Pipeline protection starts with a good design (e.g., locating pipelines in remote regions) and good construction practices. Most pipelines are laid underground or underwater. This gives them some protection against excavating/drilling equipment or vessels/anchors that may damage them, but we protect our pipelines at all stages of their lives:
We will protect our pipeline from external interference by putting in place a series of ‘barriers’. We do not use a single method. Various methods are summarised below.
7.1 Pipeline Markers
Many Regulations require ‘markers’ (‘line marker’ or ‘pipeline marker’) to indicate the location of pipelines . These markers are above-ground signs (Figure 1) to:
- identify the location of the pipeline (but not the depth); and,
- generally alert those who might be working along the pipeline corridor.
|Figure 1. Many Regulations require ‘markers’ to indicate the location of underground pipelines.
(photograph courtesy and copyright of Penspen Ltd.)
The permanent markers are posted along the pipeline right-of-way, and may be located at where the pipeline intersects or crosses a street, highway, railroad, or waterway, or where the pipeline deviates (e.g., at bends). Other markers (‘aerial patrol’ or ‘air patrol marker’ ) are also located along a right of way to assist aerial surveillance and tracking. These markers will have a location (km or mile) identifier.
Different colour markers may indicate differing utilities; for example, in the USA:
- red indicates electric;
- yellow indicates gas, oil, or steam.
A marker will usually contain information on:
- pipeline presence and location;
- product carried;
- name and contact information (usually a toll-free telephone number) of the company that operates the pipeline.
Markers must be maintained, and the right of way clear to ensure the marker is always visible. Note that pipeline markers do not always mark the centreline of the pipeline (although where practicable, it should be close to the centerline), so they cannot be relied upon to indicate the exact position of the pipeline. Also, a pipeline may not follow a straight course between markers.
7.2 Awareness Methods
The objective of public ‘awareness’ procedures and practices is to make all people and companies who might damage the pipeline aware of the existence of the pipeline, and understand the consequences of damaging a pipeline.
The first step in an awareness program is to identify all ‘stakeholders’ in the pipeline’s safety. Stakeholders will include:
- Affected public (landowners, adjacent landowners, residents, native tribes, and places of congregation near the pipeline).
- local and state emergency planning and response officials;
- local public officials and ‘governing councils’;
- emergency responders;
- excavators (companies and municipal departments who perform excavations);
We can make people aware of our pipeline through public education programs, such as:
- clear marking of the pipeline location (‘pipeline markers’);
- personal or town hall meetings;
- direct mailings;
- printed materials (e.g., calendars);
- internet sites;
- trade shows;
- mass media communications (e.g., radio adverts);
- ‘one-call’ systems;
API 1162  gives a full description of awareness methods, but we will cover a specific method next – the ‘One-Call’ system.
7.3 One-Call Systems
Sometimes Federal or State laws require anyone who digs to notify utility companies before starting. This is because digging can be dangerous and costly, if the excavator does not know where underground facilities are located. Consequently, communication systems have been developed that assist excavators, contractors, and property owners in complying with state law by notifying the appropriate utilities before digging.
In the USA this has involved excavators calling a number to check if underground facilities are in the vicinity of their excavating activities. This ‘One-Call’ to a dedicated telephone call centre, financed by interested parties (i.e., utility companies), is aimed at reducing damage to our pipelines.
Excavators can communicate with a One-Call center, where just one call, prior to digging, can request that all underground facilities in the area of a planned excavation be located and marked:
- excavators call the One-Call centre before commencing excavating;
- the One-Call system can then notify member companies of proposed excavation projects if they are in the vicinity of the excavation;
- the member companies can then monitor the excavation, and guide the excavator with an agreed communication system and procedure.
