ERT 422/4ERT 422/4Piping and instrumentation Piping and instrumentation

diagram (P&id)diagram (P&id)

MISS. RAHIMAH BINTI OTHMAN(Email: rahimah@unimap.edu.my)

Fundamentals of Pressure Relief Devices

What is the Hazard?

Despite safety precautions …

– Equipment failures– Human error, and– External events, can sometimes lead to …

Increases in process pressures beyond safe levels, potentially resulting in …

OVERPRESSURE due to a RELIEF EVENT

What are Relief Events?

External fire Flow from high pressure source Heat input from associated equipment Pumps and compressors Ambient heat transfer Liquid expansion in pipes and surge

Potential Lines of Defense

Inherently Safe Design

Passive Control

Active Control

– Low pressure processes

– Install Relief Systems

– Overdesign of process equipment

What is a Relief System?

A relief device, and

Associated lines and process equipment to safely handle the material ejected

Why Use a Relief System?

Inherently Safe Design simply can’t eliminate every pressure hazard

Passive designs can be exceedingly expensive and cumbersome

Relief systems work!

T

L

PSV-2

PSV-3

TTLT

TCR

LCR

P-2

AIR PENYEJUK

PSV-7

FCR

FT

S-1

BIOREACTOR CONTROL SYSTEM

Pressure Terminology

MAWP Design pressure Operating pressure Set pressure Overpressure Accumulation Blowdown

Pressure Relief DevicesWhat’s coming

Basic terminology Code requirements Safety relief valves Rupture discs

Pressure Terminology

Operating pressure MAWP Design pressure Set pressure Accumulation Overpressure Blowdown

Code Requirements

General Code requirements include:

– ASME Boiler & Pressure Vessel Codes– ASME B31.3 / Petroleum Refinery Piping– ASME B16.5 / Flanges & Flanged Fittings

Code Requirements

All pressure vessels subject to overpressure shall be protected by a pressure relieving device

Liquid filled vessels or piping subject to thermal expansion must be protected by a thermal relief device

Multiple vessels may be protected by a single relief device provided there is a clear, unobstructed path to the device

At least one pressure relief device must be set at or below the MAWP

Code Requirements

Relieving pressure shall not exceed MAWP (accumulation) by more than:

– 3% for fired and unfired steam boilers

– 10% for vessels equipped with a single pressure relief device

– 16% for vessels equipped with multiple pressure relief devices

– 21% for fire contingency

Relief Design MethodologyLOCATE RELIEFS

CHOOSETYPE

DEVELOP SCENARIOS

SIZE RELIEFS(1 or 2 Phase)

CHOOSE WORST CASE

DESIGN RELIEF SYSTEM

Locating Reliefs – Where? All vessels Blocked in sections of cool liquid lines that

are exposed to heat Discharge sides of positive displacement

pumps, compressors, and turbines Vessel steam jackets Where PHA indicates the need

LOCATE RELIEFS

Choosing Relief Types

Spring-Operated Valves

Rupture Devices

CHOOSETYPE

Spring-Operated Valves

Conventional Type

CHOOSETYPE

Picture: Conventional Relief Valve

ConventionalRelief Valve

CHOOSETYPE

Spring-Operated Valves

Balanced Bellows Type

CHOOSETYPE

Picture: Bellows Relief ValveBellows

Relief Valve

CHOOSETYPE

Pros & Cons:Conventional Valve

Advantages+ Most reliable type if properly sized and operated+ Versatile -- can be used in many services

Disadvantages– Relieving pressure affected by back pressure– Susceptible to chatter if built-up back pressure is too high

CHOOSETYPE

Pros & Cons:Balanced Bellows Valve

Advantages+ Relieving pressure not affected by back pressure+ Can handle higher built-up back pressure+ Protects spring from corrosion

Disadvantages– Bellows susceptible to fatigue/rupture– May release flammables/toxics to atmosphere– Requires separate venting systemCHOOSE

TYPE

Rupture Devices

Rupture Disc

Rupture Pin

CHOOSETYPE

ConventionalMetal Rupture Disc

CHOOSETYPE

ConventionalRupture Pin Device

CHOOSETYPE

When to Use a Rupture Disc/Pin

Capital and maintenance savings Losing the contents is not an issue Benign service (nontoxic, non-

hazardous) Need for fast-acting device Potential for relief valve plugging High viscosity liquids

