Failure Analysis of Pharmaceutical Clamp Ferrules
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of Pharmaceutical Clamp Ferrules Jian Feng
Submitted: 2 March 2020 / Published online: 6 August 2020 Ó The Author(s) 2020
Abstract The purpose of this case study is to determine the cause of failure of DIN 1.4435 BN2 (AISI 316L with very low ferrite contents) clamp ferrules applied in pharmaceutical systems. Leakage was observed during operation in the clamp pipe connections of the ultra-pure fluid delivery systems. The surface of clamp ferrules showed remarkable discoloration and cracking. It was identified that the failure was caused by defects related to the autogenous laser conduction welding procedures. The intragranular cellular welded structures, which solidified with austenite as the primary product of solidification, showed a complete absence of hot cracks, minor delta ferrite, and minimum microsegregation. The welded components failed eventually owing to unstable welding profiles and significant porosity. Recommendations were given to prevent the recurrence of similar failures. Keywords Failure analysis Austenitic stainless steel Welding metallurgy Metallography Fractography Microhardness Porosity
Introduction The particular demands of pharmaceutical systems place many requirements on welded components used in the production environment. The piping connections with improved surface cleanliness must be highly corrosion resistant to withstand the cleaning regimes essential to guarantee drug purity and integrity. These requirements J. Feng (&) Centre of Materials Engineering, Heilbronn University, Max-Planck-Str. 39, 74081 Heilbronn, Germany e-mail: [email protected]; [email protected]
have led to the selection of type AISI 316L stainless steel for most pharmaceutical and biotechnological applications. The delta-ferrite content in 316L is further restricted in the Mo-, Ni-, and Cu-rich grade DIN 1.4435 BN2, since delta ferrite can be detrimental in certain chemical environments and some transformation products of delta ferrite can drastically deteriorate the corrosion resistance of welds [1]. The piping connections of 1.4435 BN2 are often joined by autogenous laser conduction welding (ALCW), which offers several compelling advantages. ALCW can be easily automated and applied to thin-wall parts. Sound strength of welds with clean appearances can be obtained by ALCW without any filler material. The inherent rapid solidification makes the use of ALCW very attractive, as the obtained microstructures with adapted solidification behavior, minimum segregation, and fine grain sizes can often improve the mechanical properties of welds [2]. In the present case, clamp connections of 1.4435 BN2 pipes used in pharmaceutical systems were orbitally welded together by ALCW without purging in the air. Electropolishing was subsequently conducted on the top surfaces in order to eliminate the distortion. Leakage was observed during operation on the clamp pipe connections of the ultra-pure fluid delivery systems. The clamp connections were finished according
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