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OVERPRESSURE

PROTECTION -- USING

RUPTURE DISCS FOR

PRESSURE RELIEF

Tappi PLC Conference

August 2000Fike Corporation

Cross Sectional View

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Screwdriver Slot Configuration

Hex Head Configuration

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Hex Head with Threaded Outlet

Wrench Flat Configuration

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Typical Installations

Typical Installations

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Sizing Considerations Account for rupture disc

assembly length

Viscosity of the fluid

Sizing for fluids with viscosity

> 10 cP

calculate min. diameter using the

flow through an orifice

calculation

Poiseuilles viscosity equation

min. flow diameter = larger of the

two

Poiseuilles Viscosity Equation

D = [128 LQ/ P]1/4

where: P = (Po)(1.10) - Pe

D = pipe or inside diameter

= absolute or dynamic viscosity

L = pipe or tube length

Po = relieving pressure

Pe = exit pressure

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Flow through an Orifice

A = Q/37.98K S/P

(sizing for Liquids equation)

A = cross-sectional flow area (in2)

Q = volumetric flow rate (gpm)

K = 0.62 (per ASME)

Rupture Disc Sizing Methods

Coefficient of

Discharge Method -

KD

Resistance to Flow

Method - KR

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Coefficient of Discharge MethodUG-127(a)(2)(a)

Methodology for simple systems

Coefficient of discharge KD= 0.62

KDis applied to the calculated theoretical

flow capacity of the device based on the

certified minimum net flow area MNFA

Q = Qcalc* KD

Coefficient of Discharge Method- Guidelines for Usage UG-127(a)(2)(a)

Disc must discharge to the atmosphere

Disc must be installed within 8 pipe

diameters of the vessel nozzle

Length of discharge piping not greater than

5 pipe diameters

Certified MNFA includes vessel exit effects

and the 8 & 5 piping losses

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Resistance to Flow MethodUG-127(a)(2)(b)

Sizing is done on a relief system basis not

by capacity of individual components

Rupture disc is treated as another

component in the relief system that provides

some resistance to flow

System relief capacity must be multiplied

by a factor of 0.90 to allow for uncertaintiesinherent with this method

Resistance to Flow - Cont.

Based on Darcy formula (Crane 410)

hL = f L/D v2/2g

K ~ f L/D

API recommendation for rupture discs has

been L/D = 75K = .02 (75) = 1.5

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Proper Specification Standard burst diameters from

3/16 to 1-3/4

Larger sizes up to 6

Max burst pressure is 12,000

psig @ 800 F for soldered

Higher burst pressures for

welded designs

Materials of Construction

Stainless steel body

Inconel rupture disc

Conventional prebulged type

Standard manufacturing range

of +6% to -3%

Rupture tolerance of +/-5%

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Common Questions Q: What is the difference between the burst

tolerance and the manufacturing range?

A: The burst tolerance is the variation

around the stamped burst pressure in which

the individual rupture disc burst pressures in

a lot are required by the ASME code to fall. 5% of marked burst pressure for pressures above 40

psi

2 psi of marked burst pressure for pressures 40 psi

and below

Common Questions

A: The manufacturing design range is a

range of pressure within which the average

burst pressure of the test discs must fall to

be acceptable as agreed upon between the

manufacturer and the user.

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Common Questions Q: What manufacturing ranges are

available?

A: Standard-- +0 to -10%

Maximum Stamped-- All values below

Minimum Stamped-- All values above

Reduced-- +0 to -5%

Special Min/Max-- All tolerances included

Zero-- no range

Common Questions

Q: How do I choose the proper burst

pressure?

A: As the primary relief device, the disc

shall be set to operate at a pressure not

exceeding the MAWP.

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Common Questions Q: How does the operating ratio help me

decide what burst pressure I should use?

A: The operating ratio is the ratio of the

operating pressure to the stamped burst

pressure. Each family of discs will have a

maximum recommended operating pressure

that will ensure good service life for thatdisc.

Common Questions

Q: How do I calculate the operating ratio?

A: Divide the operating pressure by the

minimum possible burst pressure

Requested B.P.: 900 psig

Manufacturing Range: 954 to 873 psig

Operating Pressure: 600 psig

600 psig/873 psig= 68.73%

Maximum Operating Ratio: 70%

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Common Questions Q: How many discs are burst tested from

each lot?

A: The number increases with the lot size.

Lot Size Sample Size

1 or 2 2

3 to 15 3

16 to 25 4

26 to 40 541 to 65 7

66 to 100 10

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Rupture disc tooling

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Common Questions Q: How does temperature affect the burst

pressure of the disc?

