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IS 3690:1985 is the Indian Standard (BIS) for methods of test for preformed thermal insulating materials. This standard prescribes the methods of test for preformed thermal insulating materials in the form of blocks, slabs, and pipe sections. It covers essential physical and mechanical tests including bulk density, compressive strength, moisture content, and water absorption to evaluate insulation quality.
Describes methods of test for preformed thermal insulating materials.
! Proper conditioning of samples in standard laboratory conditions is crucial before determining moisture content or dry density to avoid erratic results.
! Ensure uniform load distribution across the testing surface area when determining compressive strength.
! Thermal conductivity is not covered in this specific standard and must be evaluated separately as per IS 3346.
ASTM C165 / C165M - 17(2022)ASTM International, USA
HighCurrent
Standard Test Method for Measuring Compressive Properties of Thermal Insulations
Directly equivalent to the compressive strength test method in IS 3690.
ASTM C203 - 05a(2017)ASTM International, USA
HighCurrent
Standard Test Methods for Breaking Load and Flexural Properties of Block-Type Thermal Insulation
Directly equivalent to the flexural strength (bending test) method in IS 3690.
ISO 29767:2019ISO (International Organization for Standardization), Switzerland
MediumCurrent
Thermal insulating products for building applications — Determination of short-term water absorption by partial immersion
Covers water absorption, but specifies partial immersion, whereas IS 3690 implies total immersion.
ASTM C167 - 17ASTM International, USA
MediumCurrent
Standard Test Methods for Thickness and Density of Blanket or Batt Thermal Insulations
Aligns on methods for determining thickness and density, but is specific to blanket/batt forms.
Key Differences
≠IS 3690 is an omnibus standard compiling multiple test methods (density, compression, flexure, water absorption, etc.) into one document. International practice, particularly with ASTM and ISO, is to publish separate, dedicated standards for each individual test method.
≠Specimen conditioning requirements differ. IS 3690 specifies conditioning at 27 ± 2 °C and 65 ± 5% relative humidity, whereas most ASTM standards specify 23 ± 2 °C (73.4 °F) and 50 ± 5% relative humidity.
≠The water absorption test methodology varies. IS 3690 requires 24-hour total immersion, while the equivalent ISO 29767 specifies 24-hour partial immersion with the bottom face 10mm below the water surface, which yields different results.
≠IS 3690 includes a method for determining 'Shot Content' specific to mineral wool, which is not typically found in general-purpose international test method standards but rather in material-specific product standards (e.g., ASTM C612).
Key Similarities
≈The fundamental principles behind the core tests (compressive strength, flexural strength, density) are identical, based on universal engineering and physics concepts of stress, strain, and mass/volume.
≈Both the Indian and international standards mandate the pre-conditioning of test specimens to a stable state at a specified temperature and humidity before testing to ensure repeatable and comparable results.
≈The basic apparatus for mechanical testing is conceptually the same, relying on a universal testing machine (UTM) to apply a controlled load or displacement for both compressive and flexural strength tests.
≈Both IS 3690 and the suite of international standards cover the same essential performance characteristics required to evaluate preformed thermal insulation: mechanical strength (compression, flexure), density, dimensional stability, and moisture resistance.
Parameter Comparison
Parameter
IS Value
International
Source
Specimen Conditioning (Temperature)
27 ± 2 °C
23 ± 2 °C (73.4 ± 4 °F)
ASTM C165
Specimen Conditioning (Relative Humidity)
65 ± 5 %
50 ± 5 %
ASTM C165
Compressive Strength Test - Loading Rate
2.5 ± 0.25 mm/min
0.1 in/min (approx. 2.5 mm/min)
ASTM C165
Compressive Strength Test - Specimen Size
150 mm x 150 mm
Varies; often 100x100mm or 150x150mm (4x4 in or 6x6 in)
ASTM C165
Flexural Strength Test - Loading Type
Three-point loading (centre-point)
Three-point loading (Procedure A) or four-point loading (Procedure B)
ASTM C203
Water Absorption - Immersion Method
Total immersion for 24 hours
Partial immersion for 24 hours (bottom face 10 mm deep)
ISO 29767:2019
Water Absorption - Specimen Size
150 mm x 150 mm x thickness
200 mm x 200 mm x thickness
ISO 29767:2019
⚠ Verify details from original standards before use