OMAE2013-10851

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1 Copyright © 2013 by ASME

Proceedings of the ASME 2013 32nd International Conference on Ocean, Offshore and Arctic EngineeringOMAE2013

June 9-14, 2013, Nantes, France

OMAE2013-10851

PIPELINE SHORE APPROACH INSTALLATION BY HORIZONTAL DIRECTIONALDRILLING

Danilo Machado L. da SilvaDETNORSKE VERITAS

Rafael F. SolanoPETROBRAS

Antonio Roberto de MedeirosSUBSEA7

Marcos V. RodriguesDETNORSKE VERITAS

Fabio B. de AzevedoPETROBRAS

ABSTRACTWhenever an export pipeline coming from offshore fields

to onshore facilities is designed, a shore approach solution

needs to be provided, once it can become a very complex

project in terms of offshore pipeline installation. At this phase

the pipeline on-bottom stability is analyzed for surf zone, the

possibility of using concrete coating is verified as well as the

necessary burial depth. In addition, the pipeline installation

stress analysis is performed, the potential for local scour isverified, among other things. In this context, horizontal

directional drilling (HDD) emerges as an alternative method in

which, in addition to overcome the technical aspects mentioned

above, the environmental issues can also be minimized.

Many factors determine the success of an HDD project.

Failure to complete the borehole is often the main concern, as

the project would not be attempted if the pipeline could not be

installed. However, the successful design and construction of an

HDD is measured in more than a successful pullback. The

achievements, as in any project, include the completion of the

project for a reasonable cost with minimal environmental

impact and according to the schedule. And of course, the

pipeline integrity shall be ensured. That is the focus here in thiswork.

This paper presents discussions regarding to the proper

design of the export pipeline section installed by HDD in the

shore approach area. To ensure a proper design and pipeline

integrity are important parts in the success of a shore approach

HDD crossing. It must be noted that there are no methods for in

situ repair of damaged pipelines installed by HDD. The point is

a proper design, construction and installation, which includes,

for instance, do not overstress the pipeline during installation,

mainly pullback operation, as well as the proper selection of the

drill path in order to place the pipeline within stable ground and

isolated from obstacle’s active conditions, to properly consider

the corrosion protection, etc., for the design life of the product

pipe.

INTRODUCTIONThe advantages that HDD could bring to pipeline shore

approaches, compared with the conventional shore pull, open-

cut methods, are now accepted and several pipelines shore

approaches were installed worldwide. The main reasons are that

HDD can mitigate environmental impact and provide greaterburial depths [1].

It should be noted however, that the risks associated with

typical crossings also apply to shore approaches where they are

combined with specific risks related to working in the marine

environment. In fact, shore approaches using horizontal

directional drilling are much more complex and challenging to

complete than typical surface to surface installations. The

increased challenges and complexity arise from an inability to

readily access the exit location, less geotechnical information

associated with seabed sediments, elevation differences between

entry and exit locations, complexity of coordinating diving

operations, tidal and storm influences, bore stability and drilling

fluid management, casing and product pipe installationstrategies, and buoyancy control [2, 3].

The added complexity and challenges that come with

construction of shore approach HDD crossings demand that the

designer and the constructor use appropriate solutions: Planning

and coordination procedures are paramount in the success of

shore approach HDD work, co-ordination of drilling and marine

operations (diving, vessel movements, supply logistics, etc.)

must be carefully undertaken and reviewed.

The HDD design is not the focus of this work,

recommendations and guidelines can be found in [4-8]. The

design considerations that apply to more conventional land

based HDD crossings also apply to shore approach crossings.

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However, there are some areas of design that need to be

emphasized when adopting a shore approach crossing.

Geotechnical considerations remain a key component of an

HDD crossing in any environment. Together with geotechnicaland survey work undertaken to assist with design tasks, studies

and data collections relating to tides, currents and sea-states

may be required. These will not only ensure the permanent

works are suitably designed but also provide information that

will allow selection of adequate vessels to be used in crossing

construction, preparation of suitable construction procedures

(anchor plans, handling of pipeline strings etc.) and estimation

of cost and schedule.

