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51315-5742-Recent H2S Corrosion Tests of Hyper Duplex Stainless Steel

Product Number: 51315-5742-SG
ISBN: 5742 2015 CP
Author: Magnus Olaison
Publication Date: 2015
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A recent developed hyper duplex material UNS S33207 characterized by high strength and excellent localized corrosion resistance can be utilized for downhole tubing raw sea water injection umbilicals and other applications where high strength combined with high chloride induced corrosion resistance is needed as the material has a PREN minimum of 50. The minimum yield strength is 700 MPa (100 ksi) for tubes with a wall thickness larger than 4 mm. The current limit of H2S for duplex material with PREN 40 to 45 in NACE MR0175 is 20 kPa (3 PSI) H2S. Earlier it has been published that UNS S33207 pass C-ring testing at 90°C with 3 PSI H2S. However the limit for UNS S33207s performances in sour environment was not defined and the aim of this work is to investigate how UNS S33207 performs at higher H2S partial pressures than the present limit in NACE MR0175 standard for super duplex.Stress corrosion cracking experiments has therefore been performed on UNS S33207 in different simulated H2S containing low pH environments. The tests have been conducted based on NACE TM0177 using four point bend(4PB) loaded at 100% AYS as well as tensile specimens loaded at 90% AYS both at 90°C. In addition super duplex seamless tube in UNS S32750 has been tested as a reference.No cracks were observed when testing at a partial pressure ranging from 21 kPa (3 PSI) up to 35 kPa (5 PSI) H2S at 25% NaCl and at 52 kPa (7.5 PSI) H2S 15% NaCl. Cracks were observed in the environment that held the lowest pH together with the highest partial pressures of H2S (52 kPa) and NaCl concentration (25%) in constant load testing however the samples did not part but held extensive corrosion. No cracks were observed in neither of UNS S33207 and S32750 after testing using four point bend even at 55kPa (8 PSI) partial pressure of H2S. These results are set in relation to the limits in NACE MR0175.

A recent developed hyper duplex material UNS S33207 characterized by high strength and excellent localized corrosion resistance can be utilized for downhole tubing raw sea water injection umbilicals and other applications where high strength combined with high chloride induced corrosion resistance is needed as the material has a PREN minimum of 50. The minimum yield strength is 700 MPa (100 ksi) for tubes with a wall thickness larger than 4 mm. The current limit of H2S for duplex material with PREN 40 to 45 in NACE MR0175 is 20 kPa (3 PSI) H2S. Earlier it has been published that UNS S33207 pass C-ring testing at 90°C with 3 PSI H2S. However the limit for UNS S33207s performances in sour environment was not defined and the aim of this work is to investigate how UNS S33207 performs at higher H2S partial pressures than the present limit in NACE MR0175 standard for super duplex.Stress corrosion cracking experiments has therefore been performed on UNS S33207 in different simulated H2S containing low pH environments. The tests have been conducted based on NACE TM0177 using four point bend(4PB) loaded at 100% AYS as well as tensile specimens loaded at 90% AYS both at 90°C. In addition super duplex seamless tube in UNS S32750 has been tested as a reference.No cracks were observed when testing at a partial pressure ranging from 21 kPa (3 PSI) up to 35 kPa (5 PSI) H2S at 25% NaCl and at 52 kPa (7.5 PSI) H2S 15% NaCl. Cracks were observed in the environment that held the lowest pH together with the highest partial pressures of H2S (52 kPa) and NaCl concentration (25%) in constant load testing however the samples did not part but held extensive corrosion. No cracks were observed in neither of UNS S33207 and S32750 after testing using four point bend even at 55kPa (8 PSI) partial pressure of H2S. These results are set in relation to the limits in NACE MR0175.

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