Description
304 Stainless Steel Lap Joint Flanges (also known as Loose Steel Pipe Flanges with Weld-on Collar or Grade 30408 Loose Flanges) are premium two-piece piping connections designed for easy bolt hole alignment and superior corrosion resistance. Consisting of an outer loose steel backing flange paired with a welded 304 stainless steel collar (stub end), this system allows 360-degree flange rotation prior to tightening, significantly streamlining field installation in complex process pipelines.
Manufactured strictly to international standards, these loose lap joint flanges integrate perfectly with our industrial butterfly valves and form complete, leak-free pipeline loops on our industrial flanges manufacturing lines.
Technical Specifications
| Technical Parameter | Specification Details |
|---|---|
| Nominal Diameter Range | DN15 to DN600 (1/2" to 24") Standard; Custom larger sizes up to DN1200 |
| Pressure Ratings | Class 150, Class 300, Class 600; PN6, PN10, PN16, PN25, PN40 |
| Weld-on Collar Material | 304 / 304L Stainless Steel (S30408 / 1.4301 / 06Cr19Ni10) |
| Loose Backing Flange Material | Carbon Steel (ASTM A105 / S235JR), Hot-Dip Galvanized Steel, or 304 Stainless Steel |
| Collar & Stub End Type | Type A (ASME Standard), Type B, Type C, or Pressed / Forged Ring Collar |
| Manufacturing Standards | ASME B16.5, EN 1092-1 Type 02/32, DIN 2642, GB/T 9118 (30408) |
| Surface Treatment | Pickled & Passivated (Stainless Steel Collar), Anti-Rust Yellow Paint / Galvanized (Carbon Flange) |
| Quality Control & Certification | 100% Spectrometer PMI Material Test, Dimensional Check, EN 10204 3.1 MTR Provided |
Key Features & Material Cost Optimization
Utilizing 304 stainless steel lap joint flanges with weld-on collars delivