Pressure equipment - Part 7: Safety systems for unfired pressure equipment

This European Standard specifies the requirements for safety systems which protect a vessel, a system of vessels, piping, accessories or assemblies from exceeding operating conditions.
It is also applicable to safety related indicators and alarms, signals and warning devices when used in safety systems.
Equipment connected together by piping of adequate capacity, free from potential blockages and which does not contain any valve that can isolate any part from the safety system may be considered as a single pressure system when considering the requirements for overpressure protection.
Safety systems include the interconnections between the equipment to be protected and any discharge location. This location can either be an outlet to atmosphere or the entry into a closed disposal system.
NOTE   The scope of this standard and its relationship to the safety accessories and other protective devices described in the Pressure Equipment Directive are shown in annex F.

Druckgeräte - Teil 7: Sicherheitseinrichtungen für unbefeuerte Druckgeräte

Diese Europäische Norm legt die Anforderungen an Sicherheitseinrichtungen zum Schutz von Druckbehältern,         Systemen von Druckbehältern, Rohrleitungen, Ausrüstungsteilen und Baugruppen vor unzulässigen Betriebsbedingungen fest.
Sie beinhaltet auch sicherheitsrelevante Anzeige- und Alarmeinrichtungen, Signale und Warneinrichtungen, sofern diese in Sicherheitseinrichtungen verwendet werden.
Geräte, die über Rohrleitungen ausreichenden Querschnitts, ohne eventuelle Sperren und ohne irgendein Ventil, das Bereiche des Sicherheitssystems abtrennen kann, zu Systemen verbunden sind, dürfen in Bezug auf die Anforderungen an die Absicherung gegen Drucküberschreitung als einfaches Drucksystem betrachtet werden.
Sicherheitseinrichtungen schließen die Verbindungen zwischen dem zu schützenden Gerät und der gesamten Abblaseleitung ein. Es kann sich dabei um eine Ableitung in die Atmosphäre oder in ein geschlossenes Entsorgungssystem handeln.
ANMERKUNG   Der Anwendungsbereich der vorliegenden Norm, bezogen auf die in der Druckgeräte-Richtlinie be-
schriebenen Ausrüstungsteile mit Sicherheitsfunktion und weitere Einrichtungen mit Schutzfunktion ist in Anhang F dargestellt.

Equipements sous pression - Partie 7: Systèmes de sécurité pour équipements sous pression non soumis à la flamme

La présente Norme européenne prescrit les exigences applicables aux systèmes de sécurité qui protègent un
récipient, un système de récipients, une tuyauterie, des accessoires ou des ensembles vis-à-vis de dépassements
des conditions de fonctionnement.
Elle est également applicable aux indicateurs et alarmes liés à la sécurité, aux dispositifs de signalisation et
d’avertissement lorsqu’ils sont utilisés en tant que systèmes de sécurité.
Les équipements raccordés les uns aux autres dans un système par des tuyauteries de débit adéquat, exempts de
blocages potentiels et ne comprenant pas d’appareil de robinetterie susceptible d'isoler une partie quelconque
peuvent être considérés comme un système sous pression unique eu égard aux exigences de protection vis à vis
des surpressions.
Les systèmes de sécurité comprennent les interconnexions entre les équipements devant être protégés et tout
point de décharge. Cet emplacement peut être un orifice de sortie à l'atmosphère ou le raccordement à un système
de récupération fermé.
NOTE Le domaine d’application de la présente norme et ses relations avec les accessoires de sécurité et les autres
dispositifs de protection de la directive équipements sous pression sont indiqués en Annexe F.

