REMOTE VISUAL EXAMINATION OF STAINLESS PIPELINES FOR PHARMACEUTICAL INDUSTRY
For the construction and maintenance of stainless pipelines the remote visual examination is employed. The weld roots and the pipe-wall inside are inspected to detect possible defects that could result in corrosion and bio-chemical processes. Such defects are mechanical and thermal damages to the oxide layer and defects in the weld roots. The remote visual examination is mandatory with welding and mounting of pipework systems. It is also used in regular inspections of the inner surfaces and welds during pipe operation in order to detect locations of potential corrosion and nests of micro-organisms. The welded pipelines made of stainless steel should fulfil relevant general and sanitary requirements. There should be neither undercuts nor unevenness at the root side since colonies of micro-organisms may occur at such areas. The oxide layer protecting a metal against corrosion should not become dark-coloured close to the weld due to a thermal influence. The paper treats sanitary requirements concerning stainless pipelines used in pharmaceutical factories. Weak points at the weld root side are shown. The relationship between colouring of the over-heated area and corrosion resistance of the welded joint is indicated. The importance of the remote visual examination and the assurance of weld quality in the production of equipment for the pharmaceutical and food-processing industries is underlined).
Corrosion behavior of welded stainless steel
The corrosion resistance of stainless steels depends on a protective, passive film being formed at the steel surface on exposure to the service environment. The use of fusion welding for fabrication leads to local compositional variations within the material, which may significantly alter the stability of the passive layer and hence the corrosion behavior. The paper reviews published work and practical experience on such effects of a weld thermal cycle. Compositional heterogeneity and locally reduced passive film stability can stem from three main causes. Attention is given first to the consequences of alloy element segregation during weld metal solidification and to the formation of fusion boundary unmixed zone. Element partitioning as a result of solid-state phase change is then considered, with particular reference to duplex ferritic/austenitic materials. Finally, the effects are described of precipitation, both of carbide (or carbonitride) particles and of intermetallic phases, with resultant development of alloy depleted regions. Throughout, recognition is made of the different grades of stainless steel employed by industry in terms of overall composition and microstructure. Study remains necessary to ensure that corrosion resistance of welded joints is adequate for service in a range of media. However, controlling factors have in large part been defined for both established and recently developed steels, and quantitative recommendations on preferred welding procedures can generally be given.
Testing digital circuits using a Mixed-Signal Automatic Test Equipment
This paper presents the results of parametric testing of digital ICs using a dedicated Mixed Signal Automatic Testing Equipment. Due to the prohibitive price of the ATE equipment and dedicated Device Interface Board (DIB) for digital Integrated Circuits (ICs), a DIB for analog circuits was used to perform the testing. Despite the challenges presented by the experiments, the results prove to be accurate for the performed tests, according to the data sheet of the digital ICs and production test data provided by the manufacturer.