ISO/TR 10400:2018

Petroleum and natural gas industries - Formulae and calculations for the properties of casing, tubing, drill pipe and line pipe used as casing or tubing

This document illustrates the formulae and templates necessary to calculate the various pipe properties given in International Standards, including - pipe performance properties, such as axial strength, internal pressure resistance and collapse resistance, - minimum physical properties, - product assembly force (torque), - product test pressures, - critical product dimensions related to testing criteria, - critical dimensions of testing equipment, and - critical dimensions of test samples. For formulae related to performance properties, extensive background information is also provided regarding their development and use. Formulae presented here are intended for use with pipe manufactured in accordance with ISO 11960 or API 5CT, ISO 11961 or API 5D, and ISO 3183 or API 5L, as applicable. These formulae and templates can be extended to other pipe with due caution. Pipe cold-worked during production is included in the scope of this document (e.g. cold rotary straightened pipe). Pipe modified by cold working after production, such as expandable tubulars and coiled tubing, is beyond the scope of this document. Application of performance property formulae in this document to line pipe and other pipe is restricted to their use as casing/tubing in a well or laboratory test, and requires due caution to match the heat-treat process, straightening process, yield strength, etc., with the closest appropriate casing/tubing product. Similar caution is exercised when using the performance formulae for drill pipe. This document and the formulae contained herein relate the input pipe manufacturing parameters in ISO 11960 or API 5CT, ISO 11961 or API 5D, and ISO 3183 or API 5L to expected pipe performance. The design formulae in this document are not to be understood as a manufacturing warranty. Manufacturers are typically licensed to produce tubular products in accordance with manufacturing specifications which control the dimensions and physical properties of their product. Design formulae, on the other hand, are a reference point for users to characterize tubular performance and begin their own well design or research of pipe input properties. This document is not a design code. It only provides formulae and templates for calculating the properties of tubulars intended for use in downhole applications. This document does not provide any guidance about loads that can be encountered by tubulars or about safety margins needed for acceptable design. Users are responsible for defining appropriate design loads and selecting adequate safety factors to develop safe and efficient designs. The design loads and safety factors will likely be selected based on historical practice, local regulatory requirements, and specific well conditions. All formulae and listed values for performance properties in this document assume a benign environment and material properties conforming to ISO 11960 or API 5CT, ISO 11961 or API 5D and ISO 3183 or API 5L. Other environments can require additional analyses, such as that outlined in Annex D. Pipe performance properties under dynamic loads and pipe connection sealing resistance are excluded from the scope of this document. Throughout this document tensile stresses are positive.

Industries du pétrole et du gaz naturel — Formules et calculs relatifs aux propriétés des tubes de cuvelage, des tubes de production, des tiges de forage et des tubes de conduites utilisés comme tubes de cuvelage et tubes de production

General Information

• Status: Published
• Publication Date: 30-Aug-2018
• ICS: 75.180.10 - Exploratory, drilling and extraction equipment
• Technical Committee: ISO/TC 67/SC 5 - Casing, tubing and drill pipe
• Drafting Committee: ISO/TC 67/SC 5/WG 2 - Casing and tubing connections and performance properties
• Current Stage: 6060 - International Standard published
• Start Date: 31-Aug-2018
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 5362:2024 - Anaesthetic and respiratory equipment – Anaesthetic reservoir bags
• Effective Date: 06-Jun-2022
• Revises: ISO/TR 10400:2007 - Petroleum and natural gas industries - Equations and calculations for the properties of casing, tubing, drill pipe and line pipe used as casing or tubing
• Effective Date: 20-Jan-2018

Overview

ISO/TR 10400:2018 - "Petroleum and natural gas industries - Formulae and calculations for the properties of casing, tubing, drill pipe and line pipe used as casing or tubing" - provides a comprehensive collection of formulae and calculation templates for predicting pipe and tubular performance. The technical report links manufacturing input parameters (from ISO/API manufacturing specifications) to expected pipe properties such as axial strength, internal pressure resistance, collapse resistance, and other critical dimensions used in testing.

This document is a calculation and reference resource, not a design code or manufacturing warranty. It assumes benign environments and pipe material/process characteristics conforming to ISO 11960 / API 5CT, ISO 11961 / API 5D, and ISO 3183 / API 5L, and it excludes pipe modified by post‑production cold working (e.g., expandable tubulars, coiled tubing).

