Pressure Relief Devices

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Pressure Relief Devices
The-Safety-Valve.com
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Meet- en Regeltechniek
Objectives of this Presentation
The aim of this presentation is to explain
the most common phrases around Pressure Relief Devices
 Scope of this presentation
 Definition of a Safety valve
 Reasons for Excess Pressure
 Classification – Definition of Safety Valves
 Design - Options
 Applications - Installations
 Institutions, Standards and Regulations
 Set pressure – CDTP – Overpressure - Blowdown
 Back pressure – Inlet pressure
 Legal aspects
 Maintenance
 Calculation example

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Scope of this presentation – Pressure Relief Devices
 Reclosing Devices > Safety relief valves
o Set pressure
 ASME >= 15 psi (1,03 barg)
 API >= 15 psi (1,03 barg)
 CE – PED >= 0,5 barg
 Non Reclosing Devices > Rupture Disc / Pin-actuated Device
o Set pressure >= 0,5 barg
 ASME >= 15 psi (1,03 barg)
 API >= 15 psi (1,03 barg)
 CE – PED
o Set pressure <0,5 barg > Breather Valve / Emergency valve
 API2000ed7 (ISO28300)
 Tank protection
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Definition
A safety valve designed to open and relieve excess pressure and to re-
close and prevent the further flow of fluid after normal conditions have
been restored.
Asme Ptc 25

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Reasons for Excess Pressure in a System
There are a number of reasons why the pressure in a system can exceeds a
predetermined limit. API Standard 521/ISO 23251 Sect 4. provides a detailed
guideline about causes of overpressure.
The most common are:
Blocked discharge
Exposure to external fire, often referred to as “Fire Case”
Thermal expansion
Chemical reaction, often referred as “run away”
Heat exchanger tube rupture
Cooling system failure
Each of the above listed events may occur individually and separately from the
other. They may also take place simultaneously. Each cause of overpressure will
create a different mass- or volume flow to be discharged, e.g. small mass flow
thermal expansion and large mass flow in case of a chemical reaction. It is the
user’s responsibility to determine a worst case scenario for the sizing and
selection of a suitable safety valve.
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Classification-Definition Safety Valves
Loading Principle
Performance - Opening Characteristics

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Classifcation–Definition Safety Valves – Loading Principle
Safety Valves
Direct-load
Spring loaded Weight loaded
Controlled
Controlled
Safety
Pressure Relief
System
Pilot-Operated
Safety Valve
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Loading principle – Spring Loaded Safety Valves
A pressure relief valve in which the opening and closing
of the valve is controlled by a spring.

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Loading principle – Weight Loaded Safety Valves
A pressure relief valve in which the opening and closing
of the valve is controlled by a weight.
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Loading principle – Pilot-Operated Safety Valves
• A pressure relief valve in which the main valve is combined with and
controlled by an auxiliary pressure relief valve (pilot-controlled)

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Loading principle – Controlled Safety Valve System
A system consisting of a safety valve in combination with control unit.
The control unit generates an additional closing force with the aid of a
drive in the case of a spring-loaded safety valve.
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Loading principle - Rupture Disc / Safety Valve Combination
A system consisting of a main valve in combination with a
prepended rupture disc. The bursting pressure of the rupture disc is
equal to the set pressure of the safety valve

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Classification-Definition Safety Valves-AD2000-A2
Performance / Opening Characteristics
 Opening Characteristics
o Normal Safety Valve Pursuant to AD 2000 Information Sheet A2
A spring loaded pressure relief valve actuated by the static pressure upstream of
the valve. The valve opens in proportion to the pressure increase over the opening
pressure. Used primarily with liquid service (non-compressible).
100
80
60
40
20
0
Lift [%]
pc
p = set pressure pc = opening pressure
pp = popping pressure ps = closing pressure
90 100 110
ps
p
Pressure [%]
pp
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o Normal Safety Valve Pursuant to AD 2000 Information Sheet A2
A spring-loaded normal safety valve opening proportionately or suddenly within a
pressure increase of 10%.
Used with all media: steam, vapour, gas and liquids.
100
80
60
40
20
0
Lift [%]
pc
ps
p
Pressure [%]
pp
80 90 100 105 110 120
Standard 10% - Pop-Acting

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o Full-lift Safety Valve Pursuant to AD 2000 Information Sheet A2
A spring-loaded full-lift safety valve opening suddenly within a pressure increase of
5%. Primarily used for gas, steam and vapour
100
80
60
40
20
0
Lift [%]
pc
ps
p
Pressure [%]
pp
80 90 100 105 110 120
Sudden opening within 5%
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Classification-Definition Safety Valves-ASME PTC 25-2014
 Relief valve
o A pressure relief valve characterized by gradual opening that is generally
proportional to the increase in pressure. It is normally used for incompressible
fluids.
 Safety relief valve
o A pressure relief valve characterized by rapid opening or by gradual opening that
is generally proportional to the increase in pressure. It can be used for
compressible or incompressible fluids.
 Safety valve
o A pressure relief valve characterized by rapid opening and normally used to
relieve compressible fluids.
Prssure [%]

