Erosion in electrical discharge machining has been described as occurring by melting and flushing the liquid formed. Recently, however, thermal spalling was reported as the mechanism for machining refractory materials with low thermal conductivity and high thermal expansion. The process is described, here, by a model based on a ceramic surface exposed to a constant circular heating source which supplies a constant flux over the pulse duration. The calculations were based on TiBz mechanical properties along a and c directions. Theoretical predictions were verified by machining hexagonal TiBz. Large flakes of TiBz with sizes close to grain size and maximum thickness close to the predicted values were collected, together with spherical particles of Cu and Zn eroded from cutting wire. The cutting surfaces consist of cleavage planes sometimes contaminated with Cu, Zn, and impurities from the dielectric fluid. [

Integrating Layer of Protection Analysis (LOPA) with Hazard and Operability Analysis (HAZOP) has many advantages over performing these studies separately. The merits include: fewer actions from the combined effort compared to performing only a HAZOP; team continuity resulting from the combined effort as opposed to two separate teams having possibly differing points of view; and, ultimately, a time and cost savings realized by the combination. This integration defines the risk associated with a given scenario, enabling better decisions that impact business assurance. By using the Center for Chemical Process Safety guidelines to define the independent protection layers upfront, the gray areas can often be reduced or eliminated; thereby enabling a more thorough LOPA. Examples include taking credit if a unit has two independent operators (outside and inside) responding to critical alarms, or taking credit for centralized control rooms that may allow immediate operator interaction and response. This article shows how the guidelines have been used successfully in joint HAZOP/LOPA studies, and describes an initial preparation protocol that can ensure high‐quality results. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2009

Determining the correct interval for pressure relief valve inspection, testing, and maintenance remains a major challenge for facilities covered by the U.S. Occupational Safety and Health Administration Process Safety Management Standard. To this end, guidance is provided by API Standard 510, Pressure Vessel Inspection Code: In‐Service Inspection, Rating, Repair, and Alteration, by API Recommended Practice 576, Inspection of Pressure‐relieving Devices, by API Standard 520, Sizing, Selection, and Installation of Pressure‐Relieving Devices, Part II‐Installation, and by NB‐23, National Board Inspection Code—Part 2 Inspection. Furthermore, ASME BPVC, Sections I and VIII, provide general guidelines for the repair of pressure relief valves. However, the testing and inspection interval listed, up to ten years, is the maximum time span between shop inspections and overhaul. Further direction is often requested for determining the proper interval for valves in typical process services, especially in cases of PRV chattering. Recent API STD 520 Part II guidance on performing engineering analyses for PRV installations, based on service and specific installation, is included here. In this paper, a decision‐making approach to determining these intervals based on a combined understanding of risk‐based inspection, quality assurance, engineering analyses, and facility experience is presented. The approach provides process operators and managers with additional assistance in making this determination. © 2017 American Institute of Chemical Engineers Process Process Saf Prog 37:37–41, 2018