The electronic pdf versions of the documents found through http://www.dnv.com/ are the officially binding versions. Copyright Det Norske Veritas.
![[Table of Contents]](/dwicons/b_toc.gif)
|
DNV-OS-F101 Submarine Pipeline Systems
|
SECTION 3
Concept Development and Design PremisesSec.3
A. General
Sec.3
A 100 Objective
Sec.3 A
101 This section identifies and provides a basis for definition of
relevant field development characteristics. Further, key issues
required for design, construction, operation, and abandonment of
the pipeline system are identified.Sec.3
A 200 Application
Sec.3 A
201 This section applies to all pipeline systems which are to be
built according to this standard.
Sec.3 A
202 The design premises outlined in this section should be developed
during the conceptual phase.Sec.3
A 300 Concept development
Sec.3 A
301 When selecting the pipeline system concept all aspects related
to design, construction, operation and abandonment should be considered.
Due account should be given to identification of potential aspects
which can stop the concept from being realised:
| — | long lead effects of early stage
decisions (e.g. choice of material grade may affect manufacturing
aspects of linepipe, choice of diameter may give restrictions to
installation methods etc.) |
| — | life cycle evaluations (e.g. maintenance activities
etc.) |
| — | installation aspects for remote areas (e.g. non-availability of
major installation equipment or services and weather issues). |
Sec.3 A
302 Data and description of field development and general arrangement
of the pipeline system should be established.
Sec.3 A
303 The data and description should include the following, as
applicable:| — | safety objective |
| — | environmental objective |
| — | location, inlet and outlet conditions |
| — | pipeline system description with general arrangement
and battery limits |
| — | functional requirements including field development restrictions,
e.g., safety barriers and subsea valves |
| — | installation, repair and replacement of pipeline elements, valves,
actuators and fittings |
| — | project plans and schedule, including planned period
of the year for installation |
| — | design life including specification for start of design
life, e.g. final commissioning, installation etc. |
| — | data of product to be transported including possible changes
during the pipeline system's design life |
| — | transport capacity and flow assurance |
| — | pressure protection system requirements including process system
layout and incidental to design pressure ratio evaluations |
| — | pipeline sizing data |
| — | attention to possible code breaks in the pipeline system |
| — | geometrical restrictions such as specifications of constant internal
diameter, requirement for fittings, valves, flanges and the use
of flexible pipe or risers |
| — | relevant pigging scenarios (inspection and cleaning) |
| — | pigging fluids to be used and handling of pigging fluids
in both ends of pipeline including impact on process systems |
| — | pigging requirements such as bend radius, pipe ovality
and distances between various fittings affecting design for pigging
applications |
| — | sand production |
| — | second and third party activities |
| — | restricted access for installation or other activities
due to presence of ice. |
Sec.3 A
304 An execution plan should be developed, including the following
topics:| — | general information, including
project organisation, scope of work, interfaces and project development
phases |
| — | contacts with Purchaser, authorities, third party, engineering,
verification and construction Contractors |
| — | legal aspects, e.g. insurance, contracts, area planning, requirements
to vessels. |
Sec.3 A
305 The design and planning for the submarine pipeline system
should cover all development phases including construction, operation
and abandonment.Sec.3
B. System Design Principles
Sec.3
B 100 System integrity
Sec.3 B
101 The pipeline system shall be designed, constructed and operated
in such a manner that:| — | the specified transport capacity
is fulfilled and the flow assured |
| — | the defined safety objective is fulfilled and the resistance against
loads during planned operational conditions is sufficient |
| — | the safety margin against accidental loads or unplanned operational
conditions is sufficient. |
Sec.3 B
102 The possibility of changes in the type or composition of fluid
to be transported during the lifetime of the pipeline system shall
be assessed at the design phase.