CHOOSETYPE

When to Use Both Types

Need a positive seal (toxic material, material balance requirements)

Protect safety valve from corrosion

System contains solids

CHOOSETYPE

Relief Event Scenarios A description of one specific relief event Usually each relief has more than one relief event,

more than one scenario Examples include:

– Overfilling/overpressuring– Fire– Runaway reaction– Blocked lines with subsequent expansion

Developed through Process Hazard Analysis (PHA)

DEVELOP SCENARIOS

Rupture Discs A rupture disc is a thin diaphragm (generally a solid metal disc)

designed to rupture (or burst) at a designated pressure. It is used as a weak element to protect vessels and piping against excessive pressure (positive or negative).

There are five major types available– Conventional tension-loaded rupture disc– Pre-scored tension-loaded rupture disc– Composite rupture disc– Reverse buckling rupture disc with knife blades– Pre-scored reverse buckling rupture disc

Rupture Discs

They are often used as the primary pressure relief device.– Very rapid pressure rise situations like runaway reactions.– When pressure relief valve cannot respond quick enough.

They can also be used in conjunction with a pressure relief valve to:– Provide corrosion protection for the PRV.– Prevent loss of toxic or expensive process materials.– Reduce fugitive emissions to meet environmental

requirements.

Rupture Discs Are Well Suited For Some Applications

When compared with PR valves, rupture discs have:

Advantages

+ Reduced fugitive emissions - no simmering or leakage prior to bursting.

+ Protect against rapid pressure rise cased by heat exchanger tube ruptures or internal deflagrations.

+ Less expensive to provide corrosion resistance.

+ Less tendency to foul or plug.

+ Provide both over pressure protection and depressuring.

+ Provide secondary protective device for lower probability contingencies requiring large relief areas.

Rupture Discs Are Less Well Suited For Other Applications

When compared with PR valves, rupture discs have:

Disadvantages

– Don’t reclose after relief.– Burst pressure cannot be tested.– Require periodic replacement.– Greater sensitivity to mechanical damage.– Greater sensitivity to temperature

Conventional Tension-Loaded Metal Rupture Disc

Pre-Scored Tension - Loaded Rupture Disc

DiscCorrodedThrough

Composite Rupture Disc

Reverse Buckling Rupture Disc With Knife Blades

Typical RD/PRV Installation

From Process(No Pockets)

(If Req'd)

NPS 3/4"(19 m m )

TW

CSO

PI

Grade (Or Frequently Used P latform )

4' -

0"

RD

PR

CSO(If Req'd)

M in.

0302040F2

To flare headeror atm osphere(no pockets)

CSO

Min

NPS 3/4"(19 m m )

NPS 3/4"(19 m m )

1/2" (13 m m )Tubing

ExcessFlowValve

Vent to safelocation

Anything wronghere?

Pressure above RD

Reduced inlet piping

Damaged duringInstallation

ClassicAlligatoring

Conventional Rupture Pin Device

VALVES & PIPE SIZING

Sizing Reliefs

Determine relief vent area Determining relief rates

Determine relief vent area

SIZE RELIEFS(Single Phase)

Determine Relief Vent Area Liquid

Service

where

bs25.1

)ref

(

bpvovQ

gpm 38.02/1)psi(2in

PPKKKCA

A is the computed relief area (in2) Qv is the volumetric flow thru the relief (gpm) Co is the discharge coefficient Kv is the viscosity correction Kp is the overpressure correction Kb is the backpressure correction (/ref) is the specific gravity of liquid Ps is the gauge set pressure (lbf/in2) Pb is the gauge backpressure (lbf/in2)SIZE RELIEFS

(Single Phase)

Determine Relief Vent Area Gas

Service

where

MTz

PKCA

bomQ

A is the computed relief area (in2) Qm is the discharge flow thru the relief (lbm/hr) Co is the discharge coefficient Kb is the backpressure correction T is the absolute temperature of the discharge (°R) z is the compressibility factor M is average molecular weight of gas (lbm/lb-mol) P is maximum absolute discharge pressure (lbf/in2) is an isentropic expansion function