Tlačna oprema - 7. del: Varnostni sistemi za neogrevano tlačno opremo

General Information

Status
Withdrawn
Publication Date
30-Aug-2002
Withdrawal Date
29-Nov-2002
Current Stage
9093 - Decision to confirm - Review Enquiry
Start Date
03-Jun-2014
Completion Date
03-Jun-2014

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SLOVENSKI STANDARD
SIST EN 764-7:2002
01-november-2002
7ODþQDRSUHPDGHO9DUQRVWQLVLVWHPL]DQHRJUHYDQRWODþQRRSUHPR
Pressure equipment - Part 7: Safety systems for unfired pressure equipment
Druckgeräte - Teil 7: Sicherheitseinrichtungen für unbefeuerte Druckgeräte
Equipements sous pression - Partie 7: Systemes de sécurité pour équipements sous
pression non soumis a la flamme
Ta slovenski standard je istoveten z: EN 764-7:2002
ICS:
23.020.30
SIST EN 764-7:2002 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
EUROPEAN STANDARD
EN 764-7
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2002
ICS 23.020.30
English version
Pressure equipment - Part 7: Safety systems for unfired
pressure equipment

Equipements sous pression - Partie 7: Systèmes de Druckgeräte - Teil 7: Sicherheitseinrichtungen für

sécurité ppour équipements sous pression non soumis à la unbefeuerte Druckgeräte
flamme
This European Standard was approved by CEN on 29 April 2002.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official

versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,

Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 764-7:2002 E

worldwide for CEN national Members.
---------------------- Page: 2 ----------------------
EN 764-7:2002 (E)
Contents
page

Introduction .................................................................................................................................................................5

1 Scope ..............................................................................................................................................................6

2 Normative references ....................................................................................................................................7

3 Terms and definitions....................................................................................................................................7

4 Risk consideration.........................................................................................................................................9

4.1 General............................................................................................................................................................9

4.2 Identification of hazards..............................................................................................................................11

4.3 Solutions.......................................................................................................................................................12

5 Limiting devices and systems....................................................................................................................12

5.1 General..........................................................................................................................................................12

5.2 Design ...........................................................................................................................................................13

6 Pressure limitation.......................................................................................................................................14

6.1 General..........................................................................................................................................................14

6.2 Safety valves, direct loaded and pilot operated .......................................................................................16

6.3 Bursting disc safety devices ......................................................................................................................17

6.4 Safety Valves & bursting disc safety devices in series or parallel.........................................................17

6.5 Controlled safety pressure relief systems (CSPRS) ................................................................................18

6.6 Safety related measuring, control & regulation systems (SRMCR) .......................................................18

7 Hazard protection ........................................................................................................................................20

7.1 Internal ..........................................................................................................................................................20

7.2 External.........................................................................................................................................................20

7.3 Static electricity............................................................................................................................................20

8 Installation of pressure relieving devices .................................................................................................21

8.1 General..........................................................................................................................................................21

8.2 Safety valves or the main valve of a CSPRS.............................................................................................21

8.3 Installation of bursting disc safety devices ..............................................................................................23

8.4 Safety valve and bursting disc safety devices in combination...............................................................23

8.5 Isolation of relieving safety systems .........................................................................................................24

9 Indicators and alarms..................................................................................................................................25

9.1 General..........................................................................................................................................................25

9.2 Pressure indicators .....................................................................................................................................25

9.3 Temperature indicators ...............................................................................................................................26

9.4 Liquid level indicators .................................................................................................................................26

9.5 Signals and warning devices......................................................................................................................26

10 Inspection and maintenance.......................................................................................................................27

Annex A (informative) Sizing of multiple safety valves........................................................................................29

(normative)

Annex B Requirements for level limiters ..........................................................................................31

B.1 General..........................................................................................................................................................31

B.2 Floating devices...........................................................................................................................................31

B.3 Level electrode devices...............................................................................................................................31

B.4 Fault detection..............................................................................................................................................32

Annex C (informative) Selection of safety accessories for pressure limitation ................................................33

(normative)

Annex D Bursting disc safety devices downstream of safety valves .............................................36

Annex E (informative) Scope of the standard.........................................................................................................37

---------------------- Page: 3 ----------------------
EN 764-7:2002 (E)

Annex ZA (informative) Clauses of this European Standard addressing essential requirements or other

provisions of EU Directives ........................................................................................................................38

Bibliography ..............................................................................................................................................................39

---------------------- Page: 4 ----------------------
EN 764-7:2002 (E)
Foreword

This document EN 764-7:2002 has been prepared by Technical Committee CEN/TC 54 “Unfired pressure vessels”,

the secretariat of which is held by BSI with support of Technical Committee CEN/TC 267 “Industrial piping”.

