Re: Pipeline Construction

PIPELINE CONSTRUCTION
   1.1 GENERAL
   This section describes the main activities and processes involved in constructing a large
diameter onshore pipeline.

   1.2 PRINCIPLES OF PIPELINE CONSTRUCTION    A pipeline can be broken down into three basic elements where different forms of pipeline
construction method are used. They are:

    open cross-country areas, where the spread technique is used     (ii)crossings, where specialist crews and civil engineering techniques are used

    (iii)special sections such as built up urban areas, restricted working areas, difficult
terrain sections and environmentally sensitive areas

   1.3 SPREAD TECHNIQUE AS USED IN OPEN CROSSCOUNTRY  AREAS
   The basic method of constructing steel, welded oil and gas onshore pipelines in open cross-country areas is generally known as the spread technique. The spread technique utilises the
principles of the production line system, but in the case of a pipeline the product (the pipeline)
is static and the individual work force, (crews) move along the pipeline track
(right-of-

way/spread). The implementation of the spread technique is conditional on the pipeline being
welded above ground in maximum possible continuous lengths between obstructions/crossings
(which can extend to lengths in excess of 10 kilometres). These welded pipe
lengths are then

   immediately installed into unsupported/unobstructed trenches gradually in one continuous
length utilising multiple (three or more) mobile lifting tractors (side-booms) in unison.

The breaks in the continuous main spread method of working result from the location of
existing services, roads, railways, tracks, ditches, streams and river crossings, and are also
dependent upon restricted working, time constraints and physical features/obstructions. These
breaks in the main pipeline spread activities are undertaken by dedicated specialist crews

   utilising a variety of special construction techniques and are generally undertaken after the main
pipeline sections have been installed.

The main pipeline spread installation is undertaken by dedicated crews undertaking one
operation at a time commencing at one end of the pipeline and travelling forward to the other
end at anything from 500m to 1,500m per day depending on the diameter of the pipe, terrain,
soils, etc. There are a total of some 40 separate operations carried out in 7 main activity groups,

   as described in Sections A.5.1 to A.5.7 inclusive. The programme of activities and the start-up
of the crews is dependent on available resources and the risk of one crew having an impact upon
the following activities.

Because a pipeline is a production line, it is essential that the time periods between crews is
such that there is no risk of one crew causing stoppage or disruption on the preceding or

   subsequent crew. If the float between crews is not managed on a continuous basis, with the
emphasis placed on the daily moving, then a concertina effect will result with substantial
disruption and standby costs. Effectively, there can be up to a 4-week delay between crews to
ensure that the concertina bunching effect of crews does not occur. Consequently, there are in
the programme extended periods of time when there are no activities taking place along large
sections of the pipeline route. The average time from start of ROW to commencement of land
reinstatement is, typically, in the order of 10 to 15 weeks.

   1.4
   PRE-CONSTRUCTION ACTIVITIES
   Pre-construction activities need to be carried out by the Installation Contractor prior to the start
of the main pipeline installation activities. These activities include finalising the pipeline route,
detailed design finalisation, mobilisation, notification of entry to landowners, setting-up of pipe
yards and base camps, establishing temporary works requirements, setting-up of geographic

   positioning stations, design of land drainage in agricultural areas and reinstatement works,
construction of temporary access roads, pre-environmental mitigation works, and agreeing with
landowners any special requirements prior to entry onto their propertie s.

The Installation Contractor will carry out pre-entry surveys as-and-where required so as to
record the condition of the land prior to the start of any work.

   1.5 MAIN PIPELINE CONSTRUCTION ACTIVITIES    Once the pre-construction activities have been completed, then the main construction works can
commence. Generally, operations are carried out in seven main activities groups, as described in
the following sections:

1.5.1 Construction Activity Group 1 – Preparing Work Area

   1.5.2 Construction Activity Group 2 – Layout Pipe and Weld above Ground 1.5.3 Construction Activity Group 3 – Excavate Trench and Installation of Pipe 1.5.4 Construction Activity Group 4 – Pipeline Crossings, Special Sections and Tie -Ins

1.5.5 Construction Activity Group 5 – Final Backfill and Reinstatement Works
1.5.6 Construction Activity Group 6 – Facilities and Pipeline Control
1.5.7 Construction Activity Group 7 – Testing and Commissioning

General details are shown in Figure 1.