SIZE RELIEFS(Single Phase)

valverelief for the pressureset theis s

pipingfor s33.1max

fire toexposed sfor vessel s2.1max

vesselspressure unfiredfor s1.1max

7.14max

PPP

PPPP

PP

Determine Relief Vent Area Gas

Service

where

)1/()1(

125.519

is an isentropic expansion function is heat capacity ratio for the gas Units are as described in previous slide

SIZE RELIEFS(Single Phase)

E-1 : pensteril(penukar haba plat)

F-1 : fermenter penghasilan S-1 & S-2 : pemisah sel R-1 : penuras hampagasberputar

T-1 : tangki pemendakT-2 : tangki pelarut bahan mendak

C-1 : penyejat D-1 :menara semburan

P-1 : pam pensteril P-2 & P-3 : pam fermenterP-4 : pam penurashampagas berputar

P-5 : pam tangkipemendak

P-6 : pam tangki pelarutbahan mendak

media

G-1 : tangki penyimpanan

STIM

E-1

S-2

P-1

T

PSV-1

F-2

L

TAIR PENYEJUK

PSV-4

PSV-5PSV-6

AIR PENYEJUK

F-1

P-3

L

T

PSV-3

PSV-2

PSV-7

F-2: fermenter benih

S-1

I-1 & I-2 : penukar ionkation dan anionP-8 & P-9: pam penukar ion UNIVERSITI KEBANGSAAN

MALAYSIA 2003/2004

KUMPULAN A

TAJUK LUKISAN :RAJAH ALIR PROSES

BAGI SISTEM KAWALAN

PENYELIA :DR.JAMALIAH

MD.JAHIM

TAJUK :LOJI PENGHASILAN ASIDITAKONIK DARI PROSESFERMENTASI Aspergillus

terreus

DILUKIS OLEH :AZLINDA HARON

A79668

TARIKH :15 MAC 2004

LUKISAN TIDAKMENGIKUT SKALA

This drawing is aproperty of UniversitiKebangsaan Malaysiaand contains proprietyinformation

TCR

TT

LARUTAN ASIDITAKONIK 50%

FT

P-9

P-8

PSV-11PSV-10

I-1

I-2

SERBUK ASIDITAKONIK 99%

PSV-13

FCR

FCR

TCR

LCR

TCR

LCR

R-1

L

LCR

L

PCR

P-7--

T-1

P-4

LPSV-8

P-5

P-6

FT

FCR

FCR

PSV-9

T

UDARA PANAS

TCR

G-1

L

PSV-12

LCR

T-2

L

LPTT

L

PCRTCR

LCR

P-2

C-1

D-1

LCR

LCR

P-10

P-7

FT

P-7: pam penyejat

P-10 : pam menara semburan

STIM

KONDENSASIL

LCR

JADUAL 5.2 Pelega Untuk Fasa Cecair Menggunakan Persamaan 9-4 (Crowl & Louvar)

Co =0.61

Anggap Terlebih Tekanan = 25%

Anggap tekanan balik sentiasa maksimum, iaitu 50 %

Pelega q (kg/j) r (kg/m3) Qv (gpm) r/rref Kv Kp Kb Ps (kPa) Ps (lbf/in2) Pb (lbm/in2) A (in2) A (m2)

PSV-2 3.49E+02 10.39 147.7469 98.1 1 1 1 1000 145.1 72.55 8.97 0.006

PSV-3 8.13E+02 10.17 352.2017 98.1 1 1 1 1000 145.1 72.55 21.37 0.014

PSV-4 4.51E+03 10.39 1912.572 98.1 1 1 1 1200 174.12 87.06 105.94 0.068

PSV-5 1824.68 1.2 6695.562 98.1 1 1 1 1000 145.1 72.55 274.25 0.177

PSV-6 1893.83 1.2 6949.304 98.1 1 1 1 994 144.229 72.1147 285.50 0.184

PSV-7 5.26E+03 10.35 2237.064 98.1 1 1 1 1000 145.1 72.55 135.75 0.088

PSV-8 1.82E+03 9.94 808.3173 98.1 1 1 1 900 130.59 65.295 51.70 0.033

PSV-10 2.65E+04 10.26 11359.5 98.1 1 1 1 1000 145.1 72.55 689.31 0.445

PSV-11 2.93E+04 10.16 12712.39 98.1 1 1 1 1300 188.63 94.315 676.56 0.436

PSV-12 26265.9 10.41 11110.21 98.1 1 1 1 1000 145.1 72.55 674.18 0.435

bs

ref

bpvo

v

PPKKKC

Q

gpm

psiinA

25.1

/

0.38

2/12

T

L

PSV-2

PSV-3

TTLT

TCR

LCR

P-2

AIR PENYEJUK

PSV-7

FCR

FT

S-1

FERMENTER CONTROL SYSTEM

a) LIQUID STREAM

Equation; 5-14 (R.K Sinnot):

