Pressure Safety Devices

“Grace Under Pressure”

-Earnest Hemingway

Faizan Ahmad

ICET, Punjab University

Lahore, Pakistan

Pressure Terminologies

Accumulation Design Pressure Set Pressure Operating Pressure Overpressure Underpressure Popping Pressure

Causes of Over Pressure Causes of Under Pressure

Operating Problem Operating Problem

Equipment Failure Equipment Failure

Process Upset

Utility Failures

Safeguards

Safety InterlocksSafeguard Maintenance SystemsShort Stopping

Safety Interlocks

Agitator not workingAbnormal TemperatureAbnormal PressureAbnormal Heat Balance

For all these Abnormalities: Stop Feed and Add full Cooling

Safeguard Maintenance System

Routine Maintenance Mechanical Integrity Checks Records

Short Stopping Add Reaction Stopper Add Agitation with no Electrical Power

ReliefsPressure Relief Devices

1. Spring-Loaded Pressure Relief Valves

2. Rupture Disc

3. Buckling Pin

4. Miscellaneous Mechanical Means

Spring Loaded Pressure Relief Valve

Rupture Disc

Buckling Pin Relief Valve

Closed Pressure below Set Pressure

Full Open Pressure at or above Set Pressure

(Buckles in precise milliseconds at a precise set Pressure)

Simple Mechanical Pressure Relief

Other Types of Safety Valves

Balanced Bellows Pilot Operated

Balanced Bellows Safety Valve

Pilot-Operated Safety Valve

When to Use Spring-Operated Safety Valve

Spring-Operated Valve is used in following cases

Fluids above normal boiling point

Used where toxic fluids are handled

Return to normal conditions quickly

Withstand process pressure changes, including vacuum

When fluid is of the Prime Importance

When to Use Rupture Disc/Safety pin Valve

Capital and maintenance savings When fluid is not so expensive For Benign Service (Non-toxic, Non-Hazardous) Need for fast acting device Potential for Relief valve plugging Used for High Viscosity Liquids

When to Use Both Types

Need a positive Seal (Toxic Material, Material Balance Requirements)

Protect Safety Valve for Corrosion

System Contain Solids

Anything wronghere?

Bellows pluggedin spite of sign

FailedInspectionProgram

Signs ofMaintenance

Issues

Anything wronghere?

Anything wronghere?

DischargesPointing Down

Mexico City DisasterMajor Contributing Cause: Missing Safety Valve

References:

Mohammad A. Malek --- Pressure Relief Devices Chapters # 1, 3, 21

Crowl, Louver --- Chemical Process Safety Chapter # 8

End of Presentation

Thank-you