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unning under Mexican ground, there are more than 60 000 km of pipelines whose documented routes were due to be updated. Before the present study, the geographical information held was in many cases more than a decade old, and differences between the actual position and the documented co-ordinates of some pipeline sections were greater than 1000 m.1 Pemex Gas y Petroquímica Básica (PGPB), the main gas processing and transmission company of Mexico, has made efforts to update its pipeline maps using state-ofthe-art detection equipment coupled with differential global positioning systems (DGPS),

ora Mendoza, M is u L sé Jo d n ez a Víctor Domíngu , with a Básica, México ic ím u q o tr e P y Pemex Gas z, rge Canto Ibáñe Jo , n o im S y o d o Arturo G de La Escalera, z e in rt a M .

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which are integrated into a geographic information system (GIS). This results in accurate digitised pipeline maps that are interactively linked to different databases storing photographs, pipeline right of way (ROW) cross-sectional diagrams, corrosion risk parameters and more, providing a powerful tool to risk and process engineers, cathodic protection system designers and general pipeline integrity managers.

Accurate pipeline localisation and tracing

Figure 1. PGPB owns over 13 066 km of gas transmission pipelines.

Currently, PGPB has upgraded the location and tracing of approximately 63%, represented by the pink lines. In 2009, about 1000 km are due to be traced in the north (orange lines). The rest, about 30%, are to be completed in the future.

Exact localisation of pipelines is critical for many tasks associated with Internal and External Corrosion Direct Assessments (ICDA and ECDA) and general pipeline integrity management.2,3,4,5 For example, for maintenance works, engineers must know exactly where the pipeline runs and how deep it goes before beginning excavation, as well as the location of any other pipelines in the vicinity that share the same ROW. 6,7,8 Without accurate location data, the risk of accident occurrence is considerable.

Reliable pipeline maps are also crucial for emergency response to acts of terrorism, vandalism, accidental damage or any other incident that could compromise the integrity of a pipeline and its service installations.

Differential GPS and omni-directional magnetometric pipe localisation

Figure 2. A team led by a certified pipeline location and tracing engineer employed top of the line omni-directional magnetometers, differential GPS of sub-metric precision and portable data management devices.

Figure 3a. Equipped with an omni-directional precision magnetometer, the detection team sweeps the ROW perpendicularly to detect all the pipelines present.

Reprinted from World Pipelines NOVEMBER 2009

PGPB has already traced more than 8200 km of pipelines with state-of-the-art localisation systems that allow high accuracy position and depth determination of underground pipelines (Figure 1). The equipment consists of an adjustable frequency electromagnetic signal transmitter, an omni-directional magnetic field sensor (OMFS), a personal digital assistant (PDA), a DGPS and a central processing unit that merges them all into a full system (Figure 2).

Pipeline tracing campaigns usually require one or more teams of four technicians, each supported by a GIS processing team at the cabinet. Each team has its own set of detection equipment and is responsible

Figure 3b. Skilled operators avoid the usual errors caused by magnetic distortion in shortly separated pipelines, pipeline crossings, and other situations.

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for mapping a certain pipeline section. The detection procedure begins by placing the signal transmitter on the ground and then emitting an electromagnetic signal towards the buried pipeline. The electromagnetic signal induces an electrical current that flows along the pipeline, generating a magnetic field that can be detected by the omni-directional magnetic field sensor (Figure 3a).

The sensor, which is operated at least 20 m ahead of the transmitter, can accurately detect the magnetic field intensity variation as the operator moves around the pipeline ROW. By measuring the magnetic field intensity, the device can accurately detect the pipeline depth and position in the ROW in real-time, as well as pipeline branches, direction changes, and electrical bonds.

Every 500 m the pipe detection procedure is performed along a path perpendicular to the direction of the pipelines until every pipeline inside the ROW is localised. Then, the team moves along the ROW to continue with the pipeline tracing. Besides characterising the ROW at regular length intervals, each time the team encounters pipeline service installations such as rectifier stations or cathodic protection system components, the ROW is characterised, co-ordinates and installation data are registered, and photographs are taken. This also happens when there is an invasion of the ROW by walls, fences, and houses, and also each time the ROW crosses rivers, roads, railroads, and canyons. Thus, the campaign not only corrects pipeline maps, but also updates the pipeline asset inventory, particularly the real pipeline network length, and generates valuable risk management data.

or pipelines that run too close together.6 In such cases, an inexperienced operator may find himself with fewer pipelines than expected or with inconsistent readings.

The basic problem that arises in these cases is that the magnetic field emitted by the pipeline gets distorted, making it difficult to determine the real depth and position of the pipeline (Figure 3b). Nevertheless, these particular difficulties can be overcome by connecting directly to the pipelines by the test stations that are periodically positioned along the ROW (Figure 3c), or by making additional localisation procedures, between the current position and the last correct characterisation, until the cause of the magnetic field distortion is elucidated.

Each time a pipeline position and depth are obtained, the data is stored in a database along with the co-ordinates acquired from the DGPS that the magnetic field sensor operator carries on its back. It is worth noting that the DGPS can determine global co-ordinates (latitude and longitude) in real-time and with sub-meter precision, which contrasts with ordinary GPS where localisation errors are usually greater than 10 m.11,12

Detection system operator expertise is a must Using the equipment described above helps determine accurate pipeline paths in a fast and reliable way; however, operator expertise is a must, since some detection problems may arise with pipelines that are electrically connected to each other, pipelines that change positions inside the ROW (crossing each other),

Figure 3c. Connecting directly to the pipeline using installed test stations can usually avoid magnetic distortions.

