4 Recommended Practice DNV-RP-F101
April 1999
DET NORSKE VERITAS
1. General
1.1 Introduction
This document provides recommended practice for assessing
pipelines containing corrosion. Recommendations are given
for assessing corrosion defects subjected to:
1) Internal pressure loading only.
2) Internal pressure loading combined with longitudinal
compressive stresses.
This Recommended Practice (RP) document describes two
alternative approaches to the assessment of corrosion, and
the document is divided into two parts. The main difference
between the two approaches is in their safety philosophy:
− The first approach, given in Part A, is in accordance to
the safety philosophy adopted in the DNV Offshore
Standard DNV-OS-F101, Submarine Pipeline Systems
(/8/). This part of the RP is a supplement to, and
complies with, DNV-OS-F101. Uncertainties associated
with the sizing of the defect depth and the material
properties are specifically considered. Probabilistic
calibrated equations (with partial safety factors) for the
determination of the allowable operating pressure of a
corroded pipeline are given.
− The second approach, given in Part B, is based on the
ASD (Allowable Stress Design) format. The failure
pressure (capacity) of the corrosion defect is calculated,
and this failure pressure is multiplied by a single usage
factor based on the original design factor. Consideration
of the uncertainties associated with the sizing of the
corrosion defect is left to the judgement of the user.
1.2 BG plc and DNV Research Projects
This document is a result of co-operation between BG
Technology (part of BG plc) and DNV. The results from
their respective joint industry projects have been merged, and
form the technical basis for this recommended practice
(/3/,/4/ and /16/).
The BG Technology project generated a database of more
than 70 burst tests on pipes containing machined corrosion
defects (including single defects, interacting defects and
complex shaped defects), and a database of linepipe material
properties. In addition, a comprehensive database of 3D
non-linear finite element analyses of pipes containing defects
was produced. Criteria were developed for predicting the
remaining strength of corroded pipes containing single
defects, interacting defects and complex shaped defects.
The DNV project generated a database of 12 burst tests on
pipes containing machined corrosion defects, including the
influence of superimposed axial and bending loads on the
failure pressure. A comprehensive database of 3D non-linear
finite element analyses of pipes containing defects was also
produced. Probabilistic methods were utilised for code
calibration and the determination of partial safety factors.
1.3 Application
The methods provided in this document are intended to be
used on corrosion defects in carbon steel pipelines (not
applicable for other components) that have been designed to
the DNV Offshore Standard DNV-OS-F101 Submarine
Pipeline Systems, /8/,/9/ or other recognised pipeline design
code as (but not limited to) ASME B31.4 /1/, ASME B31.8
/2/, BS8010 /5/, IGE/TD/1 /10/, ISO/DIS 13623 /11/,
CSA Z662-94 /7/, provided that the safety philosophy is the
design code is not violated.
When assessing corrosion, the effect of continued corrosion
growth should be considered. If a corroded region is to be
left in service then measures should be taken to arrest further
corrosion growth, or an appropriate inspection programme
should be adopted. The implications of continuing defect
growth are outside the scope of this document.
This RP does not cover every situation that requires a fitness-
for-purpose assessment and further methods may be
required.
1.4 Structure of RP
The RP describes two alternative approaches. The first
approach is given in Part A, which consists of section 2
through 5. The second approach is given in Part B, which
consists of section 6 through 9.
A flow chart describing the assessment procedure (for both
Part A and Part B) is shown in Figure 5.
Worked examples are given in Appendix A for the methods
described in Part A. and Appendix B (for the methods
described in Part B).
1.5 Applicable Defects
The following types of corrosion defect can be assessed
using this document:
1) Internal corrosion in the base material.
2) External corrosion in the base material.
3) Corrosion in seam welds.
4) Corrosion in girth welds.
5) Colonies of interacting corrosion defects.
6) Metal loss due to grind repairs (provided that the
grinding leaves a defect with a smooth profile, and that
the removal of the original defect has been verified using
appropriate NDT methods).
When applying the methods to corrosion defects in seam
welds and girth welds, it should be demonstrated that there
are no significant weld defects present that may interact with
the corrosion defect, that the weld is not undermatched, and
that the weld has an adequate toughness.