A: There is an inverse relationship -- as the

temperature increases the burst pressure

decreases

For Inconel material

Burst pressure Temperature

900 psig 72 F

915 psig 250 F

925 psig 500 F

935 psig 750 F

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Common Questions

Q: So how do I choose the correctcoincident temperature?

A: Use the maximum normal operating

temperature.

Since there is an inverse relationship -- if the

temperature continues to rise, the disc will burst at

a lower pressure

Installation, Operation, andMaintenance Procedures

Stop the screw and allow pressure to bleed

off

Remove the rupture disc while the polymer

is above the melt temperature

Wipe the polymer off the disc body with a

soft cloth to protect the tip from damage

Clean the rupture disc seat with the

appropriate tools

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Proper Installation Apply Never-Seez (pure nickel type) to the

threads of the new assembly

Insert by hand

Tighten to the specified torque with a torque

wrench

CAUTION: over-tightening can affect the

burst pressure Attach the tag to the assembly or to the

housing

Safety Considerations

Verify that the rupture disc matches the tag

Check that the disc has a safe, unblocked

point of discharge

Do not add extra piping to the disc other

than specified

Assume that there is always pressure behinda rupture disc

Use protective gloves, sleeves, and a face

shield when changing discs

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Questions?????

Agenda

Causes of high pressure build-up

Safety considerations for polymer transfer

piping

Rupture discs and the ASME code

Rupture disc design

Sizing considerations Proper specification

Installation, operation, and maintenance

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Causes Of High Pressure

Build-up Packing

LDPE expands 30% from 72 to 300 F

Cooling creates voids to allow space for

expansion

Transfer pipes can cool faster creating a

vacuum to draw in polymer from the die and

extruder

Pipes heat more quickly, so packed pipes canoverpressurize during heat-up

Causes of High PressureBuild-up

Decomposition

Extreme temperatures resulting from failed

controller, excessive set points, improper use of

heaters

At elevated temperatures, LDPE produces gases

generated by decomposition Trapped gases can cause overpressure that can

lead to expansion and rupture

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Safety Considerations in

Designing Polymer TransferPiping Use high pressure pipe design and welded fittings

Divide the pipe into multiple zones to minimize

hot spots

Use heating methods that assure uniform heating

along the pipe

Use low-watt density heaters

Use high temperature shutdown safety devices

Install pressure relief devices such as rupture discs

Rupture discs and the ASMECode Definition: RD device is a non-reclosing

pressure relief device actuated by inlet static

pressure and designed to function by the

bursting of a pressure containing disc

RD is the pressure containing and pressure

sensitive element of the RD device

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Related ASME Code Sections Section VIII Div. 1

1995 Edition, 96 Addenda: UG-125 through

UG-136

1995 Edition, 97 Addenda: UG-125 thru UG-

137 Published January 1, 1998. Mandatory for

new construction beginning January 1, 1999

1998 Edition: UG-125 through UG-137

Published July 1, 1998. No changes to rupture

disc requirements

Definitions

General: Every RD shall have a marked

burst pressure established by the rules of

UG-137(d)(3) within a manufacturing

design range at a specified disc temperature

and shall be marked with a lot number.

Manufacturing design range is a range of

pressure within which the marked burst

pressure must fall to be acceptable for a

particular requirement.

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Definitions The specified disc temperature shall be the

temperature of the disk when the disc is

expected to burst.

A lot of rupture discs is those discs

manufactured of a material at the same

time, of the same size, thickness, type, heat,

and manufacturing process including heattreatment.

Rupture Disc Applications

Primary

Secondary (Multiple)

Combination

Fire

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Primary ReliefUG-125(c)

The rupture disc is

the only relieving

device provided on

the vessel.

ASME:

Overpressure Allowance: 110% of MAWPor 3 psig, whichever is greaterMarked Burst Pressure: not to exceed100% of MAWP

Secondary or Multiple ReliefUG-125(c)(1), UG-134(a)

The rupture disc may

be used to provide

secondary relief to

other rupture disc or

pressure relief valve.

ASME:

Overpressure Allowance: 116% of MAWPor 4 psig, whichever is greater

Marked Burst Pressure: not to exceed105% of MAWP

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Rupture Disc / PRV CombinationUG-127(a)(3)(b)

The rupture disc is

used in combination

with a pressure relief

valve.

