LZ Technology (United States)

Abstract This paper reviews the theory of coating deterioration mechanisms and how these mechanisms are connected to the common test method of scribe underfilm corrosion creep. Historical corrosion creepage test data of marine coating performance in different environments is analyzed. This data is used to predict the effects of coating deterioration in marine environments as compared to rural. This analysis is used to discuss the merit of using underfilm corrosion creep of scribed panels as a coating performance indicator.

Abstract Steel structures are often fabricated by bolting (or riveting) structural components together. Bolted joints result in multiple crevices between the bolted members and fasteners. These crevices are typically more susceptible to corrosion than flat surfaces because they tend to retain water/contaminants, they are difficult to properly coat, and the crevice geometry tends to support electrochemical phenomena that accelerate corrosion. This paper will evaluate the effectiveness of various coating practices at mitigating corrosion around these joints.

Abstract Protective organic coatings are the primary form of corrosion control for steel structures exposed in a marine environment. For more than fifty years, testing of coatings suitable for various service environments has relied substantially on exposure of coated steel panels of different configurations followed by evaluation via visual inspection. Exposure may include accelerated testing or natural environmental exposure in immersion or atmospheric conditions. Common visual inspection practices include semi-quantitative evaluation of the degree of rusting, degree of blistering, and extent of scribe creep (i.e., cutback). Coatings performing well in these evaluations versus specification standards are often deemed “acceptable.” Recent research suggests that common visual inspection protocols, while useful for judging aesthetic concerns, may not be sufficient in identifying the substrate corrosion control (barrier properties) provided by a coating. Destructive physical inspection for corrosion under protective coatings post-exposure suggests that significant metal loss may be occurring in the absence of a visual indication and that actual corrosion/material loss does not correlate with the visual inspection data. With a broader dataset of similar results, the data may suggest that the industry needs to reevaluate coating performance evaluation methods wherein the primary issue is substrate corrosion control as opposed to aesthetics.

Performance problems such as sluggish response time or low throughput are especially annoying, frustrating and noticeable to users. Fixing performance problems after they occur results in unplanned expenses and time. Our vision is an MDE-intensive software development paradigm for complex systems in which software designers can evaluate performance early in development, when the analysis can have the greatest impact. We seek to empower designers to do the analysis themselves by automating the creation of performance models out of standard design models. Such performance models can be automatically solved, providing results meaningful to them. In our vision, this automation can be enabled by using model-to-model transformations: First, designers create UML design models embellished with the Modeling and Analysis of Real Time and Embedded systems (MARTE) design specifications; and secondly, such models are transformed to automatically solvable performance models by using QVT. This paper reports on our first experiences when implementing these two initial activities.

The current program examined the use of structural spray polyurethane foams (SPF) used in the pipeline industry as line supports (foam ditch pads) or as erosion-control devices (foam trench breakers). Of concern are requirements that pipelines are protected by �non-shielding� coatings and that cathodic protection design must consider �electrical shielding.� Cathodic protection current may pass through or around the foams depending on the foam properties, surrounding electrolyte conductivity, and foam bonding to the pipeline. The program studied SPF impacts on cathodic protection of simulated under-ground steel pipelines.

Abstract Stainless steels are often used in marine applications due to their superior corrosion resistance and mechanical properties. However, stainless steels are susceptible to stress corrosion cracking (SCC) and corrosion fatigue. Fatigue occurs when cracks, which initiate as the result of cyclic loading, grow and eventually lead to fracture and component failure. For this reason, it is important to include fatigue in design considerations. Unfortunately, there is little data available for corrosion fatigue in marine environments. Most fatigue studies for materials in marine environments are conducted in aqueous solutions at ambient temperatures. In reality, marine environments can include periods of cyclic wetting and drying and variations in temperature. Furthermore, components often include design parameters that can shorten fatigue life such as crevices and mating surfaces. To better understand the behavior of stainless alloys in realistic marine environments, a series of high cycle fatigue tests were conducted on several alloys. Precipitation hardened and nickel alloys have been tested in environments including ambient air, immersion in solutions of 3.5 % sodium chloride (NaCl), and cyclic wetting environments at both ambient and elevated temperatures. Studies validated the importance of testing alloys in conditions representative of the actual service environment.

Felt reusable surface insulation was used extensively on leeward external surfaces of the shuttle Orbiter, where the material is reusable for temperatures up to 670 K. For application on leeward surfaces of the Orion multipurpose crew vehicle, where predicted temperatures reach 1620 K, the material functions as a pyrolyzing conformable ablator. An arcjet test series was conducted to assess the performance of multilayer felt reusable surface insulation at high temperatures, and a thermal-response, pyrolysis, and ablation model was developed. Model predictions compare favorably with the arcjet test data.