This European Standard shall be given the status of a national standard, either by publication of an identical text or

by endorsement, at the latest by November 2002, and conflicting national standards shall be withdrawn at the latest

by November 2002.

This document has been prepared under a mandate given to CEN by the European Commission (EC) and the

European Free Trade Association, and supports the essential safety requirements of the Pressure Equipment

Directive (PED) 97/23/EC.

For the relationship with the EU Directive(s) see the informative annex ZA which is an integral part of this

document.
This European Standard consists of the following parts:
Part 1: Definitions of pressure, temperature and volume.
Part 2: Quantities, symbols and units.
Part 3: Definition of parties involved.
Part 4: Establishment of technical delivery conditions for metallic materials.

Part 5: Inspection documentation of metallic materials and compliance with the material specification.

Part 6: Operating instructions.
Part 7: Safety systems for unfired pressure equipment.

Annexes A, C, E of this European Standard are informative. Annexes B and D are normative.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,

France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain,

Sweden, Switzerland and the United Kingdom.
---------------------- Page: 5 ----------------------
EN 764-7:2002 (E)
Introduction

A safety system can be the ultimate limitation to protect pressure equipment from exceeding its allowable limits or a

means to prevent a potentially hazardous situation leading to injury. These limits consist of permissible pressure,

temperature, level, flow or a combination of these which were fixed at the design stage. Regular control and/or

monitoring devices which are not a necessary part of a safety systems are excluded from this standard since they

become active in advance of a safety system (see Figure 1).

It is essential to consider not only the pressure relieving device or safety related measurement, control and

regulation system (SRMCR) but the whole of the pressure relief system so as not to reduce the relieving capacity

or adversely effect the proper operation of the pressure relieving devices. Operating problems frequently occur in

pressure relief systems because of incorrect selection of the appropriate device or because a correctly selected

device was adversely affected by improper handling, incorrect installation or lack of maintenance.

In some cases it can be necessary to establish the basic details of the safety system before selecting the value of

the maximum allowable pressure PS for the equipment to be protected. Some safety systems need a usual margin

between the maximum operating pressure and their reseating pressure which has to be considered before

selecting PS.

NOTE The role of harmonized standards in supporting the essential safety requirements of European Directives is

described in the “Guide to the implementation of directives based on the New Approach and the Global Approach”. It can be

necessary for products to meet the requirements of more than one directive and it is the responsibility of the manufacturer to

ensure that these requirements are complied with. Annex ZA draws attention to the essential safety requirements of EU

Directive 97/23/EC “Pressure Equipment Directive” addressed by this standard. This standard also draws attention to subjects

which are not covered in detail but are relevant to safety systems.
---------------------- Page: 6 ----------------------
EN 764-7:2002 (E)

Figure 1 — Response of regulating, monitoring and safety systems in relation to PS

1 Scope

This European Standard specifies the requirements for safety systems which protect a vessel, a system of vessels,

piping, accessories or assemblies from exceeding operating conditions.

It is also applicable to safety related indicators and alarms, signals and warning devices when used in safety

systems.

Equipment connected together by piping of adequate capacity, free from potential blockages and which does not

contain any valve that can isolate any part from the safety system may be considered as a single pressure system

when considering the requirements for overpressure protection.

Safety systems include the interconnections between the equipment to be protected and any discharge location.

This location can either be an outlet to atmosphere or the entry into a closed disposal system.

NOTE The scope of this standard and its relationship to the safety accessories and other protective devices described in

the Pressure Equipment Directive are shown in annex F.
---------------------- Page: 7 ----------------------
EN 764-7:2002 (E)
2 Normative references

This European Standard incorporates, by dated or undated reference, provisions from other publications. These

normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For

dated references, subsequent amendments to or revisions of any of these publications apply to this European

Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the

publication referred to applies (including amendments).

prEN ISO 4126-1, Safety devices for protection against excessive pressure - Part 1: Safety valves (ISO/DIS 4126-

1:1999).

prEN ISO 4126-2, Safety devices for protection against excessive pressure - Part 2: Bursting disc safety devices

(ISO/DIS 4126-2:1998).

