ISO/FDIS 18991

• Abstract:

  Specifies requirements for design, performance, materials, testing, installation, inspection, and maintenance of top drive systems for onshore and offshore applications.

• Status: Not Published
• ICS: 75.180.10 - Exploratory, drilling and extraction equipment
• Technical Committee: ISO/TC 67/SC 4 - Drilling and production equipment
• Drafting Committee: ISO/TC 67/SC 4 - Drilling and production equipment
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 08-Sep-2026
• Completion Date: 08-Sep-2026

Overview

ISO/FDIS 18991 sets out comprehensive requirements for top drive systems (TDS) used in the oil and gas industries, including lower carbon energy sectors. This international standard addresses the essential elements such as design, functional performance, materials, manufacturing, testing, installation, inspection, maintenance, and recertification of TDS for both onshore and offshore drilling, production, and injection operations. The document distinguishes between two product specification levels (PSL 1 and PSL 2), specifying different levels of technical rigor required for conformity.

Key Topics

• Functional Specifications: ISO/FDIS 18991 outlines core functions for top drive systems, including bearing axial load, rotary driving, mud circulation, making and breaking pipe connections, and vertical movement along a guide rail within a drilling mast or derrick.
• Design Requirements: Clear design criteria are established to ensure TDS are safe, reliable, and suitable for diverse operational environments, including low temperatures and hazardous areas.
• Product Classification: The standard classifies TDS based on power source (electric or hydraulic) and power transmission type (direct-drive or reduction drive).
• Performance and Testing: Requirements for factory acceptance testing, type testing, and site acceptance tests ensure that each system meets operational and safety standards before deployment.
• System Components: Coverage includes rotary power assemblies, pipe handling systems, backup clamps, elevators, guide rails, counter-balance mechanisms, IBOP (inside blowout preventers), casing running tools, and driller’s control consoles.
• Documentation and Traceability: All design, testing, and maintenance actions must be documented to ensure quality and traceability throughout the lifecycle of the equipment.
• Inspection and Maintenance: Procedures for regular inspection, maintenance, repair, and recertification are provided to support ongoing safe and efficient operation.

Applications

ISO/FDIS 18991 is applicable to organizations involved in:

• Drilling Operations: Ensuring that TDS meet the stringent requirements for safety, reliability, and performance in onshore and offshore oil, gas, and lower carbon energy drilling scenarios.
• Production and Injection: Supporting production and injection operations where up-to-standard equipment is vital for minimizing downtime and risk.
• Manufacturing and Procurement: Guiding manufacturers and purchasers through a common set of specifications, helping streamline the procurement of top drive systems and their components.
• Equipment Upgrades and Recertification: Providing a benchmark for existing systems undergoing modification, retrofitting, or compliance re-assessment.
• Safety and Environmental Compliance: Aiding operators in meeting industry regulations and reducing environmental impacts, ensuring key features like dropped object prevention and hazardous area suitability.

Related Standards

ISO/FDIS 18991 references and aligns with a range of international and industry standards to ensure consistency and compatibility, including:

• ISO 13535: Petroleum and natural gas industries – Drilling and production equipment – Hoisting equipment.
• API Spec 7V: Drill Stem Valves.
• API Spec 8C: Drilling and Production Hoisting Equipment (PSL 1 and PSL 2).
• ISO 4413, ISO 4409, ISO 10100: Hydraulic fluid power systems for testing and safety requirements.
• IEC 60079, IEC 60204-1: Electrical equipment and safety in explosive atmospheres and machinery.
• ISO 9712, ISO 9606-1, ISO 15614-1: Non-destructive testing and welding qualifications.
• EN 10228-1, EN 10228-3: Non-destructive testing of steel forgings.

By adhering to ISO/FDIS 18991, stakeholders in the oil, gas, and low-carbon energy sectors can ensure top drive system safety, reliability, and global market acceptance, ultimately enhancing their operational excellence and regulatory compliance.

FINAL DRAFT
International
Standard
ISO/TC 67/SC 4
Oil and gas industries including
Secretariat: ANSI
lower carbon energy — Drilling,
Voting begins on:
production and injection equipment
2026-09-08
— Top drive systems
Voting terminates on:
2026-11-03
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 67/SC 4
Oil and gas industries including
Secretariat: ANSI
lower carbon energy — Drilling,
Voting begins on:
production and injection equipment
— Top drive systems
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviations . 5
5 Information supplied by the purchaser . 6
6 Functional specification . 7
6.1 General .7
6.2 Product classification .7
6.3 Functional components .7
6.3.1 Rotary power assembly .7
6.3.2 Pipe handler system .10
6.3.3 Counter-balance mechanism . 12
6.3.4 Dolly and guide rail . 12
6.3.5 Hydraulic TDS and their auxiliary control system . 12
6.3.6 Electric TDS and their auxiliary control system . 13
6.3.7 Control console . 13
6.3.8 Casing running tool (CRT) . 13
6.3.9 Transport skid . 13
7 Design . 14
7.1 Design requirements .14
7.2 Strength analysis .14
7.2.1 General .14
7.2.2 Equivalent stress .14
7.2.3 Design safety factors for primary-load-carrying components . 15
7.2.4 Shear strength . 15
7.3 Type and dimension of connection . 15
7.3.1 Dimension of bail . 15
7.3.2 Main shaft(quill), IBOP, and saver sub configuration .17
7.3.3 Rotating head link adaptor dimensions .18
7.4 Rotary power assembly .19
7.4.1 Main thrust bearing .19
7.4.2 Gearbox (Gearbox assembly) .19
7.4.3 Load-carrying box . 20
7.5 Pipe handler system . 20
7.5.1 Rotating head . 20
7.5.2 Link tilt mechanism . 20
7.5.3 IBOP and control device . 20
7.5.4 Tool joint lock . 20
7.5.5 Backup clamp .21
7.6 Counter-balance mechanism .21
7.7 Guide rail .21
7.8 Dolly .21
7.9 Hydraulic system .21
7.9.1 General .21
7.9.2 Hydraulic source . .21
7.9.3 Hydraulic lines and fittings.21
7.9.4 Solenoid valves . 22
7.9.5 Actuating element . 22
7.10 Electrical system . 22
7.10.1 General . 22

