EN 60079-30-2:2007

SLOVENSKI STANDARD
01-december-2007
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SIST EN 62086-2:2005
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Explosive atmospheres - Part 30-2: Electrical resistance trace heating - Application guide
for design, installation and maintenance
Explosionsfähige Atmosphäre - Teil 30-2: Elektrische Widerstands-Begleitheizungen -
Anwendungsleitfaden für Entwurf, Installation und Instandhaltung
Atmospheres explosives - Partie 30-2: Traçage par résistance électrique - Guide
d'application pour la conception, l'installation et la maintenance
Ta slovenski standard je istoveten z: EN 60079-30-2:2007
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60079-30-2
NORME EUROPÉENNE
April 2007
EUROPÄISCHE NORM
ICS 29.260.20 Supersedes EN 62086-2:2005

English version
Explosive atmospheres -
Part 30-2: Electrical resistance trace heating -
Application guide for design, installation and maintenance
(IEC 60079-30-2:2007)
Atmosphères explosives -  Explosionsfähige Atmosphäre -
Partie 30-2: Traçage Teil 30-2: Elektrische
par résistance électrique - Widerstands-Begleitheizungen -
Guide d'application pour la conception, Anwendungsleitfaden für Entwurf,
l'installation et la maintenance Installation und Instandhaltung
(CEI 60079-30-2:2007) (IEC 60079-30-2:2007)

This European Standard was approved by CENELEC on 2007-03-01. CENELEC 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 Central Secretariat or to any CENELEC 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 CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60079-30-2:2007 E
Foreword
The text of document 31/662/FDIS, future edition 1 of IEC 60079-30-2, prepared by IEC TC 31,
Equipment for explosive atmospheres, was submitted to the IEC-CENELEC parallel vote and was
approved by CENELEC as EN 60079-30-2 on 2007-03-01.
This European Standard supersedes EN 62086-2:2005.
The general revisions and updating to produce EN 60079-30-2:2007 are a result of national comments
received.
The main technical differences apart from the general revision and updating of EN 62086-2:2005 are as
follows:
– corrections;
– extensive revision and additions for design and installation recommendations.
This standard is to be used in conjunction with EN 60079-30-1:2007, Explosive atmospheres – Part 30-1:
Electrical resistance trace heating – General and testing requirements.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-12-01
– latest date by which the national standards conflicting
(dow) 2010-03-01
with the EN have to be withdrawn
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60079-30-2:2007 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - EN 60079-30-2:2007
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60079-0 (mod) 2004 Electrical apparatus for explosive gas EN 60079-0 2006
atmospheres -
Part 0: General requirements
IEC 60079-1 2003 Electrical apparatus for explosive gas EN 60079-1 2004
atmospheres - + corr. April 2006
Part 1: Flameproof enclosures "d"

1)
IEC 60079-7 2001 Electrical apparatus for explosive gas EN 60079-7 2003
atmospheres -
Part 7: Increased safety "e"
IEC 60079-10 2002 Electrical apparatus for explosive gas EN 60079-10 2003
atmospheres -
Part 10: Classification of hazardous areas

2)
IEC 60079-14 1996 Electrical apparatus for explosive gas EN 60079-14 1997
atmospheres -
Part 14: Electrical installations in hazardous
areas (other than mines)
3)
IEC 60079-17 1996 Electrical apparatus for explosive gas EN 60079-17 1997
atmospheres -
Part 17: Inspection and maintenance of
electrical installations in hazardous areas
(other than mines)
IEC 60079-30-1 2007 Explosive atmospheres - EN 60079-30-1 2007
Part 30-1: Electrical resistance trace heating -
General and testing requirements

1)
EN 60079-7 is superseded by EN 60079-7:2007, which is based on IEC 60079-7:2006.
2)
EN 60079-14 is superseded by EN 60079-14:2003, which is based on IEC 60079-14:2002.
3)
EN 60079-17 is superseded by EN 60079-17:2003, which is based on IEC 60079-17:2002.

