Pipeline Integrity Assessment and Mitigation Techniques in Unstable Soil Conditions Based on Comparison of In Line Inspection Results

The Andes Mountains, rich in geographical features and diversity, poses a significant threat to the integrity of oil and gas pipelines due to geohazards. Land movement and unstable soil conditions can trigger changes in the original trajectory of the pipeline resulting in undesired bending strain which can result on failure of the facility. OCENSA – Oleoducto Central S.A. from Colombia assesses the pipeline condition in geotechnical unstable places by comparison of In Line inspection results taking into account pipeline movements and bending strains changes along the zone of study. Bending strains in the pipe are compared against allowable values and emergency values which constitute the criteria to execute mitigation and/or remediation activities that must be done in order to maintain the pipe integrity. To project the pipeline behavior in time, 3D finite element models are developed, allowing the programming of future activities. This paper presents results obtained in a study case to show how pipeline is assessed and how different mitigation activities are developed. Mitigation Techniques such as stress relief procedures and EPS (Expanded Poly-Styrene) blocks incorporations are explained. These techniques are executed in order to reduce the pipe response due to soil displacements during landslide events and creeping slopes, with the final scope of assuring a safe operation.

Overview of Pipeline Geohazard Assessment Approaches and Strategies

Undertaking a systematic pipeline geohazard assessment may be driven by the design and regulatory permitting needs for proposed new pipelines or as an input to the integrity management of operating pipeline assets. Yet the leading international pipeline codes do not provide explicit direction on undertaking such assessments, rather providing considerable latitude in the guidance to do so which in turn provides several options. The methods for identifying and assessing the potential likelihood and severity of geohazards vary significantly, from purely expert judgment-based approaches relying largely on visual observations of geomorphology to analytically-intensive methods incorporating phenomenological and/or mechanistic models and route, pipeline properties and, where applicable, operational monitoring data. Each of these methods can be used to assess hazard and risk associated with specific geohazards in terms of qualitative, semi-quantitative or quantitative approaches provided that associated underlying assumptions are clearly understood. Some of these methods are better suited to provide a continuous contiguous geohazard risk assessment for a pipeline system while others are better suited for localized site-specific risk assessments. Following a brief review of pipeline codes, this paper provides an overview of the range of pipeline geohazard assessment approaches and explores the “fitness for purpose” strategy that allows for continuing improvement during design stages and into operations.

Protection of Pipelines Uncovered in Crossing River: A Case Study

To ensure the integrity of pipelines in failure mode Geotechnical, TRANSPETRO and the TBG perform underwater inspections of pipelines in the main crossings of rivers, lakes, dams, canals and permanently flooded areas. The inspections are designed to locate guideline and measure the covering the pipelines from the margins and underwater depth, identify any exposure of the pipelines, map the occurrences of blocks of rock or debris on the channel and evaluate the anthropic influence on stability of the sections inspected. Among the crossings rivers inspected, in the Atibaia V, with approximately 27.3 m in length, was observed a high erosive potential, which resulted in the loss cover of 3 (three) pipelines of crossing river, besides the fiber optic cable. The lengths uncovered resulted in approximately 33.0 m, with suspended pipes, damage in the concrete jacket and presence of blocks of rocks in the channel. The pipeline in the most critical situation went vain of 6.0 m, with gap up to 0,2 m in relation the background. The crossing river was studied with bathymetric survey and designed cover the pipelines with mechanical protection and anti-erosive. The pipes were supported with sacks of granular material, sequentially, the margins and pipelines were protected with geotextile filled with concrete, installed with the help of divers. The working conditions of 4.0 m depth, currents of up to 0.8 m/s, temperature and low visibility waters were challenges overcome during execution, in which the divers took turns in short periods. Due to the characteristics of the bedrock, the blankets went stylized and stitched on the field by the team, with dimensions taken on site. After positioning the blankets in the background began the underwater concreting, which occurred in stages monitored by the volume pumped and divers strategically placed. The crossing river was re-inspected approximately 1 (one) year after their stabilization and was found in good conditions. The occurrence improved the procedures for geotechnical monitoring and treatment of pipelines uncovered in crossings rivers, being who the efficiency and safety of the work performed currently serve as a reference for the design of similar works.