prEN ISO 4126-3, Safety devices for protection against excessive pressure - Part 3: Safety valves and bursting

discs safety devices in combination (ISO/DIS 4126-3:1999).

prEN ISO 4126-4, Safety devices for protection against excessive pressure - Part 4: Pilot operated safety valves

(ISO/DIS 4126-4:1999).

prEN ISO 4126-5, Safety devices for protection against excessive pressure - Part 5: Controlled Safety Pressure

Relief Systems (CSPRS) (ISO/DIS 4126-5:1999).

prEN ISO 4126-6, Safety devices for protection against excessive pressure - Part 6: Application, selection and

installation of bursting disc safety devices (ISO/DIS 4126-6:2000).

prEN ISO 4126-7, Safety devices for protection against excessive pressure - Part 7: Common data (ISO/DIS 4126-

7:2000).

EN 954-1:1998, Safety of machinery – safety related parts of control systems – Part 1: General principles for

design.

prEN 50156-1, Electrical equipment for furnaces and ancillary equipment - Part 1: Requirements for application

design and installation.

EN 60529:1991, Degrees of protection provided by enclosures (IP code) (IEC 60529:1989).

IEC 61508, Functional safety of electrical/electronic/programmable electronic safety – related systems.

EN 837-1, Pressure gauges – Part 1: Bourdon tube pressure gauges – Dimensions, metrology, requirements and

testing.

EN 837-3, Pressure gauges – Part 3: Diaphragm and capsule pressure gauges – Dimensions, metrology,

requirements and testing.
3 Terms and definitions

For the purposes of this European Standard, the following terms and definitions apply.

3.1
safety accessory

device designed and used to protect pressure equipment against the allowable limits being exceeded (see annex

3.2
safety system

system of safety accessories and other protective devices which prevents the process parameters exceeding the

ultimate limiting values determined by the hazard analysis and ensures that the following risks are eliminated or

properly controlled:
---------------------- Page: 8 ----------------------
EN 764-7:2002 (E)
 injury to personnel;
 damage to the environment;
 damage to property
3.3
monitoring system

system which periodically checks given parameters and draws attention to those which are outside normal

operating limits but which are below the limiting values determined by the hazard analysis. Normal operating

conditions of the process can be restored either directly by the system or by an operator

3.4
regulating system

system which adjusts or controls a particular parameter to maintain operation within predetermined limits

3.5
independence

ability to function as required without interference from or dependence upon other equipment

3.6
fail-safe

characteristic whereby the failure of any safety system or any energy source will leave the protected equipment in a

safe condition
3.7
hazard
potential source of harm
[ISO/IEC Guide 51:1999]

NOTE 1 Harm is the physical injury or damage to the health of people or damage to property or to the environment.

NOTE 2 The term hazard can be qualified in order to define its origin or the nature of the expected harm.

3.8
risk

combination of the probability of occurrence of harm and the severity of that harm

[ISO/IEC Guide 51:1999]
3.9
risk analysis
use of available information to identify hazards and to estimate the risk
[ISO/IEC Guide 51:1999]
3.10
risk evaluation

judgement, on the basis of risk analysis, of whether a tolerable risk has been achieved

[ISO/IEC Guide 51:1999]
3.11
risk assessment
overall process of risk analysis and risk evaluation
[ISO/IEC Guide 51:1999]
---------------------- Page: 9 ----------------------
EN 764-7:2002 (E)
3.12
reliability

ability of a system or component to perform a required function under specified conditions and for a given period of

time without failing
3.13
shutdown

automatically or manually initiated action to achieve a safe condition of the pressure equipment

3.14
lockout

system feature which preserves the shutdown action until it is released by a manual intervention

3.15
safety related measurement, control and regulation system (SRMCR)

system which by means of automatic control equipment, operating independently from other process control

functions, prevents operating parameters exceeding allowable limits in pressure equipment

3.16
limiter

device which either activates the means for correction or provides for shutdown or shutdown and lockout

3.17
safety
freedom from unacceptable risk
[ISO/IEC Guide 51:1999]
3.18
self-diagnosis

regular and automatic determination that all chosen components of a safety system are capable of functioning as

required
3.19
maximum allowable pressure (PS)

maximum pressure for which the equipment is designed, as specified by the manufacturer

3.20
maximum/minimum allowable temperature (TS)

maximum/minimum temperatures for which the equipment is designed, as specified by the manufacturer

3.21
redundancy

provision of more than one device or system which is sufficient to perform or provide the necessary function

3.22
controlled safety pressure relief systems (CSPRS)
pressure relief system conforming to prEN ISO 4126-5
4 Risk consideration
4.1 General

All service conditions shall be considered to select the most appropriate safety concept to ensure safe operation.

