|Content Type||Conference Paper|
|Title||Corrosion of Carbon Steel by H2S in CO2 Containing Oilfield Environments|
|Authors||Stephen N. Smith, ExxonMobil Production Co.; Michael W. Joosten, ConocoPhillips Co.|
|Source||CORROSION 2006, March 12 - 16, 2006 , San Diego Ca|
|Copyright||2006. NACE International|
The effect that even small concentrations of H2S can have upon CO2 corrosion has been recognized since at least the 1940's. Early studies showed that the FeS corrosion products that were formed had an impact, but disagreed whether the impact was beneficial or not. Although H2S corrosion has not received the level of attention given to CO2 corrosion, the literature has shown that there are a number of different forms of FeS that can form as corrosion products, depending upon the exposure conditions. Between the corrosion, geochemical and thermodynamics literature, a great deal is known about the corrosion chemistry involved with the formation of the various FeS species as well as the impact that each has upon further corrosion.
However, there is still a great deal that is not known. For example, there are currently no generally accepted prediction algorithms for any form of H2S corrosion. There are also still a number of unknowns about the corrosion reactions that lead to pitting, which is the most common mode of sour service equipment failure. This paper reviews a sampling of the H2S corrosion literature over the past 60 years and describes some of the areas of research that remain.
A great deal has been written over the years about the effects of CO2 on corrosion and the various changes in environmental parameters that impact the corrosion rate due to CO2. Factors such as temperature, pH, bicarbonate, velocity and a host of others had been studied extensively. By comparison, only a small amount of effort has gone into the study of the impact of H2S upon carbon steel corrosion rates. This is most likely a result of a concentrated focus on H2S cracking of various metallic materials. This does not mean that there is no information available about the effects of H2S upon corrosion mechanisms and reaction rates. Research and field work in this area dates back to the 1940's. Research relevant to iron sulfide formation chemistry has also been conducted by geochemists, microbiologists, thermodynamicists and geophysicists. Much of this work has direct relevance to the study of the mechanism of CO2/H2S corrosion.
Although there is over 60 years of H2S related corrosion research work, much of this literature is somewhat confusing and often seemingly contradictory. Iron sulfide chemistry is very complex and seemingly minor changes in test conditions can often lead to dramatically different results. The mineralogists and thermodynamicists still cannot completely agree upon the number of types of iron sulfide that actually exist, even though they have been studying the materials for far longer than corrosion engineers.
This paper reviews some of the history relative to corrosive oilfield environments that contain CO2 and H2S. We will attempt to examine the effects of H2S on the variety of different environments where the various iron sulfide corrosion products are formed. Finally, we will discuss the areas of further research needed to more fully understand the impact of H2S on CO2 corrosion in oilfield environments. This understanding will subsequently improve the accuracy of corrosion rate predictions.
HISTORY OF OILFIELD CORROSION BY H2S
Oilfield corrosion engineers have recognized since the 1940's that the presence of H2S changes the corrosivity of produced fluids as compared to sweet production with only CO2. Many investigators working with H2S have concentrated on the cracking of carbon steels. Others have studied various aspects of the role of H2S upon corrosion and the role of the various FeS corrosion products. Some have concluded that H2S reduces corrosion as compared to CO2 and others have concluded that H2S increases corrosi
|File Size||418 KB||26|