All PosiTector 6000 models comply with the IMO MSC.215(82) performance standard for protective coatings in ballast tanks. Contained in this standard is a PSPC 90/10 rule.
The PosiTector 6000 PSPC 90/10 mode simplifies the process of determining pass/fail criteria under the IMO directive. Although developed for maritime applications, this mode can be used by other industries looking for a statistical method of ensuring correct dry film thickness over a surface area.
Begin taking measurements. With each measurement the following occurs...
There are 4 methods for examining the 90/10 batch results:
NOTES:
The PosiTector 6000 90/10 feature is intended to support the PSPC Application Standard, not replace it. It is the responsibility of the user to read and understand the document, and to verify the accuracy of the gage's conclusions.
In this example, 10 measurements have been taken. The last measurement was 340 microns. Both the 90% and 10% rules have failed resulting in a B1 FAIL result. Why?
To find out why the batch PASSED or FAILED, select the Memory-View menu option.
In this example, the user entered a NDFT value of 320 microns.
Use (-) or (+) to review all measurements in the 90/10 batch.
NOTE: In this example, measurements 9 and 10 were both below 288 microns, causing the 10% rule to fail.
The International Maritime Organization (IMO) is a specialist United Nations agency tasked with improving maritime safety and preventing pollution from ships.
Premature failure of protective coating systems is often found in ballast tanks of ships in service and as a consequence will lead to rapid corrosion of unprotected steel. Following coating breakdown it is extremely difficult, if not impossible, to repair or reinstate the coating to new building standard. It is therefore of the utmost importance that coatings be correctly applied at the new building stage. The Committee felt that the best way to achieve this would be the development of mandatory performance standards, including a minimum target life, for ballast tank coatings.
On 8 December 2006, the IMO adopted the new Performance Standard for Protective Coatings (PSPC), as resolution MSC.215(82). This important new standard will also be included in the International Convention on Safety of Life at Sea (the SOLAS Convention).
The PSPC is intended to improve safety at sea by reducing corrosion encountered in steel ships. It applies specifically to the protective coatings used for dedicated seawater ballast tanks in all types of ships, and also in the double-side skin spaces of bulk carriers. The PSPC enters into force for all shipbuilding contracts placed on or after 1 July 2008.
The PSPC sets out requirements for improved procedures and better quality control via increased inspection requirements at all stages within a number of areas including dry film thickness (DFT). It introduces a new performance standard for dry film thickness – the PSPC 90/10 rule.
See also Guidelines for maintenance and repair of protective coatings.
"90% of all thickness measurements should be greater than or equal to NDFT (nominal dry film thickness) and none of the remaining 10% measurements should be below 0.9xNDFT".
Application practice of recent years appears to have approached the common standard of a 2-coat epoxy system. While different thicknesses are allowed, each coat is usually 160 microns for a total thickness of 320 microns.
"Dry film thickness shall be measured after each coat for quality control purpose and the total dry film thickness shall be confirmed after completion of final coat using appropriate thickness gauges."
The common understanding is that there is no guarantee that the 90/10 rule is perfectly achieved for the entire surface, but that such a sampling method is enough for making a practical judgment. If the sample measurements do not satisfy the criteria, additional spot checks should be taken for any area considered necessary by the coating inspector.
There are several ways to evaluate film thickness with the PosiTector 6000 ...
A large surface usually cannot be characterized accurately by a single measurement. Variations in substrate preparation, painting technique, measuring technique, etc. require an analysis of several measurements taken over a large portion of the surface.
The PosiTector 6000's statistics mode displays individual measurements AND maintains a running average value. It also displays minimum and maximum values.
Advanced (3) versions of the PosiTector 6000 have a 90/10 mode that helps the user collect measurements in conformance with the PSPC standard. Then, based on user-set target thickness, the gage indicates a pass or fail condition.
The PosiTector 6000 has on-board memory into which all measurements are stored. Individual measurements are grouped into a "batch". The gage continually monitors thickness results and reports a pass/fail condition on the current batch as a whole.
Stored results can be viewed on the display, modified or deleted. A formatted printout can be sent to the optional Bluetooth printer. Or all results can be downloaded to a PC using the included PosiSoft software and USB cable.
Related Documents:
ASTM D7091 “Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to a Ferrous Base and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals”
ISO 19840 “Paints and varnishes -- Corrosion protection of steel structures by protective paint systems -- Measurement of, and acceptance criteria for, the thickness of dry films on rough surfaces”
PosiTector 6000 Standard (1) and Advanced (3) gages have a statistics mode. When selected, the gage continuously updates running average and standard deviation calculations. Maximum and minimum values are also tracked while measurements are being taken.
The last measurement can be deleted with the (-) button, while the (+) button clears all statistics.
No. The pass/fail test is clear. The batch will only pass if both the 90% rule and 10% rules pass. Only four results are possible as shown below.
No. The 90% and 10% rule definitions are fixed and cannot be changed. The user-defined NDFT value cannot be changed after “OK” has been pressed on the SETUP screen.
However, if PosiSoft is used to export all measurement values to a text or spreadsheet file, other software programs such as WORD or EXCEL can alter values or provide additional analysis.
Yes. Use the (-) button to delete the last measurement taken. The pass/fail criteria are immediately updated. Use the "Delete" menu option to delete batches or the entire contents of gage memory.
The calculations involved in determining a pass/fail condition require arithmetic division. This can produce decimal results that need to be rounded. Switching units further complicates the mathematics. While the PosiTector 6000 and PosiSoft both enable the switching of units, it is not recommended. Switching units after taking measurements may result in slight differences in results. For example, an NDFT value equal to 280 microns converts to 11 mils. If the user takes a measurement in mils of 10.99, the gage will round the result and display 11 mils, which is equal to NDFT. But 10.99 mils converts to 279 microns, which is less than NDFT.
Calculations to determine percentages of readings and fractions of target values often result in numbers that have several significant digits after the decimal point. Since the instrument is limited as to how many digits after the decimal point can be displayed, rounding must be applied to individual measurements and to arithmetic calculations of percentages and fractions.
For example, if we select a target NDFT of 21.8 mils and multiply it by 0.9, the result is 19.62 mils. This result has 2 decimal points. But some probes have a resolution of only 1 decimal point. So measurements of 19.57 and 19.64 mils would both be displayed on the instrument's LCD as 19.6 mils, a theoretical FAIL. To be compatible with probe resolution 0.9 NDFT is rounded to 19.6 mils using the same logic as used by the probe. Therefore both the 19.57 and 19.64 values would be considered a PASS. Users are advised to verify calculations.