Key Topics

• Performance property formulae: axial (tensile) strength, triaxial yield, ductile rupture, burst strength and collapse (external pressure) resistance.
• Joint and coupling performance: tensile joint strength and internal pressure/leak resistance for common coupling and connection types.
• Test‑related dimensions and pressures: templates for product test pressures, critical sample and equipment dimensions, and flattening tests.
• Mass and geometry calculations: nominal and finished‑end masses, mass removed during threading, upset mass, and threaded/coupled masses.
• Assumptions, limitations and data requirements: concentric circular cross‑section, isotropic yield, no residual stress, and guidance on applicability to line pipe and drill pipe when used as casing/tubing.
• Scope boundaries: excludes dynamic loading behavior and connection sealing resistance; advises caution when extending formulae to other pipe types or environments (see Annex D for additional analyses).

Applications / Who Uses It

• Well and completion engineers calculating allowable loads, collapse margins, burst capacity, and material selection for casing and tubing.
• Pipe manufacturers and quality engineers verifying that manufacturing inputs align with expected performance properties.
• Test laboratories preparing test samples, specifying test pressures and equipment dimensions.
• Researchers and standards committees who need standardized calculation methods for tubular performance assessments.
• Regulators and operators seeking consistent reference methods for tubular property estimation.

Related Standards

• ISO 11960 / API 5CT (casing and tubing manufacture)
• ISO 11961 / API 5D (drill pipe)
• ISO 3183 / API 5L (line pipe, where applicable)
• Annex D (ISO/TR 10400) - recommended additional analysis for non‑benign environments

Keywords: ISO TR 10400:2018, casing, tubing, drill pipe, line pipe, collapse pressure, axial strength, ductile rupture, tubular pipe properties, pipe performance calculation.

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 10400
Second edition
2018-08
Petroleum and natural gas
industries — Formulae and
calculations for the properties of
casing, tubing, drill pipe and line pipe
used as casing or tubing
Industries du pétrole et du gaz naturel — Formules et calculs relatifs
aux propriétés des tubes de cuvelage, des tubes de production, des
tiges de forage et des tubes de conduites utilisés comme tubes de
cuvelage et tubes de production
Reference number
©
ISO 2018
© ISO 2018
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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Symbols . 4
5 Conformance .13
5.1 References .13
5.2 Units of measurement . .13
6 Triaxial yield of pipe body .13
6.1 General .13
6.2 Assumptions and limitations .13
6.2.1 General.13
6.2.2 Concentric, circular cross-sectional geometry .14
6.2.3 Isotropic yield . .14
6.2.4 No residual stress .14
6.2.5 Cross-sectional instability (collapse) and axial instability (column buckling) .14
6.3 Data requirements .14
6.4 Design formula for triaxial yield of pipe body .14
6.5 Application of design formula for triaxial yield of pipe body to line pipe .16
6.6 Example calculations .16
6.6.1 Initial yield of pipe body, Lamé formula for pipe when external pressure,
bending and torsion are zero .16
6.6.2 Yield design formula, special case for thin wall pipe with internal pressure
only and zero axial load .18
6.6.3 Pipe body yield strength .18
6.6.4 Yield in the absence of bending and torsion .19
7 Ductile rupture of the pipe body .20
7.1 General .20
7.2 Assumptions and limitations .20
7.3 Data requirements .21
7.3.1 General.21
7.3.2 Determination of the hardening index.21
7.3.3 Determination of the burst strength factor, k .
a 22
7.4 Design formula for capped-end ductile rupture .23
7.5 Adjustment for the effect of axial force and external pressure .24
7.5.1 General.24
7.5.2 Design formula for ductile rupture under combined loads .25
7.5.3 Design formula for ductile necking under combined loads .26
7.5.4 Boundary between rupture and necking .27
7.5.5 Axisymmetric wrinkling under combined loads .27
7.6 Example calculations .28
7.6.1 Ductile rupture of an end-capped pipe .28
7.6.2 Ductile rupture for a given true axial load .28
8 External pressure resistance .29
8.1 General .29
8.2 Assumptions and limitations .29
8.3 Data requirements .29
8.4 Design formula for collapse of pipe body .30
8.4.1 General.30
8.4.2 Yield strength collapse pressure formula .30
8.4.3 Plastic collapse pressure formula .31
8.4.4 Transition collapse pressure formula .33
8.4.5 Elastic collapse pressure formula .34
8.4.6 Collapse pressure under axial tensile stress .35
8.4.7 Collapse pressure under axial stress and internal pressure .35
8.5 Formulae for empirical constants .35
8.5.1 General.35
8.5.2 SI units .36
8.5.3 USC units .36
8.6 Application of collapse pressure formulae to line pipe .37
8.7 Example calculations .37
9 Joint strength .37
9.1 General .37
9.2 API casing connection tensile joint strength .37
9.2.1 General.37
9.2.2 Round thread casing joint strength .38
9.2.3 Buttress thread casing joint strength.40
9.3 API tubing connection tensile joint strength .42
9.3.1 General.42
9.3.2 Non-upset tubing joint strength .42
9.3.3 Upset tubing joint strength .43
9.4 Line pipe connection joint strength .44
10 Pressure performance for couplings .44
10.1 General .44
10.2 Internal yield pressure of round thread and buttress couplings .44
10.3 Internal pressure leak resistance of round thread or buttress couplings .45
11 Calculated masses .48
11.1 General .48
11.2 Nominal linear masses .48
11.3 Calculated plain-end mass .48
11.4 Calculated finished-end mass.49
11.5 Calculated threaded and coupled mass .49
11.5.1 General.49
11.5.2 Direct calculation of e , threaded and coupled pipe .50
m
11.6 Calculated upset and threaded mass for integral joint tubing .50
11.6.1 General.50
11.6.2 Direct calculation of e , upset and threaded pipe .51
m
11.7 Calculated upset mass .51
11.7.1 General.51
11.7.2 Direct calculation of e , upset pipe .52
m
11.8 Calculated coupling mass .52
11.8.1 General.52
11.8.2 Calculated coupling mass for line pipe and round thread casing and tubing .52
11.8.3 Calculated coupling mass for buttress thread casing .55
11.9 Calculated mass removed during threading .56
11.9.1 General.56
11.9.2 Calculated mass removed during threading pipe or pin ends .56
11.9.3 Calculated mass removed during threading integral joint tubing box ends .58
11.10 Calculated mass of upsets .59
11.10.1 General.59
11.10.2 Calculated mass of external upsets .59
11.10.3 Calculated mass of internal upsets .60
11.10.4 Calculated mass of external-internal upsets .61
12 Elongation .61
13 Flattening tests .62
13.1 Flattening tests for casing and tubing .62
iv © ISO 2018 – All rights reserved

