PosiTector^® 6000

IMO PSPC 90/10 Rule

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.

PosiTector 6000 memory (3) models with serial numbers greater than 623400 have a useful PSPC 90/10 mode that simplifies the process of determining pass/fail criteria under the IMO directive.

This addendum to instruction manual v6.0/M is intended to provide support for the PSPC 90/10 mode. 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.

Who is the IMO and what is PSPC ? What is the 90/10 Rule ? Overview of the PosiTector 90/10 mode Q&A

How to use the PosiTector 6000's IMO PSPC 90/10 mode...

Step 1 - Enter a target thickness value.

Select the Memory option from the gage menu as shown.	Next, select the 90/10 option from the Memory menu
A default target value of 320 microns (12.6 mils) appears. If necessary, adjust this value using the (-) and (+) buttons. Press the middle button to accept.

Step 2 - Take measurements.

Step 3 - Review results.

There are 4 ways to look at the results...

1. If all 90/10 criteria have been met, the word PASS will appear beside the Batch number, i.e. "B1    PASS".
2. For more detail select "View" from the Memory Menu to display all individual measurements. Scroll using the (-) and (+) buttons. Hold the (-) or (+) button down for 1 second for fast scrolling. See sample IMO PSPC 90/10 screens below
   --To replace a measurement, position the "+" symbol beside the measurement. Then take another measurement with the probe.
   --To delete a measurement or to exit the View screen, press the middle button.
3. All stored measurements can be downloaded to your PC using the included PosiSoft software. PosiSoft allows entry of notes and annotations, it prints and displays basic charts and histograms, it saves measurements to your PC, and it exports measurements to a spreadsheet or document. See IMO PSPC 90/10 PosiSoft sample below
4. Preferred Method:  Print to the optional IR printer or print to a PC's default printer using the included PosiSoft software. All 90/10 information is presented including gage serial number, 90/10 parameters, individual measurements with date and time stamp, calculated averages, and PASS/FAIL conclusions. This is the best way to ensure that the 90/10 specification has been satisfied. See sample below.

NOTES:

1. Select the "Delete" menu option to erase a BATCH, or the entire contents of gage memory.
2. Select the "Close" menu option to end a 90/10 analysis but keep all existing BATCHES and measurements.
3. Calibration adjustments cannot be made while 90/10 measurements are stored in gage memory.

The PosiTector 6000's 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.

Sample IMO PSPC 90/10 VIEW Screens

	In this example, 10 measurements have been taken. The last measurement was 340 microns. Both the 90% and 90% 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. The 90% rule FAILS because only 80% of measurements were above or equal to this value. The 10% rule fails because 1 measurement was below 90% of NDFT (288 microns).
	Scrolling down reveals all measurements. “- -“ indicates measurements below NDFT. The 90% rule fails if 90% of all thickness measurements are not greater than or equal to NDFT. In this example, only 80% comply. “ x “ indicates measurements below 0.9xNDFT (288 microns). Measurements marked with an “x’ automatically cause the 10% rule to fail.

PosiSoft Software Samples

Sample IMO PSPC 90/10 PosiSoft Screen

The 12th measurement is marked in yellow because it is below NDFT but within 10% of NDFT.
The 22nd measurement is marked in red because it is below 10% of NDFT and causes a FAIL condition.

 

Sample PosiSoft Summary - Detail

 

Sample Printout

Who is the IMO and what is PSPC?

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.

What is the 90/10 Rule?

"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.

Overview

There are several ways to evaluate film thickness with the PosiTector 6000 ...

1. Take a single measurement.
2. Calculate the average of several measurements -- the PosiTector 6000's Statistics mode.
3. Analyze a larger area using a statistical approach -- the PosiTector 6000's PA2 mode.
4. Analyze a larger area using a statistical approach -- the PosiTector 6000's 90/10 mode.

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.

Memory (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.

How does the gage do this?

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 IR printer. Or all results can be downloaded to a PC using the included PosiSoft software and USB cable.

Related Documents:
ASTM D7091-05 “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 19840:2004 “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”

Statistics Mode

Q&A

Is it possible for the PSPC 90/10 rule to PASS if either the 90% rule or 10% rules FAIL?

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.

Is it possible to change PASS/FAIL criteria after all measurements have been taken?

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.

Can I delete a bad measurement?

Yes. Use the (-) button to delete the last measurement taken. The pass/fail criteria are immediately updated. Use the "View" menu option to delete any individual measurement or batch. Use the "Delete" menu option to delete batches or the entire contents of memory.
NOTE: the "View" menu option will also allow you to replace measurements.

Why do results sometimes appear a little different when I change from mils to microns and vice-versa?

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.

How many decimal points of accuracy are applied to the test results?

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 0.9NDFT 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.