Relief Valve Studies
Ascent evaluates all PRD devices against all relevant cases including fire, thermal relief, blocked equipment, power failure, loss of instrument air, loss of cooling water and all other relevant utility failures. We simulate scenarios to insure accurate relief valve sizing. Dyamic simmultion is also performed where required.
All of our engingineers have had HAZOP and PHA training, and are familiar with OSHA requirements and standards regarding PRD devices.
Our Typical Scope of Work for a Relief Valve Study
1. Evaluating all existing relief devices based on API RP 520 and 521 for the specified Design Basis. Ascent can aid the customer in developing a Design Basis if needed, and we can simulate expansion cases and determine if all existing relief valves meet the Unit's maximum capabilities.
2. Performing rigorous hydraulic calculations to evaluate the relief devices’ inlet and outlet lines, including evaluation of whether the existing inlet and outlet lines meet API‑520/521’s 3% rule and backpressure limitations. Where existing lines do not meet API 520/521, piping modifications are recommended,. In some cases results which are over 3%, but less than 5% will be further evaluated prior to recommending modifications.
3. Where flares are involved, the relief valve discharge piping to the flare is evaluated by verifying the built-up back pressure at the relief drum using an existing model if available. Ascent can develop this model if necessary.
Typical Deliverables
We customize our packages to our customers requirements.Here is a typical deliverable list:
- A summary of relief rates for each relief device.
- A relief device heat and material balance at designed charge rate. A PFD with flow, temperature, and pressure of main streams will be provided.
- The philosophy for each relief device of why the different scenarios and flow rates were evaluated.
- A simplified PFD sketch showing what equipment is protected by each relief device.
- Detailed calculations for each relief device and relevant assumptions.
- A summary of all scenarios for each relief device identifying the limiting case.
- The maximum allowable Unit feed rate for each feed device based on required and selected relief device orifice sizes.
- A detailed list of new relief devices, specification sheets for all new relief devices, and recommended piping changes.
- The relief study results will be delivered in a binder with individual tabs for each relief device. A CD will also be provided to allow easy electronic archival of all documentation.
