Root Cause Failure Analysis of a Domestic Pressure Cooker Through Metallurgical Characterization and Computational Simulation

Pressure cooker is a closed domestic pressure cooking vessel for use with external heat source and capable of maintaining nominal cooking pressure up to 1.0 kgf/cm² (100 kN/m² approximately) gauge nominal. In pressure cookers, despite the development of electronic controllers, the basic edition of such vessels are still equipped with fewer advanced safety functions due to economic constraints. Although the provision of pressure relief valves (PRV) is considered as one of the major protective features, however, pressure cooker failure accidents have been reported frequently. This paper describes the analysis of pressure cooker failure that failed prematurely after 1 year of service considering the design life of > 5 years. It was hypothesized that the root cause of pipe failure was either material degradation from exposure to an aggressive environment or an inherent defect in the pressure cooker. To test this hypothesis, a thorough visual examination of the exhumed failed section and the fracture surface was undertaken, followed by liquid penetrant testing, material identification, hardness testing, and metallographic analysis. Computational models of static and transient loading were also used to determine the stress distribution along the actual geometry of the failed cooker and to understand the main causes of recurrent failures. Visual and macroscale examination revealed significant body deformation at the lower dish-ended shell showing distorted locking grooves. It was also noticed that dirt and food particle, from the earlier cooking, were stuck in the pressure valves orifice. In addition, no evidence of metallurgical defect was observed. The inspection indicated that the cause of failure is primarily due to the choking of pressure relief value (PRV) and overpressure safety valves. Consequently, the pressure release occurred from the sealing side of the top lid, which resulted in its ejection.     

Causal inference for time series analysis: problems,methods and evaluation

Knowledge and Information Systems - Time series data are a collection of chronological observations which are generated by several domains such as medical and financial fields. Over the years,...     

Determinants of Internet skills,uses and outcomes. A systematic review of the second- and third-level digital divide

Recently, several digital divide scholars suggested that a shift is needed from a focus on binary Internet access (first-level digital divide) and Internet skills and use (second-level digital divide) to a third-level digital divide in which the tangible outcomes of Internet use are highlighted. A plethora of studies have been conducted to identify determinants of digital divides. Unfortunately, there is a lack of consistency in the terminology used. Moreover, terms are often not theoretically grounded. Therefore, we conducted a systematic literature review of digital divide determinants. The results show that the third-level digital divide was underexposed. The primary focus is on Internet use. More importantly, the identified determinants show that digital divide research is largely limited to sociodemographic and socioeconomic determinants.