Stub End
A lap joint stub end is also called a lap joint stub, loose flange ring, and belongs to steel butt-welding pipe fittings. One end is a standard butt-welding bevel, which is welded and fixed to the pipe; the other end is formed by stamping and finish turning into a flat flanged sealing surface, which is pressed tightly together with a loose flange to achieve a detachable sealed connection. This structure allows the flange to rotate, making bolt hole alignment more flexible, and making on-site installation and later maintenance easier. Compared with using stainless steel or alloy flanges for the entire pipeline, the lap joint stub end uses corrosion-resistant material only in the part that contacts the medium, while the flange can be made of ordinary carbon steel, so material costs can be significantly reduced. We implement standards such as ASME B16.9, MSS SP43, and GB/T12459, and the products are used in pipeline systems such as petrochemicals, power station thermal systems, ship and marine, pharmaceutical clean applications, and environmental water treatment. For specific diameters, wall thicknesses, materials, and pressure ratings, please contact us to confirm.
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Long Type Lap Joint Stub End LP
The LP long-type lap joint stub end has one end machined with a butt-weld bevel for welding to the main pipe, and the other end hot-stamped to form a flat lap joint flange, which serves as the sealing pressure-bearing end face and forms a detachable connection structure with a loose flange. Compared with the short-type lap joint stub end, its straight pipe section is longer, so welding heat is not easily transmitted to the sealing surface, which can reduce the risk of leakage caused by flange annealing, warping, and end face deformation. The flange can rotate 360°, making on-site bolt hole alignment convenient, and maintenance disassembly and assembly do not require cutting the weld seam. The product diameter range covers DN15 to DN1200, wall thicknesses include STD, XS, XXS, and SCH series, pressure ratings are Class150 to 2500LB, and materials such as carbon steel, stainless steel, duplex steel, and alloy steel are available. For specific specifications, materials, and delivery requirements, please contact us to confirm.
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Short Stub End SP
The short-type lap joint stub end SP has one end as a butt-weld bevel, which is welded and fixed to the main pipe; the other end is a flat lap joint flanged face formed by integral hot stamping, serving as the sealing pressure-bearing surface of the loose flange. The loose flange can rotate 360° for alignment, making it easier to handle issues such as bolt hole misalignment, fixed equipment nozzle angles, and construction in confined spaces during on-site installation. The SP short-type lap joint stub ends we produce adopt an integral forming process, with no spliced welds, and the end face is precision-turned flat. The specifications cover mainstream diameters, and conventional models are in stock, making them suitable for small and medium-sized projects, bulk distribution for foreign trade, and standardized supporting procurement by equipment manufacturers. Specific configurations such as material, diameter, and wall thickness can be confirmed according to project requirements.
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Plate Flange Nipple
Plate-formed flanged stub end, also known as rolled flanged stub end or large-diameter steel plate lap joint stub end, is a non-standard custom pipe fitting we developed for ultra-large-diameter pipelines above DN600. The maximum forming diameter of conventional seamless stamped flanged stub ends is generally up to DN600; beyond this diameter, integral stamping is impossible. Therefore, large-diameter projects generally adopt the method of steel plate rolling, butt welding, and integral precision machining for production. The product is divided into two structures: long type LP and short type SP. It is used in conjunction with loose flange. One end is connected to the main pipe with a butt welding bevel, and the other end has a flanged sealing surface that matches the loose flange, achieving 360° rotational alignment and reducing on-site installation difficulty. The material can be adapted to carbon steel, stainless steel, duplex steel, alloy steel and other series, and supports customization of diameter, length, flanged thickness and pressure rating according to drawings.
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Controlled Flanged Short Piece
The controlled lap joint stub end is machined from a single seamless steel pipe, with no spliced welds, and is formed through processes such as facing, beveling, integral flanging, shaping, and polishing. The product is divided into two structures: long pattern LP and short pattern SP. It complies with ASME B16.9, MSS SP43, and GB/T12459 standards, and is compatible with global loose flange assembly systems. Compared with stamped lap joint stub ends, the controlled type has more advantages in end face flatness, sealing stability, and pressure resistance uniformity, making it suitable for DN15–DN600 small and medium diameter pipelines. We can provide regular specifications such as carbon steel and 304/316 stainless steel, and also support customization of non-standard diameters, thickened flanges, and special materials. Welcome to contact us to confirm the specific working condition selection and configuration.
