Assessing Potential Impacts of Releases from Highly Volatile Liquid (HVL) Pipelines

Operators of pipelines carrying highly volatile liquid (HVL) or similar products (e.g. natural gas liquids, propane, butane, etc.) need to understand the potential impacts from release incidents. This consequence analysis contributes to meeting the requirements of the US DOT Pipeline and Hazardous Materials Safety Administration’s (PHMSA) hazardous liquids pipeline transportation regulations (49 CFR § 195) or other similar regulations. The outputs from this analysis, the geographic areas where impacts may occur, can be used to identify where impacts to high consequence areas (HCA) are possible. More generally, this analysis can support better decision-making about risk and mitigation. HVL products, while transported as liquids (under pressure or at regulated temperatures), can be released as vapor and/or liquid depending on the composition of the product.

Key Details

Project Name

Assessing Potential Impacts of Releases from Highly Volatile Liquid (HVL) Pipelines

Client

Undisclosed North American pipeline operator

Sector

  • Energy

Location

  • North America

Services Provided

  • Modelling
  • Environment
  • Health, safety and risk
  • Spatial Intelligence and GIS

By analyzing the composition of the released HVL product and simulating releases of both vapors and liquids, RPS can help pipeline operators fully understand the potential impacts from these pipelines. An undisclosed pipeline operator needed to understand the potential impacts of hypothetical releases from 11 pipelines, totaling over 600 miles in length, comprising a major HVL pipeline system. The pipeline system transports a range of HVL products with varying compositions. RPS helped characterize full-bore rupture releases for each product, including the magnitude (release rate), duration, and proportion of liquid and vapor released. Both vapor dispersion and liquid trajectory and fate release simulations were performed to determine the potential areas impacted by a release. Vapor dispersion modeling was used to predict the maximum distance from the pipeline that harmful vapor concentrations could exceed to explosive and human health related limits. Liquid plume modeling was performed to assess the overland and downstream trajectory and fate of the liquid portion of the release.

Challenge

The impact area resulting from a full-bore rupture from an HVL pipeline can be affected by many factors, including the product (composition, storage temperature, and pressure), the pipeline (flow rate, size, length, and location and type of isolation valves), the environmental conditions (air temperature, wind speed, landcover, topography, hydrography), and response timing. With the size of this pipeline system (both length and number of pipelines), variability of products transported, and variable environmental conditions throughout the system and throughout the year, simulating the range of possible outcomes was complex. RPS leveraged its modeling expertise to evaluate this variability efficiently and summarize the results in a way that could be easily comprehended.

Solution

RPS created an extensive matrix of release scenarios, grouping similar pipeline segments (between valves) by length, operational characteristics, and environmental conditions. Release scenarios took into account the various response timings, product compositors, seasonal variations. RPS performed atmospheric dispersion and liquid transport and fate model simulations using a suite of model software and automation routines to quickly perform thousands of simulations. Results were compiled for the various scenarios including maximum impact radius buffers and liquid plume footprints in a GIS format allowing easy integration with HCA analysis and pipeline data management systems.
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Project Statistics

11
pipelines
600
miles of pipeline
2,200
vapor dispersion scenarios
9,900
overland liquid release simulations

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