Due to its attractive combination of strength corrosion resistance and cost 25% Cr Duplex Stainless Steel Pipe is used extensively in subsea production systems. Pipes are made by different production methods. The various production methods affect the microstructure and the mechanical properties of the final product. Components used subsea are externally exposed to cathodic protection. Experiences have shown that 25Cr duplex stainless steel is vulnerable to hydrogen induced stress cracking (HISC). The assumption is that the resulting microstructure affects the resistance. This is reflected in the DNVGL-RP-F112 design guideline which uses austenite spacing to determine a design factor. In this paper the HISC susceptibility of 25Cr duplex stainless-steel pipes produced through hot extrusion with- and without subsequent cold drawing forging and centrifugal casting have been examined. Two different test methods have been used; i) Stepwise (slow) load increase and ii) Slow Strain Rate Testing. Samples pre-charged with hydrogen and samples without hydrogen were included in the test program. Pre-charged samples were also polarised cathodically during testing under stress.The microstructure was characterised including measurements of austenite spacing. After testing the samples were examined in optical microscope for secondary cracks. In addition the fracture surfaces were examined in scanning electron microscope for characterisation of fracture morphology. Reduction in area were calculated for all samples. Finally hydrogen content in selected samples were measured with a melt extraction technique.The tests revealed that 25Cr duplex stainless steel from the different production methods included in the test showed various degree of HISC and that the effect was dependant on the production method and resulting microstructure. Hot extruded material with no cold deformation showed the highest HISC resistance while centrifugal cast material seemed to be more exposed to HISC than the other methods. The fracture surfaces of all hydrogen charged test materials showed features indicating a reduction in ductility due to HISC as well as both ductile and brittle fracture characteristics across the surfaces. The fracture surfaces for the reference specimens showed ductile fracture characteristics. The hydrogen content in the charged samples were in the range 50-80 wppm.The ranking of production methods was as follows: hot extruded pipes > hot extruded pipes with subsequent cold drawing > forged pipes >centrifugal cast pipes.The two test methods – stepwise load increase and SSRT – gave consistent test results.

For the design and materials selection of equipment in chemical plants the focus seems to mainly be on the “chemicals” but it is actually the water (steam) that causes corrosion issues in many cases. This paper presents two cases that demonstrate the poor design and materials selection that ended up causing severe corrosion issues. In both cases the equipment are fixed tubesheet type of heat exchangers (one is vertical and another is horizontal) and the concerned materials are mainly 300 series stainless steels. The root causes of failure in these two cases are due to poor design and non-ideal materials selection.Key words: Materials Selection Heat Exchangers Fixed Tubesheet Stress Design.PRESENTER BIOGRAPHYYouyu Lu Senior Corrosion Engineer Lloyd’s Register Energy Americas Inc.Vishal Lagad Senior Corrosion Engineer Lloyd’s Register Energy Americas Inc.Roxanna Alvarez Metallurgical Consultant Lloyd’s Register Energy Americas Inc.

Chloride-induced steel corrosion is one of the main causes of premature deterioration of reinforced concrete (RC) structures in marine environment. This study aims to develop a probabilistic model to evaluate the service life of reinforced concrete beam element subjected to chloride-induced corrosion attack. Concrete block specimens containing steel bars were prepared and subjected to accelerated corrosion test. As the corrosion-induced mass loss of steel bars reach different levels ranging from 0% to 30% the tests were terminated. The steel bars were took out of the concrete block and cleaned with a sand blaster and then scanned with a 3D laser scanner at intervals of 1 mm. The distribution of the residual cross-sectional areas of the steel bars was determined and fitted with mixed normal distribution functions due to the presence of pitting corrosion. In addition to describe the spatial variation of the pitting corrosion along the length of steel bars a pitting index R was introduced which is the ratio of the average to the minimum cross-section area of corroded steel bars. Probabilistic analysis showed that the pitting index R could be fitted with the Gumbel distribution function. The probabilistic model of corroded steel bars was then introduced to analyze the carrying capacity of rectangular RC beams and consequently the service life of these beams. The service life of these RC beams was defined as the critical limit state when the actual load effects exceed the resistance at any beam element. Based on Monte Carlo simulation the cumulative probability of failure was calculated and the effect of corrosion on the service life of beam element was evaluated in a probabilistic way.