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Carbon Steel Stub End
The carbon steel lap joint stub ends we produce use carbon steel materials such as 20#, A234 WPB, Q235B, 16Mn, WPL6, and comply with GB/T12459, ASME B16.9, and MSS SP43 standards. The products are divided into four processes: long pattern LP, short pattern SP, seamless pipe precision-machined, and plate-rolled, covering DN15–DN3000. One end has a standard butt-weld bevel for welding to carbon steel piping, and the other end has a flat lap face that mates with a loose flange, allowing 360° rotational alignment, solving on-site construction problems such as bolt hole misalignment, fixed equipment nozzles, and connections in confined spaces. Carbon steel material has good weldability, stable strength, and low cost, making it suitable for pipelines conveying conventional media such as water, gas, steam, ordinary oils, and fuel gas. We routinely keep DN15–DN600 stamped and seamless pipe specifications in stock, and can ship within 24–48 hours after payment confirmation. Non-standard customization and export packaging are supported.
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Austenitic stainless steel stub end
Austenitic stainless steel lap joint stub ends play the role of lap joint connection in piping systems, working with loose flanges to achieve 360° rotational alignment, solving on-site construction problems such as bolt hole misalignment, fixed equipment nozzles, and connection in confined spaces. One end of the product is a standard butt-weld bevel, which can be homogeneously fusion-welded with stainless steel pipes; the other end is formed by hot pressing or CNC precision turning into a flat lap joint sealing surface, which fits the gasket over the entire area. We provide two structures, long pattern LP and short pattern SP, covering three types of processes: integrated stamping, seamless pipe precision turning, and large-diameter plate rolling, with a diameter range of DN15–DN3000. Materials include 304, 304L, 316, 316L, 321, 904L, 254SMO and other austenitic stainless steels; low-carbon L-grade materials help reduce the risk of weld intergranular corrosion. A common matching solution is an austenitic stainless steel stub end plus a carbon steel loose flange, which controls project cost while maintaining the pipeline's corrosion resistance.
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Duplex Stainless Steel Stub End
Duplex stainless steel lap joint stub ends are used for detachable lap joint connections in high-salinity, high-chloride, strong acid and strong alkali, and high-temperature and high-pressure pipelines. We provide two structural types, LP long type and SP short type, matched with three manufacturing processes: integrated stamping, seamless pipe precision machining, and large-diameter plate rolling and fabrication, with specifications covering DN15 to DN3000. Materials cover 2101/2304 lean duplex, 2205 standard duplex, and 2507/S32760 super duplex stainless steel, manufactured according to GB/T12459, ASME B16.9, and MSS SP43 standards. One end of the product is a butt-weld bevel, which can be homogeneously fusion-welded with duplex stainless steel pipes; the other end is a dense and flat lap joint sealing surface, which, paired with a loose flange, can rotate freely for alignment, facilitating construction connection and later maintenance. The industry commonly uses the "duplex stainless steel stub end + carbon steel loose flange" solution to control engineering costs while ensuring corrosion resistance and pressure resistance.
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Alloy Steel Stub End
The alloy steel lap joint stub ends we produce cover materials such as 12Cr1MoV, 15CrMo, Cr5Mo, Cr9Mo, P11, P12, P22, P91, P92 and other chromium-molybdenum heat-resistant alloy steels, and are manufactured according to GB/T12459, ASME B16.9, and MSS SP43 standards. The products are divided into two structural types: LP long type (Type A) and SP short type (Type B). The forming processes include integrated stamping, seamless pipe precision turning, and large-diameter plate rolling, with a diameter range of DN15–DN3000. One end is a standard butt-weld bevel for homogeneous fusion welding with the pipeline; the other end is formed by hot pressing or CNC turning into a flat lap joint surface, which, matched with a loose flange, can rotate freely for alignment, solving problems such as on-site misalignment during butt joining of high-temperature pipelines, fixed equipment nozzles, and difficult installation in confined spaces. It is suitable for scenarios such as thermal power main steam pipelines, reheated steam pipe networks, high-temperature pipelines of supercritical units, petrochemical hydrogenation reaction pipelines, and high-pressure boiler supporting pipelines.
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