Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >
Skip to content

Electrochemical Testing of Welds, Cladding and Surface Coatings

 
Project Code: 0902-02

Objectives

Demonstration of the use of a rising-temperature CPT test for the derivation of pitting boundary conditions for CRAs in sour service at elevated temperature and pressure.

Identify testing techniques allowing definition of the necessary control of weld cladding procedures for corrosive service.

Identify electrochemical testing techniques allowing improved extrapolation of long term corrosion behaviour of coatings/cladding.

Project Outline

Building upon prior work CPT tests with a novel procedure will be undertaken close to existing limits using type 316 welded austenitic stainless steels. An electrochemical monitoring technique should be more reproducible and will enhance the knowledge gained during the test duration rather than awaiting the completion and inspection post-test. With such proof of concept, it is envisaged that testing of weldments will be significantly improved and allow greater confidence in the derivation of limiting conditions.

Samples of TSA on carbon steel will be prepared by appropriate spraying processes. These will be subjected to alternate immersion tests in simulated seawater and electrochemical measurements, including AC, such as EIS and DC techniques will be conducted on the coatings. The results will be correlated with physical observations of degradation of the TSA, so that preferred test methods for extrapolation can be identified.

Samples of alloy 625 weld cladding with low and high dilutions will be prepared and subjected to testing in representative brines using scanning electrode techniques. This will provide spatial electrochemical data on the relative corrosion susceptibility of the weld overlay and allow understanding of the effects of local composition fluctuation on overall corrosion resistance. These data will be used to correlate with results from scanning electron microscope (SEM) and energy dispersive x-ray (EDX) analysis of the test specimens to quantify the variation of chemical composition. Variations in welding procedure will be correlated with corrosion data in representative fluids.

Relevant Industry Sectors

Oil and Gas, Power.

Technical and Economic Benefits

Greater confidence in the cracking resistance assessment of weldments.

Improved reliability for welded CRA pressure containing equipment and pipelines.

Ability to correlate metallurgical and compositional variation with the electrochemical response of welds and cladding in corrosive service.

This work will benefit fabricators and operators of offshore structures in providing improved techniques for predicting the long term corrosion behaviour of thermal sprayed metallic coatings in demanding marine environments.

For more information please email:


contactus@twi.co.uk