Corrosion of chromium plated rotor in drilling fluid
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- 作者：Cobo ; E.O. ; Suá ; rez Baldo ; R.A. ; Bessone ; J.B.
- 关键词：Chromium plating ; Corrosive attack ; Downhole hydraulic motor ; Drilling mud
- 刊名：Surface and Coatings Technology
- 出版年：1999
- 出版时间：December 1, 1999
- 年：1999
- 卷：122
- 期：1
- 页码：39-43
- 全文大小：1000 K
文摘
The causes of hard chromium layer spalling in the rotor of a downhole hydraulic motor were analysed. The rotor rotates within a stator in contact with saline drilling mud. Zones with lost coating and base metal attack were observed along the whole rotor. Microscopic examination showed atypical macrocracks that run through the whole chromium layer. These fissures started at base steel heterogeneities or pores in the coating itself. The microprobe analysis of the metal–coating interface showed no metallic deposit between the steel and the chromium layer. Chromium plated steel and base steel showed similar electrochemical behaviour in the mud aqueous phase, whereas pure chromium remained passive up to the transpassive region. The failure was attributed to the salt solution penetrating through macrocracks to the substrate. As the steel substrate was corroded, chromium coating lost adherence and became detached under the influence of frictional forces.