Our Services

PROCESS provides a full range of services relative to the sizing, verification, and modeling of Flare Systems and Pressure Safety Relief Valves (PSVs or PSRVs, Rupture Disks, and Conservation Vents) including the following:

  • Generate all calculations and associated documentation for the sizing and selection of PSVs per API and/or ASME Code requirements for new or existing installations. This also includes:
    • Identification of and calculations for all credible scenarios, not just the controlling scenario
    • Physical properties generated by CHEMCAD process simulation models for each stream
    • Performing pressure drop calculations for both inlet and outlet piping.
  • Flare stack or vent stack sizing (height, diameter, tip configurations, etc.) to fall within API Code requirements. Flare manufacturers are also consulted to ensure the best available technology is included in the design. Knockout drums and blowdown systems are also designed and sized for each particular installation.
  • Generate all documentation needed to meet OSHA requirements and any specific company requirements
  • Generate required PSV specifications (spec sheets)
  • Construct a flare or vent header pressure drop simulation model in CHEMCAD or FlareNet, including both inlet and outlet PSV piping configurations
  • Perform flare or vent header pressure drop evaluations for specific PSV combinations associated with global relief scenarios. These global scenarios are developed by working in conjunction with the client’s plant staff and PROCESS often spends additional time on-site to collect any missing information that may be needed.

Our Experience

PROCESS has performed relief valve sizing calculations for thousands of relief devices. These include pressure safety valves of all types, traditional spring loaded relief valves, conservation vents, and rupture disks. All of these systems are designed to protect a process by safely relieving excess pressure under abnormal operating conditions. It is critical that they be sized appropriately to protect both personnel and physical assets. Many such relief devices are simple stand alone units venting to the atmosphere, while others are highly specialized devices designed to handle two-phase flow and tie into a complex process wide vapor collection or flare header system. Typically we are asked to either provide specific relief valve sizing/evaluation or we are asked to perform an entire flare header system evaluation with many relief devices connected to it.

Any changes made to piping systems where relief devices are used could cause the device to be over/undersized for its application. If relief devices feed into a common blowdown or flare header system then the sizing of the header lines and flaring devices also need to be checked after significant process modifications are made. It is also common to find such systems ‘undersized’ as a result of many smaller changes to the process that have occurred over time and had a cumulative effect on the header loading.

Project Examples Involving Relief System Sizing

PROCESS has significant experience with the entire range of system and device types. Click here to view our Relief Valve Sizing Experience and Flare Header Systems Experience.

Our Methodology

In general, PROCESS follows methodology set forth in the American Petroleum Institute (API) 520, 521, and 2000 guidelines. When performing an evaluation to determine if adequate relieving systems are in place for an existing system and if the flare header is adequately designed, the following steps are typically involved.

Relief Device Evaluation:

      1. Collect information on the existing system (PSV data, P&IDs, protected equipment information, flare header isometrics, inlet/outlet line sizes, etc.).
      2. Work with the client’s technical staff to develop the credible relief scenarios, both for individual pieces of equipment and especially for those affecting entire units or sections of the plant (blocked flow, external pool fire, loss of cooling, loss of power, etc.).
      3. Build a simulation of the process (if needed) to ensure accurate process conditions and stream compositions are available for all relieving scenarios.
      4. Calculate the required flow rate capacity for the relieving streams along with the required orifice sizes for each credible scenario.
      5. From this information, the controlling scenario is determined and the valve is sized.  PROCESS uses state-of-the-art commercial process simulation software to obtain the relieving stream physical properties required to perform the flow rate calculations.
      6. For evaluation of existing valves, the required flow rate and actual flow rate capacity for the relief valves are calculated along with the required orifice size for each scenario.  From this information, the controlling scenario is determined to check if the existing valve is sized appropriately.

Flare System Design:

PROCESS determines flare radiation, produces a contour plot and specific radiation incidences on personnel and structures. Effects of mitigation measures, such as water spray and shields, can be determined that may help minimize the flare height and cost. As needed rudimentary plume dispersion modeling may also be performed. PROCESS may also employ advanced techniques (allowable by the industry) to determine radiation below what is often produced by standard software. Common design aides such as Aspen Flare System Analyzer, FlareNet, or other software programs are employed as needed.

Flare Header Evaluation (can be performed concurrently with or started after items 1 – 5 above have been completed):

  • Create a simulation of the flare header system and check the system hydraulics for multiple devices and/or global relieving scenarios to determine backpressure issues impacting PSV sizing and type specification (conventional, bellows, etc.).
  • Engineer appropriate modifications to alleviate any sections of the system with unacceptable hydraulic parameters.
  • Inform the client of findings and deficiencies, and recommend corrective actions.
  • Provide the client with a report detailing the findings.

What We Provide

Relief valve sizing and flare header studies are somewhat repetitive type tasks that can be very complex to perform accurately. PROCESS has developed an in-house comprehensive spreadsheet-based computer program to streamline our analysis. This program is useful when multiple relief devices need to be sized (6 or more) and the information needs to be documented in such a way that it can be referenced and maintained as future changes are made to the process. Our program provides Equipment and PSV Summary sheets that are linked to other sheets using cell references and Visual Basic programming. Information can be entered in one location and this change updates automatically to other locations where the information is used in individual valve calculations. Such information can be very valuable when considering process modifications affecting the relief system or when defending system design to government regulators. The program includes the following major sections at a minimum:

  • Drawings Sheet listing all the drawings related to the relief system study
  • Equipment Summary Sheet listing all equipment involved, design conditions, sizes, etc.
  • Calculation Template Pages for efficiency and consistency in creating new PSV calculations
  • Calculation Sheet for each PSV with stream property information imported from the simulation software, listed assumptions, orifice sizes, data sheets for new PSVs to be purchased, etc.  For each PSV, the appropriate calculation procedures and formulas, for both required and actual capacities, are available for applicable relief scenarios.
  • PSV Summary Sheet listing each valve and summarizing the actual capacity and required capacity for each scenario considered. This sheet contains highlighted deficiencies and requirements.  This summary serves a Process Safety Management System (PSM) function and is often used as a major reference for a Process Hazards Analysis (PHA).
  • Reference Table Sheet listing information on standard orifice size areas, Cv’s for standard valves, pipe size diameters, steam table information, etc.
  • Scratch Sheet with pipe fitting K-factors, barometric pressure calculations, etc.

We perform all of our relief valve studies with world class process design engineers and can perform such work extremely efficiently. When unusual relieving scenarios/conditions present themselves, PROCESS is qualified to make an accurate determination of a solution that may not be obvious, thus potentially preventing our clients from having to perform expensive modifications or unnecessarily install larger PSV devices. For example, the API-based calculation for external pool fire can produce grossly conservative required capacities in some situations, which might result in unnecessary and costly modification recommendations. PROCESS has developed a time-dependent fire case model that more accurately predicts relieving rates for these scenarios. To see an example where this unique program was applied, view a host of Relief Valve Case Studies here.

When projects involve the sizing of hundreds of valves or more, PROCESS is experienced in the use of a commercially available database software program called SALUS by Smith & Burgess.

Why Choose PROCESS?

Simply because we are better, faster, and provide more value for your money.