iii
7.10.2 Electrical control system . 23
7.10.3 Protection of control circuits . 23
7.10.4 Control cabinet .24
7.10.5 Driller console . .24
7.11 Dropped object .24
8 Manufacture .25
8.1 Material . 25
8.1.1 General . 25
8.1.2 Written specifications . 25
8.1.3 Mechanical properties . . 25
8.1.4 Manufacture . 25
8.1.5 Chemical composition . 25
8.1.6 Non-destructive examination (NDE) . 25
8.2 Welding . . 26
8.2.1 General . 26
8.2.2 Written specifications . 26
8.2.3 Welding qualification . 26
8.2.4 Management of welding materials . 26
8.2.5 Weld performance . 26
8.2.6 Fabrication welds . 26
8.2.7 Welding procedure specification . 26
8.2.8 Welding procedure qualification . 26
8.2.9 Welding inspection .27
8.2.10 Post welding treatment .27
8.2.11 Repair welds .27
8.3 Surface treatment and painting .27
8.3.1 Surface treatment .27
8.3.2 Coating.27
8.4 Quality control and traceability .27
8.4.1 General .27
8.4.2 Quality control personnel qualification . 28
8.4.3 Measure and test equipment . 28
8.4.4 Quality control for specific equipment and components . 28
9 Test .28
9.1 General . 28
9.2 Factory acceptance testing(FAT) . 28
9.2.1 General . 28
9.2.2 Rotary power assembly Test . . . 29
9.2.3 Braking test . 29
9.2.4 Pipe handler system test . 29
9.2.5 Main channel sealing test (within FAT) . 30
9.2.6 Hydraulic system test . 30
9.2.7 Electrical control system test .31
9.3 Type test .31
9.3.1 General .31
9.3.2 Main channel pressure test (within type test) .31
9.3.3 Static load tensile test .32
9.3.4 Load test apparatus .32
9.3.5 Test requirements .32
9.3.6 Rotary power assemblytest . . .32
9.4 Site acceptance test(SAT) . 33
10 Training and competency .33
10.1 General . 33
10.2 Training . 33
10.3 Personnel competence . 33
11 Documentation .34
11.1 General . 34

iv
11.2 Documentation to be kept by the manufacturer . 34
11.3 Documentation to be delivered with product . 34
12 Marking, packing, transportation, and storage .34
12.1 Product marking . 34
12.2 Packing, transportation, and storage. 34
13 Inspection, maintenance, repair and recertification .35
13.1 Procedures . 35
13.2 Inspection and maintenance . 35
13.2.1 General . 35
13.2.2 Inspection . 35
13.2.3 Maintenance . 35
13.3 Repair. 36
13.3.1 Procedures . 36
13.3.2 Replacement and critical parts . . 36
13.3.3 Test . . . 36
13.3.4 Activity records . . 36
13.3.5 Recertification . 36
Bibliography .37

v
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 67, Oil and gas industries including lower carbon
energy, Subcommittee SC 4, Drilling, production and injection equipment.
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.

vi
Introduction
This document has been developed by users and manufacturers of top drive systems and is intended for
use in the petroleum and natural gas industry worldwide. This document provides requirements and
information in the selection, manufacturing, testing, documentation, marking, packaging, transportation,
storage, maintenance, inspection, repair, recertification of top drive systems as defined in the scope.
Further, this document addresses manufacturers' requirements, which set the minimum parameters with
which it is necessary that manufacturers conform to claim conformity with this document. Also, suggestions
on transportation and storage of top drive systems are put forward in this document.

vii
FINAL DRAFT International Standard ISO/FDIS 18991:2026(en)
Oil and gas industries including lower carbon energy —
Drilling, production and injection equipment — Top drive
systems
1 Scope
This document provides the classification and specifications, functions, design, manufacturing, testing,
documentation, marking, packaging, transportation, storage, inspection, maintenance and recertification
for top drive systems (TDS) and their supporting devices for the oil and gas industry, including low-carbon
energy drilling and oil production equipment.
This document is applicable to the classification and specifications, functions, design, manufacturing,
testing, documentation, marking, packaging, transportation, and storage, inspection, maintenance and
recertification for top drives and their supporting devices.
This document establishes requirements for two product specification levels (PSLs). These two PSL
designations define different levels of technical requirements. All the requirements of Clause 5 to Clause 13
are applicable to PSL 1 unless specifically identified as PSL 2. PSL 2 includes all the requirements of PSL 1,
plus the additional practices as stated herein. Supplementary requirements apply only when specified.
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 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 1436:2026, Rubber hoses and hose assemblies — Wire-braid-reinforced hydraulic types for oil-based or
water-based fluids — Specification
ISO 4409, Hydraulic fluid power — Positive-displacement pumps, motors and integral transmissions — Methods
of testing and presenting basic steady state performance
ISO 4413, Hydraulic fluid power — General rules and safety requirements for systems and their components
ISO 4986:2020, Steel and iron castings — Magnetic particle testing
ISO 4992-1:2020, Steel castings — Ultrasonic testing — Part 1: Steel castings for general purposes
ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 9223:2012, Corrosion of metals and alloys — Corrosivity of atmospheres — Classification, determination
and estimation
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10100, Hydraulic fluid power — Cylinders — Acceptance tests
ISO 10763:2020, Hydraulic fluid power — Plain-end, seamless and welded precision steel tubes — Dimensions
and nominal working pressures
ISO 11158, Lubricants, industrial oils and related products (class L) — Family H (hydraulic systems) —
Specifications for categories HH, HL, HM, HV and HG
ISO 13535:2000, Petroleum and natural gas industries — Drilling and production equipment — Hoisting
equipment
ISO 13849-1, Safety of machinery — Safety-related parts of control systems — Part 1: General principles for
design
ISO 15614-1:2017, 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 19879:2021, Metallic tube connections for fluid power and general use — Test methods for hydraulic fluid
power connections
IEC 60034-30-3:2024, Rotating electrical machines — Part 30-3: Efficiency classes of high voltage AC motors
(IE-code)
IEC 60079 (all parts), Explosive atmospheres
IEC 60204-1, Safety of machinery — Electrical equipment of machines — Part 1: General requirements
IEC 60364-5-54, Low-voltage electrical installations — Part 5-54: Selection and erection of electrical equipment
— Earthing arrangements and protective conductors
IEC 60447, Basic and safety principles for man-machine interface, marking and identification - Actuating
principles
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 61439-1, Low-voltage switchgear and control gear assemblies - Part 1: General rules
IEC 61800 (all parts), Adjustable speed electrical power drive systems
IEC 61892-3, Mobile and fixed offshore units — Electrical installations - Part 3: Equipment
API Spec 7V:2024, Drill Stem Valves
API Spec 8C:2025, Drilling and Production Hoisting Equipment (PSL 1 and PSL 2)
EN 10228-1:2016, Non-destructive testing of steel forgings — Part 1: Magnetic particle inspection
EN 10228-3:2016, Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic
steel forgings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