The member companies can mark (use paint, stakes, or flags, and a colour coding system, Figure 2) the ‘approximate location’ of their underground lines, and, attend the work area, or advise the caller there are no facilities in the area. The markings should indicate the location of the centerline and size of the pipeline, or the sides of the pipeline . If the excavator does not hear from member companies within a fixed period of time, work may commence.
|Figure 2. Colour Coding System used for Marking Utilities.|
7.4 Depth of Cover
Onshore pipelines are usually buried to give the pipeline protection from the environment (damage, temperature, etc.), and also to protect the environment. Depth of cover is obviously an effective method of protecting pipelines from damage, Figure 3. Standards require a minimum depth of cover of e.g., 0.9 m (2’ 11”) – 1.1 m (3’ 7”).
|Figure 3. Increased Depth of Cover Protects Pipelines.|
We have known for many years that depth of cover gives protection against external interference, and research work showed that the likelihood of damage is reduced by a factor of 10 as the depth of cover is increased from 1.1 m (3 ft 7”) to 2.2 m (7 ft 2”) .
Increased depth of cover will be expensive to achieve, as deeper excavations need to be prepared for the pipeline, increasing construction costs.
7.5 Increased Wall Thickness
Increased pipe wall thickness gives protection against external interference . Increased pipe wall thickness offers protection against damage such as puncturing and denting; for example, very few (about 5%) of excavating machinery used in suburban areas will be able to penetrate pipe wall thicknesses of 11.9 mm (0.469”) .
We can regularly survey our pipelines, by air (helicopter or fixed wing aircraft), or land, or sea (using both surface vessels and ‘remotely operated vehicles’ (ROVs) subsea) to check that there are no unknown activities or excavations being conducted along our pipeline route. One purpose of aerial surveillance is the periodic examination of the pipeline right-of-way to detect unauthorised excavation, or recently completed excavation by observing earth disturbance.
Pipeline company personnel, or contractors, perform the surveillance, which involves periodic ground-based or aerial patrols, or sea patrols. Aerial surveillance is typically conducted every two weeks. Surveillance effectiveness for onshore pipelines depends heavily on patrol frequency, as surveillance may be ineffective if the interval between patrols exceeds the time required for an excavation contractor to mobilise on site and commence digging .
The aerial patrols over onshore pipelines will be looking for activities such as :
- construction of any building work which may encroach on the pipeline route;
- any previously unknown third-party activity on or adjacent to the pipeline;
- the condition of pipeline marker posts;
- fires of any description (e.g., straw burning);
- tree felling and timber transportation;
- discolouration of vegetation or other evidence of leakage from the pipeline;
- blasting or mineral extraction;
- ground movement;
- erosion and changing water courses;
- soil removal;
- vegetation overgrowth on right of way.
Mechanical damage is caused when an object touches a pipeline. All impacts on pipelines create acoustic waves that travel upstream and downstream in the pipeline product. Acoustic monitoring via sensors placed along the line (e.g., every 5 km) can detect these waves. The timing and relative magnitude of these waves can determine the impact location and severity.
These monitoring systems are commercially available .
7.8 Buried Electronic Markers
Buried electronic markers can be placed above a pipeline, usually during construction. A special locator can detect these markers; therefore, they can later pinpoint the facility.
The detectable depth range for electronic markers is between 0.6-2.4 m (2-8 feet) depending on the type of marker used .
Markers consist of an electronic copper coil antenna, with the coil is tuned to respond to a specific radio frequency signal generated by the locator. The antenna reflects the signal as a wide field with a peak directly above the marker. The antennas are encased in water resistant polyethylene shells for protection from chemicals and temperature variations typically found in underground environments. The electronic markers are passive and do not require an internal power source .
The marker locator is a lightweight, portable device consisting of two pieces: an electronics package and a hand-held probe.
7.9 Buried Marker Tapes
Marker tapes (typically made from low density polyethylene) can be laid in a continuous line over the pipeline to alert excavators to the presence of a pipeline below the tape, Figure 4. Buried marker tapes or meshes can be a cost-effective protection method.
|Figure 4. Buried Marker Tape can be an Effective Warning [10, 11].|
The tape is permanently coloured with a high visibility colour, and identifies the nature/contents of the buried pipeline.
