Metal wound gasket inspection

Metal Wound Gasket Inspection – Ensuring Leak‑Tight Sealing for Australian Industrial Flange Connections

In Australia’s oil and gas, chemical processing, power generation, and mining industries, metal wound gasket inspection is essential to verify that spiral wound gaskets (SWGs) maintain their dimensional accuracy, winding density, and sealing integrity under high pressure and temperature cycles. Spiral wound gaskets consist of a V‑shaped metal strip (typically stainless steel) wound together with a soft filler (graphite, PTFE, or ceramic) and are used in pipe flanges, heat exchangers, valves, and pressure vessels. Our ISO/IEC 17025 accredited laboratory provides comprehensive inspection services – including visual examination, inner/outer ring dimensions, winding density measurement, hardness of filler, compression and recovery testing, and leakage assessment – to ensure compliance with AS 4177 (spiral wound gaskets) and AS 4331 (flange gasket standards). A systematic metal wound gasket inspection helps Australian plant operators avoid fugitive emissions, unplanned shutdowns, and flange leaks that can lead to safety incidents and environmental penalties.

Types of Metal Wound Gasket Samples We Test

Our laboratory handles a wide variety of spiral wound gaskets used across Australian industrial facilities:

• ASME B16.20 spiral wound gaskets with inner and outer rings (standard for oil and gas)
• Gaskets with different filler materials: flexible graphite (standard), PTFE (chemical resistance), vermiculite (high temperature), and mica (extreme heat)
• Metal winding materials: stainless steel 304, 316, 316L, 347, Duplex 2205, Inconel 625, Monel 400
• Gaskets for different pressure classes (Class 150, 300, 600, 900, 1500, 2500)
• Custom‑sized gaskets for heat exchangers and large‑diameter flanges (up to 1000 mm ID)
• Gaskets from production batches (incoming quality assurance for storage)
• Gaskets removed from service (post‑removal condition assessment, compression set, filler degradation)
• Competitor gaskets (benchmarking for sealing performance)
• Gaskets stored in warehouse (for shelf‑life verification)

Key Inspection Parameters and Test Methods for Metal Wound Gaskets

We evaluate multiple critical aspects to guarantee the sealing reliability of spiral wound gaskets in Australian harsh conditions – from offshore platforms in Bass Strait to desert gas plants in Moomba.

1. Visual and Dimensional Inspection – AS 4177 Clause 6

Under good lighting (500–1000 lux) and with a magnifying lamp (5×), we examine the gasket for: loose windings, broken metal strips, protruding filler, inner/outer ring deformation, rust or corrosion, and surface contamination. Using calibrated vernier calipers, micrometers, and optical comparators, we measure:

• Gasket ID and OD (mm) – tolerance typically ±0.5 mm for standard sizes
• Thickness (mm) – nominal plus tolerance (e.g., 4.5 mm ±0.2 mm)
• Inner ring thickness and outer ring thickness
• Number of winding layers (counted visually or by weight)
• Ring centricity (concentricity between inner and outer rings)

Out‑of‑tolerance gaskets may not seat correctly, leading to bypass leakage.

2. Winding Density (Number of Plies per Unit Length) – AS 4177 Clause 7

We count the number of metal plies per 10 mm of gasket circumference (or per winding layer). For standard gaskets, density is typically 5–8 plies per 10 mm. Low winding density reduces radial sealing pressure; high density increases stiffness and may require higher bolt load for compression. We also measure the gap uniformity between windings using a feeler gauge.

3. Filler Material Identification – FTIR or Thermogravimetric Analysis

We extract a small sample of the filler and analyse it using Fourier‑transform infrared spectroscopy (FTIR) to confirm the material (graphite, PTFE, vermiculite, or mica). For graphite fillers, we measure purity by ash content (ASTM D6313). Ash content > 3% indicates low‑quality graphite (high impurities) that may corrode stainless steel windings.

4. Compression and Recovery (Sealing Force) – ASTM F586 / ISO 9808

We mount a gasket specimen in a compression jig and apply a preload of 50 MPa (or specified seating stress) at room temperature. Using a calibrated load cell and displacement transducers, we measure:

• Compressibility (% thickness reduction under load) – typically 10–25% for graphite‑filled gaskets.
• Recovery (% thickness regained after load removal) – typical > 40% for high‑quality gaskets.
• Thickness after unloading – permanent compression set should be < 10% of original thickness.

Low recovery (< 30%) leads to loss of seal under pressure cycling.

5. Stress Relaxation (Bolt Load Retention) – ASTM F1574 / ISO 7489

We compress the gasket to a defined stress (e.g., 100 MPa) at ambient temperature and record the force decay over 100 hours. The residual stress is measured. Acceptable retention: > 80% of initial load after 100 hours. Poor stress relaxation results in loosening of flange bolts and gas/liquid leaks.