   1.5.1 Construction Activity Group 1 – preparing work area    The pipeline operations consist of:

1. Setting-out

The setting-out crews are the first personnel from the construction contractor’s workforce to
enter the site to commence the main construction activities. The setting out of the works should
be scheduled to commence at least four weeks prior to the remainder of the construction activity
group 1 activities. This work will be carried out with small four man crews using GPS and
surveying instruments. Setting-out pegs will be placed at all boundaries, changes in direction
and intermediate sightings on the proposed centre line and the extremities of the working

   easement.

   In areas of open country where good and level access is available along the pipeline route and it
is anticipated the rock or ground is of sufficient strength that it could impede progress of the
trench excavation, then initial ground investigations works will be carried out directly behind
the setting-out crew.

Part of the setting-out crew’s duties is to identify any existing services that cross or are in close
proximity to the pipeline and supervise the trial hole crew. The trial hole crew will hand
excavate to expose, identify and determine the exact location of all existing services. This data

   will be recorded and transferred to the engineers for incorporation into the final pipeline design.

2. Advanced archaeology major works

This applies to locations where there are substantial/concentrated archaeology remains, which
could involve extensive excavations. Provided access is available or requires minimal work
along the ROW from an established entry point, a separate advanced ROW and topsoil/top

   cover crew will be mobilised to enable the archaeology works to commence in advance of the
mainline and be completed before front-end crews pass. The topsoil/top cover at archaeology
locations will be stripped by back-actors to avoid any disturbance to the stripped subsoil.

3. Right of Way/easement boundary demarcation – secondary ground investigation

   option 1

This will commence after the setting-out. A crew of personnel and equipment comprising
mainly large heavy tracked plant will form the right of way access onto the land. The operations
will include the removal of all hedging for disposal off site, bridge or flume pipe access across
field ditches, protectio n of existing services by protection mattresses, re-grading of existing
ground contours to assist access, the erection of goalpost and safety signs at overhead electric
power lines and telecommunication cables, the placement of hard standings as required for car
parking and the blasting/removal and re-grading of rock areas or outcrops to provide a level and
safe excavation line/running track along the entire pipeline route.

Additional crews will be provided to install offsite ROW accesses along the pipeline route to
enable the ROW crew to gain access to the working areas, where access from the public road is
not available or would cause a safety risk, or as a result of locked out locations or environmental
concerns. Agreement with the landowners involved in any offsite access must be finalised prior
to pipeline commencement.

Where temporary ROW fencing is required then additional crews will be required to erect this
fencing to delineate the working area.

During the ROW and fencing operation it will be possible to undertake ground investigation
works by the excavation of trial pits at 100 metre intervals to determine actual ground substrata,
 trench stability, ground water levels and seepage. These investigations, however, can
only take place at this time on open areas where restrictions due to land use
(agricultural) and

environment do not exist.

4. Pre-construction terrain and ground stability (excluding dewatering)

At locations where there is a risk of ground movement that could result in safety risks to the
construction activities and/or undermine the pipe during installation and the period prior to final

   reinstatement then permanent stability of the affected terrain needs to be undertaken. This work
can be separated into two elements:

    Removal of material such as the overburden at the top of ravines and the removal of
loose material that could move during the installation works

    Addition of material such as Bentonite, which is injected under pressure into gravels
with high and fast water tables and deep mining areas to provide a protective curtain
around the pipe. It also includes the adding (placement) of boulders/ground at the toe of

    steep gradients on forwarded and side slopes in the second element

5. Trench excavation in rock areas

In areas where rock is confirmed as such by the initial ground investigation works then the
trench is excavated ahead of any pipe operations. This sequence of working is undertaken to
ensure that the excavation of the trench cannot cause any damage to the pipe and/or pipe coating
and provide an extended safe working width for the excavation crews allowing double -sided

   trench working by excavators/ breakers.

