# Real World Pressure Testing of PET Containers

- Link: https://flexitest.in/blogs/real-world-pressure-testing-of-pet-containers/
- Published: 2025-05-07T13:10:14+05:30
- Author: flexitest

# Real World Pressure Testing of PET Containers

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 3. Real World Pressure Testing of PET Containers

## PURPOSE

Source: Agr International, Inc. — “Real World Pressure Testing of PET Containers”(
© 2017).

Proper pressure testing of PET containers is an essential part of a smooth filling
process and favourable downstream performance of carbonated soft drinks (CSD) and
other pressure products. Whether we realize it or not, all PET containers used for
pressure products are being pressure tested, both as they are filled in high-speed
counter-pressure filling machines and in the distribution channels as they experience
varying ambient temperature conditions. Relying on the filling equipment and downstream
events of a container’s life cycle to verify container performance can be very costly
and have undesirable implications on brand confidence. For this reason, state-of-
the-art container manufacturers have adopted pressure testing protocols that simulate
all of the conditions experienced by the container during the filling process and
beyond. This paper will discuss the pressurized environments that a PET carbonated
beverage is subjected to and the test methods used to ensure that commercial quality
containers are produced.

## CONTAINER FILLING

The typical filling process for a PET carbonated beverage container uses a counter-
pressure technique. When the empty container is presented to the filling station,
it is sealed and quickly charged with CO_(2). The CO_(2) located above the carbonated
product in a holding bowl as well as in the container are pressurized higher than
the desired product carbonation level to prevent the dissolved CO_(2) in the product
from coming out of solution during filling. Typical counter pressures range from
60–100 psi for cold or ambient filling conditions. Gravity is used to transfer the
carbonated product from the bowl into the container, and after the filling process
is complete, pressure is relieved from the container. A schematic of this technique
can be seen in Figure 1.0.

![Real World Pressure Testing of PET Containers](https://flexitest.in/wp-content/
uploads/2025/05/Fig.1.webp "Real World Pressure Testing of PET Containers 1")

## INITIAL PRESSURIZATION

Of particular note in the filling process is the speed of initial pressurization
of the PET container, by far the most important step as it relates to the ongoing
performance of the container. The initial pressurization found in normal filling
machines occurs in approximately 500 milliseconds, as the ambient air in the container
is replaced with CO_(2).

## BRITTLE FAILURES

This rapid, non-linear pressurization in PET containers can trigger brittle failures,
especially in the base. Excess amorphous material that remains in the base of the
container after the blowing process creates a region, with high concentrations of
stress, between the oriented and amorphous material. The material in this region
is brittle and can fracture easily when the container is pressurized. Many of these
early failures occur well below the pressure level used in the counter-pressure 
filling process. Conversely, pressure testing containers with slow initial pressurization
characteristics is not sufficient to identify when the blowing process is making
containers that will not survive this first step of the filling process (figure 
2.0).

![Real World Pressure Testing of PET Containers](https://flexitest.in/wp-content/
uploads/2025/05/Fig.2.webp "Real World Pressure Testing of PET Containers 2")

## VOLUME EXPANSION

A container that survives the initial rapid pressurization still may not provide
acceptable performance. After the counter-pressure has been applied, the container
is subjected to a pressure hold for approximately 13 seconds (figure 3.0). Understanding
volume expansion behaviour of the container during this hold time provides an important
data point about how the container will react throughout the commercial life cycle.
A container with a weak overall structure or lower levels of material orientation
may expand beyond acceptable levels, causing thinning of the wall thickness, faster
loss of carbonation and a higher risk for side wall failures. To ensure that the
filled container will ultimately perform for the consumer, a quality pressure testing
method must include the pressure hold at a value that simulates the real-world experience
of the bottle.

