What should a salt spray test report record to compare tests?

These records apply to continuous salt spray exposure under ASTM B117 or ISO 9227 on metals and coated metals. Cyclic corrosion tests such as ASTM D5894 and humidity tests need their own cycle records. The post sets no pass or fail limit: that comes from the specification that called the test.

What do you need before recording an ASTM B117 salt spray test?

Before recording an ASTM B117 salt spray test, you need four things: the product specification or drawing that calls the test, the method and edition actually run, the rating standards for each defect, and a record template fixed before the panels go in. ASTM B117-26a states: "This practice does not prescribe the type of test specimen or exposure periods to be used for a specific product, nor the interpretation to be given to the results" (ASTM B117-26a, 2026). ISO 9227:2022 says the same of its neutral (NSS), acetic acid (AASS) and copper-accelerated (CASS) salt spray tests and adds: "Such details are provided in the appropriate product specifications" (ISO 9227:2022).

So write down, before exposure:

• Specification: number, edition and the clause that sets hours and limits.

• Method: ASTM B117-26a, or ISO 9227:2022 with its 2024 amendment, and for ISO which of NSS, AASS or CASS.

• Rating standards: one per defect type (rust, blisters, scribe).

• Template: the same fields for every test, filled in the same order.

A template fixed in advance is what makes a test run in March readable next to one run in November. The same idea, applied to visit reports, is covered in how to make every customer visit report follow one template.

How do you record specimens and pretreatment for a salt spray test?

Specimens and pretreatment for a salt spray test are recorded as the full build of each panel: substrate alloy and temper, panel size and ID, surface preparation, pretreatment chemistry and process, coating and its dry film thickness, cure, conditioning time and the number of replicates.

The alloy line is the one most often left out. MIL-DTL-5541F notes that, due to high copper content, 2024-T3 aluminum test specimens are more susceptible to salt spray failure than 6061-T6 specimens (MIL-DTL-5541F, 2006). Two conversion coatings tested on different alloys are therefore not a comparison of coatings.

Conditioning and mounting belong on the record too. MIL-DTL-5541F requires specimens to dry at 16 to 38 °C (60 to 100 °F) for 24 hours after coating, and inclines the significant surface 6 ± 2 degrees from the vertical during exposure (MIL-DTL-5541F, 2006). Write the angle and the conditioning actually used, even when a specification does not set them.

Replicates matter for the same reason. ASTM B117-26a recommends that "sufficient replicates should be included to establish the variability of the results" (ASTM B117-26a, 2026). Record how many panels were run and give each its own ID, so a single outlier panel can be seen as one panel rather than read as the result.

How should a scribe be described in a salt spray test report?

A scribe in a salt spray test report should be described by the tool, the scribe width and length, whether it reaches the metal, its position and orientation on the panel, when it was made, and which standard rates it. Scribe creep depends on how the cut was made, so two creep values from different tools or depths do not measure the same thing.

ISO 17872:2019 gives guidelines for scribing coated steel, galvanized steel, aluminum alloy and magnesium alloy panels where the coating is under 500 µm dry film thickness (ISO 17872:2019). It describes itself as "intended as a guideline only", and it does not cover electroplated or clad aluminum panels (ISO 17872:2019). Name it on the record if you followed it; if you did not, describe the tool and the cut in words.

The rating standard for the scribe is separate from the one for general rusting. ASTM D610-25 does not include evaluation of rust propagation around a scribe (ASTM D610-25, 2025). Scribe results are rated under ASTM D1654-24e1, which covers loss of adhesion and corrosion at a scribe mark, or under ISO 4628-8:2012, which assesses delamination and corrosion around a scribe or other artificial defect (ASTM D1654-24e1, 2024; ISO 4628-8:2012). Write the creep value with its unit, the method that produced it, and whether it is a mean or a maximum.

Which exposure hours and inspection intervals should a salt spray report state?

A salt spray report should state the total exposure hours, every inspection time, every interruption with its duration, and the hour at which each defect was first seen. Total hours alone hide the history: a panel that rusted at 96 hours and one that rusted at 480 hours both read "fail at 500 hours" (illustrative).