3.1
backup clamp
backup tong
grabber
grabber box
assembly in pipe handler system that can grip drill string, used to provide clamp force when the main
shaft(quill) applies torque to makeup or breakout the connection thread between saver sub and drill string
Note 1 to entry: The torque wrench consists of a clamp which can be used to make and break connections, some have
the functionality to do this without main shaft rotation.
3.2
bail
connection link
link by which the top drive system is suspended
3.3
casing running tool
CRT
specialized device used in oil and gas drilling operations to run, make up and break out casing connections,
and reciprocate, rotate, fill-up/circulate and cement casing strings into the wellbore
3.4
design safety factor
factor to account for a certain safety margin between the maximum allowable stress and the specified
minimum yield strength of a material
[SOURCE: ISO 13535:2000, 3.1.3]
3.5
design verification test
test performed to validate the integrity of the design calculations
[SOURCE: API Spec 8C:2025, 3.1.5]
3.6
direct-drive TDS
direct-drive top drive system
top drive system whose power machine rotates drill string directly with no belts, gears/gearbox, or other
power transmitting elements in the power train
3.7
dolly
torque bushing
equipment used to hold the top drive system in correct position relative to the mast/derrick along with the
guide rail during various operations
3.8
dropped objects
object is any item, tool, or material that unintentionally falls from an elevated position to a lower level,
posing risks of injury, fatality, or property damage
3.9
electric TDS
electric top drive system
top drive system whose main rotary power is provided by AC or DC motor
3.10
elevators
tools for lifting, lowering and suspending the pipe string, which are used in conjunction with the elevator
links and suspended at the lower end of the elevator links

3.11
elevator links
one of the tripping tools, which is used in pairs. It is suspended on the rotating head link adapter on both
sides of the swivel head, and its lower end is connected to the elevator
3.12
guide rail
torque track
torque guide
structural steelwork that provides smooth flat surfaces for the top drive system (TDS) to move up and down
within the rig mast/derrick and fixes the position of the TDS spin axis relative to the mast/derrick and hole
centre
Note 1 to entry: Guide rail should withstand reverse torque
3.13
hydraulic power unit
HPU
power source that uses hydraulic oil as the working medium and is used to convert hydraulic energy into
mechanical energy
3.14
hydraulic TDS
hydraulic top drive system
top drive system whose main rotary power is provided by a hydraulic motor
3.15
inside blowout preventer
IBOP
critical, high-pressure, non-return safety valve mounted directly to the top drive system main shaft (quill)
Note 1 to entry: It prevents uncontrolled flow up the drill string by automatically closing against upward pressure
while allowing downward drilling fluid circulation. The design of IBOP shall conform with the requirements of kelly
valve specified in API Spec 7V.
3.16
maximum allowable stress
specified minimum yield strength divided by the design safety factor
[SOURCE: ISO 13535:2000, 3.1.9]
3.17
pipe handler system
device that facilitates movement of the elevator links through 360 degrees
Note 1 to entry: The pipe handler system can tilt the link forwards, backward and rotate
3.18
primary-load-carrying component
component of the equipment through which the primary load is carried
[SOURCE: ISO 13535:2000, 3.1.11]
3.19
rated load
maximum operating load, both static and dynamic, to be applied to the top drive system
3.20
rotary power assembly
assembly that supports the drill string, moves with traveling block, and is designed to directly provide
rotary power to the top of the drill string during drilling operations

3.21
rotating head
assembly in top drive system that is rotated by power device around the central axis
3.22
saver sub
sub-adapter connected between the top drive system´s (TDS) lower inside blowout preventer and the drill
string, serves as a sacrificial element between the drill string and TDS, allowing for frequent connections
with drill pipes without wearing out the TDS´s main shaft itself
3.23
test type unit
prototype unit upon which a design verification test is conducted
3.24
top drive system
TDS
equipment with hoisting capabilities, consisting of rotary power assembly, pipe handler system, mud
circulation conduit and other components, which is capable of rotating the drill string, making up or breaking
out the connections, moving upward or downward (even forward) along the guide rail and operating mud
circulation
4 Symbols and abbreviations
AC alternating current
CRT casing running tool
DC direct current
ESD emergency shut down
FAT factory acceptance testing
HMI human machine interface
HPU hydraulic power unit
IBOP inside blowout preventer
MCC motor control centre
NDE non-destructive examination
OEM original equipment manufacturer
PLC programmable logic controller
PSL product specification level
SAT site acceptance test
SCR silicon controlled rectifier
TDS top drive system
VFD variable frequency drive
5 Information supplied by the purchaser
The user/purchaser should provide the following information:
a) static hoist rating, elevator load path and quill load path;
b) working height;
c) maximum continuous and maximum intermittent drilling torque;
d) maximum breakout torque;
e) brake torque;
f) rated circulating pressure;
g) inner diameter of the main shaft channel/load path;
h) power supply voltage;
i) power supply frequency;
j) speed range;
k) expected operating altitude;
l) product design conformity with PSL1 or PSL2;
m) maximum static surface pressure;
n) compatible mast/derrick dimensions;
o) minimum expected operating ambient temperature in which the TDS will be operating (including the
main motor, main motor cooling fan, hydraulic power unit motor, hydraulic cooling fan);
p) maximum expected operating ambient temperature in which the TDS will be operating (including the
main motor, main motor cooling fan, hydraulic power unit motor, hydraulic cooling fan);
q) saver sub connection thread;
r) cable length (power cable length, control cable length, cables for Driller Console length, power supply
cable length);
s) kelly hose connection (washpipe assembly connection thread, swivel hose connection thread, top thread
and orientation of kelly hose in the derrick/mast);
t) hydraulic power unit location (integrated or independent) and dimensions;
u) current and voltage harmonic distortion rate;
v) certification requirements;
w) shape and weight specifications:
1) maximum overall dimensions of the TDS;
2) maximum weight of the TDS;
3) type of guide rail;
4) maximum weight of the guide rail;
5) maximum overall dimensions of the electrical control house including VFD/SCRs;
6) maximum weight of the electrical control house;

