Bubble Point Testing: Validate the Integrity and Pore Size of Sintered SS316L Disc Filters
Bubble Point Testing: How to Validate the Integrity and Pore Size of Your Sintered Disc Filter
Product Focus: DALON SINTERED SS316L FILTER DISC 52×3 (20 µm)
1 Purpose of Bubble Point Testing
Bubble point testing is one of the most reliable non-destructive integrity tests for porous metal filters. For sintered discs, it serves two essential quality-control purposes:
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Integrity Verification — Confirms the absence of cracks, delamination, or oversized pores that could allow unfiltered flow.
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Pore Size Validation — Correlates measured bubble point pressure with the filter’s largest pore diameter to ensure consistency with design specifications.
DALON applies bubble point testing to every production batch of sintered stainless-steel filters to guarantee dimensional and performance conformity.
2 Test Principle
Bubble point testing is based on the capillary-flow theory defined in ASTM F316.
When a filter is fully wetted, its pores act like tiny capillary tubes. The minimum gas pressure required to displace the liquid from the largest pore determines the bubble point.
Where:
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d = pore diameter (µm)
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γ = surface tension of the wetting liquid (mN/m)
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θ = contact angle (degrees)
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P = bubble point pressure (bar)
For isopropyl alcohol (IPA), γ = 21.7 mN/m and θ ≈ 0°, simplifying to:
Thus, a 20 µm pore should yield a bubble point near 4.35 bar.
3 Equipment Requirements
| Component | Specification |
|---|---|
| Pressure Source | Regulated air / nitrogen (0–15 bar range) |
| Pressure Gauge | Accuracy ± 0.1 % FS (0–10 bar range) |
| Test Chamber | Transparent, chemical-resistant (polycarbonate or stainless steel) |
| Wetting Fluid | Isopropyl Alcohol (IPA), γ = 21.7 mN/m |
| Sealing System | O-ring fixture matched to 52 mm disc diameter |
| Temperature Control (optional) | Maintain 20 ± 2 °C for consistency |
4 Step-by-Step Test Procedure
A. Preparation Phase
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Clean the Filter — Ultrasonic clean if needed; remove oils and dust.
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Wet the Disc — Fully immerse in IPA for 10 minutes to ensure complete saturation.
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Assemble Fixture — Mount disc using a uniform O-ring seal; connect outlet tubing to a transparent liquid chamber.
B. Testing Phase
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Initial Pressurization — Increase gas pressure slowly at 0.1–0.2 bar/min.
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Observation — Watch the outlet submerged in IPA for the first continuous bubble stream (ignore single intermittent bubbles).
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Recording — Document the pressure at which continuous bubbling begins.
C. Calculation and Validation
Expected bubble point for 20 µm disc:
5 Product Specifications: SS316L Disc 52×3 (20 µm)
| Parameter | Specification |
|---|---|
| Dimensions | 52 mm Diameter × 3 mm Thickness |
| Pore Size | 20 µm (Absolute Rating) |
| Material | SS316L (EN 10204 3.1 Certified) |
| Theoretical Bubble Point | 4.35 bar (IPA as wetting fluid) |
| Acceptance Criteria | ≥ 3.9 bar (≥ 90 % of theoretical) |
| Compliance | SGS / RoHS / REACH / MSDS / ISO 9001:2015 |
6 Interpretation of Results
| Test Outcome | Interpretation | Action Required |
|---|---|---|
| P ≥ 4.35 bar | Pore size ≤ 20 µm; filter integrity verified | Approve for use |
| 3.9 ≤ P < 4.35 bar | Borderline result; minor surface defect possible | Retest / lot review |
| P < 3.9 bar | Oversized pores or damage present | Reject / replace filter |
This tiered acceptance criterion ensures both pore-size accuracy and mechanical integrity across production lots.
7 Common Testing Errors & Solutions
| Error | Effect | Solution |
|---|---|---|
| Incomplete Wetting | Artificially high bubble point reading | Extend immersion time or add 0.1 % surfactant |
| Rapid Pressurization | Early bubble release, false low result | Use gradual ramp (≤ 0.2 bar/min) |
| Leaky Seal or Fixture | Bubbles from O-ring instead of pores | Check and lubricate O-rings |
| Dirty Surface | Irregular bubble formation | Clean disc in ultrasonic bath before test |
| Temperature Fluctuation | Variation in IPA surface tension | Conduct test at constant room temperature |
8 Quality Assurance Integration
Incoming Inspection
Perform bubble point testing on random samples from every incoming lot to confirm supplier consistency.
