How to install corrugated metal gaskets to ensure a reliable seal?

A reliable seal with corrugated metal sealing gaskets depends on four factors executed correctly in sequence: verified flange surface finish, proper gasket selection matched to the service conditions, controlled bolt torque applied in a star pattern, and a confirmed retorque after initial thermal cycling. Skipping or shortcutting any of these steps is the primary cause of leakage in flanged joints that use corrugated metal gaskets — not the gasket material itself. When the installation procedure is followed correctly, corrugated metal gaskets routinely achieve seal integrity at pressures exceeding 2,500 PSI and temperatures from cryogenic service (-200°C) to high-temperature process environments (800°C+), depending on the metal core and coating specification.

This guide covers every installation variable that determines seal reliability: flange preparation requirements, gasket material and coating selection, torque calculation, bolt tightening sequence, and post-installation verification — with specific data values for each critical parameter.

What Corrugated Metal Gaskets Are and Why Installation Technique Matters

Corrugated metal gaskets — also referred to as corrugated metal sealing gaskets in industrial specifications — consist of a thin metal sheet (typically 0.2–0.5 mm thick) formed with a series of concentric or parallel corrugations pressed into the surface. These corrugations act as multiple independent sealing lines: when bolt load is applied, each corrugation ridge deforms slightly and embeds into the flange face, creating a series of high-stress sealing contacts rather than a single contact line. This multi-contact geometry is what gives corrugated metal gaskets their superior sealing performance compared to flat metal gaskets at equivalent bolt loads.

The corrugated profile also makes these gaskets more sensitive to installation errors than soft gaskets. A soft spiral wound or compressed fiber gasket will conform to minor flange irregularities through bulk compression. A corrugated metal gasket requires the flange surface to be within specification before installation — the gasket cannot compensate for significant surface defects or misalignment. This is why understanding the installation requirements in detail is not optional for corrugated metal gasket applications.

Custom corrugated gaskets for non-standard flange geometries follow identical installation principles but require additional verification of the gasket's dimensional conformance to the flange before any assembly begins.

Flange Surface Preparation: The Most Critical Pre-Installation Step

More corrugated metal gasket failures originate from inadequate flange preparation than from any other single cause. The flange face must meet surface finish, flatness, and cleanliness requirements before the gasket is placed — these cannot be corrected after assembly.

Surface Finish Requirements

Corrugated metal gaskets require a controlled surface finish on the mating flange face. The optimum range for most corrugated metal gasket applications is Ra 3.2–6.3 micrometers (125–250 microinches) — a slightly rougher finish than required for soft gaskets. This controlled roughness provides microscopic mechanical anchoring points for the gasket coating (typically graphite, PTFE, or soft metal plating) to adhere to during seating. A finish that is too smooth (below Ra 1.6 μm) reduces the coating's ability to fill micro-surface irregularities; a finish that is too rough (above Ra 12.5 μm) creates leak paths along the corrugation contact lines.

Measure surface finish with a contact profilometer at a minimum of four points on the sealing face (12, 3, 6, and 9 o'clock positions). Record all values — if any single measurement falls outside the acceptable range, the flange face requires re-machining or replacement before proceeding.

Flange Flatness and Parallelism

The mating flange faces must be flat and parallel within tight tolerances. Maximum allowable flatness deviation for corrugated metal gasket service is typically 0.1 mm across the full sealing width — tighter than the 0.25 mm commonly permitted for spiral wound gaskets. Check flatness using a precision straight-edge and feeler gauges or a dial indicator swept across the sealing face. Parallelism between the two mating flanges should be within 0.05 mm measured at opposite bolt positions before bolt-up.

Cleaning and Contamination Removal

Remove all traces of the previous gasket material, corrosion products, scale, and process media from both flange faces. Use a wire brush, flange facing tool, or mechanical scraper — never an angle grinder, which creates surface irregularities. After mechanical cleaning, wipe both faces with a lint-free cloth dampened with an appropriate solvent (acetone for steel flanges, isopropyl alcohol for aluminum). Allow to dry completely before gasket placement. Any residual contamination between the gasket and flange face will create a leak path that no bolt load can overcome.

Gasket Material and Coating Selection for Service Conditions

The base metal of a corrugated metal gasket and its surface coating must both be compatible with the process fluid, temperature, and pressure. Using the wrong combination leads to corrosion-driven leak paths developing after initial successful installation — often several months into service.

For custom corrugated gaskets specified for non-standard service conditions, always obtain a material compatibility confirmation from the gasket manufacturer before procurement — particularly for halogenated fluids, strong acids, or hydrogen service above 300°C where material interactions are non-intuitive.

Step-by-Step Installation Procedure for Corrugated Metal Gaskets

Follow this sequence without deviation. Each step depends on the previous one being completed correctly.