NORME CEI
INTERNATIONALE
IEC
60079-30-2
INTERNATIONAL
Première édition
STANDARD
First edition
2007-01
Atmosphères explosives –
Partie 30-2:
Traçage par résistance électrique –
Guide d’application pour la conception,
l’installation et la maintenance

Explosive atmospheres –
Part 30-2:
Electrical resistance trace heating –
Application guide for design, installation
and maintenance
© IEC 2007 Droits de reproduction réservés ⎯ Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any
utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Pour prix, voir catalogue en vigueur
For price, see current catalogue

60079-30-2 © IEC:2007 – 3 –
CONTENTS
FOREWORD.7

1 Scope.11
2 Normative references .11
3 Terms and definitions .13
4 Application considerations.13
4.1 General .13
4.2 Corrosive areas.13
4.3 Process temperature accuracy .15
4.4 Installation considerations .15
5 Thermal insulation .17
5.1 General .17
5.2 Selection of insulating material.17
5.3 Selection of weather barrier (cladding) .19
5.4 Selection of economical thickness .21
5.5 Double insulation.23
6 System design.27
6.1 Introduction .27
6.2 Purpose of, and major requirement for, trace heating .27
6.3 Heat loss calculations.27
6.4 Heat-up considerations.31
6.5 Heat-loss design safety factor .33
6.6 Selection of trace heater .33
6.7 Maximum temperature determination.41
6.8 Design information .47
6.9 Power system.49
6.10 Start-up at low ambient temperatures .51
6.11 Long trace heater runs .51
6.12 Flow pattern analysis.51
6.13 Dead-leg control technique.55
6.14 Chimney effect .55
7 Control and monitoring .55
7.1 General .55
7.2 Mechanical controllers.55
7.3 Electronic controllers.57
7.4 Application suitability.57
7.5 Location of controllers .57
7.6 Location of sensors .57
7.7 Alarm considerations.59
8 Recommendations for installation .63
8.1 Introduction .63
8.2 Preparatory work.63
8.3 Installation of trace heating circuits .65

60079-30-2 © IEC:2007 – 5 –
8.4 Installation of control and monitoring equipment.77
8.5 Installation of thermal insulation system (see also Clause 5) .87
8.6 Installation of distribution wiring and coordination with branch circuits.91
8.7 Commissioning.93
9 Maintenance.95
9.1 General .95
9.2 Fault location .95
9.3 Fault rectification.97
10 Repairs .97
10.1 General .97
10.2 Practicability of repair to electric trace heaters .97
10.3 Repair techniques for electrical trace heaters.99
10.4 Earthing .99
10.5 Testing .99

Figure 1 – Thermal insulation – Weather-barrier installation.21
Figure 2 – Typical temperature profile.25
Figure 3 – Equilibrium conditions for workpiece maintenance.37
Figure 4 – Equilibrium conditions for upper limit evaluation.39
Figure 5 – Heated tank example .53
Figure 6 – Bypass example.53
Figure 7 – Typical installation of control sensor and sensor for temperature limiting
control .81
Figure 8 – Limiting device sensor on surface of trace heater.83
Figure 9 – Limiting device sensor as artificial hot spot .85

Table 1 – Process types .15
Table 2 – Pre-installation checks .67
Table 3 – Example of pre-commissioning check and trace heater installation record.101
Table 4 – Example of trace heater commissioning record.103
Table 5 – Example of maintenance schedule and log record .105

60079-30-2 © IEC:2007 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 30-2: Electrical resistance trace heating –
Application guide for design, installation and maintenance