Sec.3 B
103 Any re-qualification deemed necessary due to changes in the
design conditions shall take place in accordance with provisions
set out in Sec.11.Sec.3
B 200 Monitoring/inspection
during operation
Sec.3 B
201 Parameters which could violate the integrity of a pipeline
system shall be monitored, inspected and evaluated with a frequency
which enables remedial actions to be carried out before the system
is damaged, see Sec.11.Guidance note:
As a minimum the monitoring/inspection frequency
should be such that the pipeline system will not be endangered due
to any realistic degradation/deterioration that may occur
between two consecutive inspection intervals.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3 B
202 Special focus shall be on monitoring and inspection strategies
for "live pipeline systems" i.e. pipeline systems
that are designed to change the configuration during its design
life.Guidance note:
Example of such systems may be pipelines that are designed
to experience global buckling or possible free-span developments---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3 B
203 Instrumentation of the pipeline system may be required when
visual inspection or simple measurements are not considered practical
or reliable, and available design methods and previous experience
are not sufficient for a reliable prediction of the performance
of the system.
Sec.3 B
204 The need for in-line cleaning and/or inspection,
involving the presence of appropriate pig launcher / receiver
should be determined in the design phase.Sec.3
B 300 Pressure Protection System
Sec.3 B
301 A pressure protection system shall be used unless the pressure
source to the pipeline system cannot deliver a pressure in excess
of the incidental pressure including possible dynamic effects. The
pressure protection system shall prevent the internal pressure at
any point in the pipeline system rising to an excessive level. The
pressure protection system comprises the pressure control system,
pressure safety system and associated instrumentation and alarm
systems.Guidance note:
An example of situations where a pressure protection system
is not required is if full shut-in pressure including dynamic effects, is
used as incidental pressure.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3 B
302 The purpose of the pressure control system is to maintain
the operating pressure within acceptable limits during normal operation
i.e. to ensure that the local design pressure is not exceeded at
any point in the pipeline system during normal operation. The pressure
control system should operate automatically. The local design pressure
is defined in Sec.4 B200. Due account
shall be given to the tolerances of the pressure control system
and its associated instrumentation, see Figure
1 in Sec.1. Hence, the maximum allowable operating pressure (MAOP)
is equal to the design pressure minus the pressure control system
operating tolerance.
Sec.3 B
303 The purpose of the pressure safety system is to protect the
downstream system during incidental operation, i.e. to ensure that
the local incidental pressure is not exceeded at any point in the
pipeline system in the event of failure of the pressure control
system. The pressure safety system shall operate automatically.
Due account shall be given to the tolerances of the pressure safety
system. Hence, the maximum allowable incidental pressure is equal
to the incidental pressure minus the pressure safety system operating
tolerance.
Sec.3 B
304 The incidental pressure shall have an annual probability of
exceedance less than 10-2.
If the pressure probability density function does not have a monotonic
decay beyond 10-2 then pressure
exceeding the incidental pressure shall be checked as accidental
loads in compliance with Sec.5 D1200.
Examples of pressure probability density distributions are given
in Figure 1 and Figure 2. See also Sec.4
B200 for definition of the incidental pressure.Guidance note:
When the submarine pipeline system is connected to another
system with different pressure definition the pressure values may
be different in order to comply with the requirements of this sub-section,
i.e. the design pressure may be different in two connected systems.
The conversion between the two system definitions will often then
be based on that the incidental pressures are equal.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Fig. 1 Typical maximum pressure distribution - monotonic
decay
Fig. 2 Schematic illustration of maximum pressure distribution for
high integrity pressure protection systems (HIPPS)
Sec.3 B
305 For the conditions given in Table 3-1, the given incidental
to design ratios shall be used. The incidental to design pressure
ratio shall be selected in order to meet the requirements in 302,
303 and 304.
Sec.3 B
| Table 3-1 Incidental
to design pressure ratios |
| Condition or pipeline system | g inc |
| Typical pipeline system | 1.10 |
| Minimum, except for below | 1.05 |
| When design pressure is equal to full
shut-in pressure including dynamic effects | 1.00 |
| System pressure test | 1.00 |
Sec.3 B
306 The pipeline system may be divided into sections with different
design pressures provided that the pressure protection system ensures
that, for each section, the local design pressure cannot be exceeded
during normal operations and that the incidental pressure cannot
be exceeded during incidental operation.Sec.3
B 400 Hydraulic analyses and flow assurance
Sec.3 B
401 The hydraulics of the pipeline system should be analysed to
demonstrate that the pipeline system can safely transport the fluids,
and to identify and determine the constraints and requirements for
its operation. This analysis should cover steady-state and transient
operating conditions.Guidance note:
Examples of constraints and operational requirements are allowances
for pressure surges, prevention of blockage such as caused by the
formation of hydrates and wax deposition, measures to prevent unacceptable
pressure losses from higher viscosities at lower operation temperatures,
measures for the control of liquid slug volumes in multi-phase fluid
transport, flow regime for internal corrosion control erosional
velocities and avoidance of slack line operations. It also includes
requirements to insulation, maximum shut-down times, requirements
for heating etc.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3 B
402 The hydraulics of the pipeline system shall be analysed to
demonstrate that the pressure control system and pressure safety
system meet its requirement during start-up, normal operation, shut-down
(e.g. closing of valves) and all foreseen non-intended scenarios.
