3. Pressure Relief valves
Define Protected System:
Design considerations
Important an understanding of the operation. One relief valve
can protect more than one equipment
Locate Relief Devices:
4. Pressure Relief valves
Define overpressure scenarios
Design considerations
• Double jeopardy design not required
• Latent failures
• Overpressure protection and instrumentation
MEGPL Basis (Z0210-09-PE-RT-00001-00)
• HP Flare system: 900 MMSCFD with back-pressure of 75 Psig
• LP Flare system: 40 MMSCFD with back-pressure of 15 Psig
• Propane Flare system: 20-22 MMSCFD with no back-pressure
• Butane Flare system: 29-36 MMSCFD with no back-pressure
“Alba_Hysysrun.HSC”
(Dated 08/27/2009).
MEGPL Considerations
Fire - The relieving pressure is 121% of MAWP
Operating - The relieving pressure is 110% of MAWP
5. Pressure Relief valves
Causes of overpressure
A. Blocked Discharge
Design considerations
Max design pressure:
1350 Psig @150F
9. Pressure Relief valves
Conventional pressure relief valve
Type of relief valves
Working principal of the conventional relief valve is the inlet pressure to the valve is directly opposed by a spring force
Conventional Pressure Relief Valve
Pro:
Wide range of materials
High Temperature version available
Lowest cost
Contra:
Prone to leak
Long simmer > 95% valve opening
Sensitive to back-pressure, < 10%
Vulnerable to inlet pressure lost
10. Pressure Relief valves
Type of relief valves
Balanced Relief Valves
Pro:
Better handling of corrosive fluids.
Less sensitivity to back-pressure
Wide range of materials
High Temperature version available
Contra:
Prone to leak
Long simmer > 95% valve opening
Higher maintenance cost
Limited bellows life
11. Pressure Relief valves
Type of relief valves
Pilot Operated Relief Valves
• Low pressure applications for tanks
Pro:
Smaller & Lighter than other valves
Easily testable on site
Not affected by back-pressure
Can address high inlet losses
Contra:
Dirty service limitations
When soft-seat or O-ring is used, limited
chemical compatibility
12. Pressure Relief valves
• Sizing for liquid service
• Sizing for gas service
Sizing relief valves
13. Pressure Relief valves
• Designed pressure relieving devices should be certified and approved under Code.
ASME- Boiler and Pressure Vessel Code Section I, Power Boilers, and Section VIII, Pressure Vessels.
ASME- Performance Test Code PTC-25, Safety and Relief Valves.
ANSI B31.3, Code for Petroleum Refinery Piping.
Application of Codes, Standard and Guidelines
• API are recommended practices for the use of Safety Relief Valves in the petroleum
and chemical industries are:
API Recommended Practice 520 Part I - Sizing and selection of components for pressure
relief systems in Refineries.
API Recommended Practice 520 Part II - Installation of pressure relief systems in
Refineries.
API Recommended Practice 521 - Guide for Pressure-Relieving and Depressuring
Systems.
API Recommended Practice 527 - Seat Tightness of Pressure Relief Valves
API Standard 526 - Flanged Steel Pressure Relief Valves
API Standard 2000 - Venting Atmospheric and Low-Pressure Storage Tanks: Nonrefrigerated
and Refrigerated
API Standard 2001- Fire Protection in Refineries.