Of course, the stresses imposed on the pipeline before,

during and after installation shall be considered and maintained

within allowable limits. Although some general “rules of

thumb” are commonly used to prepare preliminary designs,

more thorough stress analyses are required to verify finaldesign. Initial design parameters based on “rules of thumb” may

include using radius of curvature of at least 1200 times the

pipeline diameter and, for large diameter steel pipe for instance,

sizing the pipeline wall thickness to provide a diameter to

thickness ratio of 50 at most. Many companies specialized in

HDD works have their own programs to analyze the loadings

and stresses imposed on the pipeline and that can be used to

assist in refining and verifying designs [9].

Corrosion protection is also part of the design

considerations. In many cases, the pipeline coating system is

defined to provide not only adequate corrosion protection but

also to incorporate additional abrasion resistance to keep the

anticorrosive coating system during the pipeline installation intothe HDD crossing.

It should be highlighted that there are no methods for in

situ repair of damaged pipelines installed by HDD. Therefore, it

is necessary to ensure the quality of pipeline design,

construction and installation.

The objective of this work is to present relevant issues

related to the proper design of the export pipeline section

installed by HDD in the shore approach crossing.

HDD DESIGNThe preliminary characteristics of crossings are related to

crossing location and nature of the obstacle, as well as the

pipeline to be installed.

Obstacle to Be Crossed

The geotechnical conditions have an important effect on

works. Geotechnical conditions affect the feasibility of using

HDD as the method of construction, the selection of the

crossing’s trajectory, the pipeline design, the HDD construction

techniques (including the choice of tooling), and the rate of

progress for the construction. Hence, the geotechnical

conditions not only dictate the suitability of HDD as the chosen

method, but also they have a large influence on the construction

cost.

Therefore, the first step in designing a HDD drill path

consists of defining the obstacle to be crossed: the natural or

manmade feature to be negotiated shall be characterized in

terms of its existent physical dimensions as well as thepossibility for such parameters to change with the passage of

time. Adjacent property and use restrictions, as well as future

developments in the area must also be assessed.

Pipeline to Be Installed

The primary criterion governing the specification of pipe to

be installed by HDD is its service and the fluid to be

transported: the wall thickness and specified minimum yield

strength will be determined by applicable codes and regulations.

However, stresses and loads imposed by the installation method

shall be reviewed and analyzed in combination with operating

stresses to assure that acceptable limits are not exceeded.

In addition to site features, i.e., geotechnical andtopographical conditions, the geometry of the bore hole must be

matched to the pipe being installed, as during HDD installation

the pipeline is subjected to tension required to pull the pipe into

the bore hole and around curved sections. The tension comes

from the drag due to the friction between pipe and bore hole

and the fluid drag caused by pulling the pipe through the

viscous drilling mud trapped in the annulus. In addition, tension

results from the unbalanced gravity effects of pulling the pipe

into and out of the bore hole at different elevations. The

bending loads are caused as the pipe is forced through the

curves in the bore hole, and the external loads result from the

pressure exerted by the drilling mud in the annulus around the

pipe. Prior to the installation of a horizontal directional drilledpipe it is important to estimate the pipe pullback force during

installation so that:

(1) the pipe is not overstresses during HDD installation;

(2) a drill rig with sufficient pullback capacity is used;

(3) an economical design is implemented.

There are several approaches for calculation of pullback

forces during the pipeline installation by HDD [10-12], one of

the most used method was proposed by the PRCI [8].

Drill Path Design

The added complexity of the construction process for a

shore approach crossing should be kept in mind during its

design. To maximize the likelihood of a successful installation,

designs should be as simple as possible (Figures 1 and 2). For

instance, unnecessary additional lengths and horizontal curves

should be avoided. As with any crossing, the continuation of the

pipeline on either side of a crossing must be designed too. It is

generally preferable to avoid fabricated bends at the offshore

termination of the crossing. Rather than using a fabricated bend,

the exit (or entry) angle of the HDD crossing is usually

shallower than typically used on land crossings and, if

necessary, the HDD is terminated in an excavated (pre- (or post-

) dredged, jetted or trenched) pit that allows the pipeline to

transition from its exit out of the HDD bore (see Figure 5).

