How to Choose the Right ISO Tank Container Seal? A Practical Guide Beyond Material Selection

Why PTFE, EPDM and FEP Encapsulated Seals Perform Differently Under Real ISO Tank Container Conditions?

This guide is written for procurement and maintenance teams specifying an ISO Tank Container manlid seal — buyers who need a decision they can defend, not a materials lecture.

A tank container may carry acids, solvents, food ingredients or other liquid media. The seals all look broadly similar, yet the wrong sealing design shows up as leakage in transit, contamination risk, repeated replacement and unplanned downtime. Choosing a manlid seal is therefore not only a question of "PTFE or rubber" — the right design depends on the ISO Tank Container, the cleaning process, the pressure and the seal structure.

One tank cannot simply use one seal type. 899,044 tank containers were in service worldwide on 1 January 2026, up 1.93% year on year (ITCO, 2026 Global Tank Container Fleet Survey), and gasket and seal leaks appear in 48.1% of loss-of-primary-containment cases in AIChE's CCPS dataset (AIChE CCPS LOPC Survey). The part that looks cheapest is one of the most frequent sources of incidents.

Before ordering a tank container seal, check these 5 factors

Answer these five and you can shortlist a seal design in minutes.

1. Choose by application, not by material

Buyers rarely start from "I need PTFE." They start from "what is my content?" That is also the correct order.

If your tank carries aggressive chemicals → choose a PTFE contact layer or an FEP encapsulated design. The PTFE working surface is inert across pH 0–14 (except HF and certain fluorine-containing compounds) and compatible with chemicals, petroleum products and foodstuffs (SUNPASS PTFE Braided Manlid Seal).

If the tank is opened and cleaned frequently → choose an elastic core under a PTFE layer. Every closure compresses the seal, and recovery is what maintains sealing force. Pure PTFE is inelastic and cold-flows — under a sustained 7 MPa load at 23 °C it loses 12% of its thickness in 100 hours and more than 22% in 1,000 hours .

If the application runs hot → match the actual operating temperature and cleaning cycle, not the ceiling rating. Steam cleaning is often the hottest event a manlid seal sees: wine-industry practice applies steam through the manway at ≥82 °C for at least 20 minutes (OIV, Good Practices Guide).

If food, pharma or edible oils are involved → choose 100% virgin PTFE or a non-tainting elastomer. Virgin PTFE is non-absorbent, non-tainting and hygienic for foodstuffs and edible oils (SUNPASS Super Tank Lid Seal).

If the duty is standard and cost matters → an EPDM elastomer seal is often sufficient. EPDM offers good acid and alkali resistance and high elasticity across a wide temperature range, and resists oxygen, ozone and UV ageing (SUNPASS EPDM Manlid Seal).

2. Why material alone is not enough

A temperature rating is a limit, not a capability. A standard T-code tank is certificated for a design range of about −40 °C to +150 °C (Bureau Veritas initial inspection certificate, example unit), but every seal has its own narrower window: the PTFE braided manlid seal is rated −50 °C to +120 °C, the Super Tank Lid Seal −25 °C to +110 °C and the FEP encapsulated seal −60 °C to +200 °C (SUNPASS). The highest-rated part is not automatically the right one for a given tank.

Recovery keeps a joint tight. Every open/close cycle compresses the seal, so long-term sealing depends on how well it springs back. Pure PTFE's cold-flow behaviour (above) is exactly why composite, elastic-core designs exist — the same PTFE surface can perform differently depending on the core beneath it (O-Ring Supply Co.).

Compatibility is specific, not generic. "Chemical resistant" is not one property: the PTFE surface is inert to pH 0–14 except HF and certain fluorine compounds (SUNPASS), while elastomer cores cover narrower windows — which is why the media, not the material label, decides.

3. Common mistakes when selecting ISO tank seals

Mistake 1 — Choosing the highest temperature seal. A higher rating is a limit, not a promise of longer life. The Super Tank Lid Seal's +110 °C window and the FEP seal's +200 °C window describe different duties, not a ranking — pick the one that matches the tank, not the biggest number (SUNPASS).

Mistake 2 — Choosing pure PTFE for every application. PTFE has excellent chemical resistance but limited elasticity and cold-flows under load, so it suits low-cycle service better than a repeatedly opened manlid (Betts Industries, PTFE gaskets and seals).

Mistake 3 — Replacing only the material, not the structure. The same PTFE can perform differently depending on reinforcement, lubricant and core design — which is why composite structures (PTFE + elastic core) exist (O-Ring Supply Co.).

4. SUNPASS seal design options

Choose the design by the duty, then confirm the part number.

Confirmed specifications for the range (all from sunpass.cn):

• PTFE Braided Manlid Seal(e.g. AP00001): inert reinforced polypropylene yarn impregnated with PTFE and inert resin; pH 0–14 except HF and certain fluorine compounds; 2 bar max; −50 °C to +120 °C; available with or without a resilient core (source).
• Super Tank Lid Seal(EP00001): EPDM core wrapped on three sides in 100% virgin PTFE; inert pH 0–14 across all IMO classes; 4 bar max; −25 °C to +110 °C; DN500 (14×12 mm × 486 mm ID) and DN300 (14×10 mm × 294 mm ID) (source).
• FEP Encapsulated Seal(FO00009–FO00011): seamless Teflon® FEP over a silicone or Viton® core; −60 °C to +200 °C; DN500 (486 mm ID) and DN300 (294 mm ID) (source).
• Elastomer seals: EPDM Manlid Seal (EPDM001), Viton® Manlid Gasket (V00002, −60 °C to +250 °C) and Sweet White Rubber (SWR).

5. Before you contact a seal supplier, prepare

1. Tank standard / size (DN500 / DN300)
2. ISO Tank Containertype
3. Operating temperature
4. Cleaning method
5. Pressure requirement
6. Any previous leakage issue

With these six answers, a supplier can recommend a structure in one exchange rather than several. SUNPASS supports that process directly: a tank container sealing manufacturer since 2000 and a brand founded in 1979, it supplies the world's top six tank container manufacturers, including CIMC and SINGMAS, holds ISO 9001 certification with 26 patents and trademarks, is a member of ITCO, and operates an 18,000 m² workshop with over 200 workers (SUNPASS official site).

FAQ

Q1: How do I choose between PTFE and EPDM tank seals? By content compatibility, temperature and required sealing recovery — PTFE for aggressive chemicals (inert pH 0–14 except HF and fluorine compounds), EPDM for matched standard duty (SUNPASS).

Q2: Can one tank seal fit all chemical ISO Tank Containeres? No. Compatibility windows differ by material — the PTFE surface is inert pH 0–14 except HF and certain fluorine compounds, while elastomer cores cover narrower ranges (SUNPASS).

Q3: Will a higher temperature seal last longer? Not necessarily. A rating is a limit, not a life figure — the Super Tank Lid Seal's +110 °C and the FEP seal's +200 °C describe different duties, not a ranking.

Q4: What information should I provide before ordering? ISO Tank Container, temperature, pressure, tank size, cleaning method and any