Corrosion Control In Oil And Gas Pipelines

By Ben H. Thacker, Glenn M. Light, James F. Dante, Elizabeth Trillo, Fengmei Song, Carl F. Popelar, Kent E. Coulter and Richard A. Page, Southwest Research Institute® San Antonio, TX | March 2010 Vol. 237 No. 3

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. Figure 3a shows a servohydraulic load frame setup with a custom-designed test cell and redundant H2S containment systems. Full-thickness fatigue specimens (Figure 3b) are machined from riser pipes to preserve through-thickness residual stresses and to capture welds in joined pipe.

SwRI recently developed a high pressure, high temperature (HPHT) corrosion fatigue test facility. In this facility the underlying fatigue crack growth behavior of riser materials subject to HPHT H2S (and other aggressive) environments can be quantified (Figure 3c). This unique test facility provides the capability to quantify inter-related corrosion-fatigue mechanisms, and provide data for calibrating and validating corrosion-fatigue computer models.

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Figure 3: a) Servohydraulic load frame with H2S corrosion fatigue test; b) One-meter-long specimen; c) high-pressure high-temperature corrosion fatigue test.

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 (Figure 4).

Figure 4: Photograph of the API 16C – Flexible Choke and Kill line testing.