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Industry-certified high-strength fasteners designed for demanding pipeline and industrial environments
Serrated Flange Bolt for Pipeline — DIN933 10.9 Full Thread Black Fastener Hex Head Bolt
Pipeline Flange Bolt — DIN912 Black Oxide Hexagon Socket Head Cap Screws ISO4762
Pipeline Works Structural Bolt — Heavy Hexagon-Head Bolts ASTM A325
Pipeline Flange Hex Head Bolt — DIN961 Fine/Coarse Thread UNC & UNF
A serrated flange bolt is a specialized high-strength fastener that integrates a wide bearing flange with radially oriented serrations (teeth) on the underside of the flange head. This unique geometry eliminates the need for a separate flat washer while simultaneously providing exceptional resistance to loosening under vibration, thermal cycling, and dynamic loading — conditions that are inherently present throughout oil, gas, water, and chemical pipeline systems.
Manufactured in accordance with DIN 6921, serrated flange bolts are available in property classes 8.8 and 10.9, covering metric diameters from M6 to M24 and beyond. The serrations bite into the mating surface upon tightening, creating a mechanical lock that dramatically outperforms standard hex bolts in anti-loosening performance. Surface treatments including zinc plating, hot-dip galvanizing, and black oxide are applied to resist corrosion in aggressive pipeline environments — offshore platforms, buried pipelines, chemical processing plants, and high-temperature steam lines.
🔩 Key Advantage: The integrated serrated flange distributes clamping load over a larger surface area, reducing stress concentration and preventing galling on softer flange materials — a critical requirement for pipeline flange connections operating under fluctuating internal pressures.
In pipeline engineering, joint integrity is paramount. A single fastener failure in a high-pressure gas or fluid transmission line can result in catastrophic leakage, environmental damage, and significant financial loss. The serrated flange bolt addresses this challenge by combining structural strength, vibration resistance, and ease of installation into one engineered component. Its widespread adoption across pipeline infrastructure reflects both the technical advantages and the economic efficiencies it delivers to project owners and maintenance teams alike.
The demand for high-performance fasteners in pipeline works continues to grow as global energy infrastructure expands
From subsea infrastructure to municipal water networks, serrated flange bolts are the fastener of choice across the full pipeline value chain
High-pressure crude oil and natural gas pipelines demand fasteners that maintain joint integrity across thousands of pressurization cycles. Serrated flange bolts in grade 10.9 with hot-dip galvanized coating are widely specified for above-ground and buried flanged joints, compressor stations, and valve assemblies in onshore and offshore environments.
Process pipelines in chemical facilities handle corrosive fluids, high temperatures, and aggressive media. The serrated flange bolt's anti-loosening serration is critical here — thermal expansion and contraction cycles that occur during process startups and shutdowns can progressively loosen conventional bolts, but the serration maintains preload stability throughout operational life.
Urban water distribution and wastewater treatment infrastructure relies on flanged pipe connections maintained over decades. Serrated flange bolts with zinc plating or hot-dip galvanizing provide long-term corrosion resistance in buried or exposed environments, reducing lifecycle maintenance costs for municipal operators.
Steam pipelines in thermal power plants operate at extreme temperatures and pressures. The high-strength grade 10.9 serrated flange bolt maintains reliable clamping force under thermal cycling, preventing steam leakage at flanged connections — a safety-critical requirement in both fossil fuel and nuclear power generation facilities.
Offshore pipeline systems face the harshest combination of mechanical loads, saltwater corrosion, and temperature extremes. Serrated flange bolts with specialized coatings — including hot-dip galvanizing and PTFE-based treatments — are specified for riser systems, subsea manifolds, and platform piping to ensure integrity in deepwater applications.
Liquefied natural gas infrastructure presents unique challenges — cryogenic temperatures cause conventional fasteners to lose preload due to differential thermal contraction. Serrated flange bolts engineered for low-temperature service maintain joint tightness down to -196°C, making them indispensable in LNG terminals, storage facilities, and distribution networks worldwide.
The radial serrations on the flange underside mechanically embed into the bearing surface upon tightening, creating a positive lock that resists loosening from vibration, pressure pulsation, and thermal cycling — the primary failure modes in pipeline fastener joints.
The wide flange distributes bearing stress over a larger area, eliminating the need for a separate flat washer. This reduces parts count, simplifies installation, and ensures consistent load distribution even on softer flange face materials common in pipeline connections.
Available in property class 8.8 and 10.9 per ISO 898-1, these bolts provide tensile strengths of 800 MPa and 1000 MPa respectively, meeting the demanding structural requirements of high-pressure pipeline flange assemblies across international standards including DIN, ANSI, and EN specifications.
Surface treatment options — zinc electroplating, hot-dip galvanizing (HDG), and black oxide — are selected based on pipeline operating environment. HDG provides 85+ microns of zinc coating for buried or marine pipeline service, while zinc plating suits indoor and moderate-exposure applications.
Full compliance with DIN 6921 ensures dimensional interchangeability with global pipeline components. Zhongli Bolts' serrated flange bolts are tested to ISO 898-1 for mechanical properties, and the manufacturing facility holds ISO 9001, EN 15048, EN 14399, AD2000, and CE certifications.
The single-component design reduces assembly time compared to bolt-plus-washer configurations. In pipeline maintenance scenarios where thousands of flange bolts must be replaced during scheduled shutdowns, the time savings from simplified installation directly translate to reduced downtime and lower maintenance costs.
