GB/T 15171 Sealing Performance Test for Instant Noodle Packaging: Complete Method Guide

Source: Link Testing Instruments Co.,Ltd.

Instant noodles are a high-fat, low-moisture food. Their quality degrades through two parallel pathways, and both begin at the seal:

• Oxidation — residual oxygen in the headspace reacts with lipids, raising the acid value and producing rancid off-flavours well before the printed shelf life.
• Moisture ingress — even a micro-leak in the fin seal allows ambient humidity in, softening the noodle block and creating conditions for mould growth.

The seal line is the only barrier standing between the product and both failure modes. A seal that passes a visual check on the production line can still leak at 5–20 µm scale — far below what the eye can detect.

GB/T 15171, Test Method for Sealing Performance of Flexible Packages, is the Chinese national standard that defines how this seal integrity is verified. The 2025 revision (GB/T 15171-2025) is a substantive rewrite that directly affects how instant noodle manufacturers and their QC labs should be testing.

I. What Changed in GB/T 15171-2025

1. Expanded scope of application

The 1994 version covered flexible packaging only. The 2025 revision extends coverage to:

For instant noodles this matters immediately: cup noodles with film lids, bowl-type products, and shaped seasoning sachets are now explicitly in scope — they were outside the 1994 framework.

2. Addition of the vacuum decay method

This is the most operationally significant change. The 2025 revision formally adds a quantitative method alongside the traditional qualitative one:

• Old approach (bubble emission) — the operator watches for bubbles and makes a subjective pass/fail call. Two trained operators can reach different conclusions on the same sample, and a slow leak may produce no visible bubbles within the observation window.
• New approach (vacuum decay) — a high-precision pressure sensor records the pressure rise inside an evacuated chamber over time. The result is expressed as a vacuum decay rate Q (Pa/s), a number that can be trended, compared against a limit, and audited.

The decay rate is calculated as:

Where P1 is the pressure at the start of the measurement window, P2 at the end, and T the elapsed time. A package with an intact seal holds vacuum; a leaking package allows air in, and the pressure rises. The faster the rise, the worse the seal.

II. The Two Test Methods in Detail

GB/T 15171-2025 describes two complementary methods. They are not alternatives — they answer different questions.

Method A — Underwater Bubble Emission (Negative Pressure Method)

Principle: The package is immersed in water inside a vacuum chamber. The chamber is evacuated, creating a pressure differential that forces air out through any seal defect. Escaping air appears as a stream of bubbles.

Best suited to: Single-layer or thin flexible packaging where a gross leak exists — the kind of defect that causes a visible puncture or channel in the fin seal. Fast, low-cost, and needs no calibration curve.

Procedure:

1. Place the sample in the vacuum chamber and add test water — clean, transparent, non-distilled. Distilled water is excluded because its low surface tension can suppress small bubble formation.
2. Evacuate to the target pressure. For instant noodle packaging the working range is normally 20 kPa to 90 kPa, selected according to film thickness and package volume.
3. Hold pressure for 30 to 60 seconds.
4. Observe continuously during the hold. Record the pressure at which the first continuous bubble stream appears.
5. Release vacuum, remove the sample, open it slowly, and inspect the interior for water ingress.

Pass criteria: no continuous bubble stream during the hold, and no water seepage inside the package after opening.

Limitations to be aware of:

• Bubbles adhering to the film surface can be mistaken for a leak signal.
• Seals that hold at low pressure but fail at higher pressure will be missed if the test pressure is set too conservatively.
• Very small leaks may not produce bubbles at all within a 60-second window — this is precisely the gap the vacuum decay method fills.

Method B — Vacuum Decay (Quantitative Method)

Principle: The sample is placed in a sealed test chamber, which is evacuated to a target pressure. The chamber is then isolated from the vacuum source, and the pressure inside is monitored. Because the chamber contains only the sample and a fixed volume of air, any pressure rise indicates air entering from the sample's interior — which means a leaking package.

Best suited to: Multi-layer composite films, aluminium-plastic laminates, irregularly shaped bags, and any application where a numeric, auditable result is required. Also the only practical option for non-destructive testing of finished retail units.

