Anhydrous Ammonia Pipeline Safety Experience in the United States

Abstract Transporting anhydrous ammonia by pipeline is receiving greater interest with global efforts to decarbonize and transition away from carbon-based energy. In the United States, there are currently over 2,000 miles (3,200 km) of anhydrous ammonia pipelines, which were constructed between 1960 to 1978, to primarily deliver ammonia from producers in the Gulf Coast to agricultural users in the Midwest. In the United States, significant incidents have occurred with ammonia pipelines, which are regulated under the Code of Federal Regulations (CFR), Title 49, Part 195, highly volatile liquid (HVL) requirements. Carbon steels in anhydrous ammonia service are susceptible to internal corrosion and stress corrosion cracking (SCC) when certain contaminants are present, such as oxygen, carbon dioxide or sulfur dioxide. SCC can be mitigated by avoiding contamination by air, oxygen, and carbon dioxide, or by the addition of small amounts of water where oxygen may be present. Pipeline experience in the United States has shown that 0.2–0.5 wt% water is effective in preventing SCC. Specific areas of concern with anhydrous ammonia pipelines include thermal relief, ice formation, commissioning, decommissioning, and leak hazard mitigation. Strict purging practices, limiting contaminants such as oxygen and carbon dioxide, adding 0.2%–0.5% water to inhibit SCC, and operational considerations are important to ensure safe pipeline operation. Anhydrous ammonia pipeline leaks result in significantly greater immediate danger to human life than many other types pipeline leaks, where it is important that leaks are immediately detected and proper hazard mitigation actions are taken.