Prevention of Over - Pressurization

Training Package TP 05/05

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Asia Industrial Gases Association

298 Tiong Bahru Road, #20-01 Central Plaza, Singapore 168730

Internet: http//www.asiaiga.org

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Over-Pressurization

Prevention of Over - PressurizationPrevention of Over - Pressurization

Disclaimer

All publications of AIGA or bearing AIGA’s name contain information, including Codes of Practice, safety procedures and other technical information that were obtained from sources believed by AIGA to be reliable and/ or based on technical information and experience currently available from members of AIGA and others at the date of the publication. As such, we do not make any representation or warranty nor accept any liability as to the accuracy, completeness or correctness of the information contained in these publications.

While AIGA recommends that its members refer to or use its publications, such reference to or use thereof by its members or third parties is purely voluntary and not binding.

  AIGA or its members make no guarantee of the results and assume no liability or responsibility in

connection with the reference to or use of information or suggestions contained in AIGA’s publications.

  AIGA has no control whatsoever as regards, performance or non performance, misinterpretation,

proper or improper use of any information or suggestions contained in AIGA’s publications by any person or entity (including AIGA members) and AIGA expressly disclaims any liability in connection thereto.

AIGA’s publications are subject to periodic review and users are cautioned to obtain the latest edition.

AIGA 2005 - AIGA grants permission to reproduce this publication provided the Association is acknowledged as the source

Asia Industrial Gases Association 298 Tiong Bahru Road, #20-01 Central Plaza, Singapore 168730

Internet: http//www.asiaiga.org

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Over-Pressurization

What is Over-Pressurization?What is Over-Pressurization?

The increase of pressure inside a piece of equipment beyond its ability to hold that pressure.

Vessels and tanks

Cylinders and bottles

Compressors and pumps

Piping and tubing

Hoses and flex joints

Instruments and valves

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Over-Pressurization

This could hurt. Now imagine if you were near a vessel, pipe or cylinder when it

ruptured!

Imagine - Blowing Up a BalloonImagine - Blowing Up a Balloon

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Over-Pressurization

Over-Pressurization HazardsOver-Pressurization Hazards

Ruptured process vessels, cylinders, piping

Whipping hoses

Flying debris and shrapnel

Serious injury

Death

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Over-Pressurization

Hazardous resultHazardous result

An ammonia cylinder that failed due to overfilling & hydraulic-king

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Over-Pressurization

Over-Pressurization KillsOver-Pressurization Kills

Incident 1: Liquid trapped in the ball of a ball valve expanded, causing the valve to come apart. Worker dies when contents of CO2 storage tank released in his direction.

Incident 2: A chlorine cylinder ruptures during fill procedure, killing worker in the same room.

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Over-Pressurization

Over-Pressurization KillsOver-Pressurization Kills

Over-pressurization can occur at your location too!

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Over-Pressurization

Causes of Over-PressurizationCauses of Over-Pressurization

Faulty process control

Process upsets

Trapped liquefied gases

In a pipe or hose between two closed valves

In a ball or gate valve not designed to relieve internal pressure

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Over-Pressurization

Causes of Over-PressurizationCauses of Over-Pressurization

Poor equipment and process design

Uncontrolled modifications

Human ignorance

Human error

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Over-Pressurization

Faulty Process ControlFaulty Process Control

Improperly calibrated control devices (temperature, pressure, flow, level…)

Malfunctioning control sensing device such as:

Isolation valves closed

Inlet ports blocked

Devices damaged

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Over-Pressurization

Faulty Process Control (cont’d)Faulty Process Control (cont’d)

Malfunctioning control valves

Sticking control valves, solenoids

Closed or throttled isolation or bypass valves

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Over-Pressurization

Process UpsetsProcess Upsets

Sudden flow rate, temperature or pressure changes

Process operation outside of established operating limits

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Over-Pressurization

Trapped Liquefied GasesTrapped Liquefied Gases

Expand as they warm and vaporize

Pressure rises can exceed most process valves, piping and hoses pressure ratings

If no vapour in the trapped space, hydraulic loading can occur - leads to extremely high pressures in a very short time

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Over-Pressurization

Liquefied GasesLiquefied Gases

If allowed to reach ambient (room) temperatures:

Liquid carbon dioxide could reach 1,100 psi!*

Liquid gases like helium, hydrogen, nitrogen, oxygen and argon could reach 22,000 to 50,000 psi!*

* If the container could hold the pressure.

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Over-Pressurization

Liquefied Gases (cont’d)Liquefied Gases (cont’d)

Do not over-fill a cylinder or tank

Maintain proper vapour space

Do not trap liquid gases

Must be able to relieve pressure

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Over-Pressurization

Liquefied Gas (cont’d)Liquefied Gas (cont’d)

Expand 700 to 800 times in volume as they suddenly change (“flash”) from a liquid state into a gas.

Results in a tremendous force similar to that released in an explosion.

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Over-Pressurization

Trapped Liquid With vapourTrapped Liquid With vapour

As temperature rises, a given mass of liquid can require more room (its density changes)...

Vapour can be compressed. So it makes room for the expanding liquid. Pressure rises gradually with temperature. Eventually, most liquefied gases will develop pressures that will rupture the container.

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Over-Pressurization

Trapped Liquid Without vapourTrapped Liquid Without vapour

Liquid cannot be compressed, so as it gets bigger, it has to go somewhere! It quickly develops extremely high pressure.

As temperature rises, a given mass of liquid can require more room (its density changes)...