Procedure:

1. Place the sample in the test chamber. For flexible packages a compliant membrane or restraining fixture may be used to prevent package inflation from masking the signal.
2. Evacuate the chamber to the target pressure.
3. Isolate the chamber and begin the measurement window.
4. Record P1 and P2 across the interval T, and compute Q = (P1 − P2) / T.
5. Compare Q against the acceptance limit defined for the product.

Pass criteria: the decay rate Q is below the specified limit. For typical instant noodle film structures the limit is commonly set at 0.1 Pa/s or tighter, depending on package volume — a larger headspace volume releases more air for the same defect size, so the limit should be scaled to package format rather than applied uniformly.

Choosing between the two

Practical recommendation for instant noodle producers: use Method A for routine line checks on simple film bags where speed matters, and Method B for new product qualification, supplier audits, and any package format where a returned sample cannot be sacrificed.

III. Selecting Compatible Testing Equipment

LTY-01 Leak Tester — dual-mode, standard-compliant

The LTY-01 Leak Tester supports both methods required by GB/T 15171-2025 in a single unit:

• Dual-mode testing — underwater bubble emission and vacuum decay, switchable without changing instruments
• Vacuum range 0.01–90 kPa — covers the full 20–90 kPa working window required for instant noodle packaging, with low-end resolution for thin films
• One-touch segmented vacuum — automated evacuation, constant-pressure hold, and real-time data recording, removing operator-to-operator variability
• Transparent vacuum chamber — allows direct visual confirmation of bubble formation during Method A testing
• GMP-compliant — supports audit trails and data encryption for regulated environments

LTNDL-V301 Micro-Leakage Sealing Tester — for high-precision vacuum decay work

Where the application demands maximum sensitivity — multi-layer composite films, large-format bags, or non-destructive testing of finished retail units — the LTNDL-V301 Micro-Leakage Sealing Tester is designed specifically for the vacuum decay principle:

• Dual test principle with an innovative mechanical design that decouples the sample from chamber volume effects
• Scientific and rigorous structural design for repeatable chamber sealing
• High-precision, high-speed sampling chips to capture the pressure curve accurately at low decay rates
• Fully automatic pneumatic clamping with GMP design — no manual sealing variability

IV. Common Seal Failures in Instant Noodle Packaging

Knowing why seals fail makes the test data actionable. The four causes below account for the large majority of seal failures observed on noodle packaging lines.

1. Contamination in the seal area

The single most common cause. Noodle crumbs, seasoning powder, or oil film trapped between the sealing layers prevents polymer chains from interlocking across the interface. The seal looks continuous but has a channel through it.

Detection signature: bubble streams emerging from a localised point along the seal line rather than the whole length.

Fix: improve the powder-filling station's dust extraction, and add a seal-area inspection (or air knife) immediately before the sealing jaws.

2. Insufficient or excessive sealing temperature

• Too low — the polymer does not reach its melt range, producing a weak, peelable seal that fails under handling stress.
• Too high — the film is over-thinned or burnt through at the seal line, creating a fragile region that ruptures in transit.

Detection signature: for low temperature, the seal fails along its entire length and separates cleanly. For high temperature, failure occurs at the edge of the seal where the film has thinned.

Fix: establish a heat seal curve (strength vs. temperature) for each film structure and lock the set point with a margin of at least 15 °C from the failure threshold on both sides.

3. Insufficient dwell time or pressure

Sealing is a time–temperature–pressure process. A correct temperature with too short a dwell or too little jaw pressure produces the same weak seal as an under-temperature condition, but only at high line speeds — so it appears intermittently, which makes it easy to miss.

Detection signature: failures cluster at higher line speeds and disappear when the line runs slowly.

Fix: validate sealing parameters across the full production speed range, not just at nominal speed.

4. Mechanical damage after sealing

The seal survives the sealing station but is damaged downstream — by a sharp guide rail, a pinch point in the conveyor, or tearing during cartoning. The seal itself is sound; the package arrived defective.

Detection signature: the leak is a tear or puncture rather than a seal-line channel; vacuum decay shows a much larger Q than a seal defect of similar visual size would produce.

Fix: trace the package path from sealing to cartoning and inspect each contact point.

V. Frequently Asked Questions

Q: Is GB/T 15171 the same as ASTM D3078?