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Design – Codes & Standards
• API ASME / (EN)
Adjusting ring
Full nozzle
Semi-nozzle
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Design – Options – Conventional design
Full Nozzle
Full Nozzle
Semi Nozzle

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Design – Options – Balanced Bellows design
 Elastomer bellows
Protects the moving parts and spring against
dirt, corrosion, impurities and the fluid itself.
Set pressure range: p < 10 bar / 145 psig
ATTENTION: Elastomer bellows can not
be used for back pressure compensation.
 Stainless Steel or Inconel Bellows
Prevent changes in set pressure when the
valve is subjected to variable back pressure
Isolate the bonnet chamber and spring against
dirt, corrosion, impurities and the fluid itself
Should be used at variable superimposed back
pressure or if the built up pressure exceeds
15 % of the valve set pressure.
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Design – Options – Bellows design - Balanced Piston
 Ensures the back pressure compensation
and the temperature screening to the spring
room even in case of failure of the bellows
 Equal size of the piston surface and of the
seat section generates the back pressure
compensating effect
 Solution which is included in API 520
 Application field: Applications where the back
pressure compensating function needs to be
ensured

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Design – Options – Bonnets
Open Bonnet Closed Bonnet
Spring cooled by atmosphere Completely sealed safety valve
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Design – Options – Lifting devices
Open Lever Packed Lever
Not gas-tight
Gas-tight manual lifting possible
ASME Code states that a lifting device shall be used
on:
air, steam and hot water applications over
60°C/140° F

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Design – Options – Caps
Only if specification demands Standard
Screwed CapBolted Cap
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Design – Options - Lift Indicator (Proximity Switch)
Lift
Indication of valve lift to control room
(Minimum lift of 1 mm / 0.04 inch is required)
Safety Valve Open Safety Valve Closed

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Design – Options – Test Gag
Safety Valve In Use Gagged for Line Testing
The safety valve has to be gagged to perform a pressure test of the plant,
otherwise the valve has to be removed or a blind has to be installed before.
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Design – Options – Special Connections
Welded connectionsFemale Threaded Inlet Clamp connections

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Design - Sealing Surface
• To prevent leakage and costly product loss as well as reduce downtime
and maintenance costs, optional sealing surfaces are possible
Stellited O-ring disc Vulcanized Soft
Seal
Sealing plate
 For temperatures above +
450° C /
+ 842° F
 Protection of sealing
surface against abrasive
media
 Corrosion resistance
 Resistance against impacts
and changing temperatures
 Operation close
to set pressure
 Increased tightness
 compensates particles on
seat and/or disc
 Vibrations restraining
 Corrosive fluids
 Same use as O-ring disc
 Only available for Compact
Performance Series
 Due to the small disc size,
vulcanized soft seals have a
minimum set pressure of
0.2 bar / 2.9 psig
 Same use as
O-ring disc
 Also applicable for very low
temperatures own to –
270° C / - 454° F
depending on the sealing
materials
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Design - Heating Jacket
In applications with highly viscous fluids (low Reynolds number)
a heating jacket with heated bonnet spacer ensures:
• The proper function of a safety valve
• The safety valve will not clog

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Applications - Installations
• Industries
Ship building
LNG/LPG
Oil and Gas Industry
Technical Gases
 Petrochemical Industry
Chemical Industry
Pharmaceutical Industry
Food an Beverage Industry
Energy Industry
Heating and Air Conditioning
 .........
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• Applications
 Blocked discharge
Inadvertent closure of valve on the discharge side of the pressure source
 Thermal relief
Blocked in section of piping
 “Fire case”
Safety valve required to prevent vessel explosion until fire is controlled
 Downstream control or reducing valves
Safety valve has to calculated based on the failure capacity of the valve
 Heat exchanger, boiler, processtanks etc.
 All process equipment if a risk of exceeding the design pressure

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• General issues
 Upright position with the spindle vertical
 As close as possible to the pipe or equipment
 The safety valve should not be isolated
 The size of the inlet pipe should not be less than the inlet of the safety relief
valve
 The blow-off pipe should be the same size as the outlet of the safety valve
 Blow-off pipe should be mounted in such a way that there is no risk for persons
 The safety valve should be mounted in such a way that stress forces will not
occur the safety valve
 Normally each safety has his own blow-off pipe
 In case of vertical mounted blow-off pipe a drainage should be present
 Safety valve with an open bonnet should be mounted in such a way that there
is no risk for persons
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• Distance to other equipment
The safety valves should not be located where unstable flow patterns
are present.
Therefore safety valves should be installed at least 10 pipe diameters away
from the source of irrition (minimum 1 meter)
• Mounting position
 Safety valves normally should be installed in a vertical upright position,
however some applications require a “non-upright position”.
If valves are mounted in other than a vertical position, the valve manu-
facturer’s recommendations shall be considered
• Partly filled liquid Vessel
 In this case the safety valve should be located at the gas phase.
• Process Laterals Connected to the inlet of safety valves
 Process laterals should generally not be connected to the inlet of safety valve.
Exceptions should be analyzed carefully to ensure that the allowable pressure loss at the
inlet of the safety valve.

