Interaction of Elemental Mercury with Steel Surfaces 

Internet Publication – September, 2010

S. Mark Wilhelm, Mercury Technology Services

Mark Nelson, Williams Gas Pipeline

ABSTRACT

Elemental mercury in fluids produced from hydrocarbon reservoirs reacts with, and thus chemically modifies, steel surfaces on equipment and piping. In this study, process piping removed from service in which mercury was a process constituent was examined using surface analytical techniques. In addition, steel coupons were exposed to mercury vapor to measure rates and amounts of mercury uptake. The steel surfaces that were examined acquired between 1 and 4 g Hg⁰/m² of steel geometric surface area (no surface roughness factor applied). The majority of the mercury present in the interfacial area is thought to be physically adsorbed on the vapor/metal scale interface and some mercury incorporates into the scale itself, possibly by diffusion and substitution for iron in the scale lattice. In gas streams containing H₂S, mercury vapor reacts to form HgS on the surface of the surface oxide scale layer. The data are consistent with elemental mercury adsorption and chemisorption as the primary mechanisms of mercury accumulation on steel surfaces exposed to elemental mercury vapor in natural gas streams. Mercury penetration into steel grain boundaries could not be confirmed, or ruled out, using the analytical methods employed. The process of mercury scavenging by steel surfaces is reversible with rates of desorption depending strongly on temperature.