7) maximum overall dimensions of the driller’s console;
8) maximum overall dimensions of the hydraulic station including HPU (if independent);
9) the type of bail and the size of load collar ears;
10) thread type of crossover sub;
11) clamping range of the backup clamp;
12) operating pressure of the IBOP;
13) connection thread of the IBOP;
14) outer diameter of the IBOP;
15) inner diameter of the IBOP;
16) type of traveling block (fixed or telescopic);
17) dimension and design of crown beams.
6 Functional specification
6.1 General
The TDS shall have the necessary functions, which include bearing axial load during operation, rotary
driving, mud circulation, making and breaking pipe connections, and traveling up and
...

ISO/TC 67/SC 4/WG 1
Date: 2026-06-23
Secretariat: ANSI
Date: 2026-08-25
Oil and gas industries including lower carbon energy — Drilling,
production and injection equipment — Top drive systems
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviations . 5
5 Information supplied by the purchaser . 6
6 Functional specification . 7
6.1 General. 7
6.2 Product classification . 8
6.3 Functional components . 8
7 Design . 18
7.1 Design requirements . 18
7.2 Strength analysis . 18
7.3 Type and dimension of connection . 19
7.4 Rotary power assembly . 25
7.5 Pipe handler system . 26
7.6 Counter-balance mechanism . 26
7.7 Guide rail . 26
7.8 Dolly . 26
7.9 Hydraulic system . 27
7.10 Electrical system . 27
7.11 Dropped object . 29
8 Manufacture . 30
8.1 Material . 30
8.2 Welding . 31
8.3 Surface treatment and painting . 32
8.4 Quality control and traceability . 33
9 Test . 33
9.1 General. 33
9.2 Factory acceptance testing(FAT). 34
9.3 Type test . 36
9.4 Site acceptance test(SAT) . 38
10 Training and competency . 38
10.1 General. 38
10.2 Training . 38
10.3 Personnel competence . 39
11 Documentation . 39
11.1 General. 39
11.2 Documentation to be kept by the manufacturer . 39
11.3 Documentation to be delivered with product . 39
12 Marking, packing, transportation, and storage . 39
12.1 Product marking . 39
12.2 Packing, transportation, and storage . 40
13 Inspection, maintenance, repair and recertification . 40
iii
13.1 Procedures . 40
13.2 Inspection and maintenance. 40
13.3 Repair . 41
Bibliography . 43