13.2 Flattening tests for line pipe.62
14 Hydrostatic test pressures .63
14.1 Hydrostatic test pressures for plain-end pipe and integral joint tubing .63
14.2 Hydrostatic test pressure for threaded and coupled pipe .64
15 Make-up torque for round thread casing and tubing .64
16 Guided bend tests for submerged arc-welded line pipe.65
16.1 General .65
16.2 Background .67
16.2.1 Values of ε .67
eng
16.2.2 Values of A .67
gbtj
17 Determination of minimum impact specimen size for API couplings and pipe .67
17.1 Critical thickness .67
17.2 Calculated coupling blank thickness .68
17.3 Calculated wall thickness for transverse specimens .71
17.4 Calculated wall thickness for longitudinal specimens .71
17.5 Minimum specimen size for API couplings .71
17.6 Impact specimen size for pipe .73
17.7 Larger size specimens .73
17.8 Reference information .74
Annex A (informative) Discussion of formulae for triaxial yield of pipe body .75
Annex B (informative) Discussion of formulae for ductile rupture .88
Annex C (informative) Rupture test procedure .126
Annex D (informative) Discussion of formulae for fracture .128
Annex E (informative) Discussion of historical collapse formulae .135
Annex F (informative) Development of probabilistic collapse performance properties.149
Annex G (informative) Calculation of design collapse strength from collapse test data .188
Annex H (informative) Calculation of design collapse strengths from production quality data.191
Annex I (informative) Collapse test procedure .205
Annex J (informative) Discussion of formulae for joint strength .211
Annex K (informative) Tables of calculated performance properties in SI units .219
Annex L (informative) Tables of calculated performance properties in USC units .221
Bibliography .223
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 67, Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 5, Casing, tubing
and drill pipe.
This second edition cancels and replaces the first edition (ISO/TR 10400:2007), which has been
technically revised.
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 © ISO 2018 – All rights reserved

