Process equipment which employs a corrosion resistant alloy (CRA) layer cladded to steel is common in refineries, petrochemical plants and other plants processing highly corrosive media. There are two regularly employed methods for welding attachments and internals to clad process vessels. One is to remove the CRA cladding for welding the attachment to the steel base metal assuming dissimilar welds and restoring CRA by weld overlay. The other eliminates the step of removing the cladding, simplifying the attachment process by direct welding of the internals onto the clad layer. With the lack of data to prove the integrity of direct welding attachment onto the clad layer, designers frequently demand the cladding be removed or allow only a conservatively low stress limit for what can be attached directly to the clad surface. It is well understood that eliminating the step of removing clad increases the simplicity, improves the lead-time, and reduces the cost of making these attachments for trays or other internals, but there are concerns about clad disbonding risks. With the aim to provide data around the integrity of direct welding attachments for better risk assessments, a technical study was undertaken. In this study, it will be shown that the bond between clad material and the base steel is robust enough to withstand the heaviest attachments and harshest conditions. The theory behind the technical study will be presented along with the results of this study
Hydrogen sulfide gas produced by sulfate reducing microorganisms (SRM) creates significant challenges in the petroleum industry including corrosion concerns, product devaluation, and significant health risks. Biocides and inhibitors are often employed to control these detrimental activities. Recently, co-injection of a synergistic blend of biocides and the SRM inhibitor, nitrite, was proposed as an effective means to control biogenic sulfide production, however, the method only addressed inhibition of SRM activity and not kill. Inhibition can have the undesirable consequence of allowing SRM to resume full activity once the inhibitor is depleted, thus requiring the continuous input of expensive chemicals to maintain control. On the other hand, biocides are designed to reduce SRM concentrations thus reducing the need to add additional chemical until the SRM population re-establishes. Lab results, using an SRM field enrichment, demonstrated that the sequential injection of nitrite inhibitor followed by glutaraldehyde led to an 8-log reduction in SRM while only a 2-log reduction when co-injecting these chemicals at equivalent concentrations. It is proposed that pretreatment with the inhibitor, nitrite, or other respiratory inhibitor, results in a reduction in cellular ATP of the SRM creating a sublethal stress response allowing for their enhanced kill upon subsequent biocide addition.
The control of multiphase flow corrosion in oil and gas industry is one of the biggest challenging tasks. Since the 1990s, several organizations have established and operated large-scale flow loops to simulate and reproduce the field service environment of oil and gas pipelines. Based on comparison and investigation of the above loops, a new and advanced system, including several four inches internal diameter loops for studying corrosion under multiphase flows, was successfully built by us. By using this system, multiphase flows with various combinations of gas, water, oil and sand can be realized at the highest temperature of 140 oC and the highest pressure of 10 Mpa. Moreover, some loops in this system can adjust pipeline at different angels from 0 to 90°, which allow horizontal/vertical/sloping conditions to be simulated in laboratory. Many advanced measuring and monitoring technologies, such as Particle Imaging Velocimetry (PIV), high speed video camera and LPR/ER probe, are employed for simultaneously recording flow events and corrosion rates. An inhouse plane three-electrode probe is employed for conducting in situ electrochemical measurements. Such technologies would allow deep researching of corrosion behaviors and mechanisms in multiphase flow environments. Moreover, a new software based on Fluent and the existing multiphase corrosion models was developed to realize the numerical simulation of multiphase flow in loop.