iv
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 67, Oil and gas industries including lower carbon
energy, Subcommittee SC 4, Drilling, production and injection equipment.
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.
v
Introduction
This document has been developed by users and manufacturers of top drive systems and is intended for use
in the petroleum and natural gas industry worldwide. This document provides requirements and information
in the selection, manufacturing, testing, documentation, marking, packaging, transportation, storage,
maintenance, inspection, repair, recertification of top drive systems as defined in the scope.
Further, this document addresses manufacturers' requirements, which set the minimum parameters with
which it is necessary that manufacturers conform to claim conformity with this document. Also, suggestions
on transportation and storage of top drive systems are put forward in this document.
vi
Oil and gas industries including lower carbon energy — Drilling,
production and injection equipment — Top drive systems
1 Scope
This document provides the classification and specifications, functions, design, manufacturing, testing,,,
documentation, marking, packaging, transportation, storage, inspection, maintenance and recertification for
top drive systems (TDS) and their supporting devices for the oil and gas industry, including low-carbon energy
drilling and oil production equipment.
This document is applicable to the classification and specifications, functions, design, manufacturing, testing,
documentation, marking, packaging, transportation, and storage, inspection ,, maintenance and recertification
for top drives and their supporting devices.
This document establishes requirements for two product specification levels (PSLs). These two PSL
designations define different levels of technical requirements. All the requirements of Clause 5Clause 5 to
Clause 13Clause 13 are applicable to PSL 1 unless specifically identified as PSL 2. PSL 2 includes all the
requirements of PSL 1, plus the additional practices as stated herein. Supplementary requirements apply only
when specified.
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 148--1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 1436:2026, Rubber hoses and hose assemblies — Wire-braid-reinforced hydraulic types for oil-based or
water-based fluids — Specification
ISO 4409, Hydraulic fluid power — Positive-displacement pumps, motors and integral transmissions — Methods
of testing and presenting basic steady state performance
ISO 4413, Hydraulic fluid power — General rules and safety requirements for systems and their components
ISO 4986:2020, Steel and iron castings — Magnetic particle testing
ISO 4992--1:2020, Steel castings — Ultrasonic testing — Part 1: Steel castings for general purposes
ISO 6506--1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 6892--1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 9223:2012, Corrosion of metals and alloys — Corrosivity of atmospheres — Classification, determination
and estimation
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10100, Hydraulic fluid power — Cylinders — Acceptance tests
ISO 10763:2020, Hydraulic fluid power — Plain-end, seamless and welded precision steel tubes — Dimensions
and nominal working pressures
ISO 11158, Lubricants, industrial oils and related products (class L) — Family H (hydraulic systems) —
Specifications for categories HH, HL, HM, HV and HG
ISO 13535:2000, Petroleum and natural gas industries — Drilling and production equipment — Hoisting
equipment
ISO 13849--1, Safety of machinery — Safety-related parts of control systems — Part 1: General principles for
design
ISO 15614--1:2017, 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 19879:2021, Metallic tube connections for fluid power and general use — Test methods for hydraulic fluid
power connections
IEC 60034--30-3:2024, Rotating electrical machines — Part 30-3: Efficiency classes of high voltage AC motors
(IE-code)
IEC 60079 (all parts), Explosive atmospheres
IEC 60204--1, Safety of machinery — Electrical equipment of machines — Part 1: General requirements
IEC 60364--5-54, Low-voltage electrical installations — Part 5-54: Selection and erection of electrical
equipment — Earthing arrangements and protective conductors
IEC 60447, Basic and safety principles for man-machine interface, marking and identification - Actuating
principles
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 61439--1, Low-voltage switchgear and control gear assemblies - Part 1: General rules
IEC 61800 (all parts), Adjustable speed electrical power drive systems
IEC 61892--3, Mobile and fixed offshore units — Electrical installations - Part 3: Equipment
API Spec 7V:2024, Drill Stem Valves
API Spec 8C:2025, Drilling and Production Hoisting Equipment (PSL 1 and PSL 2)
EN 10228--1:2016, Non-destructive testing of steel forgings — Part 1: Magnetic particle inspection
EN 10228--3:2016, Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic
steel forgings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
backup clamp
backup tong
grabber
grabber box
assembly in pipe handler system that can grip drill string, used to provide clamp force when the main
shaft(quill) applies torque to makeup or breakout the connection thread between saver sub and drill string
Note 1 to entry: The torque wrench consists of a clamp which can be used to make and break connections, some have the
functionality to do this without main shaft rotation.
3.2 3.2
bail
connection link
link by which the TDStop drive system is suspended
3.3 3.3
casing running tool
CRT
specialized device used in oil and gas drilling operations to run, make up and break out casing connections,
and reciprocate, rotate, fill-up/circulate and cement casing strings into the wellbore
3.4 3.4
design safety factor
factor to account for a certain safety margin between the maximum allowable stress and the specified
minimum yield strength of a material
[SOURCE: ISO 13535:2000, 3.1.3]
3.5 3.5
design verification test
test performed to validate the integrity of the design calculations
[SOURCE: API Spec 8C:2025, 3.1.5]
3.6 3.6
direct-drive TDS
TDSdirect-drive top drive system
top drive system whose power machine rotates drill string directly with no belts, gears/gearbox, or other
power transmitting elements in the power train
3.7 3.7
dolly
torque bushing
equipment used to hold the TDStop drive system in correct position relative to the mast/derrick along with
the guide rail during various operations
3.8 3.8
dropped objects
object is any item, tool, or material that unintentionally falls from an elevated position to a lower level, posing
risks of injury, fatality, or property damage
3.9 3.9
electric TDS
TDSelectric top drive system
top drive system whose main rotary power is provided by AC or DC motor
3.10 3.10
elevators
tools for lifting, lowering and suspending the pipe string, which are used in conjunction with the elevator links
and suspended at the lower end of the elevator links
3.11 3.11
elevator links
one of the tripping tools, which is used in pairs. It is suspended on the rotating head link adapter on both sides
of the swivel head, and its lower end is connected to the elevator
3.12 3.12
guide rail
torque track
torque guide
structural steelwork that provides smooth flat surfaces for the top drive system (TDS) to move up and down
within the rig mast/derrick and fixes the position of the TDS spin axis relative to the mast/derrick and hole
centre
Note 1 to entry: Guide rail should withstand reverse torque
3.13 3.13
hydraulic power unit
HPU
power source that uses hydraulic oil as the working medium and is used to convert hydraulic energy into
mechanical energy
3.14 3.14
hydraulic TDS
TDShydraulic top drive system
top drive system whose main rotary power is provided by a hydraulic motor
3.15 3.15
inside blowout preventer
IBOP
critical, high-pressure, non-return safety valve mounted directly to the TDStop drive system main shaft
(quill).)
Note 1 to entry: It prevents uncontrolled flow up the drill string by automatically closing against upward pressure while
allowing downward drilling fluid circulation. The design of IBOP shall conform with the requirements of kelly valve
specified in API Spec 7V:2024.

3.16 3.16
maximum allowable stress
specified minimum yield strength divided by the design safety factor
[SOURCE: ISO 13535:2000, 3.1.9]
3.17 3.17
pipe handler system
device that facilitates movement of the elevator links through 360 degrees
Note 1 to entry: The pipe handler system can tilt the link forwards, backward and rotate
3.18 3.18
primary-load-carrying component
component of the equipment through which the primary load is carried
[SOURCE: ISO 13535:2000, 3.1.11]
3.19 3.19
rated load
maximum operating load, both static and dynamic, to be applied to the TDStop drive system
3.20 3.20
rotary power assembly
assembly that supports the drill string, moves with traveling block, and is designed to directly provide rotary
power to the top of the drill string during drilling operations
3.21 3.21
rotating head
assembly in TDStop drive system that is rotated by power device around the central axis
3.22 3.22
saver sub
sub-adapter connected between the top drive system´s (TDS´s Lower IBOP) lower inside blowout preventer
and the drill string, serves as a sacrificial element between the drill string and TDS, allowing for frequent
connections with drill pipes without wearing out the TDS´s main shaft itself

