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Abstract Cased pipeline crossings are segments typically situated at road and railway crossings where the pipeline (carrier pipe) is surrounded by a larger diameter pipe (casing) for protection from mechanical damage. Although these locations face a similar threat of external corrosion as those which are conventionally buried; the management approach is considerably different. With time, spacers and end seals deteriorate and an environment conducive to external corrosion is created inside the casing leaving the pipeline vulnerable to damage if the coating system has also become compromised at any point. Execution of repair activities under these circumstances is very expensive and logistically challenging. Recently, a major North American pipeline operator has implemented gel-based vapor corrosion inhibitors (VCIs), in conjunction with cathodic protection to contend with such situations and control external corrosion of the carrier pipe at cased crossings. A VCI fluid mixture is initially injected into the casing’s annular space at a water equivalent viscosity and within a designed period of time it sets to a gel-like consistency. Since the gel is electrically conductive, it enables the carrier pipe to also receive cathodic current. Although the technique is proving to be very effective based from pipe-to-soil potential and ER probe measurement perspectives; some debate exists within industry regarding the simultaneous application of the two mitigation practices. This paper presents compatibility testing of VCI gel and CP and discusses the influences, effects or interactions between the two corrosion control methodologies. The overall objective of the project is to comprehensively identify and understand any offsetting effects between the concurrent use of VCI gel and cathodic protection inside a casing. The paper details results of laboratory experiments on VCIs for mitigating corrosion of casings. Introduction Onshore oil and gas pipelines routings often must pass beneath other critical infrastructure, such as highways, railroads, and waterways. Many North American operating pipelines were constructed over 50 years ago therefore corrosion prevention and related repairs are becoming more prevalent to avoid dangerous and costly releases. Ironically, pipeline segments that lie beneath some of the most sensitive areas are also among the most difficult to inspect and therefore require attention. Cased pipelines are subject to not only the normal corrosion caused by time, moisture, and soil chemistry, but also galvanic corrosion caused by contact between the metals of the carrier pipe and its casing. Furthermore, the outer casings can adversely affect cathodic protection systems installed to reduce corrosion if there is metallic contact between the casing and the carrier pipe.
- Research Report > New Finding (0.40)
- Research Report > Experimental Study (0.40)
Abstract A major pipeline Company has an inventory of approximately 2300 cased crossings throughout the various regions of Canada and the USA. Emphasis for managing and controlling corrosion within cased pipeline crossings is increasing from both operator and regulatory perspectives. Understanding the causes and characteristics of carrier pipe corrosion is an important stride towards improved integrity management of cased crossings. An excavation at a cased highway location is a complicated and intrusive process considering the impact to traffic and the numerous permits required prior to initiating any repair activity. Execution of repair activities under these circumstances is also very expensive and time constrained. The pipeline industry has recognized these challenges and responded with a proactive solution to prevent situations of this nature. A vapor phase corrosion inhibitor gel solution is being applied to control the corrosiveness of the environment within the annular space of the casing and its effectiveness is continually monitored using remote telecommunication technologies. The technique is very effective on a case by case basis; however due to the number of casings within the system, it becomes impractical to qualify the entire inventory. Subsequently, a prioritization method has been developed to select cased crossings that require immediate mitigation and also schedule long range planning for repairs. The innovative and systematic process evaluates critical information and attributes within an expert environment using established decision making techniques. Priority for all locations is determined by structuring a hierarchy of criteria and eliciting technical judgment of company’s Subject Mat ter Exper ts (SMEs), stakeholders, and unbiased industry specialists. Experts’ opinions are supported by combining Cathodic Protection (CP) and Inline Inspections ( ILI) results within a structured, multi-criteria decision making matrix to create an enterprise listing for the casing management program. Introduction The liquid pipeline system is large and complex, comprised by several regions and lines with pipe diameters ranging from 6 to 48 inches (168mm to 1219mm). These pipelines cross creeks, farm lands, highways, railroads and rivers. In order to alleviate the mechanical loads induced on these terrains due to traffic flow or other activities, concentric casings are installed around the carrier pipe. While casings effectively minimize mechanical damage; the environment within the casing annulus can promote corrosion of the carrier pipe through ingress of water, oxygen, microbial activity and metallic shorts or electrolytic coupling conditions that affect Cathodic Protection (CP). The presence of a casing substantially increases the complexity and expense when the carrier pipe requires repair from such circumstances. Permitting and interruption of road/rail traffic can increase the duration of the repair planning cycle from the normal 2-3 months to several years. Therefore, the Operator has introduced vapor phase corrosion inhibitor (VCI) gel solution within the casing annular space to control the corrosiveness of the environment and continually monitor inhibitor effectiveness through remote telecommunication technologies. The technique is proving to be very effective at controlling external corrosion on a case by case basis; however impractical to apply to the numerous locations where casings occur.
- North America > Canada (0.49)
- North America > United States > Texas (0.20)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Abstract The preferred method of new pipeline construction for a major liquid products transmission company at significant watercourse and roadway crossings is horizontal directional drilling (HDD). This Operator is responsible for a pipeline network with a total length of over 25 000 km’s containing 100’s of HDD and bored crossings throughout North America. Pipelines installed by HDD have an increased likelihood of experiencing coating damage as opposed to those constructed through conventional open trench techniques. Currently available methods for identifying damaged coating regions within pipe installed by HDD cannot always provide absolute or accurate information on the location, size and geometry of the holidays. Although cathodic protection monitoring at HDD locations can be validated within the entry/exit extremities; the region between is either assumed or speculated. Additionally, soil resisivity variations may adversely affect CP current distribution, leaving coating some coating defects in high resistivity areas unprotected and susceptible to corrosion. The Company has initiated a comprehensive evaluation of the CP performance at HDD locations. The approach utilizes a combination of monitoring techniques and field surveys with computational modeling technology to ascertain the external corrosion threat on pipelines within HDD locations. This article discusses a proof-of-concept for measuring procedures and demonstrates how field data is applied into computational modeling for predicting the CP effectiveness throughout critical, inaccessible regions of the HDD’s. Introduction HDD installed pipelines are typically installed at locations where repair is not practical therefore absolute compliance with the design life requirements of the pipeline is necessary to avoid the very costly and only alternative of replacement. However, due to limited options in inspection techniques and technology, the acceptance criteria for a HDD pipeline are lower than that for usual trenched construction. Pipelines installed by horizontal directional drilling (HDD) have an increased likelihood of experiencing coating damage than those constructed through conventional open trench techniques. Current methods for identifying damaged coating regions on buried pipe cannot always provide absolute or accurate information on the location, size and geometry of the holidays.