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• Drainage
 Adequate drainage of the outlet line to achieve a proper safety valve
performance
This means that normally no medium or condensate will stay inside the safety
valve.
The following directions should be followed:
 The drainage should always run via the outlet line
At the lowest point of the outlet line sufficient drainage should be installed for
discharging condensate
To avoid back-flow, a drip pan elbow can be used
Some standards require an additional drain hole within the safety valve (API526)
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Institutions, Standards and Regulations > Most usual
Area of application Applicable
regulations
Issuer of regulations Symbol Monitoring organisation
USA ASME > Law
ASME I > XII
ASME Section I
ASME Section II
ASME Section VIII
American Society of
Mechanical Engineers
National Board (NB)
Europe P(pressure) E(equipment)
D(directive) > Guideline
European Council/
European Parliament
Office appointed (TUEV –
AIB – Apragaz f.e.)
ISO EN 4126
Part 1 > 11
International
Organization for
Standardization
International API > Recommended
Practices
RP520/521/576
Std 526/527
American Petroleum
Instistute (API)
Manufacturer

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Institutions, Standards and Regulations > Local
• TSSA/CSA/CRN/ABSA (Canada)
• AQSIQ (China)
• KOSHA (Korea)
• EAC (Russia, Belarus, Kazakhstan)
• UDT Poland
• Indian Boiler Code
• …
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Institutions, Standards and Regulations > ASME
ASME Code Section I
•This is a construction code covering power, electric and miniature boilers and high
temperature boilers (fired) used
in stationary service above 15 psig.
ASME Code Section II
• This is a construction code listing materials suitable
for the construction of safety valves according to ASME Code.
• In order for a part to be used in the construction of a safety valve,
the material must appear in ASME Code Section II.
• This section also provides the pressure and temperature limits
for the available materials of safety valve bodies and bonnets
ASME Code Section VIII
• This is a construction code covering the basic rules
for the construction, design, fabrication, inspection and
certification of pressure vessels (unfired) above 15 psig.

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Institutions, Standards and Regulations > National Board of Boiler and
Pressure Vessel Inspectors (NB)
•The NB represents the enforcement agencies who assure adherence
to provisions of the ASME boiler and pressure vessel codes.
•The NB:
• Sets inspection standards
• Qualifies inspectors
• Works for owners, insurers
• Maintains records (Red Book – NB-18)
• Looks into violations
• Covers repair (VR Stamp)
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Institutions, Standards and Regulations > EN ISO 4126
• This is a European code related to the PED covering safety devices for
protection against excessive pressure
• Different Sections of the EN ISO 4126 deal
with the requirements, design and manufacture of safety devices
• EN ISO 4126-1 > Safety Valves (spring loaded)
• EN ISO 4126-2 > Bursting Discs Safety devices
• EN ISO 4126-3 > Safety Valves and Bursting Discs in Combination
• EN ISO 4126-4 > Pilot Operated Safety Valves
• EN ISO 4126-5 > Controlled Safety Valves Pressure Relief Systems
(CRPRS)
• EN ISO 4126-6 > Application, Installation of Bursting discs
• EN ISO 4126-7 > Sizing (Common data > steam tables, etc…
• EN ISO 4126-8 > Performance testing bursting Discs (draft)
• EN ISO 4126-9 > Application and Installation
• EN ISO 4126-10 > Performance testing SRV… just starting

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Institutions, Standards and Regulations > American Petroleum Institute
(API)
•API publishes several standards dealing with safety valves:
• API 520 Part 1 – Sizing & Selection of Pressure Relief Devices
• API 520 Part 2 – Installation
of Pressure Relief Devices
• API 521 – Guide for Pressure-Relieving & Depressurizing Systems
• API 526 – Flanged Steel Safety Relief Valves
• API 527 – Seat Tightness
of Pressure Relief Valves
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Institutions, Standards and Regulations > API 520
• API 520 Part 1
• Applies to the sizing and selection of pressure relief devices
for equipment with an MAWP of 15 psig or greater.
• Protection of unfired vessels
• Basic definitions
• Operational characteristics of pressure relief devices
• Sizing procedures and methods
• API 520 Part 2
• Covers methods of installation for pressure relief devices
on equipment with an MAWP of 15 psig or greater.