Introduction
Performance design of tubulars for the petroleum and natural gas industries, whether it is formulated
by deterministic or probabilistic calculations, compares anticipated loads to which the tubular can
be subjected to the anticipated resistance of the tubular to each load. Either or both of the load and
resistance can be modified by a design factor.
Both deterministic and probabilistic approaches to performance properties are addressed in this
document. The deterministic approach uses specific geometric and material property values to calculate
a single performance property value. The probabilistic method treats the same variables as random
and thus arrives at a statistical distribution of a performance property. A performance distribution in
combination with a defined lower percentile determines the final design formula.
Both the well design process itself and the definition of anticipated loads are currently outside the scope
of standardization for the petroleum and natural gas industries. Neither of these aspects is addressed
in this document. Rather, it serves to identify useful formulae for obtaining the resistance of a tubular
to specified loads, independent of their origin. It provides limit state formulae (see annexes) which are
useful for determining the resistance of an individual sample whose geometric and material properties
are given, and design formulae which are useful for well design based on conservative geometric and
material parameters.
Whenever possible, decisions on specific constants to use in a design formula are left to the discretion
of the reader.
TECHNICAL REPORT ISO/TR 10400:2018(E)
Petroleum and natural gas industries — Formulae and
calculations for the properties of casing, tubing, drill pipe
and line pipe used as casing or tubing
1 Scope
This document illustrates the formulae and templates necessary to calculate the various pipe properties
given in International Standards, including
— pipe performance properties, such as axial strength, internal pressure resistance and collapse
resistance,
— minimum physical properties,
— product assembly force (torque),
— product test pressures,
— critical product dimensions related to testing criteria,
— critical dimensions of testing equipment, and
— critical dimensions of test samples.
For formulae related to performance properties, extensive background information is also provided
regarding their development and use.
Formulae presented here are intended for use with pipe manufactured in accordance with ISO 11960 or
API 5CT, ISO 11961 or API 5D, and ISO 3183 or API 5L, as applicable. These formulae and templates can
be extended to other pipe with due caution. Pipe cold-worked during production is included in the scope
of this document (e.g. cold rotary straightened pipe). Pipe modified by cold working after production,
such as expandable tubulars and coiled tubing, is beyond the scope of this document.
Application of performance property formulae in this document to line pipe and other pipe is restricted
to their use as casing/tubing in a well or laboratory test, and requires due caution to match the heat-
treat process, straightening process, yield strength, etc., with the closest appropriate casing/tubing
product. Similar caution is exercised when using the performance formulae for drill pipe.
This document and the formulae contained herein relate the input pipe manufacturing parameters in
ISO 11960 or API 5CT, ISO 11961 or API 5D, and ISO 3183 or API 5L to expected pipe performance. The
design formulae in this document are not to be understood as a manufacturing warranty. Manufacturers
are typically licensed to produce tubular products in accordance with manufacturing specifications
which control the dimensions and physical properties of their product. Design formulae, on the other
hand, are a reference point for users to characterize tubular performance and begin their own well
design or research of pipe input properties.
This document is not a design code. It only provides formulae and templates for calculating the
properties of tubulars intended for use in downhole applications. This document does not provide
any guidance about loads that can be encountered by tubulars or about safety margins needed for
acceptable design. Users are responsible for defining appropriate design loads and selecting adequate
safety factors to develop safe and efficient designs. The design loads and safety factors will likely be
selected based on historical practice, local regulatory requirements, and specific well conditions.
All formulae and listed values for performance properties in this document assume a benign
environment and material properties conforming to ISO 11960 or API 5CT, ISO 11961 or API 5D and
ISO 3183 or API 5L. Other environments can require additional analyses, such as that outlined in
Annex D.
Pipe performance properties under dynamic loads and pipe connection sealing resistance are excluded
from the scope of this document.
Throughout this document tensile stresses are positive.
2 Normative references
There are no normative references in this document.
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
Cauchy stress
true stress
force applied to the surface of a body divided by the current area of that surface
3.2
coefficient of variance
dimensionless measure of the dispersion of a random variable, calculated by dividing the standard
deviation by the mean
3.3
design formula
formula which, based on production measurements or specifications, provides a performance property
useful in design calculations
Note 1 to entry: A design formula can be defined by applying reasonable extremes to the variables in a limit
state formula to arrive at a conservative value of expected performance. When statistically derived, the design
formula corresponds to a defined lower percentile of the resistance probability distribution curve.
3.4
deterministic
approach which assumes all variables controlling a performance property are known with certainty
Note 1 to entry: Pipe performance properties generally depend on one or more controlling parameters. A
deterministic formula uses specific geometric and material property values to calculate a single performance
property value. For design formulations, this value is the expected minimum.
3.5
ductile rupture
failure of a tube due to internal pressure and/or axial force in the plastic deformation range
3.6
e
Euler's constant
2,718 281 828
2 © ISO 2018 – All rights reserved

