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Influence of K-Rate and Hydrogen Charging on Fracture Toughness of a Super Duplex Stainless Steel

To evaluate through fracture toughness tests the susceptibility of SDSS to HISC and to determine the effect of the cathodic protection potential and the stress intensity factor rate (K-rate).

Product Number: 51318-10891-SG
Author: Carlos Eduardo Fortis Kwietniewski / Tiago Renck / Fabrício Pinheiro dos Santos / Adriano Scheid / Marcelo Sartori / Afonso Reguly
Publication Date: 2018
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Super duplex stainless steels (SDSS) combine excellent corrosion resistance especially to the localized forms of corrosion with medium to high mechanical strength. This unique combination of properties has made these alloys very successful in the oil and gas industry. However, in some specific scenarios, even these steels have to be protected against corrosion, which is usually accomplished by cathodic protection. The synergic effect of hydrogen produced during cathodic protection with service mechanical loads may produce the embrittlement phenomenon known as hydrogen induced stress cracking (HISC). Indeed, documented cases of failure due to HISC have somehow deteriorated the image of the SDSS and raised some concerns. The aim of this investigation is to evaluate through fracture toughness tests the susceptibility of SDSS to HISC and more specifically to determine the effect of the cathodic protection potential and the stress intensity factor rate (K-rate) on the results produced. Within the range of parameters studied here, the degradation of fracture toughness due to HISC is strongly dependent on the testing parameters employed, especially the cathodic potential with a less pronounced effect of the K-rate. The results also suggest that the issue of HISC might not be a material’s problem but instead can be mitigated by the optimization of cathodic protection design.

Keywords: Super Duplex Stainless Steel (SDSS), Fracture Toughness, Hydrogen Induced Stress Cracking (HISC)

 

Super duplex stainless steels (SDSS) combine excellent corrosion resistance especially to the localized forms of corrosion with medium to high mechanical strength. This unique combination of properties has made these alloys very successful in the oil and gas industry. However, in some specific scenarios, even these steels have to be protected against corrosion, which is usually accomplished by cathodic protection. The synergic effect of hydrogen produced during cathodic protection with service mechanical loads may produce the embrittlement phenomenon known as hydrogen induced stress cracking (HISC). Indeed, documented cases of failure due to HISC have somehow deteriorated the image of the SDSS and raised some concerns. The aim of this investigation is to evaluate through fracture toughness tests the susceptibility of SDSS to HISC and more specifically to determine the effect of the cathodic protection potential and the stress intensity factor rate (K-rate) on the results produced. Within the range of parameters studied here, the degradation of fracture toughness due to HISC is strongly dependent on the testing parameters employed, especially the cathodic potential with a less pronounced effect of the K-rate. The results also suggest that the issue of HISC might not be a material’s problem but instead can be mitigated by the optimization of cathodic protection design.

Keywords: Super Duplex Stainless Steel (SDSS), Fracture Toughness, Hydrogen Induced Stress Cracking (HISC)

 

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