10 Coating Standards and Tests Engineers Should Ask For

Coating Standards and Tests: Key Points

• Polylloy bulletins require SSPC-SP10 / NACE No. 2 near-white metal blast with a surface profile above 3 mils (75 µm); a site that cannot reach it is not a fit.
• Field checks to request: application condition logs (steel 10 to 50 °C, relative humidity (RH) below 90 %, 5 °C above dew point), dry film thickness against the grade's range, and holiday testing before final cure.
• Datasheet tests to read with their method named: ASTM D4541 pull-off adhesion, ASTM D4060 Taber abrasion, ASTM D2240 and D3363 hardness, and ASTM D471 one-week immersion.
• FlueGard®-225SQC lists adhesion above 3,000 psi (ASTM D4541); WearGard®-625S above 1,000 psi; FlueGard-455CHT is cited as Elcometer above 1,000 psi with no standard named.
• Polylloy's own six-month 56 % sulfuric acid test on FlueGard-225SQC (NACE TM0174 basis) passed holiday testing at 2.0 kV with electrochemical impedance spectroscopy (EIS) above log 9; it is not an independent test.
• Ask every supplier for the method, conditions and limits behind each number, not the number alone.

Severe-service coatings start from SSPC-SP10 / NACE No. 2 near-white blast with a surface profile above 3 mils (75 µm), the requirement on every Polylloy bulletin. Eight more checks follow: condition logs, dry film thickness, holiday testing, ASTM D4541 adhesion, Taber abrasion, hardness, ASTM D471 immersion and long-term immersion with EIS.

Coating Inspection Standards and Tests in Severe-Service Specifications

Coating inspection is the set of measurements and records that show a coating was applied to its specification and that its datasheet values were measured by named methods.

Why Named Standards Matter

Field checks during the outage cover preparation, profile, conditions, film thickness and holiday testing; datasheet tests cover adhesion, abrasion, hardness, chemical resistance and long-term immersion. A number without its method cannot be compared with another supplier's.

Short definitions sit in the flue gas corrosion glossary, and how the steps run in a shutdown is covered in the coating outage planning steps.

How the 10 Coating Standards and Tests Were Selected

Each standard or test in this list meets four criteria:

• It appears in a Polylloy bulletin, technical data sheet or cleared test report.
• It produces a record an engineer can request.
• It maps to a failure mode in flue gas service: poor adhesion, pinholes, thin film, abrasion or chemical attack.
• Acceptance values come from the grade's own document, never a generic number.

The order follows the project, from before application to datasheet evidence; it is not a ranking.

Ten Coating Standards and Tests at a Glance

The table lists the ten checks in order, each with an example Polylloy value; RH means relative humidity and DFT means dry film thickness.

SSPC-SP10 / NACE No. 2 Near-White Metal Blast Cleaning

Every later check depends on this first standard.

What It Measures

SSPC-SP10 / NACE No. 2 is the joint Society for Protective Coatings (SSPC) and NACE standard for near-white metal abrasive blast cleaning. It defines how clean the steel must be before coating.

What Polylloy Documents Show

Every Polylloy bulletin and the FlueGard-455CHT technical data sheet specify SSPC-SP10 near-white, and most also cite NACE No. 2. A FlueGard-225SQC fan housing at a French cement plant was coated over SSPC-SP10.

What to Ask For

Name the standard, request blast inspection records per area, and confirm the site can reach it before the outage date is fixed. A site that cannot blast to SSPC-SP10 is not a fit for Polylloy grades.

Limits

The standard defines the result, not the procedure, which belongs to the outage plan.

Surface Profile Above 3 Mils

Profile is checked at the blast inspection.

What It Measures

Surface profile is the peak-to-valley depth of the anchor pattern left by blasting, which gives the coating its mechanical key.