Following the review of the data from the initial ripper and trial hole surveys, the ground will be
classified in ease of excavation into five groups defined by the method of removal. These are (i)
utilising standard excavation, (ii) larger more powerful excavators (face shovels converted to
back-actors), (iii) ripping/hydraulic hammer and excavation, (iv) blasting/hydraulic hammer and
excavation and (v) rock trenchers (saw and blade). The finished trench should be to the correct

   depth and width to suite the pipe diameter, plus any bedding and pipe cover. The trench should
also be in a straight line so that the pipe can la y central in the trench without coming into
contact with the trench sides. All loose and jagged outcrops, which could come in contact with
the pipe during lay operations, will be removed.

The excavation will commence with dedicated crews immediately following the ROW operation. The forward progress will be dependent upon the ground strength, grain structure,
terrain, access, method of removal and number of crews/equipment employed.

6. Pre-construction cut-off drains

All cut-off drainage works, which comprise the connection of existing drains to a new header
pipe, will commence immediately after the right of way and fencing operations.

Cut-off drainage works will be undertaken at locations where there are existing concentrated

   drainage schemes on agricult ural land and where agreement is reached with the landowners
and/or occupiers to their installation. This work will be resourced taking account of the scope of
work and the requirement to achieve pipeline installation progress of, say, 500 to 1,500 metres
per day along the pipeline route.

7. Topsoil strip -secondary ground investigation Option 2

Topsoil strip operations commences after cut-off drainage operations and is scheduled to allow

   adequate time for completion of the drainage works in the event that unforeseen obstacles or
circumstances are highlighted during the execution of the drainage installation operations.

The topsoil operation consists of 1 crew with plant comprising up to 8 excavators/ bulldozers
removing the topsoil to its full depth (typically, = 300mm) and storing in a single stack on the

   opposite side of the easement to the trench excavation material. The topsoil is stripped with 2 to
3 excavators along the easement boundary on the opposite side to the topsoil stack area. This
provides a subsoil interface/cutting edge for the dozers to work from in pushing the topsoil
across the easement.

In areas where topsoil removal is required then the ground investigation works are undertaken
following the removal of the topsoil as this avoids any risk of topsoil contamination with the
subsoil. The investigation works are as those detailed in the ROW section and comprise the

   excavation of trial pits at 100 metre centres to determine actual ground sub-strata, trench
stability, ground water levels and seepage.

   1.5.2 Construction Activity Group 2 – layout pipe and weld above ground

   The pipeline operations consist of:

1. Project mechanical procedures/testing of welders

Prior to the start of any mechanical works the Contractor will issue for Client approval a full set

   of mechanical procedures for bending, welding, x-ray and coating. These procedures will
address how the Contractor intends to undertake the work in accordance with the project
specifications detailing equipment and specific mandatory requirements. The procedures,
particularly with regard to welding and x-ray will be sufficient to cover the full ranges of the
various parameters characteristic of the project in terms of diameter, wall thickness and
technique. Once the documented procedures are approved then full trials for each element of the
works will be carried out, fully inspected and witnessed by the Client. The welding will include

   non-and full destructive testing to ensure that the procedure welds are undertaken in strict
compliance with the contract requirements and fully comply with the minimum strength,
hardness and quality requirements of the relevant specifications.

Once the procedures have been approved then the welders will be tested to ensure that they can
comply with the requirements of the procedure welds. A register will be maintained of the
welders employed on the project with the various welding techniques they are approved to work

   on.

2. Double-jointing

Double-jointing of the single approximately 12 metre long pipes into 24 metre lengths will, if
considered economically viable by the project, be carried out in the pipe yards prior to pipeline
stringing. Double -jointing permits the doubling of the welding progress with the same basic
welding resources or allows the same production with a much smaller crew.

In considering double -joints due consideration needs to be given to the use of specialist pipe
bogies for the moving of the 24 metre pipes, the capability of the local road system to
accommodate the vehicles and the requirement for special road movement permits. The double -
jointing can be placed on the easement but this results in additional cost due to double handling
of the pipe and the need to continually move the double joint equipment, which can offset any
savings from increased welding production.

   3. Pipe stringing

The pipes and pre-formed bends will be scheduled to be delivered to, and stock piled at, the
proposed pipeline pipe yards some 4 to 8 weeks in advance of stringing operations. The pipe
supply should ensure that the various grades, wall thicknesses and coatings are supplied in
sufficient and correct quantities to meet the programme.