6. Leakage (Sealing Performance) – Shell and Core – ISO 15848‑2 or ASTM F2839

We mount the gasket in a test fixture between two flat platens and pressurise the ID side with helium (or nitrogen) at 1.1× design pressure. A mass spectrometer (for helium) or bubble detector (for nitrogen) measures leakage rate across the gasket. For Class 150 gaskets, allowable leakage is typically ≤ 0.1 cm³/s for gas. Any leakage > 0.5 cm³/s fails inspection.

7. Filler Hardness and Integrity – Shore OO or Micro‑hardness

Using a Shore OO durometer (soft materials), we measure the hardness of the filler on the gasket surface. For graphite fillers, hardness should be consistent (no soft or crumbling spots). Low hardness (< 50 Shore OO) may indicate excessive filler content or degradation; high hardness (> 80 Shore OO) may cause insufficient embedment into flange surface.

8. Metal Strip Tensile Strength – ASTM E8 / AS 1391

From a witness sample of the metal winding strip (provided by the manufacturer), we machine a tensile specimen and measure ultimate tensile strength (MPa). For stainless steel 316L, typical UTS is 480–620 MPa. Low tensile strength (< 400 MPa) may cause strip rupture during winding or under high bolt load.

9. Galvanic Corrosion Risk – Salt Spray Test (ASTM B117) for Assembled Gaskets

For gaskets with dissimilar metals (e.g., stainless steel winding with carbon steel outer ring), we expose the assembled gasket to neutral salt spray (5% NaCl, 35°C) for 240 hours. After exposure, we inspect for corrosion at the interface and any loosening of windings. No red rust on critical sealing surfaces is allowed.

10. Post‑Service Condition Assessment (Used Gaskets)

We receive used gaskets removed from flanges during maintenance. Our inspection includes: visual assessment of filler extrusion, compression set measurement (by comparing original thickness to current thickness), evidence of bypass channeling (streaks on sealing face), and pitting corrosion on windings. We issue a report on whether the gasket failed due to overcompression, undercompression, or chemical attack.

11. Shelf‑Life and Aging – Thermal Aging at 150°C for 168 hours

We place new gaskets in an oven at 150°C (typical maximum storage temperature) for 7 days. After aging, we re‑test compression/recovery and leakage. Loss of recovery > 20% indicates that the filler material has degraded and the gaskets should be replaced.

Quality Grading and Acceptance Criteria

Based on our metal wound gasket inspection, we classify gaskets into three serviceability grades (clients provide specific acceptance criteria referencing AS 4177 or ASME B16.20):

• Grade A (Premium – Critical Services) – Dimensions within ±0.2 mm, winding density 6–8 plies/10 mm, compressibility 15–20%, recovery > 50%, stress relaxation retention > 85%, helium leakage < 0.01 cm³/s, no corrosion.
• Grade B (Standard – General Process) – Dimensions within ±0.5 mm, winding density 5–8 plies/10 mm, compressibility 10–25%, recovery 40–50%, retention > 80%, helium leakage < 0.1 cm³/s, minor discoloration allowed.
• Grade C (Reject – Not Fit for Service) – Dimensions out of tolerance, loose windings, filler cracks or crumbling, recovery < 30%, leakage > 0.5 cm³/s, visible rust – immediate replacement required.

Reporting and Deliverables

Our metal wound gasket inspection report includes: gasket identification (manufacturer, size, pressure class, winding/filler material, batch number), visual and dimensional findings (photos), winding density count, filler identification method, compression‑recovery curve, stress relaxation plot, leakage rate (cm³/s), hardness values, metal tensile strength (if tested), salt spray corrosion images, aging test results, and a clear pass/fail recommendation for each batch or individual gasket. Raw data (test curves, photographs, spectrometer traces) are archived for 10 years.

In summary, comprehensive metal wound gasket inspection ensures that spiral wound gaskets used in Australian oil refineries, gas plants, water treatment facilities, and chemical plants provide reliable, leak‑tight seals throughout their service life. Contact our laboratory to schedule batch testing for your next flange gasket procurement or to analyse used gaskets from your recent turnaround.

Applications in the Australian Industry

• Oil and gas (offshore Gippsland Basin, LNG plants in Karratha and Gladstone, Moomba gas processing): Inspection of Class 600 and Class 900 gaskets for gas pipelines.
• Chemical processing (Newcastle, Botany, Altona): PTFE‑filled and graphite‑filled gaskets for corrosive chemical services.
• Power generation (coal‑fired, gas turbine, solar thermal): High‑temperature gaskets for steam and HRSG flanges.
• Mining (Olympic Dam, Pilbara iron ore, Hunter Valley coal): Large‑diameter gaskets for slurry pipelines and process tanks.
• Water and wastewater (Sydney desalination, Melbourne Water): Gaskets for potable water and sewage treatment.