Graver Tank v. Linde Air Products Co.
339 U.S. 605 (1950)

  • Linde invented a welding process and received a patent on it. Linde sued Graver for infringement for using a very similar process.
    • Graver argued that it wasn't the same process at all. Sure, 99% of the process was identical, but where the Linde patent specified a welding compound that consisted of calcium and magnesium, the Graver process used calcium and manganese.
      • For all you non-chemists out there, magnesium and manganese are both elements on the period table that have similar, but not identical properties.
  • The Trial Court found for Linde. Graver appealed.
    • The Trial Court found that even though the Linde patent did not claim manganese, it was close enough that it met the standard of non-textual infringement (aka the Doctrine of Equivalents).
  • The Appellate Court affirmed. Graver appealed.
  • The US Supreme Court affirmed.
    • The US Supreme Court found that the Graver process infringed on the Linde patent via the Doctrine of Equivalents.
    • The Court found that there are two tests that courts could use to determine non-textual infringement:
      • Under the triple identity test something is equivalent if:
        • It performs substantially the same function,
        • in substantially the same way,
        • to yield substantially the same result.
      • Under the insubstantial change test, something is equivalent if there is only an insubstantial chance between each of the features of the accused device or process and the patent claim.
    • The Court found that the substitution of magnesium for manganese was obvious to anyone working in the field, and was an insubstantial change.
  • In a dissent it was argued that the courts should not expand the scope of the patent beyond what the USPTO had determined.
    • In the dissent's opinion, if Linde failed to claimed manganese, it was their own fault for messing up their claims. There was nothing stopping them from claiming manganese.
  • Note that the Doctrine of Equivalents is a common law doctrine that doesn't have a statutory basis. It was developed because courts understood that an infringer wouldn't be dumb enough to copy an invention exactly, they would make a minor change here or there so they didn't literally infringe on the patent.