3.23 3.23
test type unit
prototype unit upon which a design verification test is conducted
3.24 3.24
top drive system
TDS
equipment with hoisting capabilities, consisting of rotary power assembly, pipe handler system, mud
circulation conduit and other components, which is capable of rotating the drill string, making up or breaking
out the connections, moving upward or downward (even forward) along the guide rail and operating mud
circulation
4 Symbols and abbreviations
AC alternating current
CRT casing running tool
DC direct current
ESD emergency shut down
FAT factory acceptance testing
HMI human machine interface
HPU hydraulic power unit
IBOP inside blowout preventer
MCC motor control centre
NDE non-destructive examination
OEM original equipment manufacturer
PLC programmable logic controller
PSL product specification level
SAT site acceptance test
SCR silicon controlled rectifier
TDS top drive system
VFD variable frequency drive
5 Information supplied by the purchaser
The user/purchaser should provide the following information:
a) a) static hoist rating, elevator load path and quill load path;
b) b) working height;
c) c) maximum continuous and maximum intermittent drilling torque;
d) d) maximum breakout torque;
e) e) brake torque;
f) f) rated circulating pressure;
g) g) inner diameter of the main shaft channel/load path;
h) h) power supply voltage;
i) i) power supply frequency;
j) j) speed range;
k) k) expected operating altitude;
l) l) product design conformity with PSL1 or PSL2;
m) m) maximum static surface pressure;
n) n) compatible mast/derrick dimensions;
o) o) minimum expected operating ambient temperature in which the TDS will be operating
(including the main motor, main motor cooling fan, hydraulic power unit motor, hydraulic cooling fan);
p) p) maximum expected operating ambient temperature in which the TDS will be operating
(including the main motor, main motor cooling fan, hydraulic power unit motor, hydraulic cooling fan);
q) q) saver sub connection thread;
r) r) cable length (power cable length, control cable length, cables for Driller Console length, power
supply cable length);
s) s) kelly hose connection (washpipe assembly connection thread, swivel hose connection thread,
top thread and orientation of kelly hose in the derrick/mast);
t) t) hydraulic power unit location (integrated or independent) and dimensions;
u) u) current and voltage harmonic distortion rate;
v) v) certification requirements;
w) w) shape and weight specifications:
1) maximum overall dimensions of the TDS;
2) maximum weight of the TDS;
3) type of guide rail;
4) maximum weight of the guide rail;
5) maximum overall dimensions of the electrical control house including VFD/SCRs;
6) maximum weight of the electrical control house;
7) maximum overall dimensions of the driller’s console;
8) maximum overall dimensions of the hydraulic station including HPU (if independent);
9) the type of bail and the size of load collar ears;
10) thread type of crossover sub;
11) clamping range of the backup clamp;
12) operating pressure of the IBOP;
13) connection thread of the IBOP;
14) outer diameter of the IBOP;
15) inner diameter of the IBOP;
16) type of traveling block (fixed or telescopic);
17) dimension and design of crown beams.
6 Functional specification
6.1 General
The TDS shall have the necessary functions, which include bearing axial load during operation, rotary driving,
mud circulation, making and breaking pipe connections, and traveling up and down along the guide rail, after
assembly of components and complete machine. Tests shall be conducted to evaluate whether the functions
can meet design requirements.
6.2 Product classification
The TDS can be classified as electric TDS and hydraulic TDS according to the type of power source rotating the
main shaft.
The TDS can be classified as reduction drive TDS and direct-drive TDS according to the transmission of main
power.
6.3 Functional components
6.3.1 Rotary power assembly
6.3.1.1 Structure and component
The rotary power assembly consists of the bail, motor, gooseneck, washpipe assembly, gearbox/load-carrying
box, braking device, bail pin, main shaft (quill)and any other sub-components that complete the system.
NOTE The reduction drive TDS rotary power assembly is shown in Figure 1Figure 1. The direct-drive TDS rotary
power assembly is shown in Figure 2Figure 2.
Key
1 bail
2 brake system
3 motor
4 gooseneck
5 washpipe assembly
6 gearbox
7 bail pin
8 main shaft (quill)
Figure 1 — Example of the reduction drive TDS rotary power assembly structure
Key
1 bail
2 gooseneck
3 washpipe assembly
4 motor
5 load-carrying box
6 bail pin
7 main shaft
Figure 2 — Example of the direct-drive TDS rotary power assembly structure
6.3.1.2 Bail
The bail connects the TDS to the rig hoisting system, bearing the total load of the top drive and drill string.
6.3.1.3 Motor
6.3.1.3.1 6.3.1.3.1 The motor provides power for rotating the drill string and can be electric motor
or hydraulic motor.
6.3.1.3.2 6.3.1.3.2 The motor may be located either at the upper part (see Figure 2Figure 2)) or
the lower part of the load--carrying box.
6.3.1.4 Brake device
6.3.1.4.1 6.3.1.4.1 The brake device functions to stop the rotation of the main shaft and withstand
reverse torque. Two braking methods can be used:
— — Disc brakes and drum brakes are two mechanical methods by which braking is achieved. In the case
of disc brakes, the braking force is applied by the brake caliper clamping onto a disc that is mounted on
the extension of the motor shaft. The braking energy is proportional to the pressure applied.
— — Electric (or electromagnetic) brake is an electrical approach in braking that is achieved by torque
produced by electromagnetic effects to stop the rotation of the motor.
—
6.3.1.4.2 6.3.1.4.2 TDS should use dynamic braking to reduce speed before applying the disc
brake/drum brake at a lower speed. The mechanical brake can also be used for emergency braking to prevent
the drill string from backing off in case of sudden power failure.
6.3.1.5 Gooseneck and washpipe assembly
Washpipe assembly's upper end is connected to gooseneck and the lower end is connected to the main shaft.
Washpipe is able to provide rotary sealing to the main shaft and circulation channel for drilling fluid.
6.3.1.6 Gearbox (Gearbox assembly)
The gearbox includes gear, main thrust bearing, main shaft transmits the power of the motor to the main shaft,
driving the drill string to rotate. It also has the functions of bearing the load and transmitting the drilling
power. The lower part of the main shaft of the gearbox is connected to the IBOP and the drill string, while the
upper part is connected to the washpipe box assembly and the gooseneck pipe, forming a circulation channel
for the drilling fluid.
6.3.1.7 Load-carrying box (direct-drive only)
The direct-drive TDS is directly driven by the direct-drive motor to rotate the main shaft and the load-carrying
box shall bear the load. The lower end is connected to the IBOP and the drill string, its upper end is connected
to the washpipe assembly and gooseneck which form the drilling fluid circulating channel. The motor may be
positioned at the upper part (see Figure 2Figure 2)) or the lower part of the load-carrying box.
6.3.2 Pipe handler system
6.3.2.1 Structure and component
The pipe handler system consists of rotating head, IBOP, link tilt mechanism, saver sub, backup clamp, grabber
leg, pipe guide. An example of structure is shown in Figure 3Figure 3.
Key
1 rotating head
2 IBOP
3 link tilt mechanism
4 tool joint locks
5 saver sub
6 backup clamp
7 grabber leg
8 pipe guide
Figure 3 — Example of the pipe handler system structure
6.3.2.2 Rotating head
The rotating head shall be equipped with rotating head link adapter on both sides for connecting to the
elevator links and elevators. The rotating head link adapter shall allow the elevator links and elevators to
rotate freely (or within a specified angle) 360° in both clockwise and counterclockwise directions around the
main shaft. It shall cooperate with the link tilt mechanism to grip singles from the mousehole or align stand
with the racking platform, as well as to position the elevator links and elevators in a specific orientation
without interfering with the drilling operation of the TDS itself.
6.3.2.3 Link tilt mechanism
The link tilt mechanism shall be capable of tilting the elevator forward and backward and shall have the
floating function.
6.3.2.4 IBOP
The IBOP connects the main shaft and the saver sub, and the internal channel of the drill string can be blocked
by closing the IBOP .
The IBOP and its safety factor shall be designed in accordance with the kelly valve specified in API Spec 7V for
the maximum drill stem load and a defined maximum static operating surface pressure.
If installed, a dual ball IBOP should also include a mud saver component.
6.3.2.5 Tool joint lock
Tool joint locks should be installed between the main shaft, IBOP, and saver sub to ensure that the threaded
connections do not become excessively tightened or loosened during drilling, make-up, or break-out
operations of the drill string connections.
6.3.2.6 Backup clamp
The backup clamp can grip the drill string subs to perform tightening or loosening operations of the drill string,
as well as grip the IBOP and saver sub to facilitate their installation and removal. The backup clamp shall be
designed with an appropriate gripping range to accommodate drill strings of different specifications.
6.3.2.7 Saver sub
Saver sub is mounted below the IBOP to protect the connection thread.
6.3.3 Counter-balance mechanism
The counter-balance mechanism is used to balance the weight of TDS body (or TDS body and the stands) to
reduce wear of threads when tightening or loosening the drill string threads. It is also adopted for reducing
shock load acting on the bail with the buffering capability.
6.3.4 Dolly and guide rail
6.3.4.1 6.3.4.1 The purpose of guide rail and dolly is to move the TDS up and down along the
mast/derrick and hold it in the correct position relative to the mast/derrick during operations and to bear
reactive drilling torque.
6.3.4.2 6.3.4.2 TDS guide rails are generally classified as single rail or double rails.
6.3.4.3 6.3.4.3 The double rails are rigidly connected to the mast/derrick over the entire
height, transmitting torque to the mast/derrick during drilling.
6.3.4.4 6.3.4.4 The upper part of the single guide rail is hinged with the crown block and the
bottom is fixed to the anti-torque beam of the mast/derrick by anti-torque device. The torque is transmitted
to the lower end of the mast/derrick during drilling.
6.3.5 Hydraulic TDS and their auxiliary control system
6.3.5.1 6.3.5.1 The hydraulic TDS comprises of both the hydraulically driven drive system and a
hydraulically driven auxiliary control system.
6.3.5.2 6.3.5.2 Hydraulically driven TDS can comprise of either a mechanical motor or an electric motor.
Both systems can drive hydraulic pumps to provide rotational speed and torque control.
6.3.5.3 6.3.5.3 Auxiliary hydraulic systems are hydraulic circuits driven by electric motor and can provide
for the following functions:
— — counter-balancing the weight of the top drive body;
— — gripping and releasing the backup clamp;
— — raising and lowering the backup clamp;
— — tilting the elevator links;
— — controlling the elevators;
— — rotating and locking of the rotating head;
— — opening and closing the IBOP;
— — braking and releasing of the main motor;
— — retracting the dolly.
6.3.6 Electric TDS and their auxiliary control system
6.3.6.1 6.3.6.1 The electric TDS comprises of electrically driven drive system and a
hydraulically driven auxiliary control system.
6.3.6.2 6.3.6.2 Electrically driven TDS comprises of a VFD/SCR and/or PLC system to provide
rotational speed and torque control.
6.3.6.3 6.3.6.3 The VFD/SCR assembly comprises the drive unit and connection accessories used to
regulate the main motor’s speed through variable frequency control. The PLC assembly includes the power
distribution, PLC, and MCC systems, along with their accessories, and performs the system’s logic control.
6.3.6.4 6.3.6.4 The auxiliary system is specified in 6.3.5.36.3.5.3.
6.3.6.5 6.3.6.5 Electrical installations shall be rated to conform with the requirements of the hazardous
areas in which they will be operating.
6.3.7 Control console
The TDS should be equipped with a driller control console, providing the basic operational functions required
for drilling. The purpose of the control console is to control the speed, torque, operating mode of TDS and
drilling conditions. The control console should have an ESD installed.
6.3.8 Casing running tool (CRT)
A CRT can be connected to the top drive sub to facilitate a more efficient casing installation. A CRT combines
the functions of a casing elevator, power tong, and fill-up/circulation tool, often without the need for manual
handling or manual tongs.
6.3.9 Transport skid
A transport skid is a skid-mounted structure that provides stable support for the TDS during transportation
and installation.
7 Design
7.1 Design requirements
7.1.1 7.1.1 The equipment shall meet all functional performance requirements defined by the user.
7.1.2 7.1.2 The equipment shall comply with all applicable regulatory and industry standards.
7.1.3 7.1.3 The design shall incorporate hazard identification and risk reduction measures.
7.1.4 7.1.4  The equipment shall be safe to install, operate, maintain, and dispose of.
7.1.5 7.1.5 The design shall minimise environmental impact across its lifecycle. The minimum operating
design temperature for TDS shall be -20 °C, unless supplementary requirement SR2 specified in API Spec
8C:2025, Annex A.3 has been applied.
7.1.6 7.1.6 The equipment shall meet defined reliability and quality performance targets.
7.1.7 7.1.7 The design shall ensure secure handling of data and configuration settings.
7.1.8 7.1.8 The design shall be verified and validated against defined acceptance criteria.
7.1.9 7.1.9 All design outputs shall be documented, controlled, and traceable.
7.2 Strength analysis
7.2.1 General
7.2.1.1 7.2.1.1 The strength analysis of TDS primary-load-carrying components shall be based
on the elastic theory. An ultimate strength (plastic) analysis should be in accordance with the requirements
specified in API Spec 8C:2025, 4.3.5. Finite-element mesh analysis, or in conjunction with analytical methods,
should be used. The analysis of rotary shouldered connection (RSCs) shall conform with API Spec 8C:2025,
4.3.8.
7.2.1.2 7.2.1.2 All forces that may govern the design shall be taken into consideration. For each
cross section to be considered, the most unfavorable combination (for example the combination of maximum
load ,, maximum torque and minimum temperature) position and direction of forces shall be used.
7.2.2 Equivalent stress
The nominal equivalent stress, according to the Von Mises-Hencky theory, caused by the rated load shall not
exceed the maximum allowable stress 𝑅𝑅 as calculated by Formula (1)Formula (1)::
max
𝑅𝑅
𝑒𝑒1
𝑅𝑅 =
max
𝑛𝑛
𝑠𝑠
(1)
where
𝑅𝑅 is the maximum allowable stress in MPa;
max
𝑅𝑅 is the specified minimum yield strength in MPa;
e1
𝑛𝑛 is the design safety factor (shall meet the requirements specified in 7.2.37.2.3).).
𝑠𝑠
7.2.3 Design safety factors for primary-load-carrying components
The design safety factor for primary load-carrying components shall be complied with ISO 13535:2000,
Table 1.
7.2.4 Shear strength
The shear strength shall conform with ISO 13535:2000, 4.8.
7.3 Type and dimension of connection
7.3.1 Dimension of bail
The connection dimensions shall conform with Table 1Table 1 and Figure 4Figure 4 when hook is required to
be connected using bail. The connection dimensions shall conform with Table 2Table 2 and Figure 5Figure 5
when bail is connected directly to travelling block.
Table 1 — Connection dimensions of bail and hook
Bail and hook contact-surface Other connection
radius dimensions
Rated load
mm mm
kN
E F d e
2,max 2,min 2,max 2,min
891 to 1 334 57,15 114,30 130 470
1 335 to 2 224 63,50 114,30 165 530
2 225 to 3 114 69,85 114,30 170 580
3 115 to 4 448 82,55 114,30 180 620
4 449 to 5 782 82,55 114,30 — —
5 783 to 6 672 101,60 114,30 — —
6 673 to 11,120 127,00 127,00 — —