1. Verify gasket dimensions before installation. Measure the gasket inner diameter, outer diameter, and thickness with calipers. Compare against the flange specification drawing. Even a 0.5 mm ID error on a gasket can cause the gasket to overhang the pipe bore, creating a flow restriction and turbulence-driven erosion of the gasket edge. For custom corrugated gaskets, dimensional verification is mandatory — do not assume the delivered gasket matches the drawing without measurement.
2. Inspect the gasket for surface defects. Under good lighting, examine both faces of the corrugated metal gasket for radial scratches across the corrugations, dents, or coating voids. A scratch that crosses two or more corrugation ridges provides a direct leak path from the bore to the atmosphere. Reject and replace any gasket with radial surface defects — the cost of the gasket is trivial compared to the cost of a failed joint.
3. Apply gasket lubricant or seating compound if specified. Some corrugated metal gasket applications call for a thin coating of anti-seize or gasket seating compound on the flange face (not on the gasket). This reduces the friction force required during seating and improves the uniformity of initial contact. Do not apply lubricant to graphite-coated gaskets without manufacturer confirmation — lubricant can compromise graphite coating adhesion.
4. Center the gasket precisely on the lower flange face. Use the bolt holes as guides — the gasket should be centered such that the bolt holes align concentrically with the gasket's bolt hole pattern and the inner diameter is concentric with the pipe bore. Use alignment pins in two bolt holes if available. An off-center gasket places uneven seating stress across the corrugation pattern and creates a higher-stress zone that overcompresses the corrugations on one side while leaving the opposite side unseated.
5. Bring the upper flange down carefully without displacing the gasket. Guide the upper flange onto the alignment studs or bolts without dropping it — impact on the gasket can dent the corrugations and create leak paths before torquing even begins. With the flange faces parallel and the gasket centered, hand-tighten all nuts finger-tight to hold the assembly in position.
6. Apply bolt lubricant to threads and bearing faces. Lubricate bolt threads and the underside of the nut bearing face with the specified lubricant — typically a moly-disulfide or nickel anti-seize compound. Bolt lubricant is not optional: without it, a significant fraction of applied torque is consumed by thread friction rather than generating bolt load, resulting in under-stressed joints that leak. The nut factor (K factor) used in torque calculations assumes the lubricant specified — changing lubricant without recalculating target torque produces incorrect bolt load.
7. Tighten bolts in a star pattern in multiple passes. Never tighten bolts in a circular sequence — this produces uneven gasket seating and bending stress on the flange. Use a star (cross) pattern, progressing through three torque passes: first pass at 30% of target torque, second pass at 70% of target torque, third pass at 100% of target torque. For flanges with 8 or more bolts, add a fourth verification pass in the rotational direction to confirm all bolts have reached target torque without relaxation.
8. Perform retorque after initial thermal cycling. After the first heat-up and cool-down cycle under operating conditions, retorque all bolts to the original target value. Corrugated metal gaskets undergo stress relaxation as the coating materials creep under sustained load, and this relaxation is accelerated by the first thermal cycle. A single retorque pass recovers the lost bolt load and establishes the long-term seal integrity.

Bolt Torque Calculation: Getting the Numbers Right

Correct bolt torque is the most numerically precise requirement in corrugated metal gasket installation. The target torque must generate sufficient bolt load to seat the gasket corrugations fully and maintain adequate seating stress under operating pressure — but must not exceed the flange's structural capacity or the gasket's crush limit.

The chart illustrates a critical practical point: lubricated bolts require 30–35% less torque than dry bolts to generate the same bolt load. Applying the dry-bolt torque value to lubricated bolts overloads the gasket and flanges. Always use the torque value calculated for the specific lubricant being used, and never substitute lubricant types without recalculating.

The general torque formula for corrugated metal gasket flange joints is:

T = K × F × d

Where T = target torque (Nm), K = nut factor (0.12–0.15 for moly-lubricated; 0.18–0.22 for dry), F = required bolt load (N) calculated from gasket seating stress requirements, and d = nominal bolt diameter (m). For standard flange classes, the required bolt load F is derived from ASME PCC-1 or EN 1591 calculations using the gasket's minimum seating stress (m factor) and operating pressure data.

Common Installation Errors and Their Consequences

Understanding the most frequent installation errors and their direct consequences allows inspection teams to identify and correct problems before the joint is pressurized.

Post-Installation Verification and Leak Testing

Completing the installation procedure correctly does not eliminate the need for post-installation verification. A systematic post-installation check catches errors before the joint is exposed to full operating conditions where a failure is costly and potentially hazardous.

