“WELDED STEEL PIPE FOR LINE PIPE WITH EXCELLENT LOW-TEMPERATURE TOUGHNESS, AND METHOD OF MANUFACTURING THE SAME”

Overview:

In an appeal against an Examiner’s rejection for lack of an inventive step, the court decided in favor of the applicant, holding that the claimed invention overcomes the cited reference.

Legal Issue:

Whether or not it would have been easy to reconcile differences from the cited reference, to achieve the claimed invention.

Summary of Conclusions:

The court reasoned as follows, with respect to a “Difference 1″. The problem to be solved is to improve low-temperature toughness in a welded heat-affected zone on an outer surface of a steel plate.  To solve this problem, the claimed invention specifies upper and lower limits of a ratio L2/L1, in which L2 represents a thickness from an outer surface of the plate to a fusion line formed between the outer surface and an inner surface of the plate, and L1 represents a thickness from the inner surface to the fusion line. The cited reference seeks to prevent low-temperature cracking which occurs in a welding metal, at a weld seam zone that forms an inner surface.  To solve this problem, the cited reference specifies upper and lower limits of a ratio W2/W1, in which W2 represents a thickness of a layer formed between the weld seam and a next weld seam, and W1 represents a thickness of a layer formed between the weld seam and a previous weld seam.  Accordingly, the cited reference differs in the problem to be solved, as well as in the solution.  Consequently, the court found no motivation to replace W2/W1 of the cited reference with L2/L1 of the claimed invention to reconcile Difference 1.
With respect to a “Difference 2″, the court reasoned as follows. At the time of filing the application in question, it was known that given a steel plate having a tensile strength of 600 to 800 MPa corresponding to a circumferential direction of a steel pipe, an abutting portion of the steel pipe may be subjected to submerged arc welding from inner and outer surfaces one pass at a time, in order to manufacture a welded steel pipe for line piping with excellent low-temperature toughness (Cited Example 2).  The court held that even taking this knowledge into consideration, there is no motivation to resolve Difference 2, by applying the cited reference in which W2/W1 is optimized for a steel plate having a tensile strength of 850 MPa to 1,200 MPa, to the claimed steel plate having a tensile strength of 570 to 825 MPa.
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Consequently, the court held that the claimed invention could not have been easily achieved based on the cited reference and the knowledge in the art disclosed in Cited Example 2.

Comments:

The Defendant (Japanese Patent Office) asserted that a steel pipe which satisfies the range for W2/W1 in the cited reference also satisfies the range for L2/L1 as claimed, and that therefore, Difference 1 is not a substantial difference.  The Defendant further asserted that even if a tensile strength of a steel plate is less than 850 MPa, it is reasonable to consider that low-temperature cracking in the welding metal is not entirely prevented in the cited reference, and that consequently, there is motivation to apply a steel pipe with a tensile strength of less than 850 MPa, to the cited reference.  Nevertheless, the court dismissed the Defendant’s assertions holding that the range for W2/W1 in the welding metal of the cited reference cannot be maintained if the tensile strength of the steel plate is made to be less than 850 MPa.