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•API 521 is designed to aid in the selection of the system
that is most appropriate for the risks and circumstances
involved in various installations.
• This standard provides guidelines for:
• Examining the principal causes of overpressure
• Determining individual relieving rates
• Including fire vapor generation and fire gas expansion
• Selecting and designing disposal systems
42
•API 526 is a purchasing specification for flanged steel
pressure relief valves. Requirements are given for
spring loaded pressure relief valves and pilot-operated
relief valves.
• API 526 has standardized the following items:
• Orifice designation and area
• Valve size and pressure rating, inlet and outlet
• Materials
• Pressure-temperature limits
• Center-to-face dimensions, inlet and outlet
• Inspection and shop tests
• Identification and preparation for shipment

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•API 527 describes tests to determine the seat tightness
of metal and soft-seated pressure relief valves.
Valves of conventional, bellows, and pilot-operated designs
are covered. Acceptable leakage rates are defined.
• It contains criteria for:
• Testing with air
• Testing with steam
• Testing with water
• Testing with air – another method
44
Set pressure – CDTP – Overpressure - Blowdown
Set Pressure Definition
 ASME PTC 25, 2001, 2.7 OC of PRD
o The value of increasing inlet static pressure at which
a pressure relief device displays one of the operational
characteristics as defined under:
opening pressure, popping pressure,
start-to-leak pressure, burst pressure or
breaking pressure.
o (The applicable operating characteristic for a specific
device design is specified by the device manufacturer).
 API 520, 2000, 1.2.3.3 a.
o The set pressure is the inlet gauge pressure
at which the pressure relief device is set to open
under service conditions.

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Set pressure – CDTP – Overpressure – Blowdown
Set Pressure Definition
 ISO 4126-1, 2004, 3.2. 1
o Predetermined pressure at which a safety valve
under operating conditions commences to open.
o Note:
It is the gauge pressure measured at the valve inlet
at which the pressure forces tending to open the valve
for the specific service conditions are in equilibrium
with the forces retaining the valve disc on its seat.
 The symbol is p.
46
Set Pressure Tolerance – Codes & Standards
• DIN EN ISO 4126-1
 +/- 3% of the set pressure or +/- 0,15 barg, whichever is greater
• ASME Code Section I
 ≤70 psi (0,5 MPa) > +/- 2 psi (15 kPa)
 >70 (0,5) and ≤300 (2,1) > +/- 3% of set pressure
 >300 (2,1) and ≤1000 (7,0) > +/- 10% of set pressure
 >1000 (7,0) > +/- 1% of set pressure
• ASME Code Section VIII
 ≤70 psi (0,5 MPa) > +/- 2 psi (15 kPa)
 >70 (0,5) > +/- 3% of set pressure

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Set Pressure Tolerance – Codes & Standards
• Suggestion for setting tolerances during the setting of safety valves by TüV
Nord, no minus tolerance allowed due to the operation pressure of the
installation
 ≤1,0 bar > +0,05 bar of set pressure
 >1,0 bar ≤5 bar > +0,10 bar of set pressure
 >5 barg > +3% of set pressure
• AD 2000, memorandum A2, chapter 11
• API 526, API 527, API 576
• DIN EN 837-1
48
Definition of Cold Differential Test Pressure (CDTP)
Codes and Standards
 CDTP is used if correction of set pressure of safety valves
according to deviation of service conditions is necessary.
ASME PTC 25, 2001, 2.7 OC of PRD
o The inlet static pressure at which a pressure relief valve is adjusted
to open on the test stand. This test pressure includes corrections for service conditions
of superimposed back pressure and/or temperature.
 API 20, 2000, Part I, 1.2.3.3 b.
o The cold differential test pressure (CDTP) is the pressure at which
a pressure relief valve is adjusted to open on the test stand.
The cold differential test pressure includes corrections for the service conditions of
back pressure or temperature or both.
 ISO 4126-1, 2004, 3.2.5
o The inlet static pressure at which a safety valve is set to commence
to open on the test bench. NOTE: This test pressure includes corrections
for service conditions, e.g. back pressure and/or temperature.

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Reason Why
The safety valve in the plant shall open during operation at a certain
pressure. This pressure is called Set Pressure.
The Cold Differential Test Pressure (CDTP) shall assure
the right Set Pressure in the plant during operation.
The CDTP considers the influence of Temperature and Back Pressure
for settings on a test bench.
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Influence of Temperature
The relevant part of the safety valve
influenced by the temperature is the spring.
The higher the temperature at the spring
the lower the spring rate.