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60079-30-2 has been prepared by IEC technical committee 31:
Equipment for explosive atmospheres.
This edition cancels and replaces the first edition of IEC 62086-2 published in 2001 and
constitutes a technical revision.
The general revisions and updating to produce the first edition of IEC 60079-30-2 are as a
result of National comments received.
The main technical differences apart from the general revision and updating a former edition
of IEC 62086-2, are as follows:
a) corrections;
60079-30-2 © IEC:2007 – 9 –
b) extensive revision and additions for design and installation recommendations.
This Part 30-2 is to be used in conjunction with the first edition of IEC 60079-30-1:2006,
Explosive atmospheres – Part 30-1: Electrical resistance trace heating – General and testing
requirements.
The text of this standard is based on the following documents:
FDIS Report on voting
31/662/FDIS 31/672/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The list of all parts of IEC 60079 series, under the general title Explosive atmospheres, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
60079-30-2 © IEC:2007 – 11 –
EXPLOSIVE ATMOSPHERES –
Part 30-2: Electrical resistance trace heating –
Application guide for design, installation and maintenance

1 Scope
This part of IEC 60079 provides guidance for the application of electrical resistance trace
heating systems in areas where explosive gas atmospheres may be present, with the
exception of those classified as zone 0.
It provides recommendations for the design, installation, maintenance and repair of trace
heating equipment and associated control and monitoring equipment. It does not cover
devices that operate by induction heating, skin effect heating or direct pipeline heating, nor
those intended for stress relieving.
This part supplements the requirements specified in IEC 60079-30-1.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60079-0:2004, Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
IEC 60079-1:2003, Electrical apparatus for explosive gas atmospheres – Part 1:Flameproof
enclosures “d”
IEC 60079-7:2001, Electrical apparatus for explosive gas atmospheres – Part 7: Increased
safety ‘e’
IEC 60079-10:2002, Electrical apparatus for explosive gas atmospheres – Part 10:
Classification of hazardous areas
IEC 60079-14:1996, Electrical apparatus for explosive gas atmospheres – Part 14: Electrical
installations in hazardous areas (other than mines)
IEC 60079-17:1996, Electrical apparatus for explosive gas atmospheres – Part 17: Inspection
and maintenance of electrical installations in hazardous areas (other than mines)
IEC 60079-30-1:2006, Explosive atmospheres – Part 1: Electrical resistance trace heating –

General and testing requirements

60079-30-2 © IEC:2007 – 13 –
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60079-0,
IEC 60079-1 and IEC 60079-7 apply.
NOTE Additional terms and definitions applicable to explosive atmospheres can be found in IEC 60050 (426) .
4 Application considerations
4.1 General
This standard supplements the requirements of IEC 60079-14 and IEC 60079-17.
Where trace heating systems are to be installed in explosive gas atmospheres, full details of
the hazardous area classification(s) (IEC 60079-10) shall be specified. The specification shall
state the zone (1 or 2), gas group (IIA, IIB or IIC) and temperature classification in
accordance with IEC 60079-0. Where special considerations apply or where site conditions
may be especially onerous, these conditions shall be detailed in the trace heating
