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Flammability Tests on Hot Surface for Several Hydraulic Fluids
2018/09/12
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Industrial equipment using hydraulic fluids are design to accept higher load and speed, implicitly higher temperatures, including for fluids. Leakages from enclosures like gear boxes or hydraulic systems could increase the risk of fluid reaching hot surfaces, thus producing fires hard to be controlled and isolated. The designer have to evaluate the flammability of fluids and they should select several solutions for a particularm application in order to estimate the costs of different solutions and to mitigate the risk of having accidental fires due to a specific fluid grade.
The tests were done with the help of an original equipment allowing a dedicated soft assistance in order to protect the operator and to sustain reproducibility, according to the standard SR EN ISO 20823:2004 Petroleum and related products. The determination of the flammability characteristics of fluids in contact with hot surfaces -Manifold ignition test, There were tested the following grades of hydraulic oil HLP 68 X-Oil, HFC Prista, MHE 40 Prista (100% oil), a rapeseed oil (obtained after a dewaxing process) and an emulsion oil-in-water (5% vol. MHE 40 Prista). There were identified distinct behaviours of these fluids under the test conditions
INTRODUCTION
European directives [2-4, 7] and other documents [1, 5, 6, 8] emphasis the necessity of reducing the flammability risk when using industrial fluids (hydraulic fluids, lubricants, processing fluids like those used in steel treatment and cutting etc.), especially in explosive atmosphere. Thus, “in particular, where fluids are used, machinery must be designed and constructed for use without risks due to filling, use, recovery or draining.” [7] Risk assessment implies a complex analysis of design, equipment, procedures and operators. Thus, the same document [7] underlines that “machinery must be designed and constructed to avoid all risk of fire or overheating posed by the machinery itself or by gases, liquids, dust, vapours or other substances produced or used by the machinery.” Both manufacturers and users ask for tests thatcould certify fluid flammability characteristics,preferring ISO or ASTM standards [1, 10, 20, 21].
Many documents, including EU Directives, give recommendations to use standardised tests for estimating flammability of fluids [1-4, 6-8, 14-16].The evaluation of fire resistance of a hydraulic fluid cannot be done by one test only and the aspects of fire resistance have to be pointed out by several tests, including those simulating on small scale the worst scenario that could happen in real applications using hydraulic fluids [11, 17]. Many of these tests give a result as “pass” or “not pass” [8, 20, 21]. The fluid that passed a particular test or, better, a set of tests, is included in recommendations or approvals, but these ones are specific to regional or national reglementations [1, 6, 8, 13].
TESTING PROCEDURE
The tests were done with the help of an original equipment (Fig. 1) [27] allowing a dedicated soft assistance in order to protect the operator and to sustain reproducibility, according to the standard SR EN ISO 20823:2004 Petroleum and related products. Determination of the flammability characteristics of fluids in contact with hot surfaces - Manifold ignition test. This test simulates an accident or the hazardous event when a fluid drops on a hot surfaces: 10 ml of fluid is dropped during 40…60 seconds on a manifold kept heated at a constant temperature, from a distance of 300±5 mm above the manifold surface. For each temperature and fluid there were done 3 tests. The highest temperature, for which the fluid does not burn or ignite, was established is the same “verdict” was obtained for all the three tests. All the temperature values given in this study have the accuracy given in Figure 2. The equipment is controlled and assisted by a PC with a dedicated soft in order to protect the operator from being near the heated zone. Figure 2 presents the display of the soft.
There are several reasons of fluid leaking [11, 16]:
? fatigue of the system elements, under normal or severe exploitation (cracks, creep, ageing), or due to an adequate maintenance,
? cyclic or accidental thermal expansions, bolts stretch;
? changes of fluid properties due to exploitation, especially temperature rising that makes the fluid to become thinner,
? the efficiency loss of seals and hoses in time, due to their modifications produced by long exposure to temperature or/and chemicals, but also by trapping “foreign” particles (solid, liquid, gaseous or mixtures of them);
? screw-up operations: a controlled mounting and a preventive maintenance decrease the leak probability under functioning conditions. It is also important to respect procedures for starting and stopping the equipment;
? operator’s faults; regular trainings could significantly reduce these events [8, 11].