For carbon steel pipeline;

di, optimum = 282G0.52-0.37

Where; G = Flow rate, kg/s = , kg/s

For stainless steel pipeline;

di, optimum = 282G0.50-0.37

Where; G = Kadar aliran, kg/s = Ketumpatan aliran, kg/s

a) LIQUID STREAM

Equation; 5-14 (R.K Sinnot):

For carbon steel pipeline;

di, optimum = 282G0.52-0.37

Where; G = Flow rate, kg/s = Density of fluid, kg/s

For stainless steel pipeline;

di, optimum = 282G0.50-0.37

Where; G = Flow rate, kg/s = Density of fluid, kg/s

DIAMETER SIZING CALCULATION

b) VAPOR STREAM

For long pipeline, the velocity of vapor = sonic velocity (Crowl& Louvar 1990).

Sonic velocity;

c gg R Ta

M

where, = 1.32 untuk gas teriongc = 32.1740 ft.ibm/s2.ibf

Rg = 1545 ft.ibf /ib- mol. oR

ToR = 1.8TOC +32+460

c gg R Ta

M

DIAMETER SIZING CALCULATION

Flow rate,

Qm = UA (kg/s)

Where;

U = a = halaju sonic (m/s)A = Luas keratan rentas paip (m2)

DIAMETER SIZING CALCULATION

b) VAPOR STREAM-CONT’

EXAMPLE OF CALCULATION (DIAMETER OF PIPELINE FOR VAPOR STREAM)

ValveT

(°C) T (°R) M g = Cp/Cv a (m/s) ρ(kg/m3) Qm (kg/j) Qm (kg/s) A (m2) D (m) D (in)

PSV-1 121 709.47 180 1.145 144.380 20.170 4512.86 1.254 0.000 0.023 0.922

PSV-9 200 851.67 180 1.323 170.041 16.990 50870.00 14.131 0.005 0.079 3.107

PSV-13 140 743.67 180 1.146 147.884 20.190 121100.00 33.639 0.011 0.120 4.715

MTRga gc /gc 32.17 ft.lbm/lbf.s2Rg 1545 lbf/lb-mol°R

FCR PCV-13

FT

P

UDARA PANAS

TCR

P-10

SPRAY TOWER CONTROL SYSTEM

PIPE THICKNESS SIZING CALCULATION

From British BS 3351 standard, the thickness of pipepine is given by equation (R.K. Sinnot) ;

P

Pdt

d

20

Where;P = internal design pressure, bar.d = outside radius of pipe, mm.σd = allowable stress of pipe material at design temperature, N/mm2.

?? Reduced Inlet Piping

Anything wronghere?

ReducedInlet Piping

?? Plugged Bellows, Failed Inspection, Maintenance

Bellows pluggedin spite of sign

Anything wronghere?

FailedInspectionProgram

Signs ofMaintenance

Issues

?? Discharges Pointing DownAnything wrong

here?

Anything wronghere?

DischargesPointing Down

?? Long Moment Arm

Anything wronghere?

LongMoment Arm

?? Will these bolts hold in a relief event

Anything wronghere?

Will thesebolts hold

in arelief event?

Mexico City Disaster

Major Contributing Cause:Major Contributing Cause:Missing Safety ValveMissing Safety Valve

Summary

Pressure Relief– Very Important ACTIVE safety element– Connected intimately with Process Hazard

Analysis– Requires diligence in design, equipment

selection, installation, inspection and maintenance

References

Crowl and Louvar – Chemical Process Safety, Chapters 8 and 9

Ostrowski – Fundamentals of Pressure Relief Devices

Sterling – Safety Valves: Practical Design, Practices for Relief, and Valve Sizing