![Real World Pressure Testing of PET Containers](https://flexitest.in/wp-content/
uploads/2025/05/Fig.3.webp "Real World Pressure Testing of PET Containers 3")

## PROCESSING HISTORY ON INHERENT MATERIAL PROPERTIES

The ultimate material properties of a finished PET container are the cumulative 
result of multiple factors including the time and temperature profiles for heating
the preform, along with the stretching and blowing profiles in the formation of 
the container itself. A change in any of these variables will affect many factors,
including the pressure at which the container will experience an unrecoverable yield
or deformation. The natural frequency and potential impact of these processing changes
drive the need to regularly pressure test containers to determine how a given production
run will perform under filling and down-stream conditions.

## PRESSURE TESTING

For over 25 years, PET containers have been pressure tested with the intent of understanding
how well a container will perform under real-world filling, storage, transportation,
shelf-life and consumer-use conditions.

When PET, as a material, is tested using a tensile tester, a stretching force is
applied to determine the amount of force required to reach the yield point (where
material is permanently deformed) and is continued until failure (point where the
material stops stretching and breaks). With a container, this can be equated to 
the application of internal pressure expanding the container volume and stretching
the material to the point where the PET yields, and then a continuation of pressurization
to container failure (burst). Yield and burst are the two key material failure modes
experienced by a PET bottle. This simple ramp approach is acceptable for use only
after the 13 second hold spoken of earlier.

To simulate actual conditions, a complex test is warranted that subjects the container
to the same abrupt, non-linear pressure dynamic (counter-pressures) seen in the 
filling process, then held at actual filling pressures for the appropriate filling
time, and then subjected to a continuously increasing pressure ramp to identify 
the container yield point and ultimate failure. Testing PET containers in this manner
provides the manufacturer with the information required to understand how the containers
will perform in the filling operation and throughout the commercial life cycle.

An example of a testing system that provides the capabilities to simulate the complex
pressure profile of the filling operation is the [Agr PPT3000^(TM).](https://flexitest.in/preform-csd-bottle-container-testing-systems/ppt3000/)
The PPT3000 accurately represents the counter-pressure filling simulation by providing
a precise pressure profile that simulates a true filling environment.

This pressure profile has been dubbed the “Fill Ramp”, where the container is subjected
to an abrupt, ~500 millisecond non-linear pressurization, up to the test pressure
hold level (60–100psi). It is held at that test pressure for 13 seconds, and then
subjected to a pressure ramp increase of 10 psi/sec, leading to the identification
of the yield pressure and ultimate burst pressure. The “Fill Ramp” pressure profile(
figure 4.0) shows the change in pressure vs. time for the test and how the different
segments of the test correlate with the filling cycle.

![Real World Pressure Testing of PET Containers](https://flexitest.in/wp-content/
uploads/2025/05/Fig.4.webp "Real World Pressure Testing of PET Containers 4")

## CONCLUSION

With the trend toward high-speed, combined blow-fill operations and the propagation
of ultra-lightweight PET containers, it has become increasingly imperative to identify
and correct blow molding problems before loss-of-pressure failures occur downstream
in the filler, in the warehouse or through retail channels.

The only way to truly understand the downstream performance characteristics of PET
carbonated beverage containers is by reproducing the abrupt, non-linear pressurization
that a container experiences during the filling process. Routine pressure testing
that follows the pressure profiles applied by the filling machine, in combination
with the monitoring of material properties, form the basis for a sound testing program
that will ensure optimal container performance, both in the production/filler environment
as well as throughout the commercial life cycle.

[The Agr PPT3000](https://flexitest.in/preform-csd-bottle-container-testing-systems/ppt3000/)
is the only pressure testing system currently available that truly simulates the
filling process and, ultimately, the downstream conditions.

 [ ⌊process pilot family⌉ ](https://flexitest.in/packaging-testing-equipments/permeability-testing-instruments/wvtr-gravimetric-method-c360h/)

## 󠀁[oProcess Pilot® Family of Products](https://flexitest.in/preform-csd-bottle-container-testing-systems/process-pilot-family-of-products/)󠁿

 [  Explore   ](https://flexitest.in/preform-csd-bottle-container-testing-systems/process-pilot-family-of-products/)

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