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Figure 4. With the accuracy of the DGPS employed, the probability of finding a pipeline inside a 1 m radius around the measuring point is about 98%. In comparison, the GPS data obtained, presented a 98% probability of localising the GPS device inside a 40 m radius around the measuring point.

Reprinted from World Pipelines NOVEMBER 2009

The information obtained during the pipeline localisation campaigns was uploaded to PGPB’s asset management system: the SIIA

Figure 5. The upgraded pipeline tracing was helpful in correcting errors of the positioning of a pipeline over 1000 m.

Figure 6. The SIIA integrates pipeline maps with documents such as cross-sectional diagrams of the ROW and interactive 360º photographic compositions of surface assets (distance units are m).

Studies were undertaken to determine the measurement error of the DGPS that was employed during the localisation campaigns.

A soccer stadium was marked to set a grid of 10 x 10 m separated points over a green area of 60 x 100 m. The GPS differential equipment was used to locate each point of the grid, and the distances between points were calculated from the measured GPS co-ordinates. The relative distances between points were compared to the actual distances measured directly, and the absolute differences were registered. Finally, the difference distribution was plotted, as shown in Figure 4. Some 97.6% of the points had an error below 1 m; meanwhile, data from the literature produced in 2005 shows a much wider distribution, with 98.2% of the data with a localisation error below 40 m.11

Reprinted from World Pipelines NOVEMBER 2009

Pipeline tracing impact on a pipeline map can be important. An example of this is shown in Figure 5 where the difference between the old and the updated paths is far from negligible. But besides the obvious benefits of having accurate pipeline maps, the work done in this project has provided some key additional advantages for PGPB pipeline administrators.

Basically there has been an integration of the pipeline paths with a GIS and with file databases in a system known as SIIA (Installation and Asset Identification System) that allows rapid and intuitive access to thousands of photographs, videos, maintenance reports, corrosion risk parameters, and any other information related to particular pipeline sections, rectifying stations, cathodic protection systems, road, river and railroad crossings, and the like (Figure 6).

These tools allow swift access to key information for emergency responders in case of accidents, vandalism and acts of terrorism, allowing them to take quick decisions in order to prevent further damage to the pipelines and installations involved and to guarantee the safety of the local population. They are also very useful for project engineers and maintenance teams that need to know certain characteristics of the pipeline network on which they pretend to work, letting them do better planning, cost estimation and risk identification.

The SIIA is also a vast source of information for PGPB’s Integrity Management Program (IMP), which is a Pipeline Integrity Management System (PIMS) that makes risk assessments taking into account an enormous amount of factors including length of the pipelines, number of valves, inline inspection, corrosion potentials, maintenance status of every asset of the pipeline networks, operating temperatures and pressures, etc. The more information available, the more reliable the risk assessment, which in turn, becomes an invaluable tool for Pipeline Integrity Managers.

Yet another example of the impact that SIIA has on PGPB’s Pipeline Integrity Management, is the ability of cathodic protection system (CPS) designers to obtain data from the SIIA in order to use it in CPS design software where they can construct color coded maps of corrosion potentials along a particular pipeline network (Figure 7), and develop models that can predict the behavior of the system.13,14

Custom made databases and software were employed to update the PGPB asset management system In a pipeline map update campaign, the amounts of information obtained from the field tasks team can become quite overwhelming. To organise and classify

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that information along with the creation of standardised documents that include some information elements like photographs, numbers and codes, is not a small feat.

Fortunately for PGPB, all this is done automatically thanks to smart document templates, cleverly designed databases, and home-developed subroutines. This way,

information remains well organised and man-hour requirements are minimised (Figure 8).

PGPB’s midstream pipeline map and asset inventory With pipeline maps updating campaigns using state-of-the-art detection systems coupled with the SIIA, PGPB can be sure of having accurate pipeline maps that will help avoid future maintenance and third party accidents, and a modern, reliable, and cost-effective set of tools that allow quick and intuitive data availability for overall Pipeline Integrity Management, fast emergency response, better maintenance and cathodic protection system design, and a more complete asset inventory.

Notes The authors would like to thank Fernando Miguel Rubí Moreno, Alejandra De León Ibarra, Fernando Benítez García from Corrosión y Protección Ingeniería (CPI); Jesús Hernández and Juna Manuel Godínez from PEMEX Gas y Petroquímica Básica (PGPB); and the Centro de Investigación en Ingenierías y Ciencias Aplicadas (CIICAp) of the Universidad Autónoma del Estado de Morelos (UAEM) for their help and collaboration.

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Figure 7. Cathodic protection system engineers can benefit from the information available through SIIA for visualising corrosion potential maps and for CPS modelling.

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Figure 8. Costumed made databases and automatic document generation allowed to document the assets of PGPB pipeline surface facilities and to upload the information into SIIA in a fast and reliable way.

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14.

Pemex Gas y Petroquímica Básica (PGPB), Sistema de Identificación de Instalaciones y Activos (SIIA), unpublished data.

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Reprinted from World Pipelines NOVEMBER 2009