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Figure 1 – Typical Drill Path (onshore crossing) [8].

Figure 2 – Typical Drill Path (shore approach crossing).

Pipe-Soil Interaction

The pipeline soil interaction is the combined behavior of

the pipeline and the surrounding soil in terms of stresses and

deformations. During the pullback operation the moving

pipeline contacts the wall of the borehole and pushes with a

certain force perpendicular to the wall of borehole. These forces

determine the magnitude of the shear force in axial direction

during the pullback operation and lead to a deformation of the

soil. The distribution and the magnitude of these forces on the

borehole wall are of major importance in the pipeline soil

interaction. The pipeline-soil interaction is mainly determined

by the following aspects: pipeline stiffness, stiffness and soil

strength, shape of the borehole, effective weight of the pipelineand borehole stability [13].

The borehole stability, cleaning and geometry are the most

important factors for the success of the pullback operation.

Borehole stability requires a proper balance among various soil

parameters including: soil stress and strength, pore pressure,

drilling fluid pressure and drilling mud chemical composition.

Borehole instability is influenced by chemical effects

(formation of a filter cake) and mechanical effects (soil

sloughing and hydraulic fracturing) [14]. In case of instability

of the borehole, the pipeline-soil interaction changes rigorously.

In case of a collapsed borehole, a huge soil load exerts on the

pipeline. Whereas local borehole instability leads to higher

pulling forces, which can be overcome, borehole instability over

a larger distance will certainly lead to a stuck pipeline and thus

an incomplete pulling operation.

The proper definition of the relation between reamed

borehole and pipeline diameter has important consequences for

the proper progress during the pipeline pullback phase.

Other Issues

One of the most important considerations in shore approach

crossings is the handling of the product pipeline before and

during its installation in the HDD crossing. Control of the

pipeline string offshore must be given due regard. If the

pipeline is to be stored offshore prior to being installed in theHDD crossing its on-bottom stability may need to be

considered. As with conventional HDD crossings, ideally the

pipeline will be near neutral buoyancy in the drilled hole and its

effective weight out of the hole will be minimal (on

conventional land based crossings pipeline rollers are used to

reduce the pull load needed to pull the pipeline to the HDD

crossing).

Although some of the methods that are used on

conventional crossings to control buoyancy, such as using

internal ballast pipes and progressive flooding, may be more

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difficult to implement offshore, there are several methods that

can be used to provide suitably weighted pipeline strings.

In some cases, it can be technically feasible to increase the

pipeline’s wall thickness to provided added weight that, whenthe pipeline is empty, will give near ideal effective weight

downhole and reasonable stability on the seabed. Although that

added wall thickness may not be necessary with respect to

pipeline stresses, it may be an effective, and economical,

method of aiding and enabling installation by increasing the

submerged weight of the pipeline.

Similarly, although less common and not recommended, the

use of concrete coating on pipe that is to be installed into HDD

bores is a method of increasing the effective weight of an

otherwise buoyant pipeline. If a concrete weight coat is used to

this objective it is important to ensure that it is a high quality

application that will not spall during handling and installation. A

concrete weight coat will obviously increase the outsidediameter of the pipeline being installed. In order to minimize

the coating’s thickness, and hence minimize the size of the

reamed HDD bore, a dense concrete should be used.

PIPELINE DESIGNThe design and installation of pipelines must comply with

established standards, ensuring safety and specifying the

minimum requirements to be satisfied by the designer.

DNV-OS-F101 [15] considers a design practice based on

so-called limit states for the pipeline design. In the limit state

design, all relevant failure modes for a pipe are formulated as

limit states, which are classified into one of the four categories:

1. Serviceability Limit State (SLS),2. Ultimate Limit State (ULS),

3. Fatigue Limit State (FLS),

4. Accidental Limit State (ALS).

The limit state is the limit between an acceptable and

unacceptable condition expressed in mathematical terms

derived through design formulas for a given failure mode. The

limit state design identifies the different failure modes and

provides specific design checks to ensure structural integrity.

