Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal High pressure seal failure: Analysis of the fatigue issue originated in pressure-leak relieving slots Daniel Ballorca-Juez a,b, ⁎ , Pedro Miguel Bravo Díez a , Mónica Preciado Calzada a , José Calaf-Chica a a Universidad de Burgos, Burgos 09001, Spain b DESMASA S.L., Burgos 09001, Spain ARTICLE INFO Keywords: High pressure Toughmet 3 Fatigue Mode II propagation ABSTRACT This study was focused on a metallic part from a dynamic seal of an ultra-high pressure in- tensifier. This part developed cracks originated at pressure relieving slots. Cracks were analyzed to get information about their origin and propagation mechanisms Simulations were performed to derive stress and strain state near the initiation region. It was concluded that cracks were initiated and propagated under mode II loading. Therefore, a model has been proposed to relate the tribological properties of the material and the crack plane orientation. Finally, a new slot was designed to delay crack initiation at this part. 1. Introduction The usage of highly pressurized water has several industrial applications that have been developed over the last decades. Specifically, two different technologies appeal to this fluid using its properties when being raised at high pressure: water-jet and high pressure processing (HPP). The former uses the internal energy stored at high pressurized water to be turned into kinetic energy. As a result, a high-speed stream, known as water-jet, is used to cut many different materials [1]. These materials can be composites, fabrics, or even metallic parts. The latter uses static high-pressurized water that is contained in a vessel to deactivate microorganisms and bacteria from food that is placed inside the vessel [2,3]. That process, also known as cold pasteurization, provides good food preservation without the need of use of chemical products or heating processes. In both technologies there is a need to drive water from a low-pressure state to a high-pressure state. Machines designed for this work are called intensifiers. The required pressure level is between 400 and 600 MPa, and piston-like pumps are used for raising pressure. These pumps use the force equilibrium principle to turn low pressure (20 MPa) fluid into high pressure fluid by a ratio of areas (Fig. 1). = F F L H (1) = A p A p . . L L H H (2) In some cases, double piston intensifiers are designed to take advantage of the reciprocating movement of the system, and two plungers are attached to the central piston; then low pressurized fluid is alternatively applied on both sides of the latter [4,5]. Although the working principle of these systems is very simple, difficulties arise because the level of pressure that is reached in the high-pressure side (HPS) of the system. In fact, 600 MPa is above the elastic limit of many steel alloys, so very high-strength alloys are https://doi.org/10.1016/j.engfailanal.2019.01.077 Received 18 October 2018; Accepted 25 January 2019 ⁎ Corresponding author at: Universidad de Burgos, Burgos 09001, Spain. E-mail address: dbj0001@alu.ubu.es (D. Ballorca-Juez). Engineering Failure Analysis 100 (2019) 127–146 Available online 27 February 2019 1350-6307/ © 2019 Elsevier Ltd. All rights reserved. T