N. F. Osorio (GATE Inc.) | S. Bukkaraju (GATE Inc.) | J. L. Garduño (GATE Inc.) |L. C. Jordan (GATE Inc.)
Top of Line Corrosion (TOLC) occurs in deepwater wet gas systems when water vapor condenses on the upper internal walls of the flowline due to the heat exchange occurring between the hot fluid and the colder environment. The condensed liquid becomes enriched by the corrosive species naturally present in the gas stream and assumes a low pH because it does not contain any buffering species such as bicarbonate or iron. The predominant concern is carbon dioxide (CO2), which reacts with water to form carbonic acid (H2CO3), although hydrogen sulfide (H2S) and organic acids can also present significant challenges and drive the corrosion process.
Multiple factors influence the TOLC process. These include fluid characteristics and composition, flow regimes, pH, flowline material properties, fluid and ambient temperatures, protective and insulation layers properties, bathymetry and burial depth. These factors among others drive the heat transfer and consequentially impact the water condensation and the resulting TOLC rates. Adequate evaluation of the independent factors driving the TOLC risk is necessary in order to obtain an accurate assessment and mitigation option selection.
This paper aims to categorize and evaluate the impact of every key factor influencing TOLC risk and describes two methodologies available for TOLC assessment; Heuristic method, based on indirect determination of the TOLC rates, and the holistic method based on a system wide risk assessment, implemented through a System Component Analysis (SCA) approach supported by proven dynamic thermal-hydraulic and corrosion models and coupled with field experience. In addition, this paper presents the procedure to undertake effectively the TOLC risk assessment and mitigation option selection strategy based on the SCA methodology.
Document ID: OTC-26007-MS
Publisher: Offshore Technology Conference
Source: Offshore Technology Conference, 04-07 May, Houston, Texas, USA
Publication Date: 2015