EXPERIMENTAL STUDY OF THE INTERACTION OF CORROSION DAMAGE AND OUT-OF-CIRCULARITY IN THE COLLAPSE OF SUBMARINE PRESSURE HULLS

The effect of corrosion damage on overall collapse strength of submarine pressure hulls was studied experimentally. Ring-stiffened cylinders were machined from aluminium tubing and loaded to collapse under external pressure. In selected specimens, some of the outer shell material was machined away in large single patches, representing general corrosion. Other specimens had many smaller patches, representing corrosion pitting from the outside of the hull, followed by grinding. Large-amplitude out-of-circularity (OOC) was introduced by mechanically deforming selected cylinders. Clusters of artificial corrosion pits were found to have approximately the same effect on collapse pressure as equal-depth general corrosion covering the same region of plating. General corrosion was found to be most severe when it was “in-phase” with OOC, since, during pressure loading, high compressive stresses resulting from corrosion were compounded by compressive bending stresses associated with OOC, and furthermore, the corrosion tended to increase the geometric imperfection itself. On the other hand, out-of-phase corrosion reduced the effect of OOC, while at the same time the thinning-associated compressive stresses were counteracted by local tensile bending stresses associated with OOC, so that strength reductions were correspondingly smaller. Overall collapse pressures for corroded specimens were reduced by, on average, 0.85% for each 1% of shell thinning. That result is based on a linear approximation of the nonlinear relationship between thinning and collapse pressure. The linear trend-line, which was used to account for the experimental scatter, is based on specimens with 13 to 27% shell thinning, and with a variety of corrosion areas and OOC amplitudes.

Decarbonization and Improved Energy Efficiency Using a Novel Nanocomposite Surface Treatment

Fouling of heat exchanger equipment through the formation and attachment of hard scale, microbially induced corrosion (MIC) products, or particulate erosion is a serious challenge to reliable production in the oil and gas industry. Exchangers which become fouled in this way perform 15-30% worse than their rated ability, requiring either constant intervention to clean away biofilms, continuous injection of biocides and corrosion inhibitors, or the regular plugging of tubes to prevent leaks, representing a significant operating expense and billions of dollars in lost production time. When an exchanger is unable to provide sufficient heat due to tube fouling, additional sources of heating must be utilized to make up for this deficit and to ensure that facility processes remain within design allowances. This need for supplemental heating is a significant source of carbon emissions in the industry and represents a significant obstacle towards decarbonization efforts. However, it also represents an economically attractive way to simultaneously lower emissions while also lowering a producer's cost per barrel. This work describes an alternate strategy to control and prevent fouling in heat exchangers, through the one-time application of an omniphobic (water- and oil-repelling) nano-surface treatment. Once applied to a heat exchanger, the extremely smooth and low-surface energy material greatly reduces the ability of MIC-causing bacteria to deposit and adhere to the surface. Because it imparts functionality to the surface itself, rather than simply function as a physical barrier, it enables long lasting protection which was validated under laboratory conditions in a pressurized autoclave, as well as two pilot demonstrations. Results from both the laboratory and field evaluations of the treatment's promise showed that treated surfaces showed a corrosion rate over 36-times lower when compared to untreated surfaces, while also completely arresting the formation of corrosion pitting, tube fouling, and erosion of the tube interior. These field-validated results were then applied to the observed heating deficit of a proposed deployment site, resulting in calculated carbon emissions savings of up to 17,000 Tons CO2 per year.

Corrosion Studies on Stainless Steel 316 and their Prevention – A Review

Corrosion is a process that causes a change of metal to chemically stabled form, by reacting with a solution or with the atmospheric air. There are various types of corrosions such as crevice corrosion, intergranular corrosion, stress corrosion, pitting corrosion, galvanic corrosion and uniform corrosion. These types of corrosion and the prevention methods are investigated in this review paper. Stainless steel 316 has excellence in corrosion resistance, due to the presence of molybdenum content. From the literature survey, stainless steel 316 has been tested in various experiments to improve the properties of the material. In the present review, several coating processes and additives which are added on SS 316 to improve the material properties are studied. The advantages of these improvements are reduced cost of change of material, reduced loss of material due to corrosion and increase in materials durability. Hence, stainless steel 316 is used for all corrosion applications which causes less damage and high durability compared with other austenitic steels.