This shall also include determination of required incidental to
design pressure ratio.
Sec.3 B
403 The hydraulic analyses shall be used to determine the maximum
design temperature profile based on conservative insulation values
reflecting the variation in insulation properties of coatings and
surrounding seawater, soil and gravel.
Sec.3 B
404 The hydraulic analyses shall be used to determine the minimum
design temperature. Benefit of specifying low temperatures locally
due to e.g. opening of valves is allowed and shall be documented
e.g. by hydraulic analyses.
Sec.3
C. Pipeline Route
Sec.3
C 100 Location
Sec.3 C
101 The pipeline route shall be selected with due regard to safety
of the public and personnel, protection of the environment, and
the probability of damage to the pipe or other facilities. Agreement
with relevant parties should be sought as early as possible. Factors
to take into consideration shall, at minimum, include the following:Environment
| — | archaeological sites |
| — | exposure to environmental damage |
| — | areas of natural conservation interest including oyster
beds and corral reefs |
| — | marine parks |
| — | turbidity flows. |
Seabed characteristics
| — | uneven seabed |
| — | unstable seabed |
| — | soil properties (hard spots, soft sediment and sediment transport) |
| — | subsidence |
| — | seismic activity. |
Facilities
| — | offshore installations |
| — | subsea structures and well heads |
| — | existing pipelines and cables |
| — | obstructions |
| — | coastal protection works. |
Third party activities
| — | ship traffic |
| — | fishing activity |
| — | dumping areas for waste, ammunition, etc. |
| — | mining activities |
| — | military exercise areas. |
Landfall
| — | local constraints |
| — | 3rd party requirements |
| — | environmental sensitive areas |
| — | vicinity to people |
| — | limited construction period. |
Sec.3 C
102 Expected future marine operations and anticipated developments
in the vicinity of the pipeline shall be considered when selecting
the pipeline route.
Sec.3 C
103 Pipeline components (e.g. valves, tees) in particular should
not be located on the curved route sections of the pipeline.
Sec.3 C
104 It is recommended that pipeline ends are designed with a reasonable
straight length ahead of the target boxes. Curvatures near pipeline
ends should be designed with due regard to end terminations, lay
method, lay direction and existing/planned infrastructure.Sec.3
C 200 Route survey
Sec.3 C
201 Surveys shall be carried out along the total length of the planned
pipeline route to provide sufficient data for design and installation
related activities.
Sec.3 C
202 The survey corridor shall have sufficient width to define an
installation and pipeline corridor which will ensure safe installation
and operation of the pipeline.
Sec.3 C
203 The required survey accuracy may vary along the proposed route.
Obstructions, highly varied seabed topography, or unusually or hazardous
sub-surface conditions may dictate more detailed investigations.
Sec.3 C
204 Investigations to identify possible conflicts with existing and
planned installations and possible wrecks and obstructions shall
be performed. Examples of such installations include other submarine
pipelines, and power and communication cables.
Sec.3 C
205 The results of surveys shall be presented on accurate route
maps and alignments, scale commensurate with required use. Location
of the pipeline, related facilities together with seabed properties,
anomalies and all relevant pipeline attributes shall be shown. Reference
seawater elevation shall be defined.
