T 0333/05 03-08-2007

I. An opposition was filed by the appellant (opponent) against European patent No. 0 867 520. The opposition division held that the grounds for opposition pursuant to Article 100(a) EPC cited by the appellant did not prejudice the maintenance of the patent and therefore decided on 8 December 2004, posted on 20 January 2005, to reject the opposition.

II. The appellant lodged an appeal by notice received at the EPO on 14 March 2005 and paid the prescribed fee on the same day. A statement setting out the grounds of appeal was filed on 25 March 2005.

In support of its arguments the appellant referred to the documents

D1: EP-A-0 753 596 and

D2: Official Gazette for Kokai Patent Applications (a) Japanese Patent Application Kokai Publication Hei 8-252690 (in English language)

III. In the annex for the summons to oral proceedings requested on an auxiliary basis by the appellant, the board gave its provisional view on the case and referred to document

D7: GB-A-2 247 246 & Japanese Unexamined Patent Application Publication Hei 3-211230 cited in D2.

IV. The appellant requested that the decision under appeal be set aside and the European patent No. 0 867 520 be revoked.

The appellant's auxiliary request for oral proceedings was withdrawn with its letter dated and received at the European Patent Office on 1 June 2007. In consequence thereof, the oral proceedings were cancelled.

The respondent (patentee) requested that the appeal be dismissed.

V. Independent claims 1, 5 and 7 read as follows:

"1. A welded high-strength steel structure comprising a base metal and a weld metal, wherein the base metal is a steel whose microstructure is substantially formed of a mixed structure of martensite and lower bainite and which has a tensile strength of not less than 900 MPa; and the weld metal is a steel which has a tensile strength of not less than 900 MPa and comprises the following alloy elements based on % by weight:

C: 0.01% to 0.15%;

Si: 0.02% to 0.6%;

Mn: 0.6% to 3%;

Al: 0.004% to 0.08%;

Ti: 0.003% to 0.03%;

O(oxygen): not greater than 0.06%

B: 0.0002% to 0.005%;

Cu: 0% to 1.2%;

Ni: 0% to 3%;

Cr: 0% to 1.2%;

Mo: 0% to 1%;

V: 0% to 0.05%; and

Nb: 0% to 0.05%,

and which satisfies the equations 1) and 2) below:

1) 0.25 <= Pcm <= 0.32

Pcm = C+(Si/30)+(Mn/20)+(Ni/60)+(Cu/20)+

(Cr/20)+(Mo/15)+(V/10)+5B

2) 0.6 <= Al/O(oxygen) <= 1.4

wherein each atomic symbol in equations 1) and 2) represents its content (wt.%) within the steel."

"5. A method of manufacturing a welded steel pipe as one of the welded high-strength steel structures according to anyone of claims 1 to 4, the method comprising the steps of bending a steel plate into a tubular shape, and seam-welding butted ends of the steel plate through submerged arc welding."

"7. A method of manufacturing a pipeline comprising the steps of butting together the end portions of adjacent two steel pipes having a tensile strength of not less than 900 MPa, and welding the circumference of the butted portion through gas metal arc welding, wherein the weld metal of the welded circumference portion is a steel which has a tensile strength of not less than 900 MPa and comprises the following alloy elements based on % by weight:

C: 0.01% to 0.15%;

Si: 0.02% to 0.6%;

Mn: 0.6% to 3%;

Al: 0.004% to 0.08%;

Ti: 0.003% to 0.03%;

O(oxygen): not greater than 0.06%

B: 0.0002% to 0.005%;

Cu: 0% to 1.2%;

Ni: 0% to 3%;

Cr: 0% to 1.2%;

Mo: 0% to 1%;

V: 0% to 0.05%; and

Nb: 0% to 0.05%,

and satisfies the equations 1) and 2) below:

1) 0.25 <= Pcm <= 0.32

Pcm = C+(Si/30)+(Mn/20)+(Ni/60)+(Cu/20)+

(Cr/20)+(Mo/15)+(V/10)+5B

2) 0.6 <= Al/O(oxygen) <= 1.4

wherein each atomic symbol in equations 1) and 2) represents its content (wt.%) within the steel."

The dependent claims 2 to 4, 6 and 8 relate to preferred embodiments of the welded steel structure according to claim 1 or the method of manufacturing the steel structure set out in claims 5 or 7, respectively.