Immediately following ROW or topsoil strip or excavation in rock areas, the pipe stringing

   operations will commence, which involves laying the pipe lengths along the easement length
using pipe trailers. A typical crew will consist of two cranes - one at the base camp loading the
pipe trailers and the other on the pipeline easement off-loading the pipe trailers.

In the event that ground conditions do not permit travel down the easement with standard or
special heavy-duty pipe trailers then the pipes will be loaded on to tracked pipe carriers at the
public roads or at a point where the change in ground conditions occurs and permits the turning

   of the wheeled pipe trailers.

4. Forming field bends (cold bending)

Once the pipe has been strung along the easement, engineers will follow to determine the
location of all bends required in order that the pipeline can follow the contours of the land and
the required line and level as detailed on the drawings. There are two types of bends normally

   used ie hot pre-formed or forged bends which are manufactured off site in a factory and are to a
radius of 5 or 3 times the pipe diameter and cold bends which are to a radius of 40 times the
pipe diameter and are formed in the field.

A typical cold bending crew consists of a four-man team together with a bending machine and a
side boom tractor. The bending machine is towed along the pipeline route by the side boom and
includes “formers” consisting of 20 – 150 ton hydraulic rams, which bend the pipe to the
required radius and angle. The side boom acts as a lifting device and has a fixed jib attached to a

   tracked dozer with a capability of lifting between 15 to 120 tons, dependent upon the size of the
machine used.

The number of cold bends required depends on the route and contours of the pipeline. Typically,
they can range from 1 pipe in 10 in developed regions to 1 pipe in 50 in open country. The cold
bend angle that can be achieved ranges from maximum angles of 12 degrees (42” pipe) to 40
degrees (12” pipe).

5. Welding of the linepipe

The welding of the pipeline will commence a few days after the cold bending crew. The
welding crew will weld the pipeline in continuous lengths between features such as roads,
watercourses, tracks, railways, services and other underground obstacles that prevent the
linepipe being continuously installed in the trench.

There are primarily two methods of welding which are manual or automatic. As the names
imply manual welding involves the welding of the pipe by welders and automatic involves a
semi-automatic system. At present, and with the correct welding experience, there is no
substantial difference in quality or production.

   Automatic welding is used primarily for three main reasons:

    Ensure welding quality
    Increase/sustain a high daily production rate     Reduce the overall manpower requirements     Manual welding is used where:
A supply of experienced welders is readily availa ble

    Difficult terrain, weather and site conditions exist     Special sections and areas with a high percentage of tie -ins     High production rates cannot be achieved

Both systems generally (although certain automatic systems can now do single pass complete
welds) operate on a front-end/back-end principle. The front-end consists in a manual operation
with, say, 3 separate welding stations placed on CAT D6 carriage consisting of a HIAB for the
welding shelter (used in inclement weather or windy conditions), 4 welding bullets and a
compressor. The welding stations work on 3 separate joints and complete one pass before

   moving on with the sequence being the bead (2 - 4 welders), immediately followed by the hot
pass (2 – 3 welders) and then hot fill (2 welders). With the automatic process, 1 machine
deposits sufficient weld metal equivalent to the 3 manual passes. The weld is allowed to cool
after the front-end passes and then sufficient welders working in pairs or multiple automatic
machines follow on to fill and cap that day’s production.

The crew will achieve progress in the order of one weld approximately every 3 to 5 minutes or

   up to 90 to 150 welds per day, which is equivalent to 1,000 to 1,500 metres of linepipe on 12
metre pipes and up to twice that if double -jointed pipes are used.

6. Welding of fabrication pipework

As the mainline welding crew is set up for speed and any reduction in the speed will increase
costs and could cause delays to following operations then any fabrications or pipework
involving bends or difficult set-ups or welds that require more than the bead before lowering off

   (creating cracks) will be left out. These fabrications are welded together by a small dedicated
crew who complete these welds prior to the field joint coating crew.

7. NDT inspection

All welds on the pipeline are generally subjected to inspection by radiography. This is achieved
on the main pipeline by an internal x-ray tube travelling along the inside of the pipe carrying out

   x-rays at each weld for approximately 2 minutes per weld. On completion of the x-ray the film
is taken to a dark room and processed in time for the results to be available for inspection at the
end of the day or early the next day. Welds, which do not meet the required acceptance criteria,
are either repaired or cut out and re-welded.