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Influence of Temperature - Estimation of CDTP in Theory
Set Pressure 10 bar
Operation
Required spring force 2.000 N
Medium temperature 300 °C
Spring rate at 300°C
medium temperature
95 N/mm
Spring preloaded 21 mm
CDTP (acc. LDeS 1001.69
 + 0,5 bar temperature correction)
10,5 bar
Test bench
temperature at test lab
100 N/mm
Spring force 2.100 N
52
Influence of Temperature - Estimation of CDTP in Practice
-508 -308 -108 92 292 492 692 892
0,96
0,98
1
1,02
1,04
1,06
1,08
1,1
1,12
-300 -200 -100 0 100 200 300 400 500
Temperature T [°F]
CorrectionfactorkT
Temperature T [°C]
Conventional design with closed bonnet
upward set pressure (+3%) of allowable tolerances ( 3%)
according to EN ISO 4126-1 2003-09
downward set pressure (-3%) of allowable tolarance
( 3) according to EN ISO 4126-1 2003-09
Approved correction curve by
German TÜV Nord

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Influence of Temperature - Estimation of CDTP in Practice
54
Influence of Back Pressure
The relevant part of the safety valve which is influenced by the back pressure
is the disc.
The higher the back pressure the lower the CDTP must be
(conventional design).
Fs
Fp
Fb
p

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Influence of Back Pressure - Estimation of CDTP in Theory
Set Pressure 10 bar
Operation
Constant back pressure 2 bar
CDTP 8 bar
Test bench
(Conventional
design)
Set pressure 10 bar
CDTP 10 bar
Test bench
(Balanced bellows
design)
Set pressure 10 bar
Constant back pressure* 2 bar
56
Estimation of CDTP in case of temperature and back pressure correction
Set Pressure 10 bar
Operation
Required spring force 1.600 N
Medium temperature 300 °C
medium temperature
95 N/mm
CDTP 8,5 bar
Test bench
(Conventional design)
Temperature correction +0,5 bar
Back pressure correction -2 bar
Spring preload at 200°C 16,8 mm
temperature at test lab
100 N/mm
Spring force 1.684 N

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Estimation of CDTP in case of temperature and back pressure correction
The cold differential test pressure (CDTP) can secure
that the safety valve opens at the required set pressure
in the plant during operation.
Caution:
The specified service conditions must fit the actual operation conditions.
0
20
40
60
80
100
82 84 86 88 90 92 94 96 98
100
102
104
106
108
110
121
Lift (%)
Set Pressure CDTP
Vessel Pressure (%)
Operation at
Service Condition
Opening at
the test bench
58
Set pressure – CDTP – Overpressure – Blowdown > Codes & Standards
Overpressure Blowdown
Steam/Gases Liquids Steam/Gases Liquids
ASME I 3% -
< 67 psig: 4 psig
≥ 67…≤ 250 psig: 6%
>250…≤375 psig: 15psig
>375 psig: 4%
-
ASME VIII 10% 10%
7% with blowdown ring
No rquirements without
blowdown ring
No requirements
ASME Multiple Valve Application 16% 16% 7% No requirements
ASME Fire Case 21%
-
7% -
API 520 10% 10% 7% 20%
EN ISO 4126-1 10% 10% 15% 20%
AD 2000-Merkblatt A2 5% or 10%
Standard
10% 10% 20%

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Back pressure lost – Definition
• Back Pressure
 Build-up back pressure
 Exists only at the outlet while the safety is discharging.
It depends on the pressure loss in the outlet pipe.
 Superimposed Back pressure (constant or variable)
 Exists permanent in the blowdon system. The superimposed back pressure is
independent of the discharge of the safety valve.
60
Back pressure lost – Effects
• Superimposed back pressure changes the set pressure of a conventional spring
loaded safety valve.
• Built up back pressure influences the capacity and the function
of the safety valve.
• Reduced lift
• Chatter / Flutter
• Capacity reduction by lower flow velocity due to lower pressure difference
between inlet and outlet of the safety valve
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
Lift (%) Lift (%)Flutter Chatter

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Back pressure lost – Solutions
• Solutions for Spring Loaded Safety Valves
System - Reducing the built-up back pressure in the outlet pipe
• Increasing pipe diameter
• Shorter outlet pipe
Safety valve - Product solutions:
Depending on the type of back pressure, the following measures are typically selected to
prevent malfunction caused by back pressure
 Build-up back pressure
 ≤ 15% → None
 > 15%→ Back-pressure compensating bellows
 Superimposed back pressure
 Constant → Back-pressure compensating bellows or CDTP correction
 Variable → Back-pressure compensating bellows
62
Back pressure lost – Solutions - Inlet pressure lost
• Solutions for Spring Loaded Safety Valves
Compensation of Back Pressure with Balanced Bellows
The installation of a balanced bellows
compensates the force of the back
pressure in closing direction.
The safety valve works properly.
Back pressure compensation in % of
the set pressure:
LESER API Series 526:
up to 50% of the set pressure
All other LESER safety valves:
up to 35% of the set pressure

