Corrosion fatigue of cathodically protected high strength steels -- The role of sulphate reducing bacteria
- Cranfield Univ. (United Kingdom). Marine Technology Centre
It is now well established that the corrosion fatigue of high strength structural steels in seawater is promoted by the uptake of hydrogen that results from applying cathodic protection (CP) to control corrosion. The research described in this paper has shown that not only is hydrogen absorption caused by CP but that it is considerably enhanced by active sulphate reducing bacteria (SRB) that are generally present in marine sediments and in biofilms on steel surfaces. These bacteria can increase the quantity of hydrogen absorbed by the metal between 5 and 10 times compared to that in sterile seawater at the same protection potential. The effect of this increased hydrogen content is to promote more rapid fatigue crack propagation. In the case of static loading cracks may also develop in high strength steels by a hydrogen embrittlement mechanism. Results are presented from tests to measure the influence of marine biofilms containing SRB on the corrosion fatigue behavior of two quenched and tempered offshore steels with yield strengths of 500 MPa and 690 MPa. Particular emphasis is placed on the behavior of the heat affected zones of welds which are susceptible to these forms of hydrogen assisted failure due to the modified microstructure and regions of high hardness. The effect of the applied cathodic potential is discussed and recommendations are made regarding the optimum levels of protection to avoid hydrogen assisted crack growth in these steels.
- OSTI ID:
- 205403
- Report Number(s):
- CONF-950695--; ISBN 0-7918-1309-6
- Country of Publication:
- United States
- Language:
- English
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