In a recent webinar, Beyond Boundaries: Turbocharging Safety, Efficiency, and Green Vibes in Ethylene Production, Emerson’s Yong Tat Lee, Product Marketing Manager for Pressure Management in the Asia-Pacific region, walked through how Pressure Relief Valve (PRV) design choices shape safety, emissions, and efficiency across ethylene production. His session covered cracking, quenching, and fractionation service, along with new solutions aimed at cutting fugitive emissions and improving valve monitoring.

Why It Matters

PRVs are the last line of defense against overpressure in ethylene plants. They protect equipment and pipelines carrying flammable hydrocarbons through extreme temperature swings, high pressures, and corrosive service. When a valve leaks during normal operation, fails to reseat after relief, or suffers a bellows rupture, the consequences extend to emissions, product loss, and personnel safety. Sizing and selection decisions therefore carry weight well beyond code compliance.

Key Takeaways

• Ethylene service exposes PRVs to temperatures above 800 degrees Celsius in cracking and as low as minus 165 degrees Celsius in fractionation, requiring careful material and design selection.
• Some applications require pressure ratings exceeding American Petroleum Institute (API) Standard 526 to reduce the number of valves required.
• Balanced bellows spring valves typically handle back pressure up to 50 to 60 percent of set pressure, while pilot-operated designs can handle up to 90 percent.
• Cryogenic fractionation service demands zero-leakage sealing, verified by rigorous cycle testing under liquid-nitrogen conditions.
• Fugitive emission-compliant PRVs and real-time monitoring solutions help operators cut emissions, plan maintenance, and avoid unplanned shutdowns.

Cracking Service: Steam at Extreme Temperatures

Ethylene cracking involves the use of saturated or superheated steam at temperatures exceeding 800 degrees Celsius. Flanged or welded connections may be required to maintain system integrity, with welded connections typically used where pressures and temperatures are highest. Yong Tat highlighted the Crosby H series as a top choice for steam service, meeting American Society of Mechanical Engineers (ASME) Section I requirements. Material options include WCC, WC6, WC9, and C12A, giving engineers flexibility across pressure and temperature ranges.

The Isoflex or Flexi-Disc design maintains seat tightness up to 93 percent of set pressure and seals more effectively as pressure rises. Each steam valve undergoes 100 percent factory steam testing, which supports reliability, minimizes steam losses, and reduces service demands after installation.

Quenching: Handling High Back Pressure Without Bellow Risk

Quenching often produces back pressure exceeding 80 percent of set pressure. Conventional balanced bellows spring valves generally handle only 50 to 60 percent, which creates both performance and safety gaps. Elevated back pressure also increases the risk of bellow rupture and unintended emissions into the atmosphere.

Yong Tat pointed to the Anderson Greenwood high-pressure pilot-operated PRV as a fit for this service. The valve is inherently balanced against back pressure and handles back pressure up to 90 percent of set pressure. A full-rated body with matching inlet and outlet ratings allows engineers to exceed API 526 inlet and outlet requirements, reducing valve count and oversizing. An optional backflow preventer stops reverse flow when back pressure exceeds the inlet pressure and maintains a tight seal during vacuum events. Combined with a soft seat, these features cut product loss and emissions while supporting yield.

Fractionation: Sealing Integrity at Cryogenic Temperatures

Fractionation units operate at temperatures as low as minus 165 degrees Celsius. Stainless steel construction is typical, and soft-seat sealing must stay tight under cryogenic conditions. Traditional pop-action spring valves can drive product loss and emissions during relief events.

The Anderson Greenwood pilot-operated PRV is cycle-tested under cryogenic conditions to verify functionality and zero-leakage performance. Its true modulating pilot lifts the main valve only as much as needed to control overpressure, which reduces product loss, limits piping reaction forces, and holds performance even in the presence of inlet loss. Third-party approvals from TS, Lloyd’s, ABS, DNV, and BV are available for cryogenic service and have been tested using liquid nitrogen at Emerson’s own test bench.

Emissions Control and Digital Monitoring

About three-quarters of valve fugitive emissions in a plant come from pipeline valves, with roughly 10 percent from relief valves. No specific fugitive emission standard exists for PRVs yet, so Emerson developed a testing protocol drawing on the International Organization for Standardization (ISO) 15848 and API Standards 622 and 624. Compliant valves are tested at independent laboratories using a mass spectrometer leak detector, and Emerson’s designs meet the more stringent Class A criterion.

For live insight into valve behavior, Emerson’s PRV monitoring solution combines transmitters, wired or WirelessHART connectivity, a gateway, and analytics. It shows when a valve opens, how high it lifts, and for how long. Yong Tat noted that a 2-inch leak at 200 pounds per square inch (psi) operating pressure, at 0.1 percent of rated flow, can reach roughly $640,000 USD in losses.

Bellow rupture is another common failure mode. Analysis of more than 30,000 valve service records shows 2 to 6 percent of balanced bellows valves experience bellow damage in service. The Beyond Bellows solution adds a backup piston that maintains back-pressure balance, contains up to 90 percent of leakage, and enables early detection of pinhole ruptures through pressure sensing in the backup chamber. Operators gain time to plan maintenance rather than shut down unexpectedly.

Watch the Full Session

For the complete discussion, including audience questions on fugitive emission test criteria, wired versus wireless monitoring, and cryogenic certifications, watch the on-demand webinar and visit the Pressure Relief Valves section on Emerson.com.