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Back pressure lost – Solutions
• LESER pilot-operated Safety Valves Series 810 and Series 820
 The pilot valve controls the opening and closing of the main valve
 The pilot valve reacts only to the pressure at the valve inlet and is not influenced by
the back pressure
 The maximum back pressure to set pressure ratio of a POSV is 70%
64
Inlet pressure lost - General Remarks
• Description
 Inlet pressure drop (p) is the pressure loss
from the vessel to the seat of the safety valve
while blowing.
 If the inlet pressure drop is to high
a proper operation can not be guaranteed.
 The maximum inlet pressure drop
according to the most common
codes and standards shall be 3 %.
p

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Inlet pressure lost - Parameter
• Influencing Factors
The following parameters are influencing
the inlet pressure drop:
Diameter of the inlet piping
Length of the inlet piping
Pressure loss in the inlet piping
(e. g. roughness)
Components
(e. g. bends, contractions)
66
Inlet pressure lost - Effects
•An inlet pressure drop above 3 % has an
effect on the proper function of the safety valve.
•This can cause the following malfunction
0
20
40
60
80
100
94 96 98 100 102 104 106 108 110 121
ChatteringLift (%)
Vessel Pressure (%)

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Inlet pressure lost - Definitions
• For the most common international codes and standards a maximum pressure loss
of 3 % from the vessel to the safety valve is required (API-EN ISO)
 When a pressure relief valve is installed on a line directly connected to a vessel,
the non-recoverable pressure loss between the protected equipment and
the pressure relief valve should not exceed 3 % of the set pressure of the
valve.
 An engineering analysis of the valve performance at higher Inlet losses
may permit increasing the allowable pressure loss above 3%.
68
Inlet pressure lost - Measures
•The following adjustments prevent malfunction
are based on inlet pressure drop:
 Reduction of flow speed by
• increasing pipe diameter
• reduction of flow capacity using a smaller valve
• reduction of flow capacity using a lift restriction
• reduction of flow capacity using an O-ring damper
 Reduction of flow resistance by
• shorter inlet pipe
• smooth connection to the vessel false correct

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69
Legal aspects- Overview of different legislations concerning Safety
Valves
 Royal Decree steam of ´91
 Compressed air installations
 Gasstorage
 LPG storage
 Additional conditions in environmentalpermit for other applications
(proces, … )
 CE-declaration
70
Legal aspects - Royal Decree steam of ´91
 Precommisioning testing
o Testing of discharge capacity
 Life test
 Calculations (No longer permitted by EN 12953, only life test)
o Verification of documents
 Periodical examination
o At the same time as Internal inspection

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71
Type of equipment Maxi interval internal
inspection (months)
SG of group1 (SG=Steam Generator)
SG of group 2
SG of group 3
SG of group 4
24
18
24
13
SV (SV=Steam Vessel)
SV connected to SG of 1 and 3
SV with high frequence of pressure- and depressurising
36
48 if agreed by NoBO
13
HE (HE=Heat Exchanger)
HE connected to SG of 1 and 3
36
48
Group 1: 100 t/h (*)
Group 2: water-tube boilers
• 500 m2 and (*)
• or build after 1945 and (*)
Group 3: integrated part of a productionunit intended to work
for 1 minimum year without interruption (*)
Group 4: all others
(*) with internal inspection by NoBo
+ inspection of boilerfeed- and
boilerwater
NoBO shall inspect the
watertreatment and analyse
watersamples every year
72
 Testing of set pressure
o Testing on test unit
o Onstream testing (trevitest, hydrotest, prevent test, …)
o Live test
 Approved valveshops → no new approvals possible !!
o What ?
o 2 different kinds: at owners site / external companies
o Yearly audit by Vinçotte is mandatory to keep the approval.

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73
Legal aspects – Compressed air installations
 Flanders
o Vlarem II art. 5.16.3.2
 Brussels
o 24/AV 56 Gas + 24bis/AV 56 Gas
 Walloon
o DGW 03/04/2003
 Scope of the legislations/differations between the 3 regions
o Capacity of the vessel
o Demands in environmentalpermit
o Precommisioning testing
o Periodical examination
74
Legal aspects – Gas storage facilities
Flanders
o Vlarem II art. 5.16.6
 Brussels
o No legislation → Demands in environmentalpermit
 Walloon
o No legislation → Demands in environmentalpermit
 Scope of the legislations/differations between the 3 regions
o Capacity of the vessel
o Demands in environmentalpermit
o Precommisioning testing
o Periodical examination

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75
Legal aspects – LPG storage (overview)
76
Maintenance – Why testing and revision/repair?
• The law
• Recommended Practice
 API 576
 API510
 Local regulations
• The maintenance program
 Depending of the time interval
 Depending of the pretest
• In case of problems with the safety relief valve
 The safety valve is opened during production
 The safety valve will not open (e.g. adhesive effect)
• More economical and faster sometimes than a new safety valve

