Differences between ISO 19902:2007 and ISO 19902:2020. Chapter 13: Strength of tubular members

SDC Verifier implements two member checks versions of ISO 19902 – Petroleum and natural gas industries – Fixed steel offshore structures from the International Organization for Standardization.

• ISO 19902 (1^st, 2007) Petroleum and natural gas industries— Fixed steel offshore structures
• ISO 19902 (2^nd, 2020) Petroleum and natural gas industries — Fixed steel offshore structures

Both standard versions provide recommendations applicable to the following types of fixed steel offshore structures for the petroleum and natural gas industries: caissons, freestanding and braced; jackets; mono towers; towers. Also, they are applicable to compliant bottom founded structures, steel gravity structures, jack-ups, other bottom founded structures and other structures related to offshore structures (such as underwater oil storage tanks, bridges and connecting structures), to the extent to which requirements are relevant.

Below are highlighted the changes between the 2007 and the 2020 version in Chapter 13 – Strength of tubular members.

13.1 General

Foremost, there are differences in yield strength requirement (increased) and diameter to thickness ratio:

	ISO 19902:2007	ISO 19902:2020
Diameter to thickness ration	D/t ≤ 120	D/t ≤ 0,2E/fy
Yield strength	fy < 500 MPa	fy ≤ 800 MPa

13.2 Tubular members subjected to tension, compression, bending, shear, torsion or hydrostatic pressure

13.2.3 Axial compression

13.2.3.1 General

Torsion is added to the list of stresses tubular members are subjected to (subclause 13.2). In the subclause devoted to axial compression (13.2.3.1) the parameter – partial resistance factor for axial compressive strength (Ɣ_R,c) decreased from 1,18 to 1,10:

	ISO 19902:2007	ISO 19902:2020
Partial resistance factor for axial compressive strength	ƔR,c =1,18	ƔR,c =1,10

13.2.3.2 Column buckling

Symbol – cross-sectional area symbol changed from A to A_r under formula 13.2-7

13.2.4 Bending

Condition for formula 13.2-15 in a bending subchapter (13.2.4) has changed

\(f_{b}=[0,94-0.76(\frac{f_{y}D}{Et})](\frac{Z_{p}}{Z_{e}})f_{y}\)

 

ISO 19902:2007	ISO 19902:2020
for 0,1034 < fyD/Et ≤ 120fy/E	for 0,1034 < fyD/Et ≤ 0,2

13.2.5 Shear

13.2.5.1 Beam shear

Symbol – A_r instead of A used (formulae 13.2-16 and 13.2-17)

3.2.5.3 Combined beam shear and torsional shear

The new subclause 13.2.5.3 Combined beam shear and torsional shear is now present in the standard ISO 19902:2020 (2nd edition), where the formulae 13.2-20 (reduced representative shear strength) and 13.2-21 (new formula for utilization of a member under beam shear) added. The utilization of the member under torsional shear unchanged – still 13.2-19:

\(f_{\nu,t}=(1-\frac{\tau_{t}}{f_{\nu}/\gamma_{R,\nu}})f_{\nu}\)	(13.2-20)
\(U_{m}=\frac{\tau_{b}}{f_{\nu}/\gamma_{R,\nu}}=\frac{2V/A}{f_{\nu}/\gamma_{R,\nu}}\)	(13.2-21)

All the following formulae numbering in chapter 13.2 (from 13.2-20 to 13.2-37) are now incremented by 2, so e.g., 13.2-20 is now 13.2-22:

13.2.6 Hydrostatic pressure

13.2.6.1 Calculation of hydrostatic pressure

Symbol – H_w instead of H (ISO 19902:2007) wave height description used in formula 13.2-21.

13.2.6.2 Hoop buckling

In Hoop buckling (13.2.6.2) formula numbering in f_h changed under formula 13.2-22:

ISO 19902:2007	ISO 19902:2020
fh is the representative hoop buckling strength, in stress units, see Equations (13.2-23) to (13.2-25)	fh is the representative hoop buckling strength, in stress units, see Formulae (13.2-25) to (13.2-27)

13.3 Tubular members subjected to combined forces without hydrostatic pressure

13.3.2 Axial tension and bending

In subclause 13.3.2 – Axial tension and bending formulae 13.3-1 and 13.3-2 changed:

ISO 19902:2007	ISO 19902:2020
\(\frac{\gamma_{R,t}\sigma_{t}}{f_{t}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\leq1.0\)	\(1-\cos(\frac{\pi}{2}\frac{\gamma_{R,t}\sigma_{t}}{f_{t}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\leq1.0\)	(13.3-1)
\(U_{m}=\frac{\gamma_{R,t}\sigma_{t}}{f_{t}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\)	\(U_{m}=1-\cos(\frac{\pi}{2}\frac{\gamma_{R,t}\sigma_{t}}{f_{t}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\)	(13.3-2)

