Duplex Stainless Steel Patents: Top Companies & Filing Trends 2026
- Concentrated at the top: the top 5 assignees hold 67.5% of all 268 records in scope, and the top 10 hold 82.1% — a long tail of single-filer entrants fills the rest.
- Filing has cooled since 2019: activity peaked at 17 records that year and has since flattened, with 2022 sitting at just 5 — publication lag means the last year or two will understate true activity.
- Heat treatment is the second-densest claim zone: C21D appears in 36.9% of records behind the near-universal C22C alloy composition class, while welding, powder metallurgy and pipe fittings each sit under 8%.
What this landscape covers
This landscape tracks 268 published records filed between 2015 and mid-2026 that combine duplex or super duplex stainless steel compositions with the specific technical language of pitting resistance equivalent number, sigma phase precipitation, welding procedure and ferrite balance, chloride stress corrosion, or cost comparisons against super austenitic grades. The scope is narrow by design: it is not general stainless steel metallurgy, but the subset built for seawater and aggressive chemical service, where pitting resistance and phase stability after welding decide whether a grade is specified at all.
The IPC filter layers alloy composition (C22C38), membrane and separation-relevant filtration (B01D61) and heat treatment of metals (C21D6), which is why the technology mix below is dominated by alloy and heat-treatment classes rather than by equipment or process claims.
Filing trend and technology composition
The filing curve and the IPC breakdown below are drawn from the same 268-record set and use the same denominator throughout, so the two views can be read side by side.
A single peak year, then a plateau
Filings rose to a peak of 17 records in 2019, then settled into a flatter pattern; the midpoint year 2022 recorded only 5. Read the final one to two years with caution — publication typically lags filing by around 18 months, so recent totals are still filling in.
Alloy composition dominates, heat treatment is the clear second
C22C (alloys) appears in 99.3% of the 268 records, which is expected given the search scope. C21D (heat treatment of metals) follows at 36.9%, reflecting how much of the claim activity concerns post-weld heat treatment and ferrite balance rather than composition alone. Welding (B23K), layered products (B32B), powder metallurgy (B22F), metal rolling (B21B), catalysis-adjacent processes (B01J) and pipe fittings (F16L) each account for under 8% of records — these are the narrower, less-crowded branches.
Shares are the percentage of the 268 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Duplex Stainless Steels for Desalination and Chemical Service with Eureka
This page is one run against one query. Ask Eureka your own question about duplex stainless steels for desalination and chemical service and every answer comes back with the patent numbers behind it.
Try EurekaMost-cited records and a recent representative filing
Preparation method for welded and extended super duplex stainless steel seamless pipe coil for deep-sea umbilical cable
The filing discloses a preparation method for a welded and extended super duplex stainless steel seamless pipe coil intended for deep-sea umbilical cable service. It specifies an AOD furnace with Al deoxidation, calcium treatment and external refining to hold oxygen content at 25 ppm or below, paired with integrated cold-deformation control across hot piercing, high-temperature intermediate solution heat treatment and deformation distribution.Filed by Jiangsu Wujin Stainless Steel Pipe Group, published 2025-10-16 — one of the more recent records in scope and a useful marker of where current process-control claims are heading.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US7347903B2 | Duplex stainless steel for urea manufacturing plants | 64 |
| 2 | CN102605284A | 一种双相不锈钢及其制造方法 | 48 |
| 3 | US6551420B1 | Duplex stainless steel | 39 |
| 4 | US6623569B2 | Duplex stainless steels | 38 |
| 5 | WO2013064746A1 | Duplex stainless steel | 32 |
| 6 | WO2003038136A1 | Duplex stainless steels | 30 |
| 7 | WO2006049572A1 | Duplex stainless steel | 29 |
| 8 | US20040050463A1 | High manganese duplex stainless steel having superior hot workabilities and method for manufacturing thereof | 29 |
| 9 | WO2013034804A1 | Duplex stainless steel | 26 |
| 10 | WO2010070202A1 | Ferritic-austenitic stainless steel | 26 |
Citation counts reward older filings simply because they have had more time to accumulate citations within the searched corpus — treat this table as a signal of historical influence, not of which claims matter most today.
Patent titles are shown in the language they were filed in, not translated, so that each record stays verifiable against the original filing — a translated title will not match in Eureka or in any national register. Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns stand out once the assignee ranking, the technology mix and the citation table are read together.
Composition claims are largely spoken for
With the top 5 assignees holding 67.5% of all 268 records and the top 10 holding 82.1%, new composition claims around core PREN and phase-balance parameters face dense prior art from a small group of established steelmakers. Freedom to operate in this zone likely depends on narrow processing or application limitations rather than broad alloy ranges.