What Polylloy Documents Show

Polylloy bulletins require a profile above 3 mils (75 µm), and the FlueGard-455CHT data sheet states above 3 mils peak to valley. The 56 % sulfuric acid test panel was blasted to about 3 mils, and the Woodland Biomass Power Plant trial compartment to 3 to 5 mils.

What to Ask For

Request profile readings recorded with the blast inspection, by area.

Limits

Polylloy documents name no profile measurement standard, so the measurement method is agreed in the project inspection plan.

Application Condition Records for Surface Temperature, Humidity and Dew Point

Condition records prevent defects at the source.

What It Measures

Application condition records log steel surface temperature, relative humidity (RH) and dew point before and during each application shift.

What Polylloy Documents Show

The KilnGard®-600SCW, FlueGard-225SQC, FlueGard-425S, StackGard®-255SQW, CorrosionGard®-160S and WearGard-625S bulletins set the steel surface at 10 to 50 °C (50 to 122 °F), RH below 90 % and steel at least 5 °C above the dew point. The FlueGard-455CHT data sheet lists none, so confirm limits per project.

What to Ask For

Request shift-by-shift condition logs as part of the quality record.

Limits

These are application conditions, not cure conditions.

Dry Film Thickness Measured Against the Grade Bulletin Range

Dry film thickness verifies the applied film.

What It Measures

Dry film thickness (DFT) is the thickness of the coating on the steel, measured after application and checked against the grade's published minimum and maximum.

What Polylloy Documents Show

Bulletin ranges differ by grade:

• KilnGard-600SCW: 15 to 25 mils (0.38 to 0.63 mm) single coat, maximum 25.
• CorrosionGard-160S: 20 to 30 mils single coat, maximum 60.
• FlueGard-425S: 20 to 25 mils single coat, maximum 40.
• StackGard-255SQW: 20 to 25 mils, maximum 35.
• FlueGard-455CHT: 16 to 20 mils (400 to 500 µm) over two coats.

In the field, the French fan housing carried about 25 mils (635 µm) of FlueGard-225SQC and the Woodland Biomass trial 20 mils. Each grade's duty is summarized in coating grades by temperature and gas chemistry.

What to Ask For

Request DFT readings by area, including welds, edges and stiffeners, with low and high readings flagged and corrected before final cure. The FlueGard-225SQC and KilnGard-600SCW bulletins state that before final cure the film can be inspected for thickness and integrity and any defect recoated.

Limits

Polylloy documents name no DFT gauge standard; the gauge and reading plan are set in the project inspection plan.

Holiday Testing for Pinholes Before Final Cure

Holiday testing finds defects before final cure.

What It Measures

Holiday (continuity) testing applies a voltage across the film to find pinholes and other through-film defects that would expose steel to condensate.

What Polylloy Documents Show

Polylloy's 56 % sulfuric acid report applied a maximum of 100 V per mil on a NACE TM0174-91 basis, giving 2.0 kV at 20 mils, and the panel passed before and after six months. In the Taipower 12-month flue gas desulfurization (FGD) field trial, FlueGard-225 coupons passed a 2 kV holiday test with no pinholes.

What to Ask For

Request holiday records with the voltage stated and tied to the measured DFT. Defects should be marked, cleaned, recoated and retested before final heat cured activation, which is completed during start-up using process heat.

Limits

The 100 V per mil figure is the test report's basis, not a general rule, so confirm the voltage for other grades per project. When a missed holiday shows up in service, the steps to diagnose coating failures in flue gas apply.

Pull-Off Adhesion to ASTM D4541

Pull-off adhesion is one of the most widely compared datasheet tests.

What It Measures

Pull-off adhesion under ASTM D4541 measures the tensile stress needed to pull a bonded dolly off the coated steel, reported in psi, and notes where the failure occurred.

