diameter tubes, one with a ferrite content of 52.3% and a second with a ferrite content of 57.3%. The ferrite content of the OneSubSea Standards were verified using destructive metallographic techniques and represent the much tighter tolerance range required of their duplex stainless. The actual measurements carried out by OneSubSea Ltd involve taking four measurements at 90 degree spacing around the circumference of welded tubes. The mean of these four values are recorded as being representative of the ferrite content of the sample under test. Calibration and application data can be stored on the instrument for easy recall, allowing measurements to be taken in a matter of seconds. The results from any measurements can be viewed statistically on the instrument or downloaded to PC for further evaluation or archiving. The ability to easily, flexibly and accurately measure the ferrite content in welds or heat affected zones and the ability to cross reference with in-house standards were significant in the decision by OneSubSea Ltd to purchase and use the Fischer Feritscope® FMP30. Contact the Fischer team 01590 684100. Fischer’s Alun Lund is Applications Manager for OneSubSea Ltd. www.fischergb.co.uk

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