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04/14
MPC Varnish Potential Testing
(ASTM D7843)
MPC varnish potential testing (ASTM D7843) is an essential analytical test to determine the propensity for a lubricant
to form varnish deposits. With the probability of lubricant varnish-related failures reported to be as high as 100% (as
per GE TIL 1528-3), monthly MPC varnish potential testing is recommended for all critical turbine installations. The
ASTM-approved MPC test is straightforward and can be completed as part of your existing lubricant analysis testing
program. It can also be performed on-site using a modified test method for rapid assessment of potential varnish-related problems. EPT has prepared a video demonstration of the MPC test method which can be found at
http://www.cleanoil.com/products/varnish-potential-testing-mpc.html. The full test procedure for ASTM D7843 can be
purchased from: www.astm.org.
MPC Test Overview
There are 2 main parts to the MPC test. The first involves the preparation of a 47mm filter patch using 50mL of solvent
and 50mL of the lubricant to be tested. The patch is then rinsed with solvent and dried. The intensity and color of the
patch are then measured using a spectrophotometer that calculates the ∆E value by measuring the L, A, B values
generating a result from 0 to ∞. The ∆E value and the corresponding propensity for the formation of lubricant varnish
deposits are then assessed according to an MPC scale (shown below).
MPC Scale
The following scale has been developed as a guideline to help users assess their lubricant’s potential for varnish formation. There is 4 levels on the varnish potential scale: Good (∆E<15), Monitor (∆E = 15-25), Abnormal (∆E = 25-35)
and Critical (∆E >35). The higher the MPC value, the higher amount of varnish precursors that are dissolved in the
lubricant and the greater the propensity for the lubricant to form harmful varnish deposits.
Good
Monitor
Abnormal
Critical
< 15
15 – 25
25 – 35
> 35
Leading The Clean Oil Revolution
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EPT 4772-50th Ave. S.E. Calgary, AB, Canada T2B-3R4
T 403.246.3044 F 403.249.8096 [email protected]
04/14
MPC Varnish Potential Testing
(ASTM D7843)
Why a higher MPC value is a problem and what MPC value should be the
operating target?
Ideal lubricant operating condition (from a varnish perspective) is achieved when the MPC ∆E value is <15. When the
MPC ∆E value is continually maintained at <15, the lubricant‘s solvency characteristics are maximized which prevents
varnish deposit formation and forces existing deposits back into their less harmful dissolved form.
MPC and varnish potential values increase as dissolved oil breakdown products (varnish precursors) accumulate.
These breakdown products are produced by oxidation and begin to accumulate from the first moment that the
lubricant goes into service. Each lubricant has a finite capacity to hold these dissolved oxidation products in solution.
Once this limit is reached, the lubricant becomes saturated and excess break-down products are forced from the fluid,
forming harmful lubricant varnish deposits. Once formed, lubricant varnish has a natural attraction for metal surfaces
because of the polar nature of both the varnish and the metal. As varnish begins to coat metal surfaces, fine clearances are reduced, decreasing equipment performance and, ultimately, leading to failure.
Complicating matters, the saturation point, beyond which varnish deposits will form, varies with lubricant temperature, pressure and flow. These parameters are dynamic in most mechanical systems. For this reason, varnish is often
deposited in sensitive mechanical areas prior to appearing in the oil reservoir. It is, therefore, important to select a
lubricant maintenance program that will be effective under all system conditions.
When MPC values are maintained at ∆E <15, the lubricant contains very few varnish precursors and is not prone to
deposit formation. Moreover, such a lubricant has high solvency characteristics under all system conditions and will
actively remove any already-existing varnish deposits from the system’s metal surfaces.
Sample MPC Trending Data -­‐ Gas Turbine Lubricant Reservoir 60 MPC ΔE 50 Varnish Removal Unit (SVR) Installed SVR Elements Changed. MPC ΔE High Risk of Varnish-­‐
Related Failure. 40 30 20 10 Target 0 Sample Date Leading The Clean Oil Revolution
Rethink.
Rethink.
Rethink.
Remove.
Remove.
Remove.
Restore.
Restore.
Restore.
EPT 4772-50th Ave. S.E. Calgary, AB, Canada T2B-3R4
T 403.246.3044 F 403.249.8096 [email protected]
04/14
MPC Varnish Potential Testing
(ASTM D7843)
Required Materials for MPC Testing
The following apparatus and consumables are required to complete MPC testing. There are 3 primary components:
Patch test kit apparatus, vacuum pump, and spectrophotometer. EPT offers two different patch test kits (glass or
heavy duty stainless steel), two different vacuum pumps (hand or electric) and one type of spectrophotometer.
APPARATUS REQUIRED
47mm Patch Kit
Assembly to hold one 47 mm patch, 100 mL reservoir capacity, with waste
container. There are 2 options:
1) Standard Laboratory Glassware
2) Durable Stainless Steel for portability and field use. Optional water tight
suitcase offered.
Both patch test kits come with all consumables listed below except solvent.
See Product Sheets
Vacuum Pump
Hand pump is suitable where a few tests are done monthly, while an electric
vacuum pump is more suitable when many tests are being done monthly.
See Product Sheets
Spectrophotometer
Ci7, Gas-filled tungsten lap, 6 silicon photocell detector to measure
(L*a*b*)/∆E*ab; ∆(L*C*H*)/∆E*ab, L*: 10 to 100.
See Product Sheet
Oven
The ASTM test method requires that the lubricant sample is heated at 60°C
for 24 hours and then aged at room temperature for 68-72 hours. Required for
laboratory test. Modified Field test method can achieve similar results by aging
sample for the same period.
Any laboratory grade oven is sufficient
CONSUMABLES REQUIRED
Petroleum Ether
50 –100 mL petroleum ether required per test.
Not offered
Filter Patch
47 mm, 0.45 µm Nitro-Cellulose patch.
Quantity 25, included with patch test kits
Plastic Container
Graduated beaker to mix solvent and lubricant, >100 mL capacity. Solvent wash
bottle to rinse patch after test, 100 mL capacity.
Quantity 1 Each, included with patch test kits
Expert Support
Included with the purchase of our varnish potential testing products is access to our expert chemistry team, who have
completed 1000’s of varnish potential tests. From answering a quick question to in-depth technical support, you will
have invaluable access to experts that will ensure that your varnish potential testing program is successful.
Contact Information
For a list of authorized distributors please see
http://www.cleanoil.com/contact/distributors.html
For additional information contact:
[email protected]
Leading The Clean Oil Revolution
Rethink.
Rethink.
Rethink.
Remove.
Remove.
Remove.
Restore.
Restore.
Restore.
EPT 4772-50th Ave. S.E. Calgary, AB, Canada T2B-3R4
T 403.246.3044 F 403.249.8096 [email protected]