There were tested the following grades of hydraulic ils HLP 68 X-Oil [25], HFC Prista [23], Shell Irus luid DR 46 [22], a rapeseed oil (obtained after a ewaxing process) [9] and an emulsion 5% MHE 46 n water as recommended by Prista producer [24]. here were identified distinct behaviours of these luids under the test conditions.
Shell Irus Fluid DR 46 is a tri-aryl phosphate ester ire resistant hydraulic fluid. It contains carefully elected additives to give superior oxidation and ydrolytic stability. Shell Irus Fluid DR 46 should be sed in hydraulic systems operating in close roximity to potential ignition sources. This includes quipment such as die-casting machines, billet oaders, electric arc furnaces, forging presses and thers operating in fire hazard situations.
PRISTA HFC is a fully synthetic fire resistant waterglycol ased hydraulic fluid blended with an additive ackage to improve the anti-wear properties and orrosion protection of the finished product [23].
HLP 68 X-Oil [25] is an optimized alloyed hydraulic il with a high performance level and a broad field f industrial application. It especially distinguishes ith good viscosity-temperature behaviour, high ageing stability and reliable corrosion protection. dditives provide an excellent wear protection under xtreme loads, too. The behaviour against sealing aterials is neutral.
Prista MHE-40 is used as 5% working fluid in oil-inwater mulsion for hydraulic systems with high risk f flammability [24]. The tests were done on the ully mineral oil and for the emulsion 5% MHE 40 vol.) in water.
RESULTS AND DISCUSSION
Analysing the recorded films of the tests (Figs. 3-10),the authors noticed the followings: there were stages
when the fluid only evaporates or change structure
without ignition, these being useful in establishing the
time response of fire/security sensors.
The hydraulic fluids HFC Prista, Shell Irus Fluid
DR 46 and the emulsion 5%MHE Prista in water
does not burn even for the highest tested
temperature (700°C±5°C), a temperature also
included as imposed for hydraulic fluids with the
best behaviour under the conditions of EN ISO
20823:2003. The other two tested fluids burn. The
rapeseed oil has 551°C the highest temperature at
which it does not burn for repeated test (at least
three) and HLP 68 X-Oil h The behaviour of this rapeseed oil (dewaxed grade)
[9] under the testing conditions imposed by SR EN
ISO 20823:2003 could be grouped in the following
ranges, characterised by temperatures for which the
fluid behaviour is the same :
1. a temperature range for which there are
repeatedly obtained the same results when
testing the fluid on hot manifold
(200…551?C, the fluid does not burn);
2. a temperature range for which the test results
is randomly different (in one test the fluid
does not burns, but in the following one it is
burning and so on): 551…557?C; in practice
it could be included in the range for which the
fluid burns and the use of the fluid in this
range is strongly not recommended;
3. The temperature range for which the fluid
burns, θ > 560?C.
Any test is irrelevant for the temperature range
552…562?C for the dewaxed rapeseed oil because the
difference (10°C) is the same to the allowance range
(±5°C).
The flammability risk could be substantially reduced
by using emulsions as that one obtained from 5% vol.
MHE 40 in water. The authors noticed that this
emulsion does not burn on the surface heated at 700°C, but the mineral oil – 100% MHE 40 Prista
does burn at a much lower temperature of 450°C and
it is very sensitive to the surface quality. The authors
also noticed that the test done at this temperature of
450°C gives inconsistent results. From 9 tests, during
6 ones, the fluid ignited and burnt when it was
dropped on the clean surface of the heated manifold.
When the test was done on the same manifold, but
dirty from previous tests, the temperature of ignition
of the same fluid was even lower: 415°C. This is a
conclusion that could be the subject of a further
investigation, as in practice many surfaces could be
far for being clean due to the technological process or,
worse, due to the “leak” of operators’ responsibility or
an inadequate maintenance.
The designer has two possibilities for reducing the
flammability risk: to use a fluid that does not burn or
to change the design in order to have a better
protection against hazardous events that could cause
fluid ignition. Of course, the first solution is better
especially when the equipment works in a particular
environment, including mining, metallurgy, glass
industry etc. The designer has to select the hydraulic
fluid from families like the synthetic, mineral or that
of emulsions. The synthetic ones have some
advantages, but they are still expensive. The engineer
has to balance the advantages and disadvantages of
each group. For instance, the emulsions could be much less expensive, but they have to be circulated in
systems (piping, pumps etc.) exhibiting a good
corrosion resistance or, at least, an acceptable
resistance for a particular application.
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