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Corrosion Risk Evaluation of Duplex Stainless Steel UNS S82551 in Treated Seawater Injection Well Service

In seawater handling systems, better dissolved oxygen controls would permit the use of more cost effective materials such as duplex stainless steel UNS S82551. Corrosion testing of tubes joined together with a proprietary premium threaded connection was performed in controlled seawater loops simulating service conditions at 30°C.

 

Product Number: 51317--9608-SG
ISBN: 9608 2017 CP
Author: Perry Nice
Publication Date: 2017
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$20.00
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In seawater handling systems the available well tubing materials are GRE lined low alloy steel or the so-called Corrosion Resistant Alloys (CRA’s) such as super duplex stainless steel. However in treated seawater (e. g. with dissolved oxygen removed) the corrosion risk can be controlled and lower grade alloys can be considered. Past experience has shown that treated seawater injection systems if not correctly operated can lead to high dissolved oxygen concentrations (DOC) in the seawater injected into the wells resulting in corrosion failures. Recent efforts have focused attention on better DOC controls which permits the investigation and possible use of more cost effective materials such as the duplex stainless steel UNS S82551. Full scale testing of tubes joined together with a proprietary premium threaded connection was performed in controlled seawater loops simulating service conditions at 30°C. The flow rate and DOC were controlled at 6 m/s and <20 ppb respectively. Weekly DOC excursions corresponding to 24h at 100 ppb followed by 1hour at 300ppb was performed during the 5 months exposure. Corrosion results of UNS S82551 tubing were compared to UNS S31803 and UNS S39274. In parallel laboratory exposures of coupons were performed in DOC controlled cells with and without CREVCORR crevice formers allowing the assessment of electrochemical potentials as function of DOC (e. g. biofilm ennoblement monitoring) and the related corrosion resistance. The results showed that DOC should be properly controlled below critical values to avoid crevice corrosion of the lesser alloyed stainless steels. In the full scale loop test UNS S82551 tubes did not show crevice corrosion at threaded connection interfaces under the defined test conditions. Key Words: duplex stainless steel crevice corrosion treated seawater dissolved oxygen
In seawater handling systems the available well tubing materials are GRE lined low alloy steel or the so-called Corrosion Resistant Alloys (CRA’s) such as super duplex stainless steel. However in treated seawater (e. g. with dissolved oxygen removed) the corrosion risk can be controlled and lower grade alloys can be considered. Past experience has shown that treated seawater injection systems if not correctly operated can lead to high dissolved oxygen concentrations (DOC) in the seawater injected into the wells resulting in corrosion failures. Recent efforts have focused attention on better DOC controls which permits the investigation and possible use of more cost effective materials such as the duplex stainless steel UNS S82551. Full scale testing of tubes joined together with a proprietary premium threaded connection was performed in controlled seawater loops simulating service conditions at 30°C. The flow rate and DOC were controlled at 6 m/s and <20 ppb respectively. Weekly DOC excursions corresponding to 24h at 100 ppb followed by 1hour at 300ppb was performed during the 5 months exposure. Corrosion results of UNS S82551 tubing were compared to UNS S31803 and UNS S39274. In parallel laboratory exposures of coupons were performed in DOC controlled cells with and without CREVCORR crevice formers allowing the assessment of electrochemical potentials as function of DOC (e. g. biofilm ennoblement monitoring) and the related corrosion resistance. The results showed that DOC should be properly controlled below critical values to avoid crevice corrosion of the lesser alloyed stainless steels. In the full scale loop test UNS S82551 tubes did not show crevice corrosion at threaded connection interfaces under the defined test conditions. Key Words: duplex stainless steel crevice corrosion treated seawater dissolved oxygen
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