In-Process Validation
DALON conducts routine testing during sintering-batch certification to verify pore-size uniformity and absence of defects.
Post-Cleaning Integrity Check
After chemical or thermal cleaning, confirm pore recovery using the same method; a ≥ 80 % bubble-point retention validates successful regeneration.
Documentation and Traceability
All results are logged under DALON’s ISO 9001:2015 system and attached to customer documentation packages for quality records.
9 Practical Guidelines for Accurate Testing
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Use fresh IPA for each test; reused liquid alters surface tension.
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Avoid vibrations near the test chamber to prevent premature bubbling.
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Perform tests in a controlled environment (20 ± 2 °C, 40–60 % RH).
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Always verify instrument calibration every six months.
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For automated testing, set data-logging intervals ≤ 0.05 bar for precise detection.
10 Benefits of Bubble Point Testing for Sintered Metal Filters
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Non-destructive: The filter can be reused after testing.
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Fast and Repeatable: Results typically within 10 minutes per disc.
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Quantitative Verification: Directly correlates to maximum pore diameter.
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Universal Standard: ASTM F316 accepted for global specification control.
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Ensures Process Reliability: Guarantees that only defect-free filters enter service.
11 DALON’s Testing & Validation Expertise
Certified Reports
Each DALON sintered filter disc shipment includes a lot-specific bubble-point test report verifying pore integrity.
Custom Fixtures and Training
DALON provides:
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Customized O-ring fixtures for rapid disc mounting.
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Automated multi-station test rigs for high-volume QA environments.
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On-site training for operators on test setup and result interpretation.
Technical Assistance
Engineering specialists assist in developing acceptance criteria and troubleshooting pore-size deviations based on process conditions.
12 Ordering Information
| Item | Details |
|---|---|
| Model | DAL-SS316L-DISC-52×3-20 µm |
| Lead Time | New Orders: 40–45 days (includes 5–10 days tooling) • Repeat Orders: Within 30 days |
| MOQ | 50 pcs (standard) / custom quantities on request |
| Documentation | Lot-specific bubble point test report + dimensional inspection data |
| Packaging | Cleanroom-sealed, vacuum packed if required |
| Certifications | SGS / RoHS / REACH / MSDS / ISO 9001:2015 |
👉 Request a DALON Bubble Point Testing Guide or Quotation for SS316L Filter Discs
13 Conclusion
Bubble point testing remains the most effective and recognized method for validating the integrity of sintered metal filters.
By measuring the pressure required to displace a wetting liquid from the largest pore, engineers can confirm both maximum pore size and mechanical soundness of each filter disc.
The DALON SS316L Filter Disc (52×3, 20 µm) combines consistent porosity, excellent corrosion resistance, and traceable production control. Every batch is bubble-point verified to meet or exceed the ASTM F316 standards.
For manufacturers in chemical processing, pharmaceutical, and precision instrumentation sectors, this method ensures filters enter service with proven integrity — reducing downtime and quality risks.
In summary:
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Theoretical bubble point = 4.35 bar (for 20 µm pores)
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Acceptance limit ≥ 3.9 bar
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Validated by certified reports included with each DALON shipment
With DALON’s expertise and documentation, customers achieve confidence in filtration reliability and repeatable process validation worldwide.
FAQ
1. What is the purpose of bubble point testing?
It verifies filter integrity and confirms the maximum pore size according to ASTM F316 standards.
2. Why is IPA used as the wetting fluid?
IPA has low surface tension and fully wets SS316L pores, providing stable and repeatable results.
3. What is the expected bubble point for a 20 µm disc?
Approximately 4.35 bar (≥ 3.9 bar acceptable).
4. How often should integrity tests be performed?
At incoming inspection, after each maintenance cycle, or before critical production batches.
5. Can bubble point testing be used after filter cleaning?
Yes — it verifies that regenerated filters have retained their original pore structure and integrity.
6. What lead times apply for DALON filter discs?
New orders require 40–45 days (including 5–10 days tooling); repeat orders ship within 30 days.