Internal corrosion of metal pipe is of upmost concern to the natural gas industry, and much effort has been devoted to understanding and controlling the mechanisms, including robust mitigation strategies. Biomethane Renewable Natural Gas (RNG) is a gaseous fuel produced through the anaerobic digestion of organic materials from a variety of biomass sources. It offers a lower-carbon addition to fuel supplies. Raw biogas produced through organic waste digestion contains methane, inert gases, oxygen, sulfur compounds, including hydrogen sulfide, moisture, and a wide variety of trace constituents, ...
Internal corrosion of metal pipe is of upmost concern to the natural gas industry, and much effort has been devoted to understanding and controlling the mechanisms, including robust mitigation strategies. Biomethane Renewable Natural Gas (RNG) is a gaseous fuel produced through the anaerobic digestion of organic materials from a variety of biomass sources. It offers a lower-carbon addition to fuel supplies. Raw biogas produced through organic waste digestion contains methane, inert gases, oxygen, sulfur compounds, including hydrogen sulfide, moisture, and a wide variety of trace constituents, depending upon biogas source. Raw biogas must be conditioned to meet RNG quality specifications; acceptable concentrations of major components in RNG are in line with natural gas tariff requirements. Trace constituents have been identified as impactful and detrimental to end use applications, and human health and the environment. However, trace constituents that induce corrosion in metal pipes have not been clearly identified in RNG specifications, and acceptable limits for these compounds have not been established.
This report compiles information regarding known factors, components, and conditions associated with internal corrosion of natural gas metal pipe. It supplies context to the topic and background information for natural gas and RNG. Corrosion mechanisms and combined effects are described. It is clear that water is the most important factor influencing pipeline corrosion; corrosion mechanisms will not occur without the presence of water. This is true both of natural gas and RNG systems. Other major components contribute to corrosion in the presence of water, individually and in combinations, and the process is complicated and variable. Unless the pipeline system is completely devoid of water, there is no circumstance, with natural gas or RNG, which assures a corrosion-free environment. All constituents which contribute to a corrosive environment must be controlled as best possible, at all times, and well-constructed corrosion management programs should monitor internal pipe conditions.
The transmission and distribution sectors of the natural gas industry have been introducing RNG to their pipeline network. There is a concern that trace constituents in RNG, in combination with major components in natural gas and the pipeline environment, may increase metal pipe corrosion or influence other corrosion-causing factors. Corrosion control is a primary directive for the natural gas industry; corrosion control programs serve to ensure that internal corrosion is limited and mitigated. This report is aimed at helping the natural gas industry understand components and conditions specific to RNG which may instigate, exacerbate, and/or accelerate pipe corrosion. Natural gas transporters who accept RNG to their network seek guidance and technical information specific to the potential for increased corrosion due to particular trace constituents. Currently, internal corrosion control programs are focused on components in natural gas; this report expands the knowledge to trace constituents in RNG which may contribute to a corrosive environment. Corrosion professionals require a more comprehensive understanding of RNG impacts to corrosion. Data gaps have been identified. RNG quality specifications may require updating to limit newly identified constituents of concern.