ISO 21905:2020

INTERNATIONAL ISO
STANDARD 21905
First edition
2020-03
Gas turbine exhaust systems with or
without waste heat recovery
Systèmes d’échappement des turbines à gaz avec ou sans récupération
de la chaleur résiduelle
Reference number
ISO 21905:2020(E)
©
ISO 2020

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ISO 21905:2020(E)

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© ISO 2020
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ISO 21905:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Abbreviated terms . 3
5 Proposals . 5
5.1 Purchaser’s responsibilities . 5
5.2 Supplier’s responsibilities . 5
6 Basic exhaust system design . 5
6.1 General . 5
6.2 Exhaust system configuration . 6
6.3 Service life . 6
6.4 Supply responsibility . 6
6.5 GT characteristic data . 6
6.6 Required operating envelope . 6
6.7 Equipment specification . 6
6.8 WHRU equipment specification . 6
6.9 Operating conditions . 7
6.10 Operating environment . 7
6.11 Equipment arrangement . 7
6.12 Provision for future addition of WHRU . 7
6.13 Electrical equipment . 7
6.14 Field assembly and disassembly . 8
6.15 Special tools and fixtures . 8
6.16 Spare parts . 8
6.17 Deviations . 8
7 Documentation . 8
7.1 General . 8
7.2 Data sheets . 8
7.3 Supplier document requirements . 8
8 Exhaust system engineering and design .10
8.1 Overview .10
8.2 Typical WHRU configurations .10
8.3 General .10
8.4 TEG flow-induced vibrations .11
8.5 Exhaust system casing and ducting .11
8.5.1 General.11
8.5.2 Hot casing design and materials .13
8.5.3 Cold casing design material .14
8.5.4 Flange bolts .14
8.5.5 Surface preparation and treatment .16
8.6 Mechanical and thermal analysis .17
8.7 Insulation and refractory .17
8.7.1 Exhaust system casing and ducting external insulation (hot casing design) .18
8.7.2 Exhaust system casing and ducting internal insulation (cold case design) .18
8.8 Noise emission and silencing .21
8.9 Stacks.21
8.10 Expansion joints.22
8.11 Steel structures, stairs, ladders and platforms .23
8.12 Preservation, handling, packing and storage .24
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ISO 21905:2020(E)

8.12.1 Handling and storage of materials .24
8.12.2 Handling and storage of construction material and subcomponents at
suppers works .24
8.13 Inspection and testing .25
8.13.1 General inspection .25
8.13.2 Specific inspection requirements .25
9 WHRU engineering and design .26
9.1 WHRU process design .26
9.2 WHRU tube bundle mechanical design .28
9.2.1 General.28
9.2.2 Pressure part design .29
9.2.3 Corrosion allowances.30
9.3 WHRU tube bundle design .30
9.3.1 Tube and bend materials .30
9.3.2 Tube bundle design conditions .30
9.3.3 TEG flow-induced vibrations .32
9.3.4 Tube supports .33
9.3.5 Tube fins .34
9.3.6 Tube bundle headers .35
10 Dampers .36
10.1 General .36
10.2 WHRU dampers .36
10.2.1 Damper and isolator types and functions .36
10.2.2 Damper and isolator design .40
10.2.3 Damper and isolator TEG leakage performance .41
10.2.4 Seal air isolation system .42
10.2.5 Damper casing and insulation .43
10.2.6 Blades, shaft and operating gear .43
10.2.7 Requirements specific to damper types .44
11 WHRU system control .45
11.1 General .45
11.2 Guidance notes .45
11.2.1 WHRU control philosophy .45
11.2.2 WHRU control philosophy — Standby units .46
11.2.3 Signals .46
11.2.4 Wiring, junction boxes and protection .46
11.2.5 Control, instrumentation and protection equipment .47
11.2.6 HTM process side valves and piping .49
12 Access, inspection and maintenance .50
12.1 TEG path access .50
12.2 WHRU .51
13 Installation .52
14 Pre-commissioning and commissioning .53
15 Performance test .55
Annex A (informative) Application of computational fluid dynamics to exhaust system design .56
Annex B (informative) Application of thermal and structural analytical techniques to
exhaust system design .65
Annex C (informative) Information to be provided by purchaser .71
Annex D (informative) Fabrication and welding .84
Annex E (informative) Data sheets .94
Bibliography .95
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ISO 21905:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 192, Gas turbines.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 21905:2020(E)