What Polylloy Documents Show

Bulletin values under ASTM D4541 are above 3,000 psi for FlueGard-225SQC, above 2,000 psi for CorrosionGard-160S, above 1,000 psi for KilnGard-600SCW, StackGard-255SQW and WearGard-625S, and above 700 psi for FlueGard-425S. Taipower field coupons exceeded 1,300 psi after 12 months, with failure in the dolly adhesive rather than at the coating-steel interface.

FlueGard-455CHT lists Elcometer adhesion above 1,000 psi (7 MPa) on sandblasted carbon steel, with no test standard named.

What to Ask For

Request the method, value and failure location; a glue failure means the bond was at least that strong.

Limits

Bulletin figures are typical properties, not specifications. The knife adhesion check (ASTM D6677) in the 56 % sulfuric acid report is qualitative.

Taber Abrasion to ASTM D4060

Taber abrasion gives a laboratory index of wear resistance, relevant to dust-laden gas.

What It Measures

Taber abrasion under ASTM D4060 measures the mass a coating loses under abrasive wheels. Polylloy bulletins use CS-17 wheels, a 1 kg load and 1,000 cycles, and lower is better.

What Polylloy Documents Show

Losses run from 20 mg for FlueGard-455CHT, below 30 mg for FlueGard-225SQC and WearGard-625S and below 35 mg for KilnGard-600SCW, to below 70 mg for StackGard-255SQW, below 100 mg for CorrosionGard-160S and below 150 mg for FlueGard-425S.

What to Ask For

Request the wheel, load and cycles with any abrasion figure; values without them are not comparable.

Limits

Taber loss is a laboratory wear index, not a field wear rate. Heavy-dust zones may favor FlueGard-455CHT or WearGard-625S.

Shore D and Pencil Hardness to ASTM D2240 and ASTM D3363

Hardness rows show resistance to indentation and softening.

What It Measures

Shore D (ASTM D2240) is indentation hardness measured by durometer. Pencil hardness (ASTM D3363) is the hardest pencil grade that does not scratch or gouge the film.

What Polylloy Documents Show

Shore D is above 95 for WearGard-625S, above 90 for KilnGard-600SCW and above 80 for FlueGard-425S, FlueGard-455CHT and CorrosionGard-160S. Pencil hardness is above HB for FlueGard-225SQC and above H for StackGard-255SQW, and the 56 % test panel retained Shore D 85 and pencil H after six months.

What to Ask For

Use hardness retained after exposure as evidence of no softening. Read the impact rows (ASTM D2794 on FlueGard-225SQC, FlueGard-425S and StackGard-255SQW; ASTM G14 on KilnGard-600SCW, WearGard-625S and FlueGard-455CHT) and heat ageing (ASTM D2485) at the grade's service temperature alongside.

Limits

Hardness alone does not predict wear or chemical resistance.

Chemical Resistance by One-Week Immersion to ASTM D471

ASTM D471 rows screen chemical resistance.

What It Measures

ASTM D471 is a method for the effect of liquids on rubber; Polylloy bulletins use it to report the weight a cured coating gains after one week immersed in a named chemical, where low weight gain indicates little absorption.

What Polylloy Documents Show

CorrosionGard-160S gains below 0.5 % in 10 % hydrochloric acid (HCl), 54 % phosphoric acid, 10 % sulfuric acid and water. FlueGard-225SQC gains below 1.0 % in 37 % HCl, below 0.5 % in 54 % phosphoric and 36 % sulfuric acid, and below 1.0 % in 3 % hydrofluoric acid.

What to Ask For

Request the chemical, strength, duration and method, and compare them with your actual condensate or stored medium.

Limits

One week is a screening exposure. Untested media still need evaluation with Polylloy's technical team.

Long-Term Acid Immersion with Electrochemical Impedance Spectroscopy (EIS)

Long-term immersion gives deeper laboratory evidence.

What It Measures

A long-term immersion test on a NACE TM0174 basis exposes a coated panel with an immersed portion and a vapor phase, checked at set intervals. Electrochemical impedance spectroscopy (EIS) measures how strongly the film resists water and ions.