The main advantage of warning tape is its reliable and constant coverage. Warning tape alerts excavators who do not notify One-Call centres, and can prevent excavation hits resulting from errors in site markings.
A limitation is that it is difficult to install for existing pipelines. Also, the installation requires excavating on the pipeline right of way, which may damage the pipeline.
Buried tape needs to stretch when pulled out of the ground to serve as a visual signal to the excavator. Elongation properties for a typical tape are in the range of 500% to 700%. Buried tapes with a higher tearing capacity offer higher resistance before tearing when pulled out of the ground .
Tape widths range from 76 mm to 1200 mm (3 inches to 4 feet). The wider the tape, the more likely it is to be unearthed and seen by an excavator before contact is made with the buried pipeline .
7.10 Physical Barriers
Pipelines can be protected, using barriers to reduce the risk of pipeline damage. An example of a barrier is to place the pipeline in a protective casing or sleeve, Figure 5. These ‘barrier’ methods provide simple, effective protection to a pipeline.
|Figure 5. Protecting Pipelines by using Barriers such as Casings.|
Pipelines protected by sleeves are no longer popular due to:
- difficulty with sleeve maintenance; and,
- the possibility of corrosion (and the difficulty of finding it) in the sleeve.
Thicker walled pipe is preferred, although care must be taken in installing the pipe, and the coating must be closely monitored.
We can protect a pipeline from damage by placing a protective barrier (usually a concrete slab, but sometimes steel, or plastic) above the pipeline, Figure 6.
|Figure 6. Slabs or Concrete Barriers over Pipelines offer Protection from Impacts from Above (see ).
(photographs courtesy and copyright Penspen Ltd.)
The slabs are typically 3 m x 2 m and 200 mm thick, with steel reinforcement at the top and bottom. The slab must rest on ‘firm’ soil, and should end about 1 metre from the centreline of the pipe, to ensure the slab protects the pipe from bulldozer buckets.
- concrete slabs laid over a pipeline will not offer protection against horizontal drilling, or side impacts;
- thin concrete slabs can be penetrated by large excavation equipment (i.e., excavators over 20 tonnes);
- machines such as piling machines can penetrate the concrete slabs.
These concrete barriers are very effective. BSI PD 8010-3  states that slabs and markers reduce the failure frequency of pipelines from external interference:
- concrete slabs reduce the frequency by 0.16;
- concrete slabs, plus visible warning (e.g., marker tapes), reduce the frequency by 0.05.
7.11 Subsea Pipelines
Many subsea pipelines are coated in concrete to prevent them floating to the surface. This ‘weight’ coating prevents the pipeline from floating to the surface during construction and/or operation, but can give some protection against damage.
|Figure 7. Subsea Pipelines can be Protected by Physical Barriers.|
Laying the pipeline in a subsea trench, and backfilling, offers significant protection, but can be costly. Subsea pipelines can need extra protection from anchors, dropped objects, etc.. Protective methods include mattresses, grout bags, gravel cover, ‘dog kennels’, tunnels, ‘pipe-in-pipe, etc. , Figure 7. Rock ‘dumping’ (controlled dropping of rocks over the pipeline) can also protect a subsea pipeline, Figure 8. Note that anchors can still damage rock dumped or buried pipelines as anchors can penetrate several metres into the soil.
|Figure 8. Rock ‘Dumping’ can Protect Subsea Pipelines.|
Subsea equipment (e.g., valve manifolds) will also need protection using bespoke protection structures/cages. We can provide protection to all subsea structures against dropped objects using similar protection structures.
For major hazards such as icebergs or shipping, only routing is effective, although wellheads can be protected from icebergs by sitting them in depressions on the seabed (‘glory holes’).
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