Cortest (United States)

Abstract The ability to detect and/or monitor corrosion of structural aircraft components, located in difficult-to-access areas, may contribute to a significant reduction in annual maintenance expenditures. Reductions can be achieved in the frequency of major overhauls, corrosion inspection, and unanticipated structural rework/repairs. Existing systems and new developments for monitoring corrosion of components in these areas are discussed.

Abstract The present understanding of the mechanism of cathodic protection is too simplistic to explain when, why, and under what conditions corrosion is mitigated for a buried pipeline. This paper presents a general framework which attempts to explain why cathodic protection is achieved and what factors are critical in determining the ability of cathodic protection to mitigate corrosion. It is speculated that the changes in the "near-surface" environment due to the reduction processes on the cathodically protected steel surface play a significant role in mitigating corrosion and in defining the level of polarization achieved. This is accomplished by contributing a concentration polarization term to the overall level of polarization. Furthermore, the concentration polarization term explains many field related observations not easily explained by activation polarization and mixed potential theory.

During a prior research program, a spiking phenomenon was identified that prevented the measurement of the off potential directly from the pipe-to-soil potential waveform. Furthermore, the spike made it impossible to measure an off potential during current interruption for some period of time following interruption. In recent years, there has been discussion that the spike in the pipe-to-soil potential waveform affects the ability of the CP system to mitigate corrosion. In addition, the increased significance that has been placed on off-potential measurements within the industry has made it important to understand any phenomenon that may affect the ability to measure the off potential. This effort works to establish the cause and effects of the spiking phenomenon. To accomplish this program, a Work Plan was established that provided for the following four tasks: Task 1 - Field Measurements, Task 2 - Circuit Analog Model, Task 3 - Effect of the Spike on Off- Potential Measurements, and Task 4 - Laboratory Experiments. Through this combined effort of field evaluations, modeling, and laboratory experiments, the root cause of the spike was established along with guidelines for making the off-potential measurement. The results of this project provides the CP engineer with a standard practice for measuring off-potentials in the presence of the spiking phenomenon.

Abstract The cracking behavior of a Cu-2Mn weld alloy in concentrated phosphoric acid-alcohol solutions, in the temperature range 249 to 304 C, has been investigated using the slow strain rate test technique. Moderate amounts of air ingress in the acidic environment was found to produce intergranular cracking in the alloy. Whereas, excessive amounts of air produced severe general corrosion and minor cracking. The results have been used to determine the cause of cracking which occurred in the alcohol reactors that were lined with copper and welded with ISA-13 alloy.

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Summary This paper provides a technical review of the materials selectionprocess for sour service. It highlights H2S corrosion processes that occur onhigh-strength steels and corrosion-resistant alloys. In addition, procedures toperform materials evaluation and selection to minimize the deleterious effectsof H2S are discussed. Introduction As shallow reserves are depleted, the worldwide search for new sources ofhydrocarbons is turning to deeper reservoirs. Drilling and producing thesereservoirs requires the use of new materials not previously used. In manysituations, drilling procedures and completion schemes are now being dictatedby materials technology. Deeper drilling means that higher pressures will be encountered and that thereservoir fluids will be at a higher temperature than normal. The likelihood ofencountering acid gases (CO2 and H2S) as a reservoir component is alsoincreased. Formations containing 25% H2S + CO2 at 200 deg. C [392 deg. F] witha bottomhole pressure of more than 140 MPa [20,000 psi] are not uncommon. The mechanical requirements for materials used for production equipmentincrease substantially with well depth. Tensile loads for tubulars are greaterbecause of the greater hangoff loads, and hoop stresses increase because ofpressure. Elevated temperatures have a pronounced detrimental influence onmechanical properties. The tradeoff in economics is often between higher-strength(higher-price-per-pound) materials and thicker-walled equipment (more pounds). In most cases, higher-strength materials would be favored economically were itnot for the greater susceptibility of high-strength materials to environmentaldegradation in reservoir fluids. This paper discusses (1) the environmentalprocesses associated with H S that affect the performance of high-strengthmaterials, (2) the alloys that are used (or are being considered) to overcomethe adverse effects of corrosive environments, and (3) procedures to selectmaterials for sour service. The more difficult frontier areas where wells aredeep and hot and contain acid gas have been emphasized. Historical Background Since the early 1950's, the petroleum industry has been developing sour-gasfields. Initially, much of this activity was centered in western Canada. Asfield operations began, it was quickly realized that there was a major problemwith brittle fracturing, later called sulfide stress cracking (SSC), ofhigh-strength (high-hardness) steels when exposed to sour productionenvironments. This problem was particularly associated with the failure ofdownhole production tubulars. However. other consequences of exposure to sourenvironments were quickly recognized. JPT P. 1051^