Determination of the Separation of Diverter Berms for Erosion Control

Diverter berms are structures that are intended to control erosion by means of the reduction of the dragging forces due to runoff. In a hillside, as the slope and length increases, the towing capacity of the runoff increases; diverter berms aim to reduce the flow length and with this the water potential erosion. In Colombia is common to determine the separation of diverter berms based in the graphics presented in the NIO 0802 standard (Ecopetrol, 2001), in which separation is function of the slope of the hillside, the type of soil and the rainfall intensity. In this paper the equations proposed by Morgan (1995) and Mirtskhoulava (2001) are applied to determine the separation of diverter berms based on the maximum non-eroding velocity, the discharge flow, the surface roughness and the slope steepness. In order to compare the results of the application of the Morgan (1995) and Mirtskhoulava (2001) models, with those curves of the NIO 0802 standard (Ecopetrol, 2001), an application was made to the right-of-way for the Medellín-Cartago pipeline, along the called Sinifana variant. The information regarding topography, soils and coverage was provided by Civil and Tech SAS.

Integrity Management Program for Geo-Hazards in the OCENSA Pipeline System

Oil pipelines systems for hydrocarbons transportation are linear projects that can reach great lengths. For this reason, theirs paths may cross different geological formations, soil types, navigable or torrential waters; and they may face geotechnical and hydrological instability problems such as creeping slopes, geological faults, landslides, scour and differential settling which causes different relative movements between the soil and the pipeline. The OCENSA (Oleoducto Central S.A) 30″ and 36″ diameter system was built in 1997 to transport crude oil from the eastern foothills of the Andes to the Caribbean Coast along some 830 km of the Eastern Andes mountains range and the spurs of the central Andes mountains range of Colombia: it was a major challenge to secure the integrity of the pipeline in the face of natural events.

Landslide Followed by a Leak at the Patagonian Andes, Argentina

Gasoducto del Pacífico is a pipeline that carries natural gas from southern Argentina to Chile, through the Patagonian Andes. During previous years of operation only minor sign of soil movement were registered by the monitoring program, taking the form of ditch settlements. However, on September, 2005 a landslide took place producing a gas leak, at a segment that was previously characterized as a non-critical one. An initial office review of available information and site pictures would not yield a clear reason of land movement initiation given the terrain mild slope. Actions were taken aiming at three different time frames. Immediate remedial actions were taken such as ditch opening to free stresses and replacement of buckled pipeline. Integrity specialist flew to the site to conduct geological survey and a stress analysis was conducted at a lab, allowing to asses and manage present risk before transportation began. Mid-term solutions were implemented as the ditch remained open until the next summer season, when access to the site was guaranteed. Finally, two new river crossings were constructed to mitigate this natural hazard permanently. Lessons from this incident revealed design aspects that need to be reconsidered to assure mountain pipelines integrity.

The Challenge of Crossing the Andes: A Data Base Analysis and Peru LNG Project Description

As of the date this paper is written pipelines in South America comprises 113000 kms of transmission lines including Oil, Gas, Condensates, and refined products from which approximately 17% (19400 kms) crosses the Andes reaching elevations up to near 5000mts. Rugged terrain combined with the geology, weather conditions (especially rain intensity) and continuous pipe ruptures in the past impose serious challenges for the pipeline industry that makes the design, construction and operation substantially different from other pipelines in the world. The records have shown that the threat of Ground movement/weather-related pipeline ruptures in the Andes plays a significant role since the percentage of the risk associated with geotechnical causes is substantially higher than any other parts such as Europe or United States. Thus the rate of pipeline failures due to natural forces is significant higher than the average industry. Peru LNG is a 406km × 34in gas pipeline transporting natural gas from the jungle side of Peru to the Pacific Coast where a LNG terminal has been installed. Peru LNG’s pipeline currently holds the record of being the highest Gas Pipeline of the world with a maximum elevation of 4901 meters above sea level. Project completion was done in May 2010 and lessons learnt from similar projects were taken into account since project designs. This paper is divided in two parts. First, it compares pipeline ruptures frequencies due to natural forces in the Andes with other pipelines in different terrains based on historical cases compiled by the authors. Secondly, it explains the different phases of Pipeline Project in rugged terrain from the conceptual design until the operations stage and the role of Pipeline Geotechnical Engineers in this process based on PERU LNG’s pipeline experience. It also describes some of the main features of the PLNG pipeline project. A comprehensive flow chart provides general guidance for future pipeline projects in similar conditions.