specification.
Where trace heating systems are to be installed on mobile equipment or interchangeable skid
units, the specification for these trace heating systems should accommodate the worst
conditions in which the trace heating system may be used.
Where any parts of the trace heating system are likely to be exposed, those parts should be
suitable for the environment.
4.2 Corrosive areas
All components of electric trace heating systems should be examined to verify that they are
compatible with any corrosive materials that may be encountered during the lifetime of the
system. Trace heating systems operating in corrosive environments have a higher potential
for failure than in non-corrosive environments. Deterioration of the thermal insulation system
is made worse by corrosion of the weather barrier and the possibility of pipeline and vessel
leaks soaking the thermal insulation. Particular attention should be given to the materials of
piping systems, as well as the electric trace heating systems, as related to the effective earth-
leakage/ground-fault return path. The use of non-metallic or lined or coated piping systems
may further complicate the earth-leakage/ground-fault return path and special consideration
should be given to these piping systems. Earth-leakage/ground-fault return paths established
at the time of installation may become degraded due to corrosion during the operation of the
plant.
—————————
IEC 60050-426, International Electrotechnical Vocabulary (IEV) – Part 426: Electrical apparatus for explosive
atmospheres
60079-30-2 © IEC:2007 – 15 –
4.3 Process temperature accuracy
4.3.1 Type I
A Type I process is one for which the temperature should be maintained above a minimum
point. Ambient sensing control may be acceptable. Large blocks of power may be controlled
by means of a single control device and an electrical distribution panel board. Heat input may
be provided unnecessarily at times and wide temperature excursions should be tolerable.
Energy efficiency may be improved through the use of dead-leg control techniques (see 6.13).
4.3.2 Type II
A Type II process is one for which the temperature should be maintained within a moderate
band. Control by pipeline sensing mechanical thermostats is typical.
4.3.3 Type III
A Type III process is one for which the temperature should be controlled within a narrow
band. Electronic pipe-sensing controllers using thermocouple or resistance-temperature
detector (RTD) units facilitate field (work site) calibration and provide maximum flexibility in
the selection of temperature alarm and monitoring functions. Heat input capability may be
provided to preheat an empty pipe or raise the fluid temperature, or both, within a specified
range and time interval. Type III systems require strict adherence to flow patterns and thermal
insulation systems.
4.4 Installation considerations
If failure of any part of the trace heating system can result in a safety or process problem,
then the trace heating system may be considered to be a critical component of the total
process. The temperature control and circuit monitoring requirements of an application may
be defined according to the temperature control types described in 4.3, together with the
circuit monitoring criticality as described in Table 1.
Table 1 – Process types
Desired accuracy of process temperature control
Is trace heating a critical
component of the
Above a minimum point Within a moderate band Within a narrow band
process?
Type I Type II Type III
Yes = Critical (C-) C – I C – II C – III
No = Non-critical (NC-) NC – I NC – II NC – III

