ABSTRACT Despite the excellent corrosion and high yield strength advantages offered by ferritic-austenitic duplex stainless steel its use for submarine pipelines has been limited because of slow welding procedures and resulting high installation cost. An alternative method of joining duplex stainless steel pipe more quickly is "Friction Welding". To evaluate the ability of this process to produce suitable mechanical and corrosion resistant welds, a test program was initiated by Brown &Root. This work was carried out by The Welding Institute using their 1000kN (100 ton) axial thrust friction welding machine. Welds were evaluated by mechanical, corrosion tests and metallography, The test results indicated that mechanical and corrosion properties are not significantly degraded during friction welding and that a duplex pipeline can be installed at twice the speed currently possible. INTRODUCTION In general, ferritic-austenitic (duplex) stainless steel consists of 40-70% ferrite and a typical composition of 22%Cr-5.5%Ni-3%Mo-0.14%N. The resulting steel has properties that are normally found in both phases; the ferrite promotes increased yield strength and resistance to chloride and hydrogen sulphide corrosion cracking; while the austenite phase improves workability and weldability. Initially, the introduction of the newly developed duplex stainless steel, with its ability to resist corrosion attack, combined with yield strength (almost twice that of 300 austenitic series) offered submarine pipeline designers an ideal solution to the increasing corrosion problems, but at an increase in material cost of up to 6.5 times that of carbon steel. The significant advantages of duplex have not been fully realised, because the only way to successfully install submarine pipelines in this material has involved the use of slow weld procedures using GTAW, GMAW equipment, or combinations of both. This has resulted in lay-rates of only 20 main line welds per day (24,4m (80ft) double joints). The main reasons for this slow progress are indicated below:Slow travel speed 38.1–63.5mm (1.5–2.5ins and low deposition rate of the GTAW process.Need to maintain an internal Argon purge until two or three passes have been completed, this eliminates the main advantages of using a multi weld station lay barge.High root repair rates; as most current duplex welding specifications do not allow any root defects.Inspection of the root pass must be completed at the first welding station because it is not practical to re-establish the gas purge to perform repairs at any other location on the barge.Careful control of heat input and interpass temperature to ensure a balanced microstructure (too much heat causes too much austenite to precipitate and too little heat results in too large a ferrite content), The need to adopt welding procedures which minimize these problems have resulted in an installation cost of ten times that of an equivalent sized carbon steel line when this cost is added to the increased material cost, the use of this material becomes prohibitive. Therefore, it is essential that a new joining process be adopted if this material is to be of real benefit in combating the increasing problem of corrosion in submarine pipelines.