Failure Analysis of Railroad Components

Because of the tough engineering environment of the railroad industry, fatigue is a primary mode of failure. The increased competitiveness in the industry has led to increased loads, reducing the safety factor with respect to fatigue life. Therefore, the existence of corrosion pitting and manufacturing defects has become more important. This article presents case histories that are intended as an overview of the unique types of failures encountered in the freight railroad industry. The discussion covers failures of axle journals, bearings, wheels, couplers, rails and rail welds, and track equipment.

Failure in a pipe due to defective maintenance

Proper maintenance of energy transport pipelines is a part of energy efficiency since energy losses during transport are reduced with good maintenance practices as well as the mechanical integrity can be known. Moreover, it reduces the risk of accidents or environmental damage. This work is an example of the experiences that must be taken into account for optimal pipeline maintenance and consisted of a failure analysis performed on a 20-inch diameter "T" connection, which plays an important role in the energy transportation process and it was found to be partially buried with exposure to rainwater. Preventive maintenance consists of visual inspection, cleaning, and coating with paint. The results indicated that the failure begun due to fatigue with origin in weld defects and the fracture grew up due to an overload, which caused the crack to grow following the region of the material with loss of thickness induced by corrosion pitting.

Metallurgy Selection of Tubing in Sucker Rod Pump Wells Plagued with Pitting and Abrasion Issues

Analysis of tubing failure of SRP wells with respect to uniform corrosion, pitting and mechanical abrasion has been carried out. The primary objective includes the identification of root cause of failure and suggesting alternate metallurgy. Many wells in an onshore field in ONGC were facing the acute problem of general corrosion, pitting and rod-tubing wear. The methodology for carrying out the study consists of a Failure Analysis of a retrieved sample of the failed tubing from one of the affected wells. This included a thorough visual inspection, Scanning Electron Microscope analysis and X-Ray Diffraction analysis. The results of these tests were backed up by software simulation in Honeywell Predict. Metallurgy selection involved multiple exhaustive simulation runs in Honeywell Software Socrates which was corroborated by relevant oilfield standards as well as literature available on the subject matter. Based on the failure analysis and simulation runs, it was concluded that besides the issue of uniform corrosion and pitting, many of the affected wells are also facing the problem of tubing failures due to abrasion and mechanical wear. It is pertinent to note that the major contributor of the frequent tubing failures in the candidate wells selected for the study were pitting and corrosion. Nevertheless, Abrasion always remains a key threat to the tubing string integrity in rod-pump wells. Therefore, the existing tubing metallurgy of N-80 grade Carbon Steel was deemed inadequate in the absence of reliable corrosion inhibitor continuous dosing facilities. A tubing metallurgy that takes care of both pitting corrosion as well as abrasion and mechanical wear was sought. UNS 41426/41427 or the modified version of 13 Chrome, commercia lly known as Super Martensitic 13 Chrome, are available in 95 ksi and 110 ksi grades. These grades have a maximum hardness of 28-32 HRC which is substantially high compared to L-80 13 Cr (maximum 23 HRC). Also, as this alloy has 4-6% Nickel, it provides added protection against uniform corrosion as well as pitting and hence was recommended. The paper specifically analyses tubing failure in Sucker rod-pump wells due to corrosion, pitting and abrasion. After exploring various viable options, adequate tubing metallurgy has been recommended that should take care of corrosion, pitting as well as mechanical wear problems.

EFFECT OF CALCIUM ON THE ANODIC BEHAVIOR OF ALUMINUM CONDUCTOR ALLOY AlTi0.1 IN THE MEDIUM OF THE ELECTROLYTE NaCl

The article presents the results of an experimental study of the effect of calcium on the anodic behavior of the aluminum alloy AlTi0.1, in the medium of NaCl electrolyte. The study was carried out by the potentiostatic method in the potentiodynamic mode at the potential sweep rate of 2 mV / s. It is shown that the modification of the aluminum alloy AlTi0.1 with calcium promotes the displacement of the potentials of free corrosion, pitting formation, and repassivation to the positive range of values. The corrosion rate of the aluminum alloy AlTi0.1 when modified with 0.01-0.5 wt % calcium decreases by 10-17 %.