Characterization of Internal and External Coatings Used on Steel Pipelines

Accelerated Corrosion Testing (ACT) of external pipelines coatings traditionally has been associated with the ASTM B117 Salt Fog Test[i] (which is also similar to other standards like the BS3900[ii] Parts F4 and F12 and the ISO standard 7253[iii]). There are other types of ACT for coatings that use “salt spray” test; for example, the ASS and CASS tests which use acetic acid and acetic acid with copper chloride for the test solutions.  Recently, ACT of coatings has been performed using the presence of gases in a closed cabinet at constant temperature and with varying relative humidity (RH).  This test resembles the standard ACT for Electronic Equipment and Devices[iv]. The objective of these (cyclic) tests is to try to mimic naturally occurring wetting and drying cycles with the addition of a known acceleration factor[v].

The standard tests are important in the development of new coatings and are commonly used to qualify new coatings and surface treatments for novel material/environment applications. However, the standard tests have been shown to inaccurately predict the performance of coatings in real service conditions. This shortfall has promoted the common practice of doing a quick “round robin test” with several coatings to select the best 2 or 3 candidate systems, before proceeding with long term testing (that includes laboratory testing and/or field testing). Although this is a good approach, the main drawback is the time required to achieve results.

This paper has the main objective to compare and contrast the different ACT methods that have been recently proposed as well as to identify those ACT methods that, with a little bit of development, could potentially mimic the real environments and more accurately predict long term performance. Additionally, this work describes testing on coatings used for internal coating of pipelines. Of particular interest, to be discussed, will be the specific ranking between the mechanical tests and the corrosion testing.

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[i] ASTM B117 – 07 - “Standard Practice for Operating Salt Spray (Fog) Apparatus”

[ii] BSI BS 3900-F4 “Methods of test for paints Part F4: Resistance to continuous salt spray”, BS 3900 Part F12 “Paints & Varnishes – Determination of Resistance to neutral salt spray (fog)”

[iii] ISO 7253:1996 – “Paints and varnishes -- Determination of resistance to neutral salt spray (fog)”

[iv] “Study of Mixed Flowing Gas Exposure of Copper”, M. Reid, J. Punch, L. F. Garfias-Mesias, K. Shannon, S. Belochapkine and D. A. Tanner, Journal of The Electrochemical Society, 155, (4) C147-C153 (2008).

[v] “The Microstructural Development Of Copper Sulphide On Copper Exposed To Humid H₂S,” M. Reid, J. Punch, C. Ryan, L. F. Garfias-Mesias, S. Belochapkine, J. P. Franey, G. E. Derkits, Jr., W. D. Reents, Jr, Journal of Electrochemical Society, 154, (4) C209-C214 (2007).

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