Sec.3 C
206 Additional route surveys may be required at landfalls to determine:| — | seabed geology and topography
specific to landfall and costal environment |
| — | environmental conditions caused by adjacent coastal
features |
| — | location of the landfall to facilitate installation |
| — | facilitate pre or post installation seabed intervention
works specific to landfall, such as trenching |
| — | location to minimise environmental impact. |
Sec.3 C
207 All topographical features which may influence the stability
and installation or influence seabed intervention of the pipeline
shall be covered by the route survey, including but not limited
to:| — | obstructions in the form of
rock outcrops, large boulders, pock marks, etc., that could necessitate
remedial, levelling or removal operations to be carried out prior
to pipeline installation |
| — | topographical features that contain potentially unstable slopes,
sand waves, pock marks or significant depressions, valley or channelling
and erosion in the form of scour patterns or material deposits. |
Sec.3 C
208 Areas where there is evidence of increased geological activity
or significant historic events that if re-occurring again can impact
the pipeline, additional geohazard studies should be performed.
Such studies may include:| — | extended geophysical survey |
| — | mud volcanoes or pockmark activity |
| — | seismic hazard |
| — | seismic fault displacements |
| — | possibility of soil slope failure |
| — | mudflow characteristics |
| — | mudflow impact on pipelines. |
Sec.3
C 300 Seabed properties
Sec.3 C
301 Geotechnical properties necessary for evaluating the effects
of relevant loading conditions shall be determined for the seabed
deposits, including possible unstable deposits in the vicinity of
the pipeline. For guidance on soil investigation for pipelines,
reference is made to Classification Note No. 30.4 'Foundations'.
Sec.3 C
302 Geotechnical properties may be obtained from generally available
geological information, results from seismic surveys, seabed topographical
surveys, and in-situ and laboratory tests. Supplementary information
may be obtained from visual surveys or special tests, as e.g. pipe
penetration tests.
Sec.3 C
303 Soil parameters of main importance for the pipeline response
are:
| — | shear strength parameters (intact
and remoulded undrained shear strength for clay, and angle of friction
for sands); and |
| — | relevant deformation characteristics. |
These parameters should preferably be determined from adequate
laboratory tests or from interpretation of in-situ tests. In addition,
classification and index tests should be considered, such as:
| — | unit weight |
| — | water content |
| — | liquid and plastic limit |
| — | grain size distribution |
| — | carbonate content |
| — | other relevant tests. |
Sec.3 C
304 It is primarily the characteristics of the upper layer of soil
that determine the response of the pipeline resting on the seabed.
The determination of soil parameters for these very shallow soils
may be relatively more uncertain than for deeper soils. Also the
variations of the top soil between soil testing locations may add
to the uncertainty. Soil parameters used in the design may therefore
need to be defined with upper bound, best estimate and lower bound
limits. The characteristic value(s) of the soil parameter(s) used
in the design shall be in line with the selected design philosophy
accounting for these uncertainties.Guidance note:
For deep water areas the upper layer may be slurry with a
very small strength. In these cases emphasize should also be made
to the soil layer underneath. ---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3 C
305 In areas where the seabed material is subject to erosion, special
studies of the current and wave conditions near the bottom including
boundary layer effects may be required for the on-bottom stability
calculations of pipelines and the assessment of pipeline spans.
Sec.3 C
306 Additional investigation of the seabed material may be required
to evaluate specific problems, as for example:| — | problems with respect to excavation
and burial operations |
| — | probability of forming frees-pans caused by scouring
during operational phase |
| — | problems with respect to pipeline crossing |
| — | problems with the settlement of pipeline system and/or
the protection structure at the valve/tee locations |
| — | possibilities of mud slides or liquefaction as the result
of repeated loading |
| — | implications for external corrosion. |
Sec.3
D. Environmental Conditions
Sec.3
D 100 General
Sec.3 D
101 Environmental phenomena that might impair proper functioning
of the system or cause a reduction of the reliability and safety
of the system shall be considered, including:| — | wind |
| — | tide |
| — | waves |
| — | internal waves and other effects due to differences
in water density |
| — | current |
| — | ice |
| — | earthquake |
| — | soil conditions |
| — | temperature |
| — | marine growth (fouling). |
Sec.3 D
102 The principles and methods described in DNV-RP-C205 Environmental
Conditions and Environmental Loads may be used as a basis for establishing
the environmental conditions.Sec.3
D 200 Collection of environmental data
Sec.3 D
201 The environmental data shall be representative for the geographical
areas in which the pipeline system is to be installed. If sufficient
data are not available for the geographical location in question,
conservative estimates based on data from other relevant locations
may be used.