The pipeline capacity is then characterized by the actual

capacity of each individual failure mode.

The structural analysis of an offshore pipeline regarding

construction and installation phases deals with the computation

of deformations, internal forces, and stresses as a result of external loads and the structural properties of the pipe.

Structural deformation of the pipe during construction

depends on the method and equipment used for installation, the

structural properties of the pipe and the environmental loads.

The same design philosophy as for the offshore part of the

pipeline system applies for the shore approach and onshore

sections (Figure 3). This implies that the consequences of

failure (economical, environmental and human) shall be

quantified by the concept of safety class. The safety class

should be determined by fluid category, location class and

phase (construction, operation) of the pipeline.

The presence of people and facilities necessitates a further

refinement of the location classes used offshore. In highly

populated areas the consequences may be more severe than for

offshore, requiring a higher safety class, Very High (wherefailure during operating conditions implies very high risk of

human injury).

Requirements for shore approach and onshore sections of

offshore pipelines are presented in Appendix F of DNV-OS-

F101.

Figure 3 – Application extent of DNV-OS-F101.

The same requirements as for the offshore part of the

pipeline system should be applied to the onshore part, if

applicable. Where this is not applicable, the requirements of

ISO 13623 [16] should be complied with.

Design Parameters

The basis for design for the shore approach section should

be as given in Section 3 and the loads should be established as

described in Section 4 of DNV-OS-F101.Some parameters have a direct impact on the calculations

to be performed in the loads and stresses analysis in the pipeline

during installation.

Geotechnical Conditions

The geotechnical conditions are an important part of

establishing the pipe/soil interaction, the soil stiffness and

friction can generally describe the interaction between pipeline

and borehole wall.

The geotechnical parameters are essential for determination

of loads and stresses experienced by the pipeline as well as

efforts on the external coating during pullback.

The geotechnical parameters are defined based on the

geotechnical investigation and the friction factors should bedefined according to design rules;

Environmental Effects

The combination of environmental factors producing the

most unfavorable effects on the pipeline should be used in

design.

The combination and severity of environmental conditions

(current, wave and tide) for use in design are to be appropriate

to the project and consistent with the probability of

simultaneous occurrence of the environmental phenomena.

Long term shore profile must be considered. All

foreseeable environmental phenomena, such as soil subsidence,

soil instability, seismic activity, scour, etc., that may influence

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the pipeline integrity must be described in terms of their

characteristic parameters relevant to operational and strength

evaluations.

Definition of Design Loads

It must be verified that the pipeline, as designed, is capable

of withstanding all loads that may be reasonably anticipated for

the installation by HDD as well as testing and operation.

The following loads should be considered:

Installation Loads: tension/compression, bending and

external pressure;

Operating Loads: internal pressure, bending, thermal

expansion, external pressure.

The analysis should consider the load combination that

yields the most unfavorable conditions in terms of overall stress

utilization.

Stresses associated with each load as well as the combinedstresses shall be evaluated in accordance with the allowable

limits.

Installation Stress: tensile and compressive stresses,

bending stress, external hoop stress, combined installation

stresses.

Operating Stresses: internal hoop stress, bending stress,

thermal stress, combined stresses.

The methods used in definition of the design loads should

be selected in accordance with good engineering practice.

Methods of analysis may be based on analytical, numerical or

empirical models, or a combination of these methods.

The definition of the design loads for the HDD pipeline

design verification should be performed considering the radiusof curvature for the designed drill path and reassessed, prior

pullback operation, using the actual (as built) drilled path.

Design Criteria

Design and acceptance criteria for the possible modes of

failure are presented in Section 5 of DNV-OS-F101, together

with complementary requirements given in Appendix F.

All relevant failure modes must be considered in design for

all relevant phases and conditions listed in Section 4 of DNV-

OS-F101.