When trace heating is critical to the process, circuit monitoring for correct operation,
malfunction alarms, and back-up (redundant) trace heaters should be considered. Spare or
back-up controllers can be specified to be automatically activated in the event of a fault being
indicated by the monitoring/alarm system. This is sometimes known as "redundancy". Back-up
trace heaters may allow maintenance or repairs to be performed without a process shutdown
and may be used to enhance reliability.

60079-30-2 © IEC:2007 – 17 –
5 Thermal insulation
5.1 General
The selection, installation and maintenance of thermal insulation should be considered a key
component in the performance of an electrical trace heating system. The thermal insulation
system is normally designed to prevent the majority of heat loss with the trace heating system
compensating for the remainder. Therefore, problems with thermal insulation will have a direct
impact on the overall system performance.
The primary function of thermal insulation is to reduce the rate of heat transfer from a surface
that is operating at a temperature other than ambient. This reduction of energy loss may
– reduce operating expenses;
– improve system performance;
– increase system output capability.
Prior to any heat loss analysis for an electrically traced pipeline, vessel or other mechanical
equipment, a review of the selection of the insulation system is recommended. The principal
areas for consideration are as follows:
– selection of an insulation material;
– selection of a weather barrier (cladding);
– selection of the economic insulation thickness;
– selection of the proper insulation size.
5.2 Selection of insulating material
The following are important aspects to be considered when selecting an insulation material.
These factors should be considered and the selection optimised according to the operator’s
criteria:
– temperature rating;
– thermal conductivity, λ, of the insulation;
– mechanical properties;
– chemical compatibility and corrosion resistance;
– moisture resistance;
– health risks during installation;
– fire resistance;
– toxicological properties when exposed to fire;
– costs.
Insulation materials commonly available include:
– expanded silica;
– mineral fibre;
– cellular glass;
– urethane;
– fibreglass;
– calcium silicate;
– polyisocyanurate;
– perlite silicate.
60079-30-2 © IEC:2007 – 19 –
For soft insulants (mineral fibre, fibreglass, etc.), actual pipe size insulation may be used in
many cases by banding the insulation tightly. Care should be taken to prevent the trace
heater from being buried within the insulation, which may cause damage to the trace heater or
may restrict proper heat transfer. As an alternative, the next largest pipe size insulation that
can easily enclose pipe and electric trace heater is also acceptable. Rigid insulation (calcium
silicate, expanded silica, cellular glass, etc.), may be pipe-size insulation if board sections are
cut to fit the longitudinal joint. This type of installation technique is commonly referred to as
an extended leg installation. Alternatively, the next largest insulation size may be selected to
accommodate the trace heater. In all cases, the insulation size and thickness should be
clearly specified.
5.3 Selection of weather barrier (cladding)
Proper operation of an electrically trace heated system depends upon the insulation being
dry. Electric tracing normally has insufficient heat output to dry wet thermal insulation. Some
insulation materials, even though removed from the piping and force dried, never regain their
initial characteristics after once being wet.
Straight piping may be weather-protected with metal jacketing, polymeric, or a mastic system.
When metal jacketing is used, it should be smooth with formed, modified “S” longitudinal
joints. The circumferential end joints should be sealed with closure bands and supplied with
sealant on the outer edge or where they overlap (see Figure 1).
Jacketing that is overlapped or otherwise closed without sealant is not effective as a barrier to
moisture. A single, unsealed joint can allow a considerable amount of water to leak into the
insulation during a rainstorm.
The type of weather barrier used should, as a minimum, be based on a consideration of the
following:
– effectiveness in excluding moisture;
– corrosive nature of chemicals in the area;
– fire protection requirements;
– durability to mechanical abuse;
– cost.
60079-30-2 © IEC:2007 – 21 –
B A-A
B
A
A
IEC  2329/06
Key
1 metal jacket 5 closure band
2 insulation 6 insulated strap
3 metal jacket insulated pipe 7 movement
4 mastic sealer 8 pipe
Figure 1 – Thermal insulation – Weather-barrier installation

60079-30-2 © IEC:2007 – 23 –
5.4 Selection of economical thickness
At a minimum, an economic consideration of the insulation will weigh the initial costs of the
materials and installation against the energy saved over the life of the insulation. It should be
noted that the actual insulation thicknesses do not always correspond exactly to the nominal
insulation thickness. When choosing the insulation size, considerations should be made as to
whether or not the actual pipe-size insulation is suitable for accommodating both pipe and
trace heater.
5.5 Double insulation
The double insulation technique may be employed when the pipe temperature exceeds the
maximum allowable temperature of the trace heater. Prevention of the freezing of condensate
in high-temperature steam lines when these lines are not in use is a typical application. It
consists of locating the trace heater between two layers of insulation surrounding the pipe.
The essence of the double-insulation technique is to determine the correct combination of
inner and outer insulation type and thickness that will result in an acceptable interface
temperature for the trace heater. This relationship is illustrated in Figure 2. Note that
maximum ambient temperature conditions should be considered in this determination.