3.7
effective axial force
material axial force (pipe wall axial stress times cross-sectional area) adjusted for the effect of internal
and external pressure
Note 1 to entry: When a tubular is bent laterally into a circular arc, the pressures apply a lateral uniform
2 2
distributed load (UDL) of (p A − p A )/R. For small deflections, the curvature is defined as 1/R ≅ d y/dx , thus,
i i o o
2 2
this term can be grouped with the tension term F d y/dx in the governing differential formula. For bending and
[141]
buckling, the tubular therefore acts as if it were loaded by the effective axial force F = F − p A + p A . It
eff a i i o o
should be seen as a convenient grouping of terms, which determines the structural response: it does not exist as
a physical axial force.
3.8
engineering strain
dimensionless measure of the stretch of a deforming line element, defined as the change in length of the
line element divided by its original length
3.9
engineering stress
force applied to the surface of a body divided by the original area of that surface
3.10
fracture pressure
internal pressure at which a tube fails due to propagation of an imperfection
3.11
inspection threshold
maximum size of a crack-like imperfection which is defined to be acceptable by the inspection system
3.12
J-integral
measure of the intensity of the stress-strain field near the tip of a crack
3.13
label 1
dimensionless designation for the size or specified outside diameter that may be used when ordering pipe
3.14
label 2
dimensionless designation for the mass per unit length or wall thickness that may be used when
ordering pipe
3.15
limit state formula
formula which, when used with the measured geometry and material properties of a sample, produces
an estimate of the failure value of that sample
Note 1 to entry: A limit state formula describes the performance of an individual sample as closely as possible,
without regard for the tolerances to which the sample was built.
3.16
logarithmic strain
dimensionless measure of the stretch of a deforming line element, defined as the natural logarithm of
the ratio of the current length of the line element to its original length
Note 1 to entry: Alternatively, the logarithmic strain can be estimated as the natural logarithm of one plus the
engineering strain.
3.17
mass
label used to represent wall thickness of tube cross section for a given pipe size
3.18
pipe body yield
stress state necessary to initiate yield at any location in the pipe body
3.19
principal stress
stress on a principal plane for which the shear stress is zero
Note 1 to entry: For any general state of stress at any point, there exist three mutually perpendicular planes at
that point on which shearing stresses are zero. The remaining normal stress components on these three planes
are principal stresses. The largest of these three stresses is called the maximum principal stress.
3.20
probabilistic method
approach which uses distributions of geometric and material property values to calculate a distribution
of performance property values
3.21
synthesis method
probability approach which addresses the uncertainty and likely values of pipe performance properties
by using distributions of geometric and material property values
Note 1 to entry: These distributions are combined with a limit state formula to determine the statistical
distribution of a performance property. The performance distribution in combination with a defined lower
percentile determines the final design formula.
3.22
template
procedural guide consisting of formulae, test methods and measurements for establishing design
performance properties
3.23
TPI
threads per inch
Note 1 to entry: 1 thread per inch = 0,039 4 threads per millimetre; 1 thread per millimetre = 25,4 threads per inch.
3.24
true stress-strain curve
plot of Cauchy stress (ordinate) versus logarithmic strain (abscissa)
3.25
yield
permanent, inelastic deformation
3.26
yield stress bias
ratio of actual yield stress to specified minimum yield stress
4 Symbols
A hand-tight standoff, turns
A empirical constant in historical API collapse formula
c
A area of the weaker connection component at the critical cross section
crit
A critical dimension on guided bend test jig, denoted as dimension A in ISO 3183 or API 5L
gbtj
A area to pipe inside diameter; A = πd /4
i i
4 © ISO 2018 – All rights reserved