Filing activity has flattened, not accelerated
The trend peaked at 17 records in 2019 and has since declined toward a midpoint of 5 in 2022. Several of the largest historical filers show no activity in the latest tracked year, which is consistent with a maturing composition space rather than a growing one — though the newest one to two years are understated by publication lag.
Heat treatment is the real second front
After the near-universal alloy class C22C, heat treatment of metals (C21D) is the only other class appearing in more than a third of records. Welding, powder metallurgy, rolling and pipe-fitting classes each sit under 8%, suggesting these process-adjacent branches carry lighter claim density than the composition and heat-treatment core.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to duplex stainless steels for desalination and chemical service, with the prior art for and against each one.
Who is filing, and where the activity has slowed
The ranked leaders sit alongside a long tail of single- or few-filing entrants; recent-year momentum data shows even the largest historical filers recording no output in the latest tracked year.
One filer well ahead of the field
The leading assignee holds 74 records, well above the fifth-place total of 12 and tenth-place total of 7 — a steep drop-off that marks this as a leader-plus-long-tail structure rather than an evenly distributed field.
Co-assignee activity is limited and specific
Only 10 co-assignee pairs appear in the dataset, with the strongest pairing recorded 6 times between two related steelmaking entities. This points to mostly independent filing strategies rather than joint-venture-driven patenting.
Historical leaders have gone quiet
Every one of the six largest historical assignees tracked for recent-year momentum shows zero filings in the latest year, including a -100% year-on-year figure for one. That is consistent with the broader flattening trend but is also affected by publication lag on the newest filings.
| Assignee | Recent year | YoY |
|---|---|---|
| Outokumpu Oyj | 0 | — |
| ATI Properties Inc. | 0 | — |
| Sandvik Intellectual Property AB | 0 | — |
| Nippon Steel Corporation | 0 | -100% |
| JFE Steel Corporation | 0 | — |
| Sumitomo Metal Industries | 0 | — |
| Carpenter Technology Corporation | 0 | -100% |
| Toyo Engineering Corporation | 0 | — |
Where to take this analysis
The dataset points to specific next steps depending on whether the goal is freedom-to-operate, competitive tracking or R&D scoping.
Check freedom to operate against the leader's portfolio
With one assignee holding 74 records and the top 5 controlling 67.5% of the field, any new composition or heat-treatment filing should be checked against these portfolios before drafting claims.
Explore assignee portfolios in EurekaScope the under-claimed process branches
Welding, powder metallurgy, rolling and pipe-fitting classes each sit under 8% of records, well below the alloy and heat-treatment core — a narrower but potentially more open area for new claims.
Run a white-space search in EurekaTrack whether flat filing turns into a fresh wave
Activity has cooled since the 2019 peak, but the most recent one to two years are understated by publication lag. Monitoring incoming filings will show whether this is a genuine plateau or a temporary lull.
Set up filing alerts in EurekaCommon questions about duplex stainless steel patents
The dataset ranks 63 companies, and one assignee leads clearly with 74 records against a fifth-place total of 12 and a tenth-place total of 7. The top 5 assignees combined hold 67.5% of all 268 records in scope, and the top 10 hold 82.1%, so the field is concentrated at the top with a long tail of smaller filers below it. Anyone entering this space should expect to negotiate around a small number of established steelmakers rather than a fragmented set of competitors.
No, filing activity peaked at 17 records in 2019 and has since flattened, with the 2022 midpoint recording only 5 records. Several of the largest historical assignees show zero filings in the most recent tracked year, one with a -100% year-on-year change. That said, publication typically lags filing by around 18 months, so the last one to two years in any trend understate real activity and should not be read as a hard stop.
Alloy composition, covered by IPC class C22C, appears in 99.3% of the 268 records, which follows directly from the search scope. Heat treatment of metals (C21D) is the clear second area at 36.9% of records, reflecting the importance of post-weld heat treatment and ferrite balance control. Welding, layered products, powder metallurgy, metal rolling, catalysis-related processes and pipe fittings each account for under 8% of records, marking them as comparatively open branches.
The lower-density IPC branches — welding and joining (B23K at 7.1%), powder metallurgy (B22F at 3.7%), metal rolling (B21B at 3.4%) and pipe fittings (F16L at 3.0%) — carry far less claim density than the alloy and heat-treatment core. Process-specific niches such as post-weld sigma phase suppression, duplex-to-superaustenitic joint welding, and cold-deformation control for seamless pipe production show up in newer filings but have not yet accumulated the density seen in core composition claims. These are reasonable starting points for scoping a first claim that avoids the most crowded prior art.
Citation counts inside a searched corpus favour older filings simply because they have had more years to be cited, so a high count signals historical influence rather than current commercial importance. The most-cited record in this dataset, US7347903B2, dates back well before the most recent filing activity. Recent filings, such as the 2025 representative record on deep-sea umbilical cable pipe coils, may carry real technical significance without yet showing citation volume.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.