Figure 4 — The connection between the bail and the hook
Table 2 — Connection dimensions of bail and travelling block
Bail and travelling block contact-surface Other connection
radius dimensions
Rated load
mm mm
kN
A B a c
2,min 2,max 2,min 2,max
891 to 1 334 69,85 76,20 310 190
1 335 to 2 224 101,60 76,20 350 250
2 225 to 3 114 101,60 76,20 350 280
3 115 to 4 448 101,60 82,55 385 320
4 449 to 5 782 101,60 82,55 — —
5 783 to 6 672 152,40 82,55 — —
6 673 to 11,120 152,40 152,40 — —
Figure 5 — The connection between the bail and the traveling block
7.3.2 Main shaft(quill), IBOP, and saver sub configuration
7.3.2.1 7.3.2.1 Remote controlled (upper) IBOP, manual (lower) IBOP, or remote-controlled
dual ball IBOP is connected to lower end of the TDS main shaft, and saver sub is connected to lower end of
IBOP. The lower end of saver sub is connected to the upper end of drill string.
7.3.2.2 7.3.2.2 The connection of the main shaft, IBOP, and saver sub is shown in
Figure 6Figure 6. The main shaft and IBOP are connected using threads, and the connection type can be
specified by user/purchaser. Figure 6Figure 6 illustrates a common thread connection method.