CORROSION PROTECTIONPipeline coating and cathodic protection will not directly

influence the feasibility of a crossing. However, an operational

risk that should be addressed is external corrosion due to

damaged pipeline coatings. Protective coatings are susceptible

to damaging during pullback operation by the forces involved,

and by contact with soils, rocks, and other debris in the bore

hole. The consequences of coating damage are intensified by

the nature of the HDD method. A pipeline installed by HDD

will not be readily accessible to future pipeline or coating

repairs.

The mitigation of such effects is related to good design and

execution of borehole as well as correct specification and use of

the external coating.

External Coating

External coating refers to factory applied external coating

systems with a corrosion protection function. Coating systems

may further include an outer layer for mechanical protection.Coatings used for HDD drag sections shall be flexible and

have sufficient abrasion resistance to limit damage during

installation.

External coatings should possess suitable mechanical and

electrical properties in relation to the pipe size, environment

and operating conditions. External coatings should be factory-

applied, except for field joints and other special regions or

components, which may be coated on site.

Parameters that should be taken into account when

evaluating the effectiveness of external coatings include:

• Design/service conditions;

• Resistance to abrasion;

• Electrical resistivity of the coating;• Required adhesion between the coating and the

pipeline base material;

• Required resistance to shear forces;

• Susceptibility to cathodic disbondment;

• Resistance to ageing, brittleness and cracking;

• Resistance to chemical attack;

• Resistance to damage during handling, shipping,

storage, installation and service.

Consideration should be given to the use of coatings with

enhanced abrasion-resistant properties or with additional

abrasion resistant outer layers on sections where coated pipe is

to be installed by HDD [17].

Field Joint Coating

Field joint coating (FJC) refers to single or multiple layers

of coating applied to protect girth welds and the associated cut-

back of the linepipe coating, irrespective of whether such

coating is actually applied in the field or in a factory.

The welded joints must be coated using a system

compatible with the factory coating provided on the rest of the

pipe.

The FJC shall be designed to have its integrity guaranteed

during and after the pullback operation. If necessary,

qualification tests should be performed.

The preparation of the pipe surface and the application of

the field joint coating must be performed in accordance with a

procedure that meets the coating manufacturer’s

recommendations.

The design and quality control during manufacture of field

joint coatings is essential to the integrity of pipelines.

As for external coatings, integrity of field joint coatings

must be ensured during the pullback operation.

Cathodic Protection

External coating system defects enable the pipeline steel to

come into contact with the electrolyte in its surroundings,

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resulting in pipeline corrosion. Cathodic protection system must

be designed and installed to mitigate this corrosion.

The design of cathodic protection system should be in

accordance with ISO 15589-2 [18] or DNV-RP-F103 [19].Even though, these rules do not have specific requirements for

the HDD section.

Cathodic protection may be applied by the sacrificial anode

or impressed current method. A combination of both systems

could also be considered, but the need for insulation between

both systems should be evaluated.

The current density must be appropriate to the pipeline

temperature, the selected coating type and to the environment to

which the pipeline is exposed, considering coating degradation

and coating damage during pullback.

In all cases, points for testing should be defined as close to

the HDD ends as possible;

Simulations through cathodic protection modeling shouldbe performed to evaluate the effectiveness of the cathodic

protection design along the HDD length.

The formation characteristics (electrical resistivity) along

borehole and coating breakdown factor (related to the HDD

section) should be taken into account for the project design life.

The galvanic anodes should be installed on the submerged

side, preferably in sled structures with a reliable electrical

connection to the pipeline. The installation of anodes directly

on the pipeline is also an alternative. In both cases, it shall be

considered the effects of anodes located too close to each other,

i.e., less than 0.5 meters from each other.

The impressed current system, installed on the onshore side

of the pipeline, can be used for cathodic protection of the HDDsection if the cathodic protection potential measured at the entry

point is deficient. However, the consequences over the

sacrificial anodes at the offshore side should be evaluated.

OTHER CONSIDERATIONSOther considerations are presented as follows. In general,

the same requirements as for the offshore part of the pipeline

system should be applied to the shore approach part, whenever

applicable.