This requires a realistic assessment of risk by means of risk analysis and risk evaluation (see Figure 2).

---------------------- Page: 10 ----------------------
EN 764-7:2002 (E)
Risk analysis involves:

 Determination of the boundaries of the pressure equipment including intended use and reasonably foreseeable

misuse;
 Identification of potential hazards and estimation of the risk.

Risk evaluation involves the process in which, on the basis of risk analysis, judgement is made to achieve a

tolerable risk.

NOTE The manufacturer and the user should consider the most onerous conditions which can exist for pressure and

temperature within the allowable limits.

NOTE Risk reduction and the selection of safety systems are not part of risk analysis and risk assessment.

Figure 2 — Process for risk assessment and risk reduction
---------------------- Page: 11 ----------------------
EN 764-7:2002 (E)
4.2 Identification of hazards

During operation of a piece of pressure equipment, dangerous situations may occur due, for example to:

 operational aspects;
 human errors;
 unreliability of some functions;
 unsafe loading conditions;
 maintenance;
 physical characteristics of the fluid:
a) pressure;
b) temperature;
c) flow;
d) level;
e) fouling capability;
f) adhesion;
g) abrasion;
 chemical characteristics of the fluid:
a) corrosivity
b) toxicity;
c) flammability;
d) stability;
e) fouling;
 site conditions such as:
a) vibration;
b) temperature (e.g. freezing);
c) wear;
d) corrosion;
e) external fire (see 7.2)

Each of these factors can result in the operating limits of the pressure equipment being exceeded.

---------------------- Page: 12 ----------------------
EN 764-7:2002 (E)
4.3 Solutions

Risk assessment shall be used to produce the basic information which is needed to correctly design the pressure

equipment and to select the most efficient safety accessories. The equipment shall be designed in order to:

a) eliminate or reduce hazards;
b) provide appropriate protection measures if the hazard cannot be eliminated;

c) inform the user of residual hazards and indicate the appropriate special measures for that case;

d) prevent the danger from misuse.
Preference shall be given to inherently safe design solutions.

Operating instructions shall include instructions for inspection and maintenance to ensure that the required level of

protection is available.

NOTE Inspection and maintenance of safety systems are necessary to ensure that the required level of integrity is

maintained. A record should be kept on both the procedures and findings
5 Limiting devices and systems
5.1 General

Where the allowable limits can be exceeded, the pressure equipment shall be fitted with, or provisions shall be

made for the fitting of:
a) Regulating systems:

Where appropriate, manually or automatically operated regulatory devices for the control of operating parameters

such as measurement, control and regulation devices (MCR), pressure switches, temperature switches, level

switches and flow switches to maintain conditions during normal operation within the maximum / minimum

allowable limits;
b) Monitoring systems:

Where appropriate, adequate monitoring devices for the control of operating parameters such as measurement,

control and regulation devices (MCR), indicators, alarms, pressure switches, temperature switches, level switches,

flow switches which enable adequate action to be taken either automatically or manually or activate the means for

correction and/or provide for shutdown and lockout, to keep the pressure equipment within the allowable limits.

If the process parameter value cannot exceed the allowable limits, a monitoring system is sufficient and a safety

system unnecessary. The process parameter can be brought back into the normal operating range by:

 manual action - after a status signal; or
 automatically;
c) Safety systems:

Safety devices such as safety valves, bursting disc safety devices, buckling rods, CSPRS, etc. or safety related

measuring, control and regulation devices (SRMCR), which serve as ultimate protection to ensure that the

maximum allowable operating limits are not exceeded.

