A simple laboratory method has been developed to assess the effects of scratch and abrasion damage on the corrosion resistance of corrosion resistant alloys (CRAs) under deaerated, sweet and also sour corrosion conditions. The technique was developed in order to simulate the potential damage to tubing caused by well interventions such as wireline operations or calliper runs in oil/gas production wells. The approach could also be used to investigate the possible effects of erosion on corrosion. The test procedure was later developed to enable a cathodic current to be applied to the working electrode thereby simulating the effect of acid stimulation fluids in contact with well tubing.

13%Cr, 22%Cr duplex, and 25% duplex stainless steels were examined under sweet conditions at temperatures of 25, 50, 90, and 150°C. 13%Cr steel was also examined under sour conditions at 50°C. All the tests were carried out in a simulated oilfield formation water.

The protective film on the surface of 13% Cr steel reformed relatively quickly, returning to the original starting conditions less than or equal to 1 hour following scratching or simulated acid cleaning in deaerated, CO2 saturated solutions at temperatures of 50, 90 and 150°C. This was also true under deaerated, 1% H2S / 99% CO2 saturated conditions at 50°C. However, in sweet solutions at 25°C the recovery to starting conditions was not complete and there was a residual galvanic current, which might lead to localised corrosion. Duplex stainless steels under sweet conditions at 50°C show fast repair after scratching (i.e. within minutes).

The findings suggest that downhole tubulars are not at long term risk from occasional wireline operations, calliper runs, or acidising treatments as long as the temperature is greater than 50°C. The film repair speeds may also be indicative of the likelihood of synergistic erosion-corrosion in a stream containing solid particles such as sand.

Subject
Acids, Electric current, Coating repair, Thin films, Steel surfaces, Corrosion rate, Acidity, Constants, Steel, Brines, Duplex stainless steel, Electrodes, Cleaning
Keywords:
corrosion resistant alloy, 13% Cr steel, duplex stainless steel, scratch, acid, well, tubing
© 2004 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2004
Association for Materials Protection and Performance (AMPP)
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