In the United States, the annual cost associated with corrosion
damage of structural components is greater than the combined annual cost of
natural disasters, including hurricanes, storms, floods, fires and
earthquakes(1). Similar findings have been made by studies conducted in the
United Kingdom, Germany, and Japan. According to the U.S. Department of
Transportation Office of Pipeline Safety, internal corrosion caused
approximately 15% of all reportable incidents affecting gas transmission
pipelines over the past several years, leading to an average cost of $3 million
annually in property damage, as well as several fatalities. The need to manage
and mitigate corrosion damage has rapidly increased as materials are placed in
more extreme environments and pushed beyond their original design life.
Typical corrosion
mechanisms include uniform corrosion, stress corrosion cracking, and pitting
corrosion. Corrosion damage and failure are not always considered in the design
and construction of many engineered systems. Even if corrosion is considered,
unanticipated changes in the environment in which the structure operates can
result in unexpected corrosion damage. Moreover, combined effects of corrosion
and mechanical damage, and environmentally assisted material damage can result
in unexpected failures due to the reduced load carrying capacity of the
structure.
Ensuring long-term, cost-effective system integrity requires an
integrated approach based on the use of inspection, monitoring, mitigation,
forensic evaluation, and prediction. Inspections and monitoring using sensors
can provide valuable information regarding past and present exposure conditions
but, in general, they do not directly predict remaining life. Carefully
validated computer models, on the other hand, can predict remaining life;
however, their accuracy is highly dependent on the quality of the computer
model and associated inputs. Mitigation (corrosion prevention) methods and
forensic evaluations play a key role in materials selection, assessment and
design. All of these corrosion-control elements represent long-standing areas
of research and development at Southwest Research Institute® (SwRI®).
Pipeline Inspection
A significant portion of many pipeline systems cannot be inspected through traditional methods. Nondestructive evaluation (NDE) and inspection tools are critical to assessing the integrity of pipelines. Traditional NDE methods involve the use of pipeline inspection gauges (PIGs), which travel through the inside of a pipe and detect the presence of mechanical damage or corrosion.SwRI has also developed a guided-wave inspection technology that can be used to inspect pipelines and other structural components such as tubes, rods, cables and plates. The Magnetostrictive Sensor (MsS) inspection system uses inexpensive ribbon cables and thin magnetostrictive strips that are bonded to the component for inspection. The sensors attached to the pipe can accommodate a range of pipeline diameters, which is a significant advantage of guided-wave inspection systems that use an array of piezoelectric sensors. Because the sensors are low profile and relatively low cost, permanent installation of the sensors to perform structural health monitoring is a practical option.
A significant portion of many pipeline systems cannot be inspected through traditional methods. Nondestructive evaluation (NDE) and inspection tools are critical to assessing the integrity of pipelines. Traditional NDE methods involve the use of pipeline inspection gauges (PIGs), which travel through the inside of a pipe and detect the presence of mechanical damage or corrosion.SwRI has also developed a guided-wave inspection technology that can be used to inspect pipelines and other structural components such as tubes, rods, cables and plates. The Magnetostrictive Sensor (MsS) inspection system uses inexpensive ribbon cables and thin magnetostrictive strips that are bonded to the component for inspection. The sensors attached to the pipe can accommodate a range of pipeline diameters, which is a significant advantage of guided-wave inspection systems that use an array of piezoelectric sensors. Because the sensors are low profile and relatively low cost, permanent installation of the sensors to perform structural health monitoring is a practical option.
Corrosion Fatigue
Corrosion can degrade the mechanical integrity of a material through chemical
attack. For example, the presence of hydrogen sulfide (H2S) has been found to
reduce the fatigue life of offshore riser materials by approximately a factor
of 10, and in the presence of a notch (that acts as an initiation point for
corrosion fatigue) the fatigue performance can be decreased by a factor of 100.
SwRI has developed customized test facilities for characterizing the performance
of pipeline materials in corrosive environments.
Corrosion Exposure Testing
As new materials are developed and environmental conditions change, assessing material performance due to corrosion and stress corrosion cracking is of increasing importance. SwRI has a well-established corrosion testing facility to perform HPHT testing in extremely aggressive environments. In most cases, the testing environment consists of a simulated process or reasonable worst-case scenario. These include determining the effects of H2S, CO2, oxygen, and microbiological organisms on corrosion/cracking of pipeline materials. Testing conforms to NACE, ASTM, API, or ISO standards and test materials are analyzed for mass loss, localized corrosion or stress corrosion cracking (SSC)/sulfide stress cracking (SSC). SwRI staffers are highly experienced in designing, constructing and operating specialty tests to mimic a specific operation that does not conform to standardized methods. One such capability is performing the environmental exposure on the API 16C – Flexible Choke and Kill Systems, which evaluates the effects of gas permeation, gas decompression and test fluid exposure at the rated temperature.