60079-30-2 © IEC:2007 – 25 –
r
p
r
i
r
o
r r r
p i o
Radius
IEC  2330/06
Key
1 pipe  6 maximum temperature pipe
2 inner insulation layer  7 interface temperature
3 heat tracer  8 outer insulation surface temperature
4 outer insulation layer  9 ambient temperature
5 metal foil (aluminium)
Figure 2 – Typical temperature profile
Temperature
60079-30-2 © IEC:2007 – 27 –
6 System design
6.1 Introduction
Each trace heating application imposes unique demands on the designer to achieve the
desired temperature and maintain it within the specified conditions. Trace heating systems
necessarily interface with other specified items of equipment such as thermal insulation and
the electrical supply available to power the system. The final system will be an integration of
all these component parts so the values of these interface items have to be known and
controlled in order to design systems that will perform as required.
The design of any trace heating system shall conform to all IEC requirements for the use of
electrical equipment and with the requirements of this standard. Consideration shall be given
as to the maintenance of the systems and process equipment, to energy efficiency, and to
testing the installed systems for operational satisfaction and safety.
When designing trace heating systems for use in explosive gas atmospheres, additional
constraints are imposed due to the requirements and classification of the area under
consideration.
Persons involved in the design and planning of electric trace heating systems should be
suitably trained in all techniques required.
6.2 Purpose of, and major requirement for, trace heating
Trace heaters should be selected and installed so as to provide sufficient power for:
a) compensation of heat loss when maintaining a specified temperature of a workpiece at the
specified minimum ambient temperature; see calculation method in 6.3; or
b) raising the temperature of a workpiece, and its contents when specified, within a specified
time period; see calculation method in 6.4; or
c) a combination of a) and b).
The system heat requirements should then be multiplied by a safety factor as determined on
the basis of 6.5.
The trace heater selection shall consider the determination of the maximum possible system
temperature under worst case conditions as specified in IEC 60079-30-1. The temperature
may be reduced, for example, through adjustments to the system parameters, by the use of
multiple tracers to reduce the power produced per unit length, or by the selection of the
temperature control system. The excess of installed power over the power as required, and
the way in which trace heaters are applied, installed and operated shall not be the cause, not
even after evaluation of worst-case conditions, of any unacceptable risk in explosive gas
atmospheres.
6.3 Heat loss calculations
The heat loss of a workpiece can be calculated in simplified form as:
q = k ΔT (1)
60079-30-2 © IEC:2007 – 29 –
where
q is the heat loss per unit length of pipe, in watts per metre (W/m);
ΔT is the difference in temperature between the desired maintenance temperature (T ) and
p
the minimum design ambient temperature (T ), in degrees Celsius ( °C);
a
k is the thermal conductivity of the system that for the sake of simplification can be
considered to be a constant (W/m K).
Factor k is a function of the thickness, size, and type of the thermal insulation layer(s), the
mean temperature of the thermal insulation, and the convective film coefficients of the
workpiece contents and the outside environment. The degree of accuracy of the calculation
therefore depends on the degree of definition of the system parameters.
Given these parameters, the heat loss for pipes and tubes may be determined by using more
detailed calculations.The equation given in (1) takes the following form when the conduction
parameters are taken into account:
2πK (T − T )
p a
q = (2)
⎛ D ⎞
ln⎜ ⎟
⎜ ⎟
D
⎝ 1⎠
where
q is the heat loss per unit length of pipe, in watts per metre (W/m);
T is the desired maintenance temperature, in degrees Celsius ( °C);
p
T is the minimum design ambient temperature, in degrees Celsius ( °C);
a
D is the inside diameter of the inner insulation layer, in metres (m);
D is the outside diameter of the outer insulation layer, in metres (m);
K is the thermal conductivity of the inner layer of insulation evaluated at its mean
temperature (W/m K).
Further accuracy in the heat loss equation can be obtained by differentiating the
characteristics of the different system layers and by incorporating the convective parameters,
as given in the following equation:
(T − T )
p a
(3)
q =
D D
⎛ ⎞ ⎛ ⎞
2 3
In⎜ ⎟ ln⎜ ⎟
⎜ ⎟ ⎜ ⎟
1 D D 1 1
⎝ 1⎠ ⎝ 2⎠
+ + + +
π π 2 K D h D h
D h 2 K π π π
1 i 1 2 3 co 3 o
where
D is the outside diameter of the inner insulation layer, in metres (m), (inside diameter of the
outer insulation layer when present);
D is the outside diameter of the outer insulation layer when present, in metres (m);
K is the thermal conductivity of the inner layer of insulation evaluated at its mean
temperature (W/m K);
K is the thermal conductivity of the outer layer of insulation, when present, evaluated at its
mean temperature (W/m K);
h is the inside air contact coefficient from the pipe to the inner insulation surface when
i
present (W/m K);
60079-30-2 © IEC:2007 – 31 –
h is the inside air contact coefficient from the outer insulation surface to the weather barrier