Sec.3 D
202 Statistical data shall be utilised to describe environmental
parameters of a random nature (e.g. wind, waves). The parameters
shall be derived in a statistically valid manner using recognised
methods.
Sec.3 D
203 The effect of statistical uncertainty due to the amount and
accuracy of data shall be assessed and, if significant, shall be
included in the evaluation of the characteristic load effect.
Sec.3 D
204 For the assessment of environmental conditions along the pipeline
route, the pipeline may be divided into a number of sections, each
of which is characterised by a given water depth, bottom topography
and other factors affecting the environmental conditions.
Sec.3 D
205 The environmental data to be used in the design of pipelines
and/or risers fixed to an offshore structure are in principle the
same as the environmental data used in the design of the offshore
structure supporting the pipeline and/or riser.Sec.3
D 300 Environmental data
Sec.3 D
301 The estimated maximum tide shall include both astronomic tide
and storm surge. Minimum tide estimates should be based upon the
astronomic tide and possible negative storm surge.
Sec.3 D
302 All relevant sources to current shall be considered. This may
include tidal current, wind induced current, storm surge current,
density induced current or other possible phenomena. For near-shore
regions, long-shore current due to wave breaking shall be considered.
Variations in magnitude with respect to direction and water depth
shall be considered when relevant.
Sec.3 D
303 In areas where ice may develop or where ice bergs may pass
or where the soil may freeze sufficient statistics shall be established
in order to enable calculations of design loads, either environmental
or accidental.
Sec.3 D
304 Air and sea temperature statistics shall be provided giving
representative design values.
Sec.3 D
305 Marine growth on pipeline systems shall be considered, taking
into account both biological and other environmental phenomena relevant
for the location.Sec.3
E. External and Internal Pipe Condition
Sec.3
E 100 External operational conditions
Sec.3 E
101 For the selection and detailed design of external corrosion
control, the following conditions relating to the environment shall
be defined, in addition to those mentioned in D101:| — | exposure conditions, e.g. burial,
rock dumping, etc. |
| — | sea water and sediment resistivity. |
Sec.3 E
102 Other conditions affecting external corrosion which shall
be defined are:| — | maximum and average operating
temperature profile along the pipeline and through the pipe wall
thickness |
| — | pipeline fabrication and installation procedures |
| — | requirements for mechanical protection, submerged weight
and thermal insulation during operation |
| — | design life |
| — | selected coating and cathodic protection system. |
Sec.3 E
103 Special attention should be given to the landfall section (if
any) and interaction with relevant cathodic protection system for
onshore vs. offshore pipeline sections.
Sec.3 E
104 The impact on the external pipe condition of the third party
activities as mentioned in C101 above should be considered.Sec.3
E 200 Internal installation conditions
Sec.3 E
201 A description of the internal pipe conditions during storage,
construction, installation, pressure testing and commissioning shall
be prepared. The duration of exposure to sea water or humid air,
and the need for using inhibitors or other measures to control corrosion
shall be considered.Sec.3
E 300 Internal operational conditions
Sec.3 E
301 In order to assess the need for internal corrosion control, including
corrosion allowance and provision for inspection and monitoring,
the following conditions shall be defined:| — | maximum and average operating
temperature/pressure profile along the pipeline, and expected
variations during the design life |
| — | flow velocity and flow regime |
| — | fluid composition (initial and anticipated variations
during the design life) with emphasis on potentially corrosive components
(e.g. hydrogen sulphide, carbon dioxide, water content and expected
content of dissolved salts in produced fluids, residual oxygen and
active chlorine in sea water) |
| — | chemical additions and provisions for periodic cleaning |
| — | provision for inspection of corrosion damage and expected capabilities
of inspection tools (i.e. detection limits and sizing capabilities
for relevant forms of corrosion damage) |
| — | the possibility of erosion by any solid particles in
the fluid shall be considered. Reference is made to DNV-RP-O501 Erosive
Wear in Piping Systems. |
![[-]](/dwicons/i_colpse.gif)