The high-temperature degradation of hydraulic oils and fluids©

Abstract

The rapid darkening of hydraulic oils and fluids in use has occasionally been reported. This paper summarizes the past investigations into this phenomenon, which have largely focused on the compression of air bubbles in mineral hydraulic oil. The process leads to a form of high temperature degradation known as dieseling and the probable formation of sub-micron carbonaceous particles. The importance of system design and particularly the choice of pumps, in this process, are discussed. The primary objective, however, is to examine the effects of dieseling on phosphate ester fire-resistant fluids and to clarify if an analysis of the used fluid can indicate whether this process is taking place. An investigation of samples taken from systems displaying rapid degradation suggests that the presence of certain breakdown products may infer the approximate level of temperature to which, at least, small amounts of the fluid are being subjected. The presence of carbonaceous material in the dieseling process is also confirmed. Some suggestions made for the mechanism of its formation as well as the formation of other major degradation products. Lastly, recommendations are made for ways of minimizing this form of breakdown not only in terms of system design but also with respect to fluid properties, fluid maintenance and the use of in-situ conditioning.

Phosphorus cardanol: chemical characterization and thermal stability

“…Therefore, degradation products, if any, are present in small amounts under this condition. This result is in accordance with literature, once that some authors related that, the thermal degradation of phosphate esters only becomes significant at very high temperatures (above 150 °C) [29,38,[40][41][42]. …”

“…Therefore, the obtained results suggest the possibility of application of these compounds as antioxidants for lubricant oils, once the degradation of these petrochemical products, in general, starts at 91 °C [4]. As the phosphate esters find use in a variety of commercial applications (lubricants, hydraulic fluids, polymers and others), and some of these systems may be contaminated by solids and/or metals, water, engine oils, solvents and oxygen; it is very important know their thermal behaviors, once that degradation can be a limiting factor of the application of these phosphorus compounds [39][40][41][42].…”

“…Based on the evidences reported in the literature, four mechanisms can contribute to the degradation of alkyl and aryl phosphate esters, depending of the environmental conditions to which the compound is exposed [37,40]. In the case of phosphate esters, all decomposition pathways produce 'strong' acids (phosphoric acid derivatives) as the main degradation product, normally as result of hydrolysis and oxidation (see Figure 5).…”

“…In the case of phosphate esters, all decomposition pathways produce 'strong' acids (phosphoric acid derivatives) as the main degradation product, normally as result of hydrolysis and oxidation (see Figure 5). In lubrication systems, this step is followed by reaction of the acid with the metals components to form metal soaps that cause an increase of oxidation of the lubricant, more acid and higher levels of metal soaps [40,41,42]. Therefore, the information on thermal behavior of phosphate esters has significant practical importance.…”

Maintenance practices for steam turbine control fire resistant fluids: Part 1

“…Fortunately, the duration of the fluid exposure to this heat is short and usually lasts only a few milliseconds. In general, low temperature degradation causes slow fluid darkening, while high temperature degradation results in rapid fluid darkening, the generation of a burnt odour and sub-micrometre-size carbon particles [7].…”