Monitoring and Control System in an Area of Geotechnical Risk Unstable in the Camisea Gas Transport System

The experience gained during the operation and maintenance activities on the Camisea Pipeline Gas Transport System (SDT) owned by TGP in Peru — which goes from the Amazon rainforest in the region of Cusco to the Pacific coast near Lima, along 729 Km — has led to the evolution and the optimization of the design, construction and maintenance processes regarding works focused on the stabilization of the slopes along the right of way of the pipeline carrying natural gas and natural gas liquid. This section of the right of way is 95 km long and crosses tropical mountains in the Amazon rainforest, in a transitional area between the Manugaly valley and the basin top boundary. It was noticed since 2005 that the right of way had being affected by a land slide consisting of a horizontal crack in the ground, between both pipelines and along them. So, after number of in-site inspections, the team concluded that the area was being affected by a large ground removal event. As a consequence, traces of geotechnical instability were found on the right side of the right of way, consisting of stress cracks, transverse settlements and leaks. All of those were affecting the stability conditions of the ground. From the annual in-site follow-up, monitoring and geotechnical testing, the team established that this process affecting the right of way was caused by a large mass removal process directly related to the increase of the imbalance rate of an old colluvial deposit below the entire area, triggered by the heavy rainfall in the area — ca. 3 500 mm a year, mainly between October and April. It is to be mentioned that the axis of the NG and NGL pipelines is located on the top of this colluvial deposit, which is susceptible to landslides. This is noticeable because of cracks present in the place. Local geomorphology and heavy deforestation — caused by locals — triggers an increase of the rainfall water filtration rate into the ground, thus speeding up the slide processes. Piezometers installed in the area showed high levels of the local water table. Movement readings are: top length: 70 m; length: 250 m; width: 150 m. Criteria for the construction of landslide mitigation structures in the pipeline área are being established based on a permanent land survey monitoring system — including inclinometers, piezometers and strain-gages — as this is a large regional movement. This control action allowed the operation to continue free of damages to the pipelines and under controlled costs.

The Assessment of Pipeline Integrity in Geohazard Areas Using ILI Data

In-line inspection by inertial mapping techniques is an essential tool for pipeline operators in areas susceptible to geohazards. The detection of previously unknown movements can provide early warning of the presence of a hazard. Positional change and the nature of the loading process can be monitored using the results of multiple inspections over time. Structural modelling is required to fully evaluate the integrity of the pipeline and whether a failure condition is being approached. Finite element techniques can be used, including the effects of soil-pipe interaction, axial forces and operational loads. This enables the prediction of future performance, based on trends from multiple inspections, so that mitigation or intervention methods are efficiently designed and scheduled. This paper considers some key aspects of the analysis process. The use of ILI mapping data to detect small movements below the tool measurement tolerance is examined. The importance of structural analysis is demonstrated by consideration of the axial force component. The inherent variability of the soil surrounding the pipe and its influence on the load transfer effects is illustrated, together with the issues of significant interaction within the transition zones of landslides or faults.

A Rating Method for Assessment Risk at River Crossings

Detailed studies performed to design works at river crossings provide all the information needed to asses hydro technical hazards. TGN performed such studies for critical rivers as part of its Integrity Management Program. By monitoring performance of remediation works, experience was built throughout 10 years comprising different hydrological years. This was the base for the development of a simpler methodology aimed at assessing risk using information that can be readily available in regions such as Latin America where the existence of gaging stations and historic records at most rivers are not common. The method is based in river geomorphology, summarized with two parameters: area of drainage basin area and river slope at the crossing. They characterized the type of problems that can be expected and they can be estimated from topographic maps or digital terrain models available from the internet. The rating method follows a basic structure consisting in the product of two factors: causes and consequences. Causes include: bank erosion, river bed scour, meanders and river diversion along the right of way. Then, increasing factors are applied accounting for deforestation, land use and the occurrence of debris flows; decreasing factors consider proper remediation works, design and construction aspects implemented during construction. Finally, consequences are focused at loss of human life, impact on the environment, and interruption of fluid transport. This method is aimed to be performed by a pipeline operator that can have a good feeling of problems related to rivers, without having the technical knowledge of a specialized consultant. While rating, subjective judgment still plays an important role. However, this methodology provides a systematic approach that includes all aspects affecting river crossings, allows for prioritizing works based on rates and, as new rivers are included from new watersheds, it can be improved as prediction and characterization tool.