30" Dual BISEPS, Cortez Pipeline, New Mexico, USA

When a 500-mile CO2 pipeline in New Mexico needed upgrading, the operator faced a challenge that had never been attempted before.

At 148 bar (2,140 psi) and ambient temperature, the carbon dioxide flowing through the Cortez Pipeline exists in a supercritical fluid state. Isolating it safely - without halting delivery to downstream customers - required engineering that simply had no precedent.

The Cortez Pipeline runs 500 miles from source fields in southwestern Colorado to Denver City, delivering CO2 used primarily for enhanced oil recovery. As part of a larger programme to convert the system from a non-piggable to a piggable pipeline, Kinder Morgan needed to install full-bore inline valves and retrofit pigging launchers and receivers - all without interrupting pipeline operation.

The operating conditions made this unlike any previous line-stop project. CO2 at pipeline pressure and ambient temperature behaves as a supercritical fluid: when vented to atmospheric pressure it flashes to vapour, with a sharp temperature drop that can produce solid CO2 (dry ice) if the process is not carefully controlled. Temperatures below -57 degrees Celsius introduce ductility concerns for the steel components and risked blocking the pressure communication connections within the BISEP that monitor seal annulus performance. There was no established method for managing this - STATS had to develop one.

Standard line-stop technology provides a mechanical barrier, but it cannot prove that barrier is leak-tight. For a supercritical CO2 system, that level of verification was non-negotiable. The BISEP isolation tool delivers double block and bleed isolation through a single hot tap penetration, with each of its dual elastomer seals independently pressure-tested before any breaking of containment. The annulus between the seals provides a monitored zero-energy zone for the duration of the isolation.

A 24-inch bypass line was installed around the isolated section to maintain continuous production throughout the workscope. Two 30-inch BISEPs provided mid-line isolation at each intervention location, with the bypass diverting product flow around the work site.

While the pipeline operated under normal conditions, the site contractor excavated the pipeline and welded split-tee fittings using qualified in-service welding procedures. Two 30-inch fittings at each location provided access for the BISEPs; two additional 24-inch fittings accommodated the bypass line. STATS installed their double block and bleed slab valves and used their SureTap hot tap drilling machine to break containment and recover the pipeline coupons under full operating pressure.

With the bypass line installed, purged, leak-tested and live, the BISEPs were deployed into the flowing pipeline and hydraulically set. During isolation barrier proving, each seal was tested independently at full pipeline pressure in the direction of the expected differential - confirming both seals of the double block isolation were leak-tight before any work on the isolated section began.

The CO2 venting challenge was addressed through careful management of blowdown speed. By controlling the rate at which the isolated section was vented, the temperature of the CO2 could be kept above the design limits of the elastomer seals and the selected steel specification - preventing both seal degradation and the formation of dry ice within the tool.

Nitrogen was used to purge CO2 from the seal annulus, allowing pressure to be reduced in the annulus without bringing the temperature down to dangerous levels. The annulus could then be held at a pressure that was safe from a total contained energy perspective while remaining just high enough to prevent solid-phase CO2 formation. This managed approach to venting was a key development that made the entire operation possible.

STATS have completed isolations at four sites along the Cortez CO2 pipeline, all operating at around 138 bar (2,000 psi). Across those interventions, STATS have accumulated more than 160 days of individual BISEP isolation time. Throughout, there has been no degradation of the seals and no leaks past the primary barrier - allowing Kinder Morgan to carry out its launcher and receiver upgrades safely and without any uncontrolled release of pipeline product.

Careful selection of elastomer and steel materials for CO2 service, combined with pre-deployment testing and verification trials, were central to the consistency of performance across multiple sites. The managed approach to CO2 phase change during venting has since provided a repeatable methodology for future high-pressure CO2 interventions.