Pipeline Installation

The pipeline laying of the HDD section shall be performed

according to the same requirements applied to the offshore partof the pipeline.

For marine crossings where the pipeline construction will

be continued away from the crossing after the HDD installation

has been completed, it is usual that the pipeline segment that is

pulled into the HDD crossing will have a “tail” length of

pipeline attached. Generally, such a tail will be left on the

seabed at the conclusion of the HDD pullback and be of such alength that, at a later date, a laybarge will be able to bring the

pipe into its welding stalls and conventionally lay-away. The

length of these tail sections is usually determined based on the

depth of water and the vessel(s) being considered (Figure 4).

The designer must be mindful that the tail section will add to

the forces required during pullback. Buoyancy comes into play

again with the tail section since, in order to provide a tail that is

stable, or easily controlled, and that does not prohibitively add

weight to pullback string, the effective weight of the pipe when

submerged must be considered. The tail section may have

different stability issues compared with those associated with

the pipe being installed in the HDD bore. Since the tail section

is not being installed in the HDD bore it will not only requirecontrol prior to and during the pullback operation but it will

also need to be stable and secure during operational conditions

(via, for instance, pre-trenching, post-burial, and protection

measures) [9].

To ensure that the exit point (product pipe entry point) will

not be affected by the pipeline recovery and tie-in operations, a

proper pipeline length to remain outside borehole shall be

considered, in addition to the catenary length required for lifting

and tie-in operations. This pipeline length shall guarantee that

vessel movements will not be transferred to the exit point.

Product pipe position before pullback

It is recommended to place the pipeline section to be

installed into borehole as close to the exit point as possible,considering the laying corridor and installation route;

The minimum distance from the pull head to exit point

must allow all necessary corrections due to misalignment

between product pipe and drill path. Therefore, this procedure

ensures that the product pipe will have the correct alignment at

exit point during pullback.

The pipeline section to be pulled through the borehole must

be positioned as aligned as possible with the drill path

(alignment with the drill path exit point).

If such alignment is not possible, the mechanical loads to

be experienced by the product pipe (tension, friction and

possible damage to external coating, increase in pulling force,

etc.) should be considered. Furthermore, aspects related to theintegrity of borehole exit point should also be considered

(widening, collapse of borehole exit point).

Figure 4 – Total Pipeline Length of HDD Section.

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Pipeline Hydrotest

Gauging and hydrostatic test should be performed prior and

after pullback operation.Hydrostatic test procedures should be in accordance with

requirement in DNV-OS-F101, but, a reduced hold period could

be accepted provided that the HDD section will be pre-

commissioned after connection the to the remain sections of the

pipeline system.

On-Bottom Stability Considerations

The pipeline (HDD section) must be designed to be stable

during installation, hydrotest and operation, in accordance with

the applied design standards.

On-bottom stability may be an issue for the length of the

HDD pipeline section that remains outside borehole after

pullback.

Pipeline on-bottom stability analysis must be performed in

order to evaluate if the pipeline may experience movements that

could adversely affect its integrity.

Note that actions should be taken to ensure that the pipeline

will be prevented from movements before pullback. Such

actions include flooding and/or anchor the pipeline prior

pullback.

Free-Span

Depending on the exit angle, the pipeline configuration

may results in free-spans at the exit point.

Exit angles for shore approach should be set as close as

possible to the seabed slope at the exit point. Furthermore, the

exit point should be prepared (exit pit, trench, etc.) in order tomake the curvature (catenary) as smooth as possible during

pullback and prevent the occurrence of free-spans, Figure 5.

Figure 5 – Catenary without and with a smoothed exit

point.

If it is not possible to eliminate the free-spans at the exit

point, analyzes should be performed to evaluate necessary

interventions in accordance with the design standards.

Local Scour

The seafloor contours in installation areas may change

considerably over time due to scour erosion, which is removal

of soil due to current and waves caused either by natural

geological processes or by external elements (the pipeline in

this case) interrupting the flow regime near the seafloor.

When applicable, the magnitude and time scale of scourerosion is to be estimated based on geologic studies and its

impact on design appropriately accounted for.

