Improving Regulatory Compliance with Pressure Relief Device Monitoring

I caught up with Emerson’s Ricardo Garcia, who shared an update on the MON PRD regulations for miscellaneous organic chemical (MON) emissions from pressure relief devices (PRDs).

The first U.S. National Emission Standards for Hazardous Air Pollutants (NESHAPs) were initially required by the 1970 Clean Air Act (CAA). These standards were developed for sources and source categories determined to pose adverse risks to human health by the emission of HAPs. The EPA Administrator was directed to set the standard “at the level which in his judgment provides an ample margin of safety to protect the public health from such hazardous air pollutants.” These risk-based NESHAPs are located in 40 CFR part 61 and incorporated by reference in 45 CSR 34. The NESHAPs apply to all existing and new/modified sources.

Congress directed the EPA to develop a program to further the regulation of HAPs in Section 112 of the 1990 Clean Air Act Amendments (CAAA). While the standards for primary sources of HAPs developed per this section are also designated as NESHAPs, they are established according to Maximum Achievable Control Technology (MACT) requirements. MACT is a technology-based standard instead of the original conception of NESHAPs as a risk-based standard. These technology-based NESHAPs are located at 40 CFR 63 and incorporated by reference in 45CSR34.

EPA has set MACT standards for over 100 source categories as specified under Section 112(d). While these MACT standards typically apply to significant sources (those at facilities with greater than 10 tons/year of a single HAP or greater than 25 tons/year of aggregate HAPs), many MACTs also apply to area sources (sources with less than 10/25 tons/year HAP thresholds); a few MACTs apply only to area sources. The MON MACT standards are codified at 40 CFR part 63, subpart FFFF.

The EMACT standards were promulgated on July 12, 2002 (67 FR 46258) and codified at 40 CFR part 63, subparts XX and YY. They regulate HAP emissions from ethylene production units located at primary sources. In 2020, the EPA published final rules for MON MACT and EMACT, based on the residual risk and technology reviews conducted for the ethylene production source category regulated under NESHAP and the Miscellaneous Organic Chemical Manufacturing NESHAP. Both final rules include a work practice standard for pressure relief devices that vent to the atmosphere.

The PRD work practice standard requirements include prevention measures, monitoring systems, and root cause analysis. Compliance with these requirements went into effect in late 2019 for all MON-affected sources that commenced construction.pressure relief valve regulatory requirements

The regulatory requirements include:

  • Identify in-scope PRDs
  • Apply at least three redundant prevention measures to each PRD
  • Equip each PRD with a monitoring device(s)/system
  • Develop root cause analysis and corrective action analysis procedures

Violations of these pressure release management practice standards include:

  • Any release event for which the event’s root cause was determined to be operator error or poor maintenance.
  • A second release event, not including force majeure events from a single pressure relief device in a 3-calendar-year period, for the same root cause for the same equipment.
  • A third release event that does not include force majeure events from a single pressure relief device for any reason in a 3-calendar year period.

The Emerson team conducted a study of 10,000 pressure relief valve (PRV) pre-test service records from a large North American refining complex. The study authors found that 20% of the PRVs leak below 50% of set pressure, and 8% leak so excessively that they do not pop on overpressure events. There is no indication of when and why the PRV began to leak.

The code requires the owner or operator to equip each pressure relief device in organic HAP service with a device(s) or parameter monitoring system that is capable of:

  • Identifying the pressure release.
  • Recording the time and duration of each pressure release.
  • Notifying operators immediately that a pressure release is occurring. The device or monitoring system must be either specific to the pressure relief device itself or must be associated with the processing system or piping, sufficient to indicate a pressure release to the atmosphere.

The Plantweb Insight Pressure Relief Device application provides a dashboard view, asset summary and details, and event logs of your relief events.

Some options for monitoring PRVs include using limit/proximity switches, acoustic transmitters, direct-spring position monitors, and pilot-operated PRVs with differential pressure monitoring. Some of these technologies provide discrete (on/off) information about PRV events, but for applications where there is a bigger valve or higher concentration of HAPs, then monitoring lift percentage prevents overreporting of events. This higher-level monitoring can be achieved by using technologies such as direct spring position monitoring or pilot valve differential pressure monitoring.

Analytical software that collects this data along with PRV type, line size, orifice size, pressure inlet, and material cost can provide actionable information on release events and key performance indicators such as production loss and excess emissions.

Incorporating these technologies into your production process can help you avoid violations, operate with less operational risk, and achieve greater efficiency and reliability.

For a deeper dive into this subject, check out the on-demand webinar, Beyond regulatory compliance: A deep dive into the MON PRD regulation and potential solutions. Also, visit the Pressure Relief Valves section on for more information on the types of pressure relief valves and monitoring options for your operating facilities.

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