The hours come from the specification, not the method. ASTM B117-26a sets no exposure period (ASTM B117-26a, 2026), while MIL-DTL-5541F, for one, calls for 168 hours of 5 percent salt spray in accordance with ASTM B117 for aluminum conversion coating specimens (MIL-DTL-5541F, 2006).

Interruptions belong on the record because ASTM B117-26a ties reproducibility to "the control of the operating variables" (ASTM B117-26a, 2026), and each chamber opening, power cut or refill is a change to those variables. Log the date, time and reason, and the hours lost.

Inspection intervals should be written as a plan before the test and as actual times after it, for example 24, 96, 240 and 500 hours (illustrative). Inspect and rate every panel at each interval with the same standard, and photograph it then, not only at the end.

Which rating standard and photos should a salt spray result cite?

A salt spray result should cite one rating standard per defect type, with its edition, and a photo of each panel at each inspection. For rust on painted steel, ASTM D610-25 rates rusting on a 0 to 10 scale based on the percentage of visible surface rust and classifies its distribution as spot, general, pinpoint or hybrid rust (ASTM D610-25, 2025). ISO 4628-3:2024 assesses the degree of rusting of coated surfaces by comparison with pictorial standards and does not include edges (ISO 4628-3:2024).

For blisters, ASTM D714-25 describes the size and density of blisters against photographic reference standards so that severity can be compared (ASTM D714-25, 2025). For the scribe, cite ASTM D1654-24e1 or ISO 4628-8:2012.

Write the rating in the standard's own notation, not as "slight" or "acceptable", which cannot be mapped back to a scale.

Photos support the rating but do not replace it. ASTM D610-25 states that its visual examples form part of the standard and that, in the event of a dispute, "the written definition prevails" (ASTM D610-25, 2025). Photograph each panel with its ID and a scale in frame, under the same lighting at every inspection, and keep the written rating next to each photo.

Why do salt spray acceptance limits differ between specifications?

Salt spray acceptance limits differ between specifications because the test methods set none of their own: each product specification, or each buyer and seller, writes its limit for its own coating, substrate and service. ASTM B117-26a does not prescribe the interpretation of results (ASTM B117-26a, 2026), and ASTM D714-25 states that "the permissible degree of blistering of the paint system shall be agreed upon by the purchaser and the seller" (ASTM D714-25, 2025).

The limits that result are written in different terms. MIL-DTL-5541F counts pits: no more than 5 isolated spots or pits per specimen, none larger than 0.031 inch (about 0.8 mm) in diameter, after 168 hours (MIL-DTL-5541F, 2006). A coatings maker's published example reads "No more than 1/32-inch rust creepage at scribe after 10,000 hours of exposure" (Tnemec, 2026). One counts pits on unscribed panels; the other measures creep at a scribe.

Sources also differ on whether salt spray results can rank coatings at all. ASTM B117-26a says the practice is used "to produce relative corrosion resistance information for specimens of metals and coated metals exposed in a given test chamber" (ASTM B117-26a, 2026). ISO 9227:2022 states its methods "are not intended to be used for comparative testing as a means of ranking different materials relative to each other with respect to corrosion resistance" (ISO 9227:2022). ASTM B117-26a supports relative comparison within one chamber, while ISO 9227:2022 limits its methods to checking that a material's quality is maintained; neither supports ranking across chambers or predicting service life.

How do you check two salt spray records are comparable?

You check two salt spray records are comparable by matching them line by line against the record items below; any item that differs or is missing limits what the comparison can say. The table decides, item by item, whether two salt spray results can sit side by side.

The chamber row is the one most often skipped. ASTM B117-26a states that "Variability has been observed when similar specimens are tested in different fog chambers even though the testing conditions are nominally similar" (ASTM B117-26a, 2026), and ISO 9227:2022 includes a method to evaluate the corrosivity of the test cabinet (ISO 9227:2022). Log the operating variables a B117 chamber is held to: exposure-zone temperature of 35 °C, a fog collection rate of 1.0 to 2.0 mL per hour per 80 cm² of collecting area, and a 5 percent sodium chloride solution at pH 6.5 to 7.2 (Infinita Lab, 2026). Results from two chambers are a weaker comparison than results from one, so name the chamber on every record. In Lubinpla, test photos and result files can be attached to a work log, and an organization's work log template keeps the same record items in the work logs its agent writes.