13.3.3 Axial compression and bending

Formulae 13.3-4 and 13.3-8 changed:

ISO 19902:2007	ISO 19902:2020
\(\frac{\gamma_{R,c}\sigma_{c}}{f_{yc}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\leq1.0\)	\(1-\cos(\frac{\pi}{2}\frac{\gamma_{R,c}\sigma_{c}}{f_{yc}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\leq1.0\)	(13.3-4)
\(U_{m}=\frac{\gamma_{R,c}\sigma_{c}}{f_{yc}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\)	\(U_{m}=1-\cos(\frac{\pi}{2}\frac{\gamma_{R,c}\sigma_{c}}{f_{yc}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b}}\)	(13.3-8)

13.3.4 Axial tension or compression, bending, shear and torsion

ISO 19902:2020 has the new subclause 13.3.4 Axial tension or compression, bending, shear and torsion, which gives a list of formulae and conditions that define representative yield strength (f_y,t), representative tensile strength (f_tv), local buckling strength (f_yc,v), representative bending strength (f_bv) and Utilization (U_m)

13.4 Tubular members subjected to combined forces with hydrostatic pressure

13.4.1 General

In subclause 13.4.1 General of 13.4 Tubular members subjected to combined forces with hydrostatic pressure, the formula numbering changed in a check for hoop buckling under hydrostatic pressure alone:

ISO 19902:2007	ISO 19902:2020
Equation (13.2-22)	Formula (13.2-24)

σ_q definition (under formula 13.4-3). The compressive axial stress due to the capped-end hydrostatic actions, calculated using the value of pressure from:

ISO 19902:2007	ISO 19902:2020
Equation (13.2-20)	Formula (13.2-22)

13.4.2 Axial tension, bending and hydrostatic pressure

In 13.4.2 Axial tension, bending and hydrostatic pressure the formula 13.4-7 changed:

ISO 19902:2007	ISO 19902:2020
\(\frac{\gamma_{R,t}\sigma_{t,h}}{f_{t,h}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b,h}}\leq1.0\)	\(1-\cos(\frac{\pi}{2}\frac{\gamma_{R,t}\sigma_{t,c}}{f_{t,h}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b,h}}\leq1.0\)	(13.4-7)

 

13.4.3 Axial compression, bending and hydrostatic pressure

In 13.4.3 Axial compression, bending and hydrostatic pressure the formulae 13.4-13 and 13.4-19 changed:

ISO 19902:2007	ISO 19902:2020
\(\frac{\gamma_{R,c}\sigma_{c,c}}{f_{yc}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b,h}}\leq1.0\)	\(1-\cos(\frac{\pi}{2}\frac{\gamma_{R,c}\sigma_{c,c}}{f_{yc}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b,h}}\leq1.0\)	(13.3-1)
\(U_{m}=\frac{\gamma_{R,c}\sigma_{c,c}}{f_{yc}}+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b,h}}\)	\(U_{m}=1-\cos(\frac{\pi}{2}\frac{\gamma_{R,c}\sigma_{c,c}}{f_{yc}})+\frac{\gamma_{R,b}\sqrt{\sigma_{b,y}^{2}+\sigma_{b,z}^{2}}}{f_{b,h}}\)	(13.3-2)

13.4.4 Axial tension or compression, bending, hydrostatic pressure, shear and torsion

A new subclause 13.4.4 Axial tension or compression, bending, hydrostatic pressure, shear and torsion covers the new algorithm:

The effect of shear and torsion when combined with axial tension or compression, bending and
hydrostatic pressure should follow the approach described in 13.3.4.

Thus, the effect of torsion can be ignored if Formula (13.3-9) is satisfied and, if not, accounted for using
Formula (13.2-20) and by substituting Formula (13.3-10) into the relevant formulae in 13.4.2 and 13.4.3.
Shear can be ignored if Formula (13.3-11) is satisfied and, if not, using Formulae (13.3-12) to (13.3-17) with f_t and f_b replaced by f_t,h and f_b,h respectively

ISO 19902:2020 13.4.4

SDC Verifier Implementation

All the changes that have been shown above have already been implemented in SDC Verifier as a new standard for beam member and joint checks, based on ISO 19902:2020. SDC Verifier has a wide range of implemented industry standards for beam member and joint checks, including:

• AISC ASD 1989 Members (9th, 1989)
• AISC 360-10 Members (14th, 2010)
• API RP 2A-LRFD (1st, 1993)
• API RP 2A-WSD (21st, 2007)
• Eurocode 3 Members (EN1993-1-1, 2005)
• ISO 19902 (1st, 2007)
• ISO 19902 (2nd, 2020)
• Norsok N004 (rev.3, 2013)

You can use these standards in SDC Verifier Professional or in the dedicated Beam Member and Joint Checks App.