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Over-Pressurization

With and Without vapourWith and Without vapour

Heat Input

Pre

ssu

re (

psi

g)

Liquid and vapour pressure rises gradually, but still reaches higher pressures than what typical equipment can contain.

The pressure of liquid without vapour rises quickly.

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Over-Pressurization

Ball Valve Hazard PotentialBall Valve Hazard Potential

(Side View)

Seal

Stem

Downstream (Lower Pressure)

Upstream (Higher Pressure)

Trapped Liquid

Valve Body

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Over-Pressurization

Hazardous ResultHazardous Result

(Side View)

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Over-Pressurization

Downstream (Lower Pressure)

Upstream (Higher Pressure)

Ball valves have1/8” hole in ball

Alternatively, ball valves have special self-relieving seats

Valve Design for Internal ReliefValve Design for Internal Relief

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Over-Pressurization

Gate ValveGate Valve

Notch cut in gate

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Over-Pressurization

Faulty System DesignFaulty System Design

Equipment not designed for pressure or temperature extremes

Missing or isolated pressure relief devices

Relief devices that are too small

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Over-Pressurization

Faulty System Design (cont’d)Faulty System Design (cont’d)

Relief devices not set properly

Unanticipated modes of operation

Stressed piping, tubing, connectors

Relying solely on humans to control pressure

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Over-Pressurization

Case Study: Faulty System DesignCase Study: Faulty System Design

A gas heater vessel ruptured at a CO2 plant in 1998

A dryer switching valve failed in open position.

High pressure process gas (800 psig) then entered the lower-pressure regeneration gas system.

The regeneration gas heater safety relief valve was not big enough to handle process gas flow rates.

The heater vessel ruptured.

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Over-Pressurization

Human Ignorance & ErrorHuman Ignorance & Error

Filling a low pressure cylinder on a high pressure filling manifold

Replacing relief devices with devices of a different design or pressure setting

Replacing a section of pipe, a valve or other process component with one that has a lower pressure rating than the original

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Over-Pressurization

Human Ignorance & Error(cont’d)Human Ignorance & Error(cont’d)

Compromising the integrity of a process component (dents, crimping, unchecked corrosion)

Not following established procedures

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Over-Pressurization

Case Study: Human Ignorance & ErrorCase Study: Human Ignorance & Error

Whipping hose during leak test:

Employee connected a 250 psig rated air hose to a high pressure nitrogen source.

He pressurized hose and manifold to 350 psig.

He discovered manifold leak, vented pressure and repaired leak.

Blow gun was attached to hose and employee claims that pressure was set to 200 psig.

Hose fitting failed, hose whipped and shredded a portion of employee’s coveralls.

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Over-Pressurization

Protecting OurselvesProtecting Ourselves

Knowledgeable Employees

Proper training

Properly Designed Processes

Equipment that is good for the pressure

Control system designs that consider all scenarios

Valves with internal relief capability (for liquefied gases)

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Over-Pressurization

Protecting Ourselves (cont’d)Protecting Ourselves (cont’d)

Pressure Relief Devices

Relief valves, rupture disks

Dual relief valves with diverter valves

Proper Operating Procedures

Proper Maintenance Procedures

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Over-Pressurization

Proper MaintenanceProper Maintenance

Relief Valves Calibration

Bench tested and reset every 5 years

Relief devices missing their wire seal must be removed from service and tested

Recalibration must be by a qualified person

Malfunctioning Relief Devices

Plugged or restricted inlets or outlets

Rust and dirt or ice in spring mechanism

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Over-Pressurization

Proper Maintenance (cont’d)Proper Maintenance (cont’d)

Process Controls and Sensing Devices Calibration

Gauges and thermometers

Metering devices

Solenoids

Temperature and pressure limit controls

Mercoids

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Over-Pressurization

Proper Maintenance (cont’d)Proper Maintenance (cont’d)

Ensure Replacement Parts are “Replacement-In-Kind”

Pipe, fittings and components with same pressure rating

Valves with same pressure relief capabilities

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Over-Pressurization

Management of ChangeManagement of Change

Follow established review procedures

Consider all modes of operations

For each process, ask “How can we have high pressure?”

Ensure proper pressure relief strategy for every process component

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Over-Pressurization

High Pressure ValveHigh Pressure Valve

Pressure Relief Device

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Over-Pressurization

Portable Liquid ContainerPortable Liquid Container

Rupture Disk

Pressure Relief Device

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Over-Pressurization

ForkliftForklift

Pressure Relief Device

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Over-Pressurization

Dual Storage Tank Safety ValvesDual Storage Tank Safety Valves

Pressure Relief Device

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Over-Pressurization

High Pressure Line SafetyHigh Pressure Line Safety

Pressure Relief Device

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Over-Pressurization

Solenoid Shut-off ValveSolenoid Shut-off Valve

Pressure Relief Device

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Over-Pressurization

Pressure / Temperature SwitchPressure / Temperature Switch

Pressure Inlet to SensorTemperature Sensor

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Over-Pressurization

Mercoid SwitchMercoid Switch

Mercoid Switch

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Over-Pressurization

High Pressure Shut-Off SwitchesHigh Pressure Shut-Off Switches

Pressure Shut-off Switches

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Over-Pressurization

Review QuestionsReview Questions

Give examples of processes or pieces of equipment at your location which can present an over-pressurization hazard?

What are the causes of over-pressurization?

Liquefied gases can expand up to __________ times in volume from liquid to gas.

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Over-Pressurization

Review QuestionsReview Questions

Which is the most dangerous hazard, trapped liquid with or without vapour? Why?

What kinds of things can we do to protect from over-pressurization hazards?