Does a material swap avoid patent infringement?

Not always. If the substitute performs the same function in the same way to get the same result, it can still infringe under the doctrine of equivalents.

Is the doctrine of equivalents limited to machines?

No. Graver Tank confirms it also covers chemical compositions, based on expert evidence and real-world performance.

What test do courts use for equivalence?

Courts often use the function–way–result test to see if the differences are only colorable or truly substantial.

Why protect against trivial substitutions?

To prevent easy workarounds that would drain patent value and undermine incentives for innovation.

What kind of proof shows chemical equivalence?

Expert testimony, lab tests, and operational results showing that the substitute behaves like the claimed ingredient.

Graver Tank & Manufacturing Co. v. Linde Air Products Co

Graver Tank & Manufacturing Co. v. Linde Air Products Co.

Patent (Chemistry) Doctrine of Equivalents Infringement U.S. Supreme Court 339 U.S. 605 (1950) ~6 min read

PUBLISH_DATE: 2025-11-01

AUTHOR_NAME: Gulzar Hashmi

LOCATION: India

/graver-tank-manufacturing-co-v-linde-air-products-co/

Quick Summary

The Supreme Court said that swapping one ingredient for another can still infringe a patent if the swap does the same work in the same way to reach the same result. This is the doctrine of equivalents.

CASE_TITLE: Graver Tank & Manufacturing Co. v. Linde Air Products Co., 339 U.S. 605 (1950)
PRIMARY_KEYWORDS: doctrine of equivalents, chemical substitutions, patent infringement
SECONDARY_KEYWORDS: welding flux, alkaline earth silicates, manganese vs. magnesium, Supreme Court

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Issues

Does using a similar but unclaimed material avoid infringement?
Does the doctrine of equivalents apply to chemical compositions as it does to mechanical devices?

Rules

Doctrine of Equivalents: Even if the accused product does not literally fall within the claim words, it infringes when it performs substantially the same function, in substantially the same way, to achieve substantially the same result.
The doctrine applies to chemical compositions and mechanical devices alike.

Facts (Timeline)

Timeline graphic for Graver Tank v. Linde Air Products

Linde held an improvement patent for an electric welding flux: alkaline earth metal silicate + calcium fluoride.

Graver Tank produced a flux swapping manganese silicate for the patent’s magnesium/calcium silicates.

Linde sued for infringement, arguing the swap was an equivalent, not a real change.

Lower courts, relying on expert evidence, found manganese silicate worked like the claimed ingredient.

Arguments

Appellant (Linde)

Manganese silicate performs the same function in the flux.
The process and result are substantially the same; the swap is cosmetic.
Allowing such swaps would gut patent protection and policy incentives.

Respondent (Graver Tank)

Our flux does not literally match the claim wording.
We used manganese, not the patent’s claimed alkaline earth metals.
Literal differences should avoid infringement.

Judgment

Gavel representing the Supreme Court’s decision

The U.S. Supreme Court upheld infringement. It confirmed that the doctrine of equivalents applies to chemical compositions. Expert proof showed manganese silicate was an equivalent to the claimed ingredient.

Ratio

If a change is only a colorable substitution, and the accused product works in the same way for the same end, the patent is still infringed—even without literal overlap of claim words.

Why It Matters

Stops infringers from dodging patents by trivial swaps in formula or parts.
Protects the economic value of inventions and encourages R&D.
Guides courts to use function–way–result and expert evidence in chemistry cases.

Key Takeaways

Literal difference ≠ safe harbor if equivalent in function, way, and result.
The doctrine covers chemical compositions, not just machines.
Expert testimony can prove equivalence in practice.

Mnemonic + 3-Step Hook

Mnemonic: “Same Work, Same Way, Same Win.”

Check Function: What job does the ingredient do?
Check Way: How does it do that job?
Check Result: Do we end up at the same place?

IRAC Outline

Issue

Does a material swap (manganese for magnesium) avoid infringement, or is it an equivalent?

Rule

Equivalence exists when the accused product performs substantially the same function, in the same way, with the same result.

Application

Experts showed manganese silicate behaved like the claimed silicates in the welding flux; the change was only nominal.

Conclusion

Infringement found. The substitution was an equivalent, so the patent remained protected.

Glossary

Doctrine of Equivalents: A rule that captures non-literal but equivalent infringements of a patent claim.
Function–Way–Result: A test to evaluate whether two elements are substantially the same.
Colorable Change: A minor tweak that does not change how the invention works in substance.