2 2
A area of the coupling cross section; A = π/4 (W − d )
jc jc 1
A area of the pipe cross section under the last perfect thread
jp
A area to pipe outside diameter; A = πD /4
o o
A area of the pipe cross section; A = A − A
p p o i
2 2
A average area of the pipe cross section; A ave = π/4 [D − (D e − 2 t ) ]
p ave p ave av c ave
A cross-sectional area of the tensile test specimen in square millimetres (square inches),
s
based on specified outside diameter or nominal specimen width and specified wall thick-
2 2 2 2
ness, rounded to the nearest 10 mm (0.01 in ), or 490 mm (0.75 in ) whichever is smaller
a for a limit state formula, the maximum actual depth of a crack-like imperfection; for a
design formula, the maximum depth of a crack-like imperfection that could likely pass the
manufacturer’s inspection system
a imperfection depth associated with a specified inspection threshold, i.e. the maximum
N
depth of a crack-like imperfection that could reasonably be missed by the pipe inspection
system. For example, for a 5 % imperfection threshold inspection in a 12,7 mm (0.500 in)
wall thickness pipe, a = 0,635 mm (0.025 in)
N
a average value of t/D ratios used in the regression
t/D
B empirical constant in historical API collapse formula
c
B maximum bearing face diameter, special bevel, in accordance with ISO 11960 or API 5CT
f
b Weibull shape parameter
C empirical constant in historical API collapse formula
c
C random variable that represents model uncertainty
iR
c tube curvature, the inverse of the radius of curvature to the centreline of the pipe
D specified pipe outside diameter
D average outside diameter after cutting
ac
D average pipe outside diameter
ave
D average outside diameter before cutting
bc
D maximum pipe outside diameter
max
D minimum pipe outside diameter
min
D major diameter, in accordance with API 5B
d pipe inside diameter, d = D − 2t
d inside diameter of pin upset, in accordance with ISO 11960 or API 5CT
iu
d inside diameter at end of upset pipe
ou
d inside diameter based on k t; d = D − 2k t
wall wall wall wall
d1 diameter at the root of the coupling thread at the end of the pipe in the power-tight position
E Young’s modulus
E pitch diameter, at centre of coupling
c
E pitch diameter, at end of coupling
ec
E pitch diameter, at plane of seal
s
E pitch diameter, at end of pipe
E pitch diameter at the hand-tight plane, in accordance with API 5B
E pitch diameter, in accordance with API 5B
ec eccentricity
e mass gain due to end finishing
m
F material axial force
a
F effective axial force; Feff = Fa − pi Ai + po Ao
eff
F empirical constant in historical API collapse formula
c
F material axial force at yield, historical API formula
YAPI
f degrees of freedom = N − 1
t
 
joint probability density function of the variables in x
fx
()
f root truncation of the pipe thread of API line pipe threads, as follows:
rn
0,030 mm (0.001 2 in) for 27 TPI;
0,046 mm (0.001 8 in) for 18 TPI;
0,061 mm (0.002 4 in) for 14 TPI;
0,074 mm (0.002 9 in) for 11-1/2 TPI;
0,104 mm (0.004 1 in) for 8 TPI
f tensile strength of a representative tensile specimen
u
f tensile strength of a representative tensile specimen from the coupling
uc
f specified minimum tensile strength
umn
f specified minimum tensile strength of the coupling
umnc
f specified minimum tensile strength of the pipe body
umnp
f tensile strength of a representative tensile specimen from the pipe body
up
f yield strength of a representative tensile specimen
y
f equivalent yield strength in the presence of axial stress
yax
f equivalent yield stress in the presence of axial stress
ye
f specified minimum yield strength
ymn
f specified minimum yield strength of the coupling
ymnc
f specified minimum yield strength of the pipe body
ymnp
6 © ISO 2018 – All rights reserved

f specified maximum yield strength
ymx
f yield strength of a representative tensile specimen from the pipe body
yp
G empirical constant in historical API collapse formula
c
G influence coefficient for fracture limit state FAD curve
G influence coefficient for fracture limit state FAD curve
G influence coefficient for fracture limit state FAD curve
G influence coefficient for fracture limit state FAD curve
G influence coefficient for fracture limit state FAD curve
g length of imperfect threads, in accordance with API 5B

limit state function
gx
()
H thread height of a round-thread equivalent Vee thread, as follows:
0,815 mm (0.032 1 in) for 27 TPI,
1,222 mm (0.048 1 in) for 18 TPI,
1,755 mm (0.069 1 in) for 14 TPI,
1,913 mm (0.075 3 in) for 11-1/2 TPI,
2,199 6 mm (0.086 60 in) for 10 TPI,
2,749 6 mm (0.108 25 in) for 8 TPI
Ht decrement factor for design collapse strength, as given in Table F.9
des
Ht a decrement factor for ultimate collapse strength, as defined in Formula (F.4)
ult
h buttress thread height: 1,575 for SI units, 0.062 for USC units
B
h stress-strain curve shape factor
n
h round thread height
s
4 4
I moment of inertia of the pipe cross section; I = π/64 (D − d )
4 4
I average moment of inertia of the pipe cross section; I = π/64 [D − (D − 2 t ) ]
ave ave ave c ave
I length from the face of the buttress thread coupling t
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