ASTM C149: Thermal Shock Resistance Testing of Glass Containers
Glass containers — bottles, jars, vials, and other commercial packaging — are used across industries to contain beverages, preserves, chemicals, and other products that frequently undergo temperature changes during processing, filling, transport, and use. When a glass container experiences a sudden change in temperature — hot filling followed by cold water rinsing, sterilization cycles, refrigeration, or accidental immersion in hot water — the differential thermal stresses induced by uneven heating or cooling can cause fracture. ASTM C149 provides the standardized test methodology for evaluating this thermal shock resistance.
What Is Thermal Shock in Glass Containers?
Thermal shock is the stress induced in a material when different regions are at different temperatures simultaneously. In glass containers, this occurs when the outer surface of the container rapidly changes temperature while the inner glass remains at its initial temperature. The resulting differential thermal expansion creates tensile stresses at one surface and compressive stresses at the other. If the tensile stress exceeds the glass’s strength at that location — particularly at surface defects or stress concentrations — fracture occurs.
The thermal shock resistance of glass depends on: the magnitude of the temperature differential, the thermal expansion coefficient of the glass, the thermal conductivity (how quickly heat propagates through the glass thickness), and the surface condition (surface defects significantly reduce effective strength).
Typical thermal shock resistance values for common glass types:
- Float glass (soda-lime): Approximately 40°C differential before risk of fracture
- Toughened (tempered) glass: Tolerates temperature differentials up to 200°C
- Borosilicate glass (Pyrex-type): 160–200°C (low thermal expansion coefficient)
- Fused silica: Extremely high thermal shock resistance (near-zero expansion)
What Is ASTM C149?
ASTM C149 — Standard Test Method for Thermal Shock Resistance of Glass Containers determines the relative thermal shock resistance of commercial glass containers — bottles and jars — by subjecting them to sudden, controlled temperature changes and measuring the fraction that survive or the minimum temperature differential causing failure.
The test is applicable to commercial glass packaging that must withstand sudden temperature changes during service — including hot-fill packaging, pasteurization, carbonated beverage filling, and glass containers subjected to rapid temperature changes in use or processing.
ASTM C149 Test Variants
ASTM C149 provides multiple test variations depending on the testing objective:
Simple Pass/Fail Test: Containers are subjected to a defined temperature differential (e.g., 42°C) and the number of containers that survive determines a pass or fail result for a lot.
Progressive Test (Breaking a Specified Percentage): The temperature differential is increased progressively until a defined percentage of containers fracture — establishing the temperature differential at which a defined fraction of the population fails.
Full Progressive Testing: A complete breakage curve is established by testing containers at multiple temperature differentials, characterizing the distribution of thermal shock resistance across the container population.
High-Level Thermal Shock Test: Used for containers designed for high-temperature service (e.g., autoclave-sterilized containers), testing at higher temperature differentials than standard tests.
Test Procedure
The standard procedure involves the following steps:
- Specimen selection: Defect-free containers are selected and cleaned before testing to remove surface contamination that might affect results.
- Hot water immersion: Containers are immersed in hot water (typically 60–90°C depending on the test level) for a defined dwell time (1–2 minutes) to uniformly heat the container.
- Cold water transfer: Containers are immediately transferred to cold water (typically 0–20°C, per the specified differential) to create the rapid temperature change constituting thermal shock.
- Inspection: Containers are inspected for fracture (complete failure) or cracking. Results are recorded as passed (survived) or failed (fractured).
- Reporting: Pass/fail percentages, temperature differential applied, and any observed fracture patterns are documented.
Industrial Applications of ASTM C149
Beverage Packaging: Beer, soft drink, juice, and water bottles undergo repeated thermal cycling during washing, filling, pasteurization, and refrigeration. Thermal shock resistance testing per ASTM C149 qualifies container designs for these process conditions.
Pharmaceutical Packaging: Glass vials and bottles used for injectables and sterile solutions undergo autoclave sterilization (121°C) and must survive the thermal shock of sterilization cycles. ASTM C149 testing is part of packaging qualification for pharmaceutical applications.
Chemical Packaging: Laboratory and industrial glass containers that may be filled with hot or cold contents or subject to temperature changes during storage require thermal shock qualification.
Infinita Lab’s ASTM C149 Testing Services
Infinita Lab provides ASTM C149 thermal shock resistance testing of glass containers through its nationwide accredited laboratory network. Services include all test variants — pass/fail, progressive, and high-level thermal shock — with complete documentation supporting packaging qualification, quality control, and regulatory submissions.
Contact Infinita Lab: (888) 878-3090 | www.infinitalab.com
Frequently Asked Questions (FAQs)
What is the thermal shock test for glass? Thermal shock testing assesses glass containers' reaction to abrupt temperature fluctuations. These alterations may occur when hot liquids are poured into cold containers or vice versa, subjecting the containers to extreme temperature swings.
What is the temperature difference for glass thermal shock? Float glass can be thermally shocked at merely a 40-degree temperature differential. The typical toughened glass made by IQ can tolerate temperature variations of up to 200 degrees across its surface.
What materials are resistant to thermal shock? Fused silica (synthetic quartz or silicon oxide, SiO2), cordierite, and silicon nitrides (Si3N4) have very low thermal expansion coefficients, making them relatively resistant to thermal shock.
Why do some glass types have higher thermal shock resistance than others? Glass types with lower thermal expansion coefficients (borosilicate, fused silica) develop lower thermal stresses for a given temperature differential — providing higher thermal shock resistance. Soda-lime glass (standard container glass) has a higher expansion coefficient and lower thermal shock resistance than specialty glasses.
What is the progressive thermal shock test in ASTM C149? The progressive test increases the temperature differential incrementally, testing groups of containers at each level until a defined percentage fractures. This establishes the temperature differential at which a specific fraction of the container population fails — providing a statistical characterization of thermal shock resistance distribution rather than a single pass/fail result.
