ABSTRACT

This paper gives brief descriptions of the mechanisms of common types of corrosion attacks in petrochemical and refinery environments viz. Wet H2S, Caustic, Amine, Carbonate corrosion and cracking. It then provides suggested guidelines for classifying the severity of the Wet H2S services and for all the listed services, accordingly provides a ready reckoner tool for Design Engineers to prescribe control measures to mitigate these risks. The control measures fall into three categories. The first is added material requirements such as mill heat treatments, chemistry restrictions, or additional requirements on material physical properties. The second class of control measures involves fabrication steps such as heat treatment, testing and inspection. Even with these practices, for some of the mechanisms, it is recommended to also have process or operational controls which are typically applied as Integrity Operating Windows (IOW), and it is beneficial to highlight these IOWs on the Materials Selection Diagram (MSD) and Piping and Instrumentation Diagrams (P&ID). Examples are velocity limit in amine services or temperature limits in caustic service. Collectively, these three categories of practices mitigate the risks associated with these corrosive services.

INTRODUCTION

In a petroleum refinery, cost of corrosion-caused failures is a high percentage of maintenance cost. According to a comprehensive survey in US (year 1996), the total annual direct cost in refineries was estimated at 3.76b USD. Moreover, indirect cost of corrosion due to unit shut downs, loss of productivity and environment pollution can be even one order higher than the direct corrosion cost. In addition corrosion failures not only increase direct and indirect cost to industries but can also be associated with accidents for which cost can’t be estimated. It has been indicated that about 10-40% of corrosion cost can be avoided with appropriate engineering during the design phase and corrosion management during operation practices. In view of that it is emphasized to adopt best engineering practices at the engineering design and construction stages as a primary and effective measure for corrosion and cracking control at facilities.

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