VI. The arguments of the appellant are summarized as follows:

Document D1 as the closest prior art related to an ultra-high strength steel excellent in toughness and weldability. The steel exhibits a tensile strength (TS) of at least 950 MPa as well as a martensite - lower bainite structure. In coincidence with the patent, this steel was typically formed as the "base metal" into welded steel pipes for transporting crude oil and gas. However, document D1 failed to disclose the composition of the "weld metal" in the welded zone. Starting from D1, the problem underlying the patent at issue therefore resided in providing a "weld metal" which - after the welding with the base metal - achieved a high toughness at low temperatures and a high TS in the welded zone. In his search for an appropriate "weld metal" satisfying these properties in line pipes conveying oil or natural gas, the skilled person would be prompted to resort to the weld metal disclosed in document D2 given that this material was designed for the same purpose and provided the desired strength and toughness. As it was evident from the comparative table given on page 4 of the grounds of appeal, an overlap existed between the elements making up the claimed "weld metal" and that given in D2, including the range of 0.15 <= Pcm <= 0.28 and also the ratio of 0 <= Al/0 <= 0.75 to 6. The opposition division's reliance on document D2 was misplaced in that it focused its attention mainly on the examples rather than on the teaching of document D2 as a whole, contrary to the precepts given in the decisions T 12/81, T 562/90,

T 373/95, T 12/90, T 658/91 and T 247/91. Considering D2 as a whole, the relevant passages [0012], [0020] and [0022] would have led a skilled person to note that the proportions of Al, O, Ti and N should be controlled in the welded zone, in particular in that the amount of Al did not exceed 0.06% and oxygen was kept within a range from 0.01 to 0.08%. From these data, the ratio of Al/O could be calculated to be 0.06/0.08 = 0.75 which fell in the middle of the range of 0.6 to 1.4 claimed for the Al/O ratio in the patent. Therefore, the teaching of D1 and D2 in combination with the results of a few routine welding tests around the known values would have evaluated the optimum welding results and would have led the skilled person in an obvious way to the claimed welded high-strength steel structure. The subject matter of product claim 1 and method claims 5 and 7 therefore lacked an inventive step.

VII. The arguments of the respondent are summarized as follows:

Document D1 related exclusively to the "base metal" having a mixed martensite/bainite structure, a TS of at least 950 MPa and an excellent low-temperature toughness. The known steel composition focused on the combination of high amounts of Mn with Ni-Mo-Nb which was, however, less important in the claimed alloy. More importantly, it was noted that the formula expressing the P value in D1 was entirely different from the Pcm value claimed in the patent in suit.

The "weld metal" disclosed in document D2, on the other hand, was designed in the first place for improving the corrosion resistance of oil and gas pipelines. The alloy composition was particularly resistant to corrosion by CO2 and also possessed sufficient strength and toughness in the circular weld metal sections. Although not specifically mentioned, it seemed evident from Japanese unexamined patent application Hei 3-211230 referred to in D2, paragraph [0003] that the "base metal" the pipes were made of exhibited a TS of less than 667 MPa which was far below the TS >= 900 MPa claimed in the patent. Already for this reason, a skilled person would not combine D1 with D2 in an obvious manner, as alleged by the opponent.

In addition, D2 neither explicitly nor implicitly taught the ratio Al/O and failed to mention the requirement of adhering to the Al/O ratio in combination with the Pcm value. As shown in the patent in suit, a TS of not less than 900 MPa, an upper shelf energy >= 80J and a transition temperature of fracture appearance vTs <= -50ºC was not obtained unless both conditions are met simultaneously. Specifically, none of the examples given in D2 satisfied both conditions for Pcm and Al/0, and there was no teaching whatsoever in D2 linking these values with the specific microstructure and the TS associated therewith.

As to its general disclosure referred to by the opponent, document D2 required to regulate the balance between hardenability and Ti, Al, N and O so that the inequality

(2): -50 <= alpha' = {1,5(0-0.89Al) + 3.4N - Ti}x10**(3) <= 50

was satisfied to prevent a deterioration in toughness and cleanliness. Hence, the general disclosure of document D2 pointed to a different direction and taught away from the present invention. The claimed subject matter therefore involved an inventive step.