What Polylloy Documents Show

FlueGard-225SQC spent six months in 56 % sulfuric acid at 60 °C with no observed deterioration and an EIS log modulus above 9 at 0.1 Hz. It is Polylloy's own test, not an independent one; details are in the sulfuric acid immersion test results.

What to Ask For

Request who ran and reviewed the test, the conditions and the limits.

Limits

One concentration, one temperature and no thermal cycling make it screening evidence, not a service-life prediction.

How to Choose Which Coating Standards and Tests to Put in Your Specification

Choosing which coating standards and tests to specify starts with two lists:

• Field records for every job: SSPC-SP10 / NACE No. 2, profile above 3 mils, condition logs, DFT to the grade range and holiday testing where specified.
• Datasheet evidence matched to the duty: adhesion and abrasion for dusty ducts and fans, ASTM D471 and long-term immersion for wet acid zones.

For the quality system, ask for the ISO 9001 certificate, its scope and issuer. Polylloy holds a self-assessed ISO 9001:2015 registration and an independent third-party design and manufacturing verification by Fuller, Jones & Associates; the wider supplier review is in how to choose an industrial coating supplier.

Polylloy formulates, supplies, specifies and supervises; certified partners apply the coatings, and records go to the plant owner. See also inspection and maintenance services. To set a project's request list, book a Coating Performance Review with equipment type, coated area, operating conditions (temperature, gas chemistry, abrasion), location and outage timing.

FAQs

What Surface Preparation Standard is Required for a Severe-Service Coating?

For Polylloy grades, abrasive blasting to SSPC-SP10 / NACE No. 2 near-white metal with a surface profile above 3 mils (75 µm), as printed on every bulletin. A site that cannot blast to that standard is not a fit. Other products set their own requirements, so take the standard from each manufacturer's data sheet.

How is Dry Film Thickness Verified After Coating Application?

Dry film thickness is measured on the applied film by area, including welds, edges and stiffeners, and checked against the grade's bulletin range, for example 15 to 25 mils for KilnGard-600SCW. Low or high readings are corrected while the film can still be inspected and recoated, before final heat cured activation at start-up.

How Are Coating Defects Repaired Before Final Cure?

Defects found by visual inspection, DFT readings or holiday testing are marked, cleaned and recoated to the project repair procedure, then retested. The FlueGard-225SQC and KilnGard-600SCW bulletins state that before final cure the film can be inspected for thickness and integrity and any defect recoated. Final heat cured activation is then completed during start-up using process heat.

What Voltage is Used for a Coating Holiday Test?

The voltage depends on film thickness and the governing procedure. In Polylloy's six-month 56 % sulfuric acid test, the report applied a maximum of 100 V per mil under a NACE TM0174-91 basis, giving 2.0 kV on a 20 mil film. Confirm the voltage for your grade and thickness with the specification.

What Does ASTM D4541 Pull-Off Adhesion Tell You?

ASTM D4541 measures the tensile stress needed to pull a bonded dolly off the coated steel and records where failure occurred. FlueGard-225SQC lists above 3,000 psi and WearGard-625S above 1,000 psi. In the Taipower field trial, coupons exceeded 1,300 psi after 12 months, with failure in the dolly adhesive rather than at the coating.

Are Datasheet Test Values the Same as a Specification?

No: Polylloy bulletins describe their figures as typical properties representative of current production, not specifications. Use them to compare grades and to set expectations, then write project acceptance criteria for field checks such as profile, DFT and holiday testing. Ask for the method, conditions and limits behind every datasheet number.

What Does Polylloy's ISO 9001 Certificate Cover?

Polylloy Coatings holds ISO 9001:2015 registration issued through HIBO ISO Certifications, valid to July 2027; the certificate states it is a self-assessed document. Fuller, Jones & Associates separately provided an independent third-party design and manufacturing verification based on a document review. Neither is a product performance certification.