Emerging technologies and evolving industry demands are reshaping how serrated flange bolts are designed, manufactured, and specified
The global push toward hydrogen as a clean energy carrier is driving massive investment in new hydrogen pipeline infrastructure. Hydrogen embrittlement presents unique challenges for fastener materials, pushing demand for specially alloyed, hydrogen-compatible serrated flange bolts with enhanced ductility and resistance to stress corrosion cracking.
Industry 4.0 is entering the fastener sector. Emerging smart serrated flange bolts embed ultrasonic sensors or strain gauges to enable real-time bolt load monitoring in critical pipeline joints. This technology is gaining traction in offshore and nuclear pipeline applications where joint integrity monitoring is a regulatory requirement.
Environmental regulations are driving the transition from hexavalent chromium-based coatings to trivalent zinc and zinc-flake systems for pipeline fasteners. Advanced geomet and dacromet coatings offer superior corrosion resistance with lower environmental impact, meeting both pipeline performance requirements and sustainability targets for global project specifications.
Major pipeline operators now require full material traceability — from raw steel heat to finished fastener — for safety-critical joints. QR code and RFID-tagged serrated flange bolts with digital material certificates are increasingly specified in EPC contracts for LNG, nuclear, and offshore pipeline projects, driving manufacturers to invest in digital quality management systems.
The trend toward modular, prefabricated pipeline spools is increasing demand for pre-assembled flange bolt sets with precise torque specifications. Serrated flange bolts are well-suited to this construction methodology, as their integrated anti-loosening function simplifies quality control during module assembly and subsequent field installation.
Rapid urbanization and energy infrastructure development across Southeast Asia, India, and the Middle East are generating unprecedented demand for pipeline fasteners. Chinese manufacturers like Ningbo Zhongli Bolts, with competitive pricing, ISO-certified quality, and export experience to 50+ countries, are well-positioned to supply this growing market with DIN 6921 serrated flange bolts.
Ningbo Zhongli Bolts Manufacturing Co., Ltd. founded in 2003, is a professional manufacturer of high-strength fasteners in different specifications for various models, which is covering an area of about 10,000 square meters, registered capital of 1,500,000 RMB, with the total annual productivity of 8,000 tons per year. The company has set up several sales branches in different provinces in China.
Meanwhile, the company's products are exported to Europe, USA, Middle East, Africa, Southeast Asia and other regions. The company has strong technical ability, complete testing equipments and a variety of fully automatic multi-station cold and hot heading machines, so as to provide you with reliable and high quality products.
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Our main products ZYL brand fasteners include structural hex bolts ASTM A325 type 1, A490, hex head bolts DIN931, DIN933, EN14399, DIN6914, ISO4014, ISO4017 Gr8.8 Gr10.9 Gr12.9, ANSI B18.2.1 UNC and UNF Gr5, Gr8, fine pitch hex bolts DIN960, DIN961 Gr8.8 Gr10.9 Gr12.9, hex socket cap screws DIN912, ISO4762 Gr8.8 Gr10.9 Gr12.9 with surface Black, Zinc plated, Hot dip galvanized. Diameters from M10 to M48, length no limited. Hex Flange bolts DIN6921 Gr8.8 Gr10.9 with serration, thread rod A193 B7 long sizes and short sizes with 2H nuts, stud bolts. We also can supply hex nuts DIN934, DIN6915, plain washers DIN125, DIN126, DIN6916, spring washers DIN127 with Black, Zinc plated and Hot dip galvanized surface.
Our physical and mechanical test results can reach to ISO898-1 for bolts and ISO898-2 for nuts.
Through scientific management, Ningbo Zhongli Bolts Manufacturing Co., Ltd. obtained ISO9001 certificate of Quality Management System. Quality is the most important for us. We have strict production and inspection equipments to support this point.
We hope to establish business relationship with all over the world, and our business can bring in mutual benefits for both parties.
Every serrated flange bolt for pipeline works passes through our rigorous 8-step manufacturing process
A Professional Sales and Technical Team with More Than 20 Years History.
We Have Our Own Testing Equipment and Laboratory, Our Products Have Initial Inspection, Patrol Inspection, And Final Inspection.
Our Factory Has Its Own Cold Forged, Hot Forged, And Heat Treatment Equipment.
Standard Fasteners in Stock, Non-standard Fasteners Can Be Customized.
We Have Passed ISO 9001, EN 15048, EN 14399, AD2000 and CE Certificates.
We hope to establish business relationship with all over the world, and our business can bring in mutual benefits for both parties.
EN 15048 CE Certification, EN14399 CE Certification, ISO9001 Certificate
Grasp first-hand information from our global pipeline industry clients
Contact Ningbo Zhongli Bolts today for competitive pricing, free samples, and expert technical support for all pipeline fastener requirements.
Get In TouchExplore our full range of high-strength bolts, stud bolts, and fastener solutions for pipeline and industrial applications
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Pipeline Hex Bolt — DIN933 10.9 Full Thread Black Fastener
Pipeline Black Oxide Bolt — DIN912 Hexagon Socket Head Cap Screws
Pipeline Heavy Hexagon Bolt — ASTM A325 Structural Bolt
Pipeline Hex Head Bolt — DIN961 Fine/Coarse Thread UNC & UNF
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