Introduction
This document has been developed in response to the international market need for a specification
relating to the exhaust and heat recovery systems for gas turbines. Purchasers and suppliers will
benefit from a standard against which equipment can be purchased, designed and constructed -
especially given the challenging nature of the turbulent exhaust gas flow and associated complexity of
mechanical design. Equipment is frequently installed in remote and challenging locations both onshore
and offshore where maintenance and repair can be prohibitively expensive.
A waste heat recovery unit recovers thermal energy from the waste heat available in gas turbine exhaust
gases, exchanged into various heat transfer media such as water, water/glycol mixtures, thermal oils
and hydrocarbon gases.
The application of heat recovery devices to gas turbines results in significant thermal efficiency gains
and resultant environmental benefit from reduction in CO emissions. Gas turbine exhaust is one of
2
many sources of waste heat energy and can be classed as medium grade within a typical temperature
range between 400 °C and 600 °C suitable for Rankine cycle applications.
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INTERNATIONAL STANDARD ISO 21905:2020(E)
Gas turbine exhaust systems with or without waste heat
recovery
1 Scope
This document specifies requirements and gives recommendations for the design, materials of
construction, modelling, controlling, fabrication, inspection, testing, installation, start-up and operation
of industrial gas turbine (GT) exhaust systems with or without waste heat recovery unit (WHRU). Gas
turbines can be on-shore or off-shore for such sectors as oil and gas, chemical and process industries,
utilities, or other intensive energy users.
For this document, the exhaust system means all items in the turbine exhaust gas stream between the
GT exhaust gas collector outlet flange and the termination/s to the atmosphere.
The following items are not covered by this document:
— heat recovery steam generator equipment (HRSG);
— supplementary fired systems;
— auxiliary fired systems;
— exhaust gas collector (also known as exhaust plenum);
— fire detection and extinguishing systems;
— emissions controls equipment intended to modify the gaseous composition of the exhaust gas;
— WHRUs that are of the firetube type, where the turbine exhaust gas (TEG) passes through the tubes.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 3744, Acoustics — Determination of sound power levels and sound energy levels of noise sources using
sound pressure — Engineering methods for an essentially free field over a reflecting plane
ISO 9614, Acoustics — Determination of sound power levels of noise sources using sound intensity
ISO 10494, Turbines and turbine sets — Measurement of emitted airborne noise — Engineering/survey
method
ISO 10474, Steel and steel products — Inspection documents
ISO 12241, Thermal insulation for building equipment and industrial installations — Calculation rules
ISO 13704, Petroleum, petrochemical and natural gas industries — Calculation of heater-tube thickness in
petroleum refineries
ISO 13705:2012, Petroleum, petrochemical and natural gas industries — Fired heaters for general
refinery service
ISO 13916, Welding — Measurement of preheating temperature, interpass temperature and preheat
maintenance temperature
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ISO 21905:2020(E)

ISO 14122, Safety of machinery — Permanent means of access to machinery
ISO 14555, Welding — Arc stud welding of metallic materials
ISO 15612, Specification and qualification of welding procedures for metallic materials — Qualification by
adoption of a standard welding procedure specification
ISO 15613, Specification and qualification of welding procedures for metallic materials — Qualification
based on pre-production welding test
ISO 15614-1, Specification and qualification of welding procedures for metallic materials — Welding
procedure test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys
ISO 19902, Petroleum and natural gas industries — Fixed steel offshore structures
ASME B16.9, Wrought steel butt-welding short radius elbows and returns
ASME B31.3, Petroleum Refinery Piping
ASTM C680-10, Standard Practice for Estimate of the Heat Gain or Loss and the Surface Temperatures of
Insulated Flat, Cylindrical, and Spherical Systems by Use of Computer Programs
EN 287-1, Qualification test of welders — Fusion welding — Steels
EN 1011-2, Welding — Recommendations for welding of metallic materials — Part 2: Arc Welding of
Ferritic Steels
EN 1991-1-4, Eurocode 1: Actions on structures — Part 1-4: General actions — Wind actions
EN 10025-2, Hot rolled products of structural steels — Technical delivery conditions for non-alloy
structural steels
EN 10025-3, Hot rolled products of structural steels — Technical delivery conditions for normalized/
normalized rolled weldable fine grain structural steels
EN 10253-2, Butt-welding pipe fittings. Non alloy and ferritic alloy steels with specific inspection
requirements
EN 13445-3:2014, Unfired pressure vessels — Part 3: Design
EN 13480, Metallic Industrial piping
EN 15614, Specification and qualification of welding procedures for metallic materials
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
analogue control signal
control or digital signal that represents a continuous range of values
EXAMPLE A traditional 4-20 mA current loop.
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ISO 21905:2020(E)

3.2
commissioning
action whereby dynamic checks and tests where the GT is running, the exhaust system is subject to
TEG flow and the WHRU is filled with circulating HTMs, progressively loaded with control systems and
functioning
3.3
data sheet
formal document containing process and/or mechanical data
3.4
insulation
material applied to either the inside or outside of the exhaust system component casings (e.g. WHRU,
ducting, stacks, dampers) in order to reduce the casing material or outer cladding temperature,
respectively
3.5
pre-commissioning
static checks and tests where the exhaust system is cold and the WHRU is not filled with HTM and the
controls are energized
3.6
purchaser
party that enters into contract with the supplier (3.8) for the supply of the exhaust system
Note 1 to entry: The purchaser is the party who specifies the technical requirements. The purchaser can also
instruct a contractor (3.7), an agent or consultant, authorized to act for, and on his behalf. The purchaser can in
some cases also be the GT supplier.
3.7
contractor
party that carries out all or part of the design, engineering, procurement, construction, commissioning
(3.2) or management of a project or operation of a facility
Note 1 to entry: The purchaser (3.6) can choose to undertake all or part of the duties of the contractor
3.8
supplier
party that manufactures or s
...