Considering proper geotechnical and oceanographic data,

the potential for local scour can be predicted and therefore,

certain areas can be avoided when defining the HDD exit point.

A proper survey program and routines for evaluating

seafloor changes should be established.

The potential for occurrence of local scour at the HDD exit

point should be evaluated and proper actions taken. The extent

of such actions should be based on the predicted consequences

and may vary from an immediate intervention to a monitoring

plan over the project lifetime.

Thermal Expansion

Pipeline thermal expansion is to be taken into account.

Thermal and pressure expansion or contraction can cause

displacements at termination points.

The expansion calculations should be carried out on

pipelines where significant temperature changes are expected

between the specified operating temperature and the

temperature during installation.

There is a likelihood of repeated thermal stress changes

giving rise to fatigue conditions, the stress range and fatigue

damage should be calculated in accordance with applicable

rules and standards.

Analysis is to be performed to model and predict the effectof combined internal pressure and thermal variation on the

longitudinal expansion as well as any other transversal

displacement of the pipeline (snaking or upheaval buckling).

Expansion analysis is to consider the most onerous load

combinations to determine the greatest potential linear strain of

the pipeline.

The design must evaluate the susceptibility of the pipeline

to experience global buckling in the HDD exit point. The

assessment should be performed in accordance with DNV-RP-

F110 [20].

FINAL REMARKS

Shore approach HDD crossings are designed in accordancewith the general parameters that govern the design of more

common land-to-land crossings, but must take into account the

added complexities of their constructability. Designers must not

only have a comprehensive understanding of standard HDD

design but also have knowledge of the construction techniques

that will be employed and how the design will impact

constructability.

Generally, onshore HDD work is able to continue in all but

extreme weather conditions. However, for shore approach

crossings, the weather conditions, tides and currents can have

significant effects on HDD operations. Typical weather and sea

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conditions can affect the selection of equipment and methods of

construction.

Two crucial points in the HDD crossing design consist of

defining the obstacle to be crossed and the pipeline to beinstalled.

It should be noted that, in general, drilling companies’ main

concern is to keep the borehole integrity and control loads and

stresses on drilling equipment. On the order hand, the

determination of loads and efforts to be experienced by the

product pipe as result of the HDD is a primary concern for

owners and pipeline designers.

The proper design and integrity assurance of the installed

pipeline is an important part in the success of a HDD crossing.

Taking into account the pipeline issues is essential for the

success of the project. It is necessary to keep in mind that not

only a finished product is important, but a finished product that

is in good working condition, considering its design life. Thismeans that the pipeline shall withstand the expected operational

conditions and design loads, maintain its integrity, and have a

proper corrosion protection system. The best way to achieve

this is to make sure that the prefabricated pipeline fulfills these

requirements before starting the pulling operation.

The pipeline design must verify adequate strength during

all installation phases in the HDD process. All loads that the

pipeline will experience over the project lifetime should be

considered, which includes installation (construction, pipelay

and pullback), tests and operation.

NOMENCLATURE

ALS: Accidental Limit StateDNV: Det Norske Veritas

FJC: Field Joint Coating

FLS: Fatigue Limit State

HDD: Horizontal Directional Drilling

ISO: International Organization for Standardization

PRCI: Pipeline Research Council International

SLS: Serviceability Limit State

ULS: Ultimate Limit State

ACKNOWLEDGMENTSThe authors would like to express their special gratitude to

company managements for allowing this paper to be published.

REFERENCES[1] Medeiros, A. R., Silva, D. M. L., Solano, R. F., Siqueira,

J., “HDD as an Alternative Solution for Shore Approach

of Offshore Pipelines in Brazilian Scenarios”, Rio Pipeline

Conference & Exposition 2011, Rio de Janeiro, Brazil,

2011.

[2] Duyvestyn, G., “Design and Construction Challenges for

HDD Shore Crossings”. Proc. of No-Dig Conference,

North American Society for Trenchless Technology –

NASTT, Orlando, Florida, USA, 2005.

[3] Smith, N., “Horizontal Directional Drilling (HDD) for

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