Experienced and qualified x-ray specialists undertake the radiography under controlled
conditions. Before the operation is started, the section of pipeline is cordoned off by marker tape

   to stop entry by non x-ray personnel and audio/flashing warning alarms are activated during all
times when the x-ray tube is energised. The x-ray personnel are on constant surveillance to
ensure that the workforce and members of the public are aware of the x-ray activities and only
authorised access is permitted.

   Welds completed by semi-automatic welding processes are examined using automatic ultrasonic
testing (AUT) techniques. This consists of an assembly that traverses the circumference of each
completed weld in order to detect any defects. The results of each ultrasonically inspected weld
are automatically recorded and are used to determine whether a weld repair is required and if so
what type.

8. Weld rectification (repairs)

A weld rectification (repair) crew follows immediately behind the NDT inspection activities to
either carry out repairs to or cut out any defective weld. On completion of all repairs a further xray
 is carried out on the weld to ensure that the finished weld conforms to the standard required.
The x-ray of repair welds is usually carried out from the outside of the weld by a two-man crew.

9. Field joint coating

The coating of the pipeline field joints to prevent corrosion starts a few days after the welding.
This extended period is to allow for any repairs or cut-outs to be completed without prejudicing
the coating crew’s operations.

   1.5.3 Construction Activity Group 3 – excavate trench and installation of pipe

   The pipeline activities consist of:

1. Trench excavation

In areas other than rock, trench excavation commences a few days after the field joint coating
operation. A typical trench excavation crew consists of 5 - 8 excavators working in line. This
operation only excavates the length of open cut trench sufficient to install the main line welded
pipe; it does not excavate any roads, ditches, services or obstacles. The number of excavators
employed will be such that the amount of trench excavated in a single day matches the rate of
progress of the welding crew. The spoil from the trench will be stored adjacent to the trench on
the opposite side of the ROW from the topsoil stack.

The finished trench will be to the correct depth and width to suit the pipe diameter, plus any
bedding and pipe cover. As far as possible, the trench should also be in a straight line so that the
pipe can lay central in the trench without touching the trench sides. All loose and jagged
outcrops, which could come into contact with the pipe during laying operations, will be
removed.

2. Trench excavation archaeology watching brief

As part of normal good practice an archaeologist will be present during the main trench
excavation undertaking a watching brief of the material being excavated. The archaeologist will
have the authority (subject to safety constraints) to stop the trenching works if he considers the
excavation has encountered a major archaeological find.

3. Finalise drainage design

In agricultural land, the Contractor will record the existing drainage system actually intercepted
by the pipeline. The information will be reviewed taking account of the intended proposals and

   any final amendments to the system finalised at this stage following discussion with the Owners
or Occupiers.

4. Pipe installation (lower and lay) – above ground tie-in sections

The linepipe will be positioned approximately 5 metres from the trench centre-line and will be
installed into the open unobstructed trench utilising a number of side-booms. This operation will
usually be carried out immediately following the excavation crew.

As the linepipe is being installed a coating crew will be present who will holiday detect the pipe
to detect any damage to the pipe coating just prior to the pipe entering the trench. Any holidays
(damage) detected will be repaired by a fast setting repair coating.

In areas of rock, the pipe installation will commence anything from 5 to 15 days after the
welding crew.

If there are any above ground breaks in the mainline due to access openings across the ROW,
expansion breaks or bend breaks, then these will be welded above ground, x-rayed and coated
during the excavation and lowered-in as part of the mainline lower & lay operation. This will
optimise the use of the side-booms within the lower & lay crew and reduce the number of below
ground tie-ins.

5. Cross trench drainage connections

In agricultural land, the permanent reinstatement of the existing land drains to be replaced
across the pipeline trench is carried out prior to the trench backfill operations. The replacement
drains extend for a short distance into undisturbed ground.