Key
1 main shaft(quill)
2 IBOP
3 saver sub
Figure 6 — Example for main shaft, IBOP, saver sub
7.3.3 Rotating head link adaptor dimensions
The link adaptor for rotating head shall complyconform with Figure 7Figure 7 and dimensions in
Table 3Table 3.
Figure 7 — Rotating head link adaptor
Table 3 — Dimensions of the rotating head link adaptor
Link eye and link ear contact-surface Other connection
radius dimensions
Rated load
mm mm
kN
D    C    f    g
1, min 1, max 1, min 1, max
891 to 1 334 38,10 63,50 135 115
1 335 to 2 224 44,45 101,60 150 120
Link eye and link ear contact-surface Other connection
radius dimensions
Rated load
mm mm
kN
D    C    f    g
1, min 1, max 1, min 1, max
2 225 to 3 114 44,45 101,60 150 155
3 115 to 4 448 57,15 101,60 170 155
4 449 to 5 782 57,15 101,60 — —
5 783 to 6 672 63,50 101,60 — —
6 673 to 11,120 76,20 114,30 — —
7.4 Rotary power assembly
7.4.1 Main thrust bearing
The main thrust bearing bears the axial load of the drill string. The rated load (Ws) of the rotary power
assembly's main thrust bearing shall be calculated in accordance with the formula specified in ISO
13535:2000, 9.9.1.
7.4.2 Gearbox (Gearbox assembly)
7.4.2.1 7.4.2.1 The gearbox shall be operated smoothly without any impacts. When the main
shaft runs at a no-load speed of rated speed, after the oil temperature stabilizes, the maximum temperature
shall be verified to not exceed OEM guidelines and lubricant operating envelope in expected climatic
conditions.
7.4.2.2 7.4.2.2 During normal operation of the TDS, all seals of the gearbox shall be free from
leakage.
7.4.2.3 7.4.2.3 The lubrication system shall be clean and reliable, ensuring the lubrication and
heat dissipation of the gear meshing and bearings in the gearbox. It shall be designed to prov
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