• Visual bolt torque verification: After completing the final torque pass, mark each bolt and nut with a paint marker or torque stripe. Any bolt that rotates during service inspection — indicated by stripe misalignment — has lost tension and requires retorquing.
• Hydrostatic pressure test: For new installations in process piping, perform a hydrostatic test at 1.5x the maximum allowable working pressure (MAWP) per ASME B31.3 or applicable code. Hold for a minimum of 30 minutes and inspect all flange joints visually for any sign of moisture or weeping. Corrugated metal gaskets should show zero leakage at test pressure when correctly installed.
• Pneumatic testing for gas service: Where hydrostatic testing is not practical (instrument lines, gas systems), pneumatic testing at a lower test pressure (typically 1.1x MAWP) using compressed nitrogen is standard. Apply soapy water solution or a dedicated leak detection fluid to the gasket periphery and observe for bubble formation over a minimum 10-minute hold period.
• Retorque inspection at first planned maintenance: Document the retorque values applied after the first thermal cycle. Any bolt requiring more than 10% torque to return to target value indicates ongoing stress relaxation that should be monitored at the next maintenance interval.

Frequently Asked Questions About Corrugated Metal Gasket Installation

Q1: Can a corrugated metal gasket be reused after a flanged joint is opened for maintenance?

No. Corrugated metal gaskets must never be reused once they have been seated under bolt load. During the initial tightening, the corrugation ridges undergo controlled plastic deformation as they embed into the flange faces and the coating material redistributes into micro-surface irregularities. This deformation is permanent — when the joint is disassembled, the corrugations are in a compressed state that cannot be restored to their original profile. Reinstalling a used gasket produces insufficient seating contact, and the initial pressurization will almost certainly result in leakage. Always install a new gasket when opening any flanged joint, regardless of how briefly the joint was in service.

Q2: What is the difference between a corrugated metal gasket and a spiral wound gasket, and when should each be used?

A corrugated metal gasket is a stamped metal sheet with formed corrugations — thin, lightweight, and requiring precise flange surface condition for reliable sealing. A spiral wound gasket consists of a metal strip and soft filler material wound together in a spiral, providing a softer, more conforming seating behavior. Corrugated metal gaskets are preferred when flange surface condition can be controlled and maintained, weight and thickness are critical (heat exchanger applications), or very high temperatures preclude soft filler materials. Spiral wound gaskets are preferred when flange surfaces may have minor irregularities, when ease of installation without precise torque control is important, or for lower-pressure utility service where their more forgiving seating behavior reduces installation risk.

Q3: How do I specify a custom corrugated gasket for a non-standard flange?

Provide the gasket manufacturer with a dimensioned drawing or CAD file showing: inner diameter, outer diameter, bolt hole circle diameter, number and diameter of bolt holes, and sealing thickness. Additionally specify the service conditions — fluid type, operating temperature, operating pressure, and any cyclic temperature or pressure variations. Include the flange material for compatibility verification. For custom corrugated gaskets in critical service (high pressure, toxic fluid, hydrogen service), also specify the required pressure class and the applicable design code (ASME, EN, or other) so the manufacturer can confirm the design meets the required safety margin.

Q4: What surface coating should be selected for a corrugated metal gasket used in steam service at 350°C?

Graphite coating is the standard and most appropriate choice for steam service at 350°C. Graphite provides excellent lubricity during seating (reducing the torque required to achieve full corrugation contact), maintains its properties through repeated thermal cycles, and is chemically compatible with steam across the full relevant temperature range. PTFE coating is not recommended above 260°C as it begins to degrade and emit harmful decomposition products above this temperature. For stainless steel base metal corrugated gaskets in steam service, a graphite-coated 316L stainless gasket represents the standard specification at 350°C and provides excellent long-term reliability.

Q5: How should corrugated metal gaskets be stored before installation?

Store corrugated metal sealing gaskets in their original packaging in a dry, temperature-controlled environment away from direct sunlight, oils, and chemical vapors. Gaskets should be stored horizontally or vertically supported on their full face — never stored resting on their edge, which can permanently distort the thin metal and compromise the corrugation profile. Graphite-coated gaskets are particularly sensitive to contamination: even fingerprint oils on the gasket face can locally reduce the coating's adhesion to the flange surface. Handle gaskets with clean cotton gloves at all times after removing from packaging. There is no defined shelf life for properly stored uncoated metal gaskets, but graphite and PTFE coated gaskets should be used within 3–5 years of manufacture to ensure coating integrity.

Q6: What is the correct procedure if a corrugated metal gasket joint shows a minor leak after initial pressurization?

First, depressurize the system to a safe working level before taking any corrective action — never attempt to tighten bolts on a pressurized joint in corrugated metal gasket service, as the gasket may be at or near its crush limit and additional torque under pressure can cause sudden catastrophic failure. Once depressurized, perform a torque verification pass in the star pattern to confirm all bolts are at the specified target value. If any bolt is found below target, bring it to target torque and repressurize for leak verification. If all bolts were at target and leakage persists, the joint must be fully disassembled — inspect the flange surfaces for damage, replace the gasket with a new unit, and verify that the flange surface finish and flatness are within specification before reassembly.