No. Both describe bubble-emission testing under vacuum, but they differ in scope and pressure specification. ASTM D3078 is limited to flexible packaging and specifies its own pressure ranges. GB/T 15171-2025 explicitly extends to semi-rigid and rigid formats and adds the vacuum decay method. If you supply to both domestic and export markets, verify which standard your customer's specification calls out — passing one does not automatically demonstrate compliance with the other.

Q: Can I test cup noodles with a film lid under GB/T 15171-2025?

Yes — this is one of the additions in the 2025 revision. The 1994 version's flexible-packaging-only scope excluded this format. Cup and bowl products should be tested using the vacuum decay method where possible, since the bubble method requires full immersion and the rigid cup geometry makes complete water contact unreliable.

Q: What vacuum decay limit should I set for a 100 g noodle bag?

The limit must be scaled to the package's free volume. A larger headspace holds more air, so the same defect produces a larger Q. A workable approach is to establish your limit empirically: test a batch of known-good units and a batch with deliberately induced pinholes of a defined diameter, then set the limit between the two populations with margin. As a starting reference, 0.1 Pa/s is a common baseline for standard 80–120 g film bags — but treat it as a starting point to validate, not a universal constant.

Q: Is vacuum decay testing destructive?

No — this is its main operational advantage. The package is not immersed and not opened, so a tested unit can be returned to the production stream. This makes Method B suitable for sampling finished goods at higher frequency than would be affordable with destructive testing.

Q: My seal passes the bubble test but the product still spoils. Why?

The bubble method cannot reliably detect leaks below roughly 10–20 µm, and a slow micro-leak in that range is enough to allow moisture ingress over a 6–12 month shelf life. Move to vacuum decay testing, and in parallel check the package's oxygen barrier performance — seal integrity and barrier performance are separate properties, and a package can have an intact seal with inadequate barrier film.

VI. Setting Up an Effective Seal Testing Programme

A single passing test tells you one package was acceptable at one moment. A testing programme tells you whether the process is under control. Four elements make the difference:

1. Establish a baseline — test at least 30 units from three separate production runs to characterise normal process variation before setting any limit.
2. Scale the limit to the package format — different bag sizes and film structures need different Q limits. Document the limit per SKU rather than applying one number across the plant.
3. Test at the extremes — sample at line start-up, at maximum line speed, and after any film roll change. Many seal failures are transient and appear only at these transition points.
4. Trend the numbers — because vacuum decay produces a value rather than a pass/fail flag, you can plot Q over time and detect a process drifting toward the limit before it starts producing failures. This early-warning capability is the main long-term benefit of adopting Method B.

Summary

With food safety requirements tightening, standardized seal testing has moved from a best practice to a baseline expectation for instant noodle packaging. The GB/T 15171-2025 revision gives producers two complementary tools — the established bubble emission method and the newer, quantitative vacuum decay method — and extends the standard's scope to cover the cup and bowl formats that dominate the category.

The practical path forward:

• Verify your current test pressure and hold time against the 20–90 kPa / 30–60 s window, and confirm your equipment can hold it repeatably.
• Adopt vacuum decay for qualification and audit testing — the numeric result is what makes seal quality defensible in a supplier agreement.
• Check whether your cup and bowl products are covered by your existing test protocol; under the 1994 scope they were not.
• Investigate failures by cause, not just by frequency — contamination, temperature, dwell/pressure, and downstream damage each require a different corrective action, and the vacuum decay rate gives you the signature to tell them apart.

About Link Testing Instruments

Link Testing Instruments Co., Ltd. is a manufacturer of packaging materials testing equipment and a supplier of flexible packaging testing instruments and complete testing schemes, providing sample commissioned testing services and laboratory construction programmes.

• Equipment referenced in this guide: LTY-01 Leak Tester · LTNDL-V301 Micro-Leakage Sealing Tester · LTGPT-02 Bottle Internal Pressure Tester
• Related reading: How to Test the Sealing Performance of Potato Chip Packaging · Common Quality Problems and Solutions of Instant Noodle Packaging · Micro-Leakage Sealing Tester Can Detect Food Packaging Sealing Issues Within 10 Minutes
• Contact: Floor 12, No.166 Dikou Road, Jinan, Shandong Province, China
• Tel: +86-15106990260 · Email: Andrew@linktesting.org · info@linktesting.org
• Website: https://www.linktesting.org