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77
Maintenance – Why testing and revision/repair?
• Leser statement
 Due to the individual operating conditions and in consideration of the different
mediums, Leser gives no general reference for an inspection time
interval.
In coordination between Leser, different operators, and the notified body the
following procedure has proven itself.
In accordance with the operating conditions an initial interval of 24 month has
proven itself.
If the safety valve opens frequently or the medium is corrosive
the inspection time interval should be 12 months.
78
Maintenance – Testing methods – Test bench – On site
• Pretest
 Set pressure
 Functional Tightness – Rules and standards
• DIN EN ISO 4126-1, 6.6 Seat leakage test: no specific requirement regarding the leak
rate
• DIN EN 12266-1, A.4 Seat tightness, Test P12: no specific requirement regarding the
leak rate
• ASME Code Section VIII Vessels, Part UG- 136(d) (5): reference to the requirements
of API 527
• API 527: the only internationally recognised standard for the seal tightness of safety
valves including requirements of the leak rate and testing method.

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79
• Pretest
 Functional Tightness
Functional tightness = seat tightness between
the disc and seat
80
• Pretest
 Functional Tightness – Test methods
Gas-tight valves Valves with open bonnet
Bubble test (Kellog test)
Helium leak
Seat tightness procedure with air, applying of test fluid
Test time: 5 Sek
Extension: Max. 5 mm
Vessel
Connection to the Safety valve outlet
Immersion depth
Water
Transparent
containerInner tube-Ø

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81
• Revision/repair
 Disassembling
 Measurement of the lift height
 Visual inspection of the inner parts
 Replacing damaged parts by original spare parts
 Lapping seat/disc
 Assembling safety valve
 Setting blow-down ring
 Setting set pressure > measurement of the lift height
 Testing set pressure and functional tighntness
 Test rapport
 Tagplate
 Sealing
82
• Revision/repair
• A lapping stamp is practical for reworking damage to rolled-in seats
and discs with a lifting aid.
• The lapping stamp is equipped with a ready-to-use lapping paste. The seat or disc is
lapped using a rotary motion of the stamp.
• A suitably coarse lapping paste must be selected depending on the size of the surface
damage.

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83
• Revision/repair
• In order to obtain a better finish, discs without lifting aids
and screwed-in nozzles can also be lapped on a glass plate.
• To do this, the mono-crystalline diamond powder is mixed
with oleic acid on the glass plate. Then, the seat and disc
are lapped with light, circular, hand movements on the glass plate.
• A suitably coarse lapping paste must be selected,
depending on the size of the surface damage
84
• Revision/repair
• To achieve even better surface smoothness,
the disc can be re-lapped on the seat.
• To do this, mix mono-crystalline diamond powder
with oleic acid and apply it selectively to the disc.
• The workpiece is re-lapped through a uniform
rotary motion of the disc.

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85
• Testing the Tightness to the Outside
 Use
• Testing the back seat tightness, called the “tightness to the outside” by
LESER, is performed for all LESER safety valves in a gas-tight design.
• The tightness to the outside refers to testing the tightness the valve cover
including its connections.
 Specifications
• DIN EN 12266-2, Test P21
• ASME Code, Section VIII, Part UG-136(d) (3).
• LGS 0201
86
• Testing the Tightness to the Outside - Flange Connections
Test pressure
• Test standard: DIN EN 12266-2
• It will be tested at 6 bar
• Exception elastomer bellows: Test pressure at 2 bar
Procedure with leak detector solution (DIN EN 1593)
• Use with flange valves
• After testing the seat tightness and the set pressure,
the outlet side of the safety valve is clamped onto
the test bench and the test pressure is applied.
• Afterwards, the safety valve is sprayed with a leak
detector solution on the connecting points and
the outlet area.
• If no foaming can be seen, then the tested areas are okay.

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87
• Testing the Tightness to the Outside - Threaded Connections
Test pressure
• Test standard: DIN EN 12266-2
• It will be tested at 6 bar
Submersion method (DIN EN 1593)
• Use for threaded valves
• The inlet side of the safety valve is sealed with a sealing cap.
• The outlet side of the safety valve is then clamped
in the testing device, submersed in an immersion basin (water)
and the test pressure is applied.
• If no bubbles form on the outer contour of the safety valve,
then the tested safety valve is okay.
88
Maintenance – Testing methods – Test bench – In-situ testing
• Why in-situ testing?
 Due to process conditions a dismantling of the safety valve is not possible
• How does it work…?
 The test system includes a universal test bracket, hardware and software.
The system proportionally generates force and automatically raises the spindle
to the “cracking” point (lift from the nozzle). The moment that the disc
commences to lift, is automatically detected and system release the force to
let the disc to reseat again.
• Physical parameters
 Ps = Psystem + F/Aw
 Ps opening pressure (set pressure)
 Psystem operating pressure
 F traction force on the spindle at the moment the disc lift
 Aw working area of the orifice

