Comparison of SSPC PA2 and ISO-19840 DFT verification method and
acceptance Criteria
Sl #RequirementsSSPC PA 2 -2004 versionSSPC PA 2 -2012
versionISO -19840
1.Specifying Coating ThicknessRecommends to specify both minimum
and maximum thickness of each Coating layer.if not Provided ,the
specified thickness shall be taken as a minimum required Coating
Thickness Recommends to specify both minimum and maximum thickness
of each Coating layer.if single value is specified the minimum and
the maximum thickness shall be +/- 20 % of the stated value i.e 80
% of specified as minimum and 120% of specified as maximum
Generally not recommends to Specify the range of coating
thickness.
The specified value shall be taken as the NDFT (nominal Dry film
thickness)
2.Gauge calibration/Zero Setting Non-repeatable reading even at
points very close, Surface irregularity, Temperature
Gauge setting to Zero should not be made.Recommended to set
gauges on blast cleaned surface.
No specific guidelines are givenGauge setting to Zero should not
be made.Recommended to set gauges on blast cleaned surface
according to ASTM D7091
Also refers to ISO 19840 for Gauge Correction values.Based on
Surface profile classification as Per ISO8503-1 such as Fine,
medium & Coarse Correction values are GivenFine 10 m, Medium 25
m and Coarse 40 m.
If correction Value is usedit shall be subtracted from the
individual reading to give DFT.
3Sampling Plan / Measurement FrequencyMeasurement frequency is
based on area/size of the structure.
Spot reading considered as individual reading. Each spot reading
in 4 cm diameter shall consist of minimum 3 gauge readings.
Each 10m2 area of Beam structure shall be measured in 5 Spot
readings.
For 10m2 area 3x5 = 15 gage readings are to be measured.
For 30 to 100 m2 areas minimum three 10m2 area must be
measured.
Measurement frequency is based on area/size and configuration of
the structure.Spot reading considered as individual reading. Each
spot reading in 4 cm diameter shall consist of minimum 3 gauge
readings.
For beam length less than 6m length, 5 spots reading per surface
shall be measured. As per this standard Total number of surface of
Beam structure including flange thickness to be measured are 12
surfaces. (If flange thick is equal or greater 25mm). In our cases
8 surfaces excluding edges of the flange. So each surface 5 spot
reading (15 gauge readings) are to be measured. Full DFT
determination -Total 120 gauge readings are to be measured for 6m
length beam.
For sample DFT measurement randomly distributed two spot
readings for the 8 surfaces are to be measured ie. 48 gage
readings
As per standard no need to go for full or Sample DFT
determination for every beam. It recommends to go for 1 beam out of
10 beam with full DFT
Determination or 1 out of 5 with sample DFT
determination.Measurement frequency is based on area/size i.e area
and length of the structure.
Single reading is considered as the individual reading
Sampling plan detailed in the form of table.It is easy to
understand and convince the client when it is necessary
For 3 to 10 m2 /m : 15 readings + 3 adjustment readings ( incase
measured values are less can be manipulated with additional
adjustment readings
For 6 meter length Beam only 15 +3 readings are sufficient.
4Acceptance CriteriaFor specified Minimum thickness.
Average of all spot readings shall not be less than minimum
specified Coating thickness.
Average of individual spot reading shall be 80% of minimum
specified thickness.
Any individual gauge reading may underrun by a greater amount
but that particular spot reading shall be 80% of minimum
specified.
For specified Maximum thickness.
Average of all spot reading shall not be maximum specified
Coating thickness.
Average of individual spot thickness shall be within 120 % of
the specified thickness.
Any individual gauge reading may overrun by a greater amount but
the particular spot reading shall be within 120% of specified
thickness.
If single value provided that means no maximum thickness given,
for High DFT no specific acceptance Criteria is given. (No
threshold ) If coating thickness specified in a range acceptance
criteria shall be similar to SSPC 2004 edition.
If single value of coating thickness is given the followings are
the acceptance criteria.
The minimum shall be 80% of coating Thickness and maximum shall
be 120 % of the coating thickness. In addition to above Acceptance
criteria is based on 5 restriction levels. This standard recommends
to specify restriction level in the contractual documents / agreed
with client.
If no restriction level is provided then the restriction level 3
shall be considered as default acceptance criteria.If Specified is
single value, the acceptance criteria in according to restriction
level 3 in addition to specified minimum coating thickness any spot
measurement less by 20 % is acceptable in lower thickness side.
For example. Specified is 250 m
Minimum allowable coating thickness for entire structure shall
200 m.Maximum shall be 300 m
Any spot reading is allowable up to 160 microns as a minimum and
360 microns as a maximumFor minimum Coating thickness The
arithmetic mean of all the individual dry film thicknesses shall be
equal to or greater than the nominaldry film thickness (NDFT)
All individual dry film thicknesses shall be equal to or above
80 % of the NDFT
Individual dry film thicknesses between 80 % of the NDFT and the
NDFT are acceptable provided that thenumber of these measurements
is less than 20 % of the total number of individual measurements
taken
All individual dry film thicknesses shall be less than or equal
to the specified maximum dry film thickness.
For maximum Coating thickness It is recommended that the maximum
dry film thickness (individual value) is not greater than three
times the nominal dry film thickness.
In cases when the dry film thickness is greater than the maximum
dry film thickness, expert agreement shall be found between the
parties
Spot reading measurment details as per SSPC PA2 -2004, &
2012
SSPC Recommended DFT Inspection report 5