As new materials are developed and environmental conditions change, assessing material performance due to corrosion and stress corrosion cracking is of increasing importance. SwRI has a well-established corrosion testing facility to perform HPHT testing in extremely aggressive environments. In most cases, the testing environment consists of a simulated process or reasonable worst-case scenario. These include determining the effects of H2S, CO2, oxygen, and microbiological organisms on corrosion/cracking of pipeline materials. Testing conforms to NACE, ASTM, API, or ISO standards and test materials are analyzed for mass loss, localized corrosion or stress corrosion cracking (SSC)/sulfide stress cracking (SSC). SwRI staffers are highly experienced in designing, constructing and operating specialty tests to mimic a specific operation that does not conform to standardized methods. One such capability is performing the environmental exposure on the API 16C – Flexible Choke and Kill Systems, which evaluates the effects of gas permeation, gas decompression and test fluid exposure at the rated temperature.
Corrosion
Prediction
Computer modeling is useful to help understand the mechanisms of internal corrosion, external corrosion and stress corrosion cracking, and to predict corrosion damage, failure and the most likely location of corrosion in oil and gas pipelines. These predictions can help support the development of practical guidelines to assist the pipeline industry in mitigating existing, or preventing future, corrosion failures.
Computer modeling is useful to help understand the mechanisms of internal corrosion, external corrosion and stress corrosion cracking, and to predict corrosion damage, failure and the most likely location of corrosion in oil and gas pipelines. These predictions can help support the development of practical guidelines to assist the pipeline industry in mitigating existing, or preventing future, corrosion failures.
Corrosion Sensing And Monitoring
While ICDA models can provide general guidelines to identify when internal inspections should occur, environmental and material uncertainties can lead to situations where excavation is performed unnecessarily, or water exists but is not predicted. In either case, costs associated with inspection or failure can be significant. To address this, sensing and monitoring technologies have been developed to enable remote interrogation of the internal corrosion of pipelines.The wireless mobile sensor, shown in Figure 6, travels inside a gas pipeline detecting the presence of water. The system communicates through a distributed wireless sensor network. The sensor body is an injection-molded polymer designed to survive high hydrostatic forces and impact on the pipeline walls while traveling along the pipe. This program has evolved using internal IR&D funding from both SwRI and Aginova, Inc.The multielectrode array sensor (MAS) probe is ideally suited for monitoring corrosion rates in process streams. Multiple discrete elements or electrodes are used to replicate the material of interest. The MAS probe measures corrosion rates by assessing the current flow between coupled electrodes. The electrodes can be manufactured from a wide range of alloys and product forms. SwRI has used this method to monitor the corrosion of a variety of materials.The wireless mobile sensor and the MAS probe sensor are just two examples of corrosion sensing and monitoring technologies. SwRI has developed a suite of corrosion sensing and monitoring devices. Significant inspection and repair costs can be avoided with the use of tools such as these.
While ICDA models can provide general guidelines to identify when internal inspections should occur, environmental and material uncertainties can lead to situations where excavation is performed unnecessarily, or water exists but is not predicted. In either case, costs associated with inspection or failure can be significant. To address this, sensing and monitoring technologies have been developed to enable remote interrogation of the internal corrosion of pipelines.The wireless mobile sensor, shown in Figure 6, travels inside a gas pipeline detecting the presence of water. The system communicates through a distributed wireless sensor network. The sensor body is an injection-molded polymer designed to survive high hydrostatic forces and impact on the pipeline walls while traveling along the pipe. This program has evolved using internal IR&D funding from both SwRI and Aginova, Inc.The multielectrode array sensor (MAS) probe is ideally suited for monitoring corrosion rates in process streams. Multiple discrete elements or electrodes are used to replicate the material of interest. The MAS probe measures corrosion rates by assessing the current flow between coupled electrodes. The electrodes can be manufactured from a wide range of alloys and product forms. SwRI has used this method to monitor the corrosion of a variety of materials.The wireless mobile sensor and the MAS probe sensor are just two examples of corrosion sensing and monitoring technologies. SwRI has developed a suite of corrosion sensing and monitoring devices. Significant inspection and repair costs can be avoided with the use of tools such as these.
Deposition Coatings
The deposition of material coatings can be effectively employed to protect
surfaces of components from wear, erosion and corrosion. A variety of coatings
have been studied including metals, ceramics and polymers. A number of
deposition techniques have also been developed. One example is magnetron
sputtering, where 20-30 µm thick Al-Ce-Co coatings are deposited on Al alloys
and 1018 carbon steel, which is sufficient for most applications where
corrosion and erosion are possible. A cross-section Al clad and Al-Ce-Co deposition
coating is shown in Figure 7a and 7b, respectively. Microstructural analyses
show that under certain deposition conditions, amorphous/nano-crystalline
structures are obtained, which show superior corrosion resistance in
electrochemical tests.
Sumber : http://pgjonline.com/2010/03/05/corrosion-control-in-oil-and-gas-pipelines/
G.H. Koch; Brongers, M.P.H.; Thompson, N.G.; Virmani, Y.P.; and Payer, J.H., “Corrosion Costs and Preventive Strategies in the United States,” FWHA-RD-01-156, U.S. Department of Transportation, Federal Highway Administration (2002).
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