SpecTopics: TPO Accelerated Weathering Tests
Accelerated weathering requirements in TPO roofing specifications generally mention the need for the roof to withstand 2,000 hours of exposure when tested according to ASTM G152, ASTM G154, or ASTM G155. What are the differences between these tests and why are they important?
All three are testing the roofing for UV exposure and have the ability to accelerate that exposure, simulating degradation that may occur many years ahead in a few months.
The first test is ASTM G152 - Standard Practice for Operating Open Flame Carbon Arc Light Apparatus for Exposure of Nonmetallic Materials. This test was first utilized in the 1930s and has a large amount of historical data using carbon arcs, and some specifications still require their use. However, carbon arc testing has been largely discontinued globally, as this technology is considered obsolete and has been replaced by xenon arc systems.
The second test on the list was developed after the carbon arc light utilized fluorescent lighting. Linear fluorescent lamps, similar to those used for residential and commercial lighting, have been developed with specific spectral distributions. These sources are incorporated into fluorescent condensation devices. These devices may be used in cycles that may vary light/dark cycles, temperature, condensing humidity, and water sprays. ASTM G154 - Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials is a test practice used to do QUV testing. QUV tests materials by exposing them to alternating cycles of ultraviolet (UV) light and moisture at controlled, elevated temperatures. The QUV simulates the effects of sunlight with fluorescent UV lamps, and it simulates dew and rain using condensing humidity and/or water spray which is used to simulate UV exposure for surface finishes, coatings, and polymers. Because it uses fluorescent light sources, ASTM G154/QUV testing isn’t often used to assess color changes as a function of time.
The third test, ASTM G155 - Standard Practice for Operating Xenon Arc Lamp Apparatus for Exposure of Materials, uses a xenon arc UV light source. While similar to the previous test, the most obvious difference between the two is that ASTM G154 testing uses fluorescent light sources to simulate UVA and UVB while ASTM G155 testing uses xenon arc UV light sources to simulate exposure to natural sunlight. Both light sources are able to accurately predict, on an accelerated basis, the effect sunlight will have on a product. And while both practices can be used to simulate indoor and outdoor sun exposure, xenon arc light is more similar to natural sunlight and, for this reason, is often a good choice for testing outdoor products. This is especially important for color changes over time. For outdoor roofing applications, the ASTM G155 test is the most appropriate of the three tests often specified for TPO.
As an example, Carlisle’s 60-mil Sure-Weld® TPO membrane was tested using the ASTM G155 test method and the membrane did not display any surface cracking or crazing after 16,000 hours (20,160 kJ/m2) when inspected under 7x magnification.
To learn more about the results of the ASTM G155 test for Carlisle SynTec’s TPO roofing membrane, refer to the Product Data Sheets on the Carlisle website or click here and look for the Typical Properties and Characteristics chart on page 4.
If you have any questions regarding accelerated weathering, please contact Craig Tyler.
All three are testing the roofing for UV exposure and have the ability to accelerate that exposure, simulating degradation that may occur many years ahead in a few months.
The first test is ASTM G152 - Standard Practice for Operating Open Flame Carbon Arc Light Apparatus for Exposure of Nonmetallic Materials. This test was first utilized in the 1930s and has a large amount of historical data using carbon arcs, and some specifications still require their use. However, carbon arc testing has been largely discontinued globally, as this technology is considered obsolete and has been replaced by xenon arc systems.
The second test on the list was developed after the carbon arc light utilized fluorescent lighting. Linear fluorescent lamps, similar to those used for residential and commercial lighting, have been developed with specific spectral distributions. These sources are incorporated into fluorescent condensation devices. These devices may be used in cycles that may vary light/dark cycles, temperature, condensing humidity, and water sprays. ASTM G154 - Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials is a test practice used to do QUV testing. QUV tests materials by exposing them to alternating cycles of ultraviolet (UV) light and moisture at controlled, elevated temperatures. The QUV simulates the effects of sunlight with fluorescent UV lamps, and it simulates dew and rain using condensing humidity and/or water spray which is used to simulate UV exposure for surface finishes, coatings, and polymers. Because it uses fluorescent light sources, ASTM G154/QUV testing isn’t often used to assess color changes as a function of time.
The third test, ASTM G155 - Standard Practice for Operating Xenon Arc Lamp Apparatus for Exposure of Materials, uses a xenon arc UV light source. While similar to the previous test, the most obvious difference between the two is that ASTM G154 testing uses fluorescent light sources to simulate UVA and UVB while ASTM G155 testing uses xenon arc UV light sources to simulate exposure to natural sunlight. Both light sources are able to accurately predict, on an accelerated basis, the effect sunlight will have on a product. And while both practices can be used to simulate indoor and outdoor sun exposure, xenon arc light is more similar to natural sunlight and, for this reason, is often a good choice for testing outdoor products. This is especially important for color changes over time. For outdoor roofing applications, the ASTM G155 test is the most appropriate of the three tests often specified for TPO.
As an example, Carlisle’s 60-mil Sure-Weld® TPO membrane was tested using the ASTM G155 test method and the membrane did not display any surface cracking or crazing after 16,000 hours (20,160 kJ/m2) when inspected under 7x magnification.
To learn more about the results of the ASTM G155 test for Carlisle SynTec’s TPO roofing membrane, refer to the Product Data Sheets on the Carlisle website or click here and look for the Typical Properties and Characteristics chart on page 4.
If you have any questions regarding accelerated weathering, please contact Craig Tyler.
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