+44 (0)1932 564391

sales@stanhope-seta.co.uk
Find your local representative

IP 565 Particle Method revised

24/4/2013

for improved accuracy

THE FUTURE OF LASER PARTICLE COUNTING

The availability of reliable automatic particle counting apparatus and test methods, including AvCount and IP 565, has made these test methods a viable option for specification purposes. The improved precision of these methods has resulted in some standardisation authorities stating their intention to replace gravimetric tests with laser obscuration particle counting tests at the earliest opportunity.

Work from the Energy Institute (EI) has underpinned this migration, revisions made to these methods in March 2013 has resulted in improved reliability of these test methods.

REVISION 1 - DETERMINING VERIFICATION TOLERANCE

The fuel industry methods of particle counting were derived from methods used for hydraulic oils originally devised in the 1960s. At that time, the technology limitations were such that accuracy, repeatability and reproducibility were relatively poor.
Furthermore a system of coding was introduced that converted particles/ml into cleanliness codes to make it easier for an operator to report results. The problem was that these codes are quasi-logarithmic which allows for a large range of particle counts to be covered by a single cleanliness code, the effect of this is potentially misleading tolerances.

Energy Institute investigations carried out during 2011 and 2012 revealed that more precise technology is now available. Instruments like AvCount now include highly coherent solid state lasers, low noise electronics and advanced digital processing which considerably improve their precision. As a result, the EI has revised the tolerances for calibration and verification.

The revised tolerance is statistically derived from the particle counts for the batch of verification material and the reproducibility (R) of the test, whereas the previous particle count tolerance for verification was based on the ISO cleanliness code. Using the reference standards recommended in ISO 11171 (the “core” ISO governing the design and calibration of Automatic Particle Counters), a particle counter would be verified using a material with a count of approximately 6000 @ =4µm(c). Using the “within 1 ISO cleanliness code” tolerance, a count between 5001 and 10 000 particles/ml would be acceptable. However, under the revised tolerances the limit would be approximately 5400 to 6400 particles/ml @ =4µm(c).

REVISION 2 - IP 565 ANNEX B: PROCEDURE TO ELIMINATE THE EFFECTS OF WATER IN PARTICLE COUNTING

As a result of trials by the Energy Institute and particle counter manufacturers, it has been possible to quantify the volume of cosolvent or chemical additive necessary to negate the effect of water on particle counting in typical jet turbine fuels.

IP 565 Annex B describes the procedure for the addition of either a cosolvent or a proprietary chemical to the sample to increase the accuracy of the particle count by eliminating free water interference. Water droplets in suspension could result in an unacceptably high particle count, even though both the particulate and water content are within specification.

The procedure outlined in Annex B is optional, some users may adopt it as a standard procedure whilst others may choose to use it only to clarify whether a high count was due to dirt or water droplets.

EXTENSION OF TESTING INTO OTHER FUEL TYPES

Test method ASTM D7619 also covers diesels, bio-diesels and bio-diesel blends which suffer from similar issues to jet turbine fuels. Diesels can contain greater levels of particulates but they can also contain a considerably greater volume of free water which exacerbates the effect on particle counting. Further, free water droplets can cause severe damage to the latest generation extreme pressure injection systems.

The whole issue is further confused by the inclusion of bio-diesel because the fatty acid methyl esthers (FAME) content has an effect on the solubility of water in diesel.

A test program is currently underway to extend the co-solvent work into these fuels with conclusions available late 2013.

For further information about the revisions and their significance click here

IP 565 Particle Counting by AvCount

Copyright Stanhope–Seta Limited 2014