co
when present (W/m K);
h is the outside air film coefficient from the weather barrier to ambient (W/m K) (typical
o
values for this term range from 5 W/m K to 50 W/m K for low-temperature applications
below 50 °C).
Vessel heat losses often require a more complex analysis to determine total heat loss. The
trace heating supplier should be consulted.
For ease of product selection, trace heating suppliers will often furnish simple charts and
graphs of heat losses for variously maintained temperatures and insulations, which usually
include a safety factor.
6.4 Heat-up considerations
In certain plant operations, it may be necessary to specify that the trace heating system is
capable of raising the temperature of a static product within a certain time period. The heat
delivery requirement of a trace heated system on piping may be evaluated by use of the
following equation:
q − U()T − T P V h
⎧ ⎫
c i a 1 c1 f
t = H ln + (4)
⎨ ⎬
q − U()T − T q − U()T − T
⎩ c f a ⎭ c sc a
where
U is the heat loss per unit length of pipe per degree of temperature difference.
(5)
U =
D D
⎛ ⎞ ⎛ ⎞
2 3
⎜ ⎟ ⎜ ⎟
In ln
⎜ ⎟ ⎜ ⎟
1 D D 1 1
⎝ 1⎠ ⎝ 2⎠
+ + + +
πD h 2πK 2πK πD h πD h
1 i 1 2 3 co 3 o
H is the thermal time constant, which is the total energy stored in the mass of pipe, fluid, and
insulation per degree of temperature divided by the heat loss per unit length per degree
temperature differential.
P C V + P C V + 0,5 P C V
1 p1 c1 2 p2 c2 3 p3 c3
H = (6)
U
P is the density of the product in the pipe (kg/m );
C is the specific heat of the product (J/kg K);
p1
V is the internal volume of the pipe (m /m);
c1
P is the density of the pipe (kg/m );
C is the specific heat of the pipe (J/kg K);
p2
V is the pipe wall volume (m /m);
c2
P is the density of insulation (kg/m );
C is the specific heat of the insulation (J/kg K);
p3
V is the insulation wall volume (m /m);
c3
T is the initial temperature of the pipe, in degrees Celsius ( °C);
i
T is the final temperature of the fluid and the pipe, in degrees Celsius ( °C);
f
60079-30-2 © IEC:2007 – 33 –
T is the ambient temperature, in degrees Celsius ( °C);
a
T is the desired maintenance temperature, in degrees Celsius ( °C);
p
t is the desired heat-up time, in seconds (s);
U is the heat loss per unit length of pipe per degree of temperature (W/m K);
H is the thermal time constant, in seconds (s);
T is the temperature at which phase change occurs, in degrees Celsius ( °C);
sc
h is the latent heat of fusion for the product (J/kg);
f
q is the output of the trace heater(s) (W/m).
c
The preceding relationships also assume that system densities, volumes, thermal conduc-
tivities and heat losses are constant over the temperature range of interest. Note that some
products do not undergo a phase change during heat-up. Although the model is
representative of a straight pipeline, it does not have provisions for equipment such as pumps
and valves.
Insulation for valves, flanges, pumps, instruments, and other irregularly shaped equipment
may be constructed for the particular configuration. This can be fabricated from block,
insulation segments or flexible removable covers.
Non-insulated or partially insulated pipe supports or equipment require additional heat input to
compensate for the higher heat loss. Insulating cements or fibrous materials should be used
to fill cracks and joints. Where insulating cements are used for total insulation of an irregular
surface, a proportionally thicker layer of insulating cement may be applied to achieve the
desired insulating capability.
6.5 Heat-loss design safety factor
Since heat-loss calculations based on theoretical values do not account for imperfections
associated with actual work site installations, a safety factor should be applied to the
calculated values. The safety factor should be based upon the user’s requirements that
typically range from 10 % to 25 %. The addition of a safety factor is used to compensate for
tolerances in the trace heating system. Safety factors should be consid
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