Safety systems or their relevant components shall be independent of other functions, unless their safety function is

not affected by such other functions.
---------------------- Page: 13 ----------------------
EN 764-7:2002 (E)
NOTE 1 See definition of independence.

NOTE 2 Regulating and monitoring systems which are not part of a safety systems are not covered by this standard.

5.2 Design
5.2.1 General

The safety system shall be designed to operate sufficiently reliably under all conditions of operation determined by

the risk analysis in 4.1, including start up, shut off, and during maintenance and repairs.

All limiters, and their components, installed in a safety system shall comply with the requirements of this clause and

6.6. Additional requirements for particular types of limiters are given in annex B.

5.2.2 Material and design

5.2.2.1 Limiters shall withstand the thermal, mechanical, chemical and electrical loads that can occur during

operation.

5.2.2.2 The use of materials with great differences in their electrochemical potential shall be avoided in order to

prevent corrosion which would affect the function of the limiter.

5.2.2.3 Chambers, connecting pipes and protection tubes for the limiters shall be designed so that they can be

cleaned and inspected. They shall also be suitably designed to prevent the build up of deposits in the

tubes/chambers.

5.2.2.4 Protection tubes and chambers shall be designed to allow the device to have an adequate response

time.
5.2.3 Internal Protection Tubes

5.2.3.1 Where an internal protection tube is necessary, for example, in order to prevent the effect of foam or

turbulence, then the protection tube shall be considered to be part of the equipment to be protected.

5.2.3.2 Openings on the protection tube which are necessary in order to ensure level equalisation shall be

properly sized and shall be positioned at the lowest point of the bottom and at the highest practicable point of the

protection tube.
5.2.4 External Chambers

The pipe connections to external chambers shall ensure that the parameter to be measured is representative of the

parameter in the main equipment.
5.2.5 Electrical equipment
5.2.5.1 Electrical equipment shall comply with prEN 50156-1.

5.2.5.2 All wiring and electrical equipment in connection with safety systems shall be adequately protected

against ingress of moisture and effects of high temperature.

5.2.5.3 Electrical components within the confines of limiting devices shall be able to withstand the temperature

of the surrounding environment. Any equipment which is in contact with parts carrying the process fluid shall be

able of withstanding the highest temperature resulting from contact with:
 the process fluid at the highest temperature; or

 the saturated vapour of the process fluid at the highest foreseeable pressure; or

---------------------- Page: 14 ----------------------
EN 764-7:2002 (E)
 any fluid used periodically to clean the equipment.

Safety accessories shall have, as a minimum, a protection rating to IP54 of EN 60529:1991. When

5.2.5.4

components are installed inside an enclosure or control box, the IP rating required for the box shall be considered

adequate.

5.2.5.5 The limiter shall be designed so that a fault in any related part shall not lead to a loss of the safety

function. This may be achieved by fault avoidance techniques, self-diagnosis, redundancy, diversity or a

combination of these methods. Fault assessment for the electrical components shall be in accordance with the

procedure in the fault analysis charts of prEN 50156-1. The figure “Fault assessment for the hardwired section of a

safety device” in this standard shall also be applied for faults in hydraulic, pneumatic and mechanical components.

5.2.5.6 Limiters shall function independently of each other and of other control systems unless their safety

function cannot be affected by other such functions. Limiters may, however, share common components (e.g.

power supplies, bus systems, circuit boards, etc.) provided each limiter is fail-safe as defined in 3.6 and no adverse

safety effect can occur from faults in other limiters or related equipment.

The limiter shall be designed in such a way that once it has been activated, sent the appropriate signals

5.2.5.7

and prevented the allowable limits being exceeded, manual resetting is required after the relevant process

parameter has been restored to a safe level and all possible causes of the fault have been corrected.

6 Pressure limitation
6.1 General
6.1.1 Selection
Safety accessories which may be suitable for pressure limitation are:
 safety valves:
a) direct loaded;
b) pilot operated;
 bursting disc safety devices;
 safety valves and bursting disc safety devices in combination;
 controlled safety pressure relief systems (CSPRS);
 safety related measurement, control and regulat
...

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