ASME:

Sizing and marking requirements determined based onwhether combination is primary or secondary device

External Fire UG-125(c)(2), UG-134(b) A supplemental relief

device may be installed

to protect against

excessive pressure

caused by unexpected

source of external heat

such as fire.

ASME:

Marked Burst Pressure: not to

exceed 110% of MAWP

Overpressure Allowance: 21%

above MAWP

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Rules to Determine the Rated

Flow Capacity of a System UG-127(a)(2)

Use the coefficient of discharge method discharges directly to atmosphere -- 8 & 5 rule

inlet and discharge = or > NPS of the device

theoretical flow for the media times K(0.62)

By analyzing the total system resistance to

flow

consider the flow resistance of disc device, piping, etc. certified flow resistance factor KRto calculate velocity

head loss

calculated capacity times factor of 0.90

Manufacturer Authorization toUse the UD Code Stamp

UG-137(c)

Conduct flow testing to have the capacities

certified at an ASME accepted test facility

Demonstrate that its manufacturing, testing,

and quality assurance systems will insure

agreement between production units and

certification units

Comply with periodic inspections by an

ASME representative

UD

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Requirements for Certifying the

Capacity of the Device Certified flow resistance KR= 2.4 or as

determined through testing

Tests shall be conducted with air or gas

Tests at inlet pressure not to exceed 110%

of device set pressure

KRfor devices tested with nonpressure

containing items (seals, support rings, and

vacuum supports) is applicable to those

without

Flow Resistance CertificationTesting UG-131(o)

One size method

Three size method

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One Size Method UG-131(o)(1)

For each disc type, 3 discs are burst testedat the minimum B.P. for that size

Same 3 discs are then flow tested to

determine KRvalue

Burst and flow values are averaged

All individual flow resistances shall fall within

the avg. flow resistance by an acceptance band

of plus or minus 3 times the average of the

absolute values of the deviations of the

individual flow resistances from the avg. flow

resistance

Three Size Method UG-131(o)(2)

Same as One Size Method

Exception: done over a range of 3 sizes

Resulting KRvalue can be used for entire

family of devices (applies to all sizes and

pressures of the design tested)

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Inspection of ManufacturingUG-137(c)(1)(2)

Demonstrate that its manufacturing,

production, testing, and quality procedures

will insure close agreement between the

performance of random samples and those

submitted for Certification

Agree to allow inspections at any time by

an ASME designee

Production Audit UG-137(c)(3)(a&b)

After one size or three size testing is

successfully performed, 2 sample discs are

selected by ASME for final verification

These discs are burst and flow tested in an

accepted flow laboratory

Must meet or exceed the performance

requirements

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Performance Requirements UG-137(c)(3)(a&b)

Burst pressures must be within the burst

tolerance specified in UG-127(a)(1)

Discs must exhibit a KRvalue that does not

exceed the claimed value

Discs must meet the minimum net flow area

(MNFA) when installed on an 8 & 5 rig

Success = permission to use the UD Code

Symbol valid for 5 year periods

Production Testing UG-137(d)(3)(a) / UG-127(a)(1)

(a) at least 2 burst tests per lot

Burst tests performed at the specified disc

temperature

The marked B.P. shall be determined so that

the sample disc burst pressures are within

the B.P. tolerance of UG-127(a)(1): 5% of marked burst pressure for pressures above 40

psi

2 psi of marked burst pressure for pressures 40 psi

and below

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More Production Testing UG-137(d)(3)(b)&(c)

(b) At least 4 sample discs burst tested at 4different temperatures

Data used to make a smooth curve of BP vs.

temperature

Value for the BP derived from the curve

(c) At least 4 sample discs using 1 size of discfrom each lot of material shall be burst at 4

different temperatures

data used to make a curve of percent change of

BP vs. temperature

Rupture Disc Marking UG-129(e)Old Requirements

Manufacturers Name

Model or Part Number

Lot Number

Disc Material

Nominal Size

Stamped Burst Pressure

Specified Disc Temperature Capacity

New Requirements

Manufacturers Name

Model or Part Number

Lot Number

Disc Material

Nom. Size (NPS of holder)

Marked Burst Pressure

Specified Disc Temperature

Minimum Net Flow Area

Cert. Flow Resistance KR year built

ASME symbolUD

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1998 Ed. Rupture Disc Tag

Rupture Disc Design for PlasticExtrusion Processes

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Rupture Disc Design for Plastic

Extrusion Processes

Rupture Disc Design for PlasticExtrusion Processes

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Cross Sectional View

Cross Sectional View

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Cross Sectional View