On completion of inspection of the reinstatement works, the trench is backfilled and compacted
in layers to the underside of the drain. This work is only undertaken in extreme locations to

   supplement the main pre- and post-drainage schemes

6. Installation of permanent cathodic protection system test posts

Either as part of the fabrication welding crew activities (if the location of the CP test posts are
known) or as the pipe is being installed Cathodic Protection lugs are welded to the pipe. These
lugs which can be 50mm square plate are welded on the pipeline using low hydrogen welding

   rods where test posts will be installed to check the ground/pipe to soil potential. The test posts
are placed at about 1km distances along the pipeline and located at fixed boundarie s such as
road crossings or other locations, which have relatively easy access. Cables are attached to the
lugs the whole area coated, checked for holidays and the cables brought to ground level during
backfilling and left. During the reinstatement activit ies the Cathodic Protection test posts are
installed with the cable running up through a duct in the test post and tied off. The test post is
then concreted into the ground directly above the pipeline.

7. Temporary cathodic protection system

As the pipeline may be buried for the full construction period before the permanent Impressed
Current Cathodic Protection (CP) System is activated, then some form of temporary system
needs to be installed prior to the backfilling of the pipe. The temporary system, typically,

   comprises a number of zinc anodes attached to the pipeline at regular intervals. These are buried
parallel to and at a distance of, say, 3 metres from the pipe.

8. Backfill of the pipeline trench

Trench backfill starts immediately following the placement of the linepipe in the trench and the
undertaking of a survey of the pipe levels by the engineers to confirm that the required pipe
cover has been achieved. There is a requirement that the initial backfill around the pipe and to

   300mm above the crown be of loose and relatively fine particles, which can be readily
compacted and do not damage the pipe coating. In areas of rock it will be necessary to place the
pipe on a 150mm bed of similar material. In order to provide this material it may be necessary
to import sand/soft material offsite, sieve the excavated material or crush the excavated
material. The sieve and crusher equipment will be portable machines, which will be transported
along the pipeline ROW.

The pipe is backfilled over the entire length except for, say, 30 metres at each end of the
pipeline work section, which is left free to facilitate the tie -in to the crossing/line break pipe
work.

   1.5.4 Construction Activity Group 4 – pipeline crossings, special sections and tie-ins

   The pipeline operations consist of:

1. Crossings

The crossings are carried out by a number of different and dedicated crews simultaneous with
the main trench excavation works and final tie -in to the main pipe installation being carried out
by subsequent tie -in crews following completion of the crossings and main pipeline installation
works. The crossings are undertaken by two distinct methods of construction consisting of
either:

     Open cut
    No dig technique

There are various options to the two methods of working and the actual method employed at
any given location will be dependent upon the ground conditions, pipe diameter, local
environment, third party restrictions and the type of obstruction being crossed.

The extent of a crossing in design terms is normally defined from fixed locations, which extends
either side of the crossing land take or boundary fencing. However, the length of a crossing in
terms of construction includes the crossing plus any temporary works to facilitate the

   installation, the swan neck offsets to bring the pipe back to normal cover and the tie -in pipes to
connect the crossing to the mainline.

A key aspect in the determination of the method of construction that will be used at any crossing
will be the requirements of the regulatory authority/owner that has jurisdiction over the
crossing. Part of the approval process with the regulating authority will be the issue of detailed
plans and calculations of the design, which will be supported by fully detailed construction

   method statements.

   Details of the various crossing methods are described herewith and are taken in the order of ease
of construction and cost.

Open cut

Open cut is generally by far the most cost effective way of crossing obstacles that cause breaks
in the mainline and is undertaken by crossing the obstruction by means of an open excavation.
The trench excavation at the obstruction, whether it be a ditch, a road, a railway, a river, or a

   service is excavated for the full length of the crossing prior to the installation of the pipe.
Accordingly, in order to minimise the time for which the crossing trench is open, the welding,
NDT inspection and field joint coating of the section of pipe required for the crossing is
completed in advance of excavating the trench. An open cut crossing can very often be installed
in one working day and the road or ditch temporary reinstated sufficiently to fulfil the function
for which it is required prior to the crew-leaving site for the day.

No-dig technique

At locations where open cut methods are impractical or not permitted for whatever reason, then
no-dig techniques have to be implemented. No-dig techniques can be classified into two main
groups - sleeve or ‘bare’ line pipe. The actual method that will be used is determined by the
ground conditions, third party restrictions, length of crossing, diameter, and design/safety
requirements.

The different options available for no-dig techniques are described briefl" Received on Sat Mar 17 11:52:00 2007