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Thermal fluid tests explained

Fluid degradation can be caused by a number of factors, from general wear and tear to flame impingement on heater coils. These causes can be identified from a series of tests that point an engineer to a system problem prior to the system operation being compromised. All system problems will show themselves in a number of test results, the combination of which can be a very useful tool to assist site engineers to improve operational efficiency and equipment up time. 

Below we provide an overview of the different tests available and their relevance.

Pensky-Martens closed cup flash test

This test involves heating a sample through a prescribed temperature increase under a closed housing. When the target temperature is reached, a source of ignition is intermittently inserted until the vapour ignites and flashes. The test is done twice; the first test is to establish the approximate flashpoint and the second to establish the accurate flashpoint.

This is the main flammability test and was originally designed for the oil shipping industry to ascertain safe ship hold temperatures when carrying oil. Industrially, this atmosphere can be produced in enclosed places such as ovens, air heat exchangers or leaks into insulation, where explosions are possible. Good ventilation is key in preventing an explosive atmosphere.

Cleveland open cup flash test

This follows the same format as the closed cup test but the sample is heated in open air. Again, the sample is heated through a prescribed temperature increase with the source of ignition applied every 2°C raise.

This test shows the temperature where the vapour will ignite in open air and can be reproduced in an industrial setting with leaks from flanges or pumps, leaks into insulation or exhaust points on vent systems.

Fire point testing

Using the same standard, the sample that has been used to establish open flash is heated further until the sample ignites and stays alight for five seconds or more.

This is the point at which, should there be an escape from the system and there is a means of ignition, the oil will light and a fire will ensue.

Total acid number

A sample of the fluid is taken to establish its acidity; most heat transfer fluids are supplied as neutral.

Chemical processes that can occur as part of fluid degradation generate small acid levels. This is a key indicator in identifying particular system problems.