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89
Maintenance – Testing methods – Test bench – In-situ testing
• Important comments
 vertical position
 only for spring loaded safety valves
 spindle and disc fixed together
 working diameter of orifice > 20 mm
 to have relevant measurements a minimum traction force requires a minimum
set pressure depending of the type of the safety valve and the operating
pressure
 no liftdstopper
 check the datasheet of the safety valve before changing the set
pressure
90
Calculation – National and International Standards – Definitions
Example
• Calculation levels for safety valves
ISO 4126-1
AD 2000-Merkblatt A2
TRD 421
API 520
ASME I and VIII
• Calculation levels on inlet pressure loss and back pressure
ISO 4126-9
Chapter 7 + 9
AD 2000-Merkblatt A2 Chapter 6
TRD 421 Chapter 6

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91
Example
• ISO 4126-1
Rated (derated) coefficient of discharge > K = 0,9 * Kd
Coefficient of discharge > Kd
Viscosity correction factor > Kv
• API 520
Viscosity correction factor > Kv
 Superheated steam correction factor > KSH
Correction factor for back pressure > Kb
Correction factor for bursting disc > Kc
• ASME I and VIII
Rated (derated) coefficient of discharge > K = 0,9 * Kd
Superheated steam correction factor > KSH
Correction factor for back pressure > Kb
Correction factor for bursting disc > Kc
92
Example
• ISO 4126-1
 Orifice area A0 (discharge area)
actual orifice area
Expressed in mm²
 Discharge diameter D0
actual discharge diameter
Expressed in mm
• API 520
Nominal according to API 526
Expressed in letter (D, E, F, G, H, J, K, L, M, N, P, Q, R, T)
Nominal according to API 526
Expressed in mm/inch

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93
Example
• Orifices API RP 526 – Steam and Gasses
Designation API Effective
Orifice Area (sq in)
API Effective
Orifice Area (mm²)
API Effective
Diameter (inch)
API Effective
Diameter (mm)
API coefficient of
discharge Kd
D 0.110 0,71 0.374 9,51
E 0.196 1,26 0.500 12,7
F 0.307 1,98 0.625 15,9
G 0.503 3,25 0.800 20,3
H 0.785 5,06 1.00 25,4
J 1.287 8,30 1.28 32,5
K 1.838 11,9 1.53 38,9 0.975
L 2.853 18,4 1.91 48,4
M 3.60 23,2 2.14 54,4
N 4.43 28,0 2.35 59,7
P 6.38 41,2 2.85 72,4
Q 11.05 71,3 3.75 95,3
R 16.00 103 4.51 115
T 26.00 168 5.75 146
94
Example
• Orifices API RP 526 – Liquids
Designation API Effective
Orifice Area (sq in)
API Effective
Orifice Area (mm²)
API Effective
Diameter (inch)
API Effective
Diameter (mm)
API coefficient of
discharge Kd
D 0.110 0,71 0.374 9,51
E 0.196 1,26 0.500 12,7
F 0.307 1,98 0.625 15,9
G 0.503 3,25 0.800 20,3
H 0.785 5,06 1.00 25,4
J 1.287 8,30 1.28 32,5
K 1.838 11,9 1.53 38,9 0.65
L 2.853 18,4 1.91 48,4
M 3.60 23,2 2.14 54,4
N 4.43 28,0 2.35 59,7
P 6.38 41,2 2.85 72,4
Q 11.05 71,3 3.75 95,3
R 16.00 103 4.51 115
T 26.00 168 5.75 146

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95
Example
• ASME I and VIII
actual orifice area after type examination
Expressed in mm²or inch²
actual discharge diameter area type examination
Expressed in mm or inch
 Coefficient of discharge K (Leser)
Steam/gasses (D/G)
 Orifice D: 0,455
 Orifice E, F, G, H, J, K, L, M, N, P, Q, R, T: 0,801
Liquids (L)
 Orifice D: 0,343
 Orifice E, F, G, H, J, K, L, M, N, P, Q, R, T: 0,579
96
Example
• Orifices as per API RP 526 and ASME VIII – Practical issue
ASME Actual Orifice Area*ASME coefficient K ≥ API Effective Orifice Area*API coefficient Kd
 Example Steam/gasses – Orifice E (Leser)
ASME Actual Orifice Area > 154 mm²
ASME coefficient K > 0,801
API Effective Orifice Area > 126 mm²
API coefficient Kd > 0,975
> 154*0,801=123,354 ≥ 126*0,975=122,85 >OK
 Example Liquids – Orifice E (Leser)
ASME Actual Orifice Area > 154 mm²
ASME coefficient K > 0,579
API Effective Orifice Area > 126 mm²
API coefficient Kd > 0,65
> 154*0,0,579=89,166 ≥ 126*0,65=81,9 >OK

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Example
........Program Files (x86)LeserVALVESTAR 7
On the web-site of Leser the Valvestar is avaible as web-version for free.
Procedure:
Choose the web-site of Leser
Under service you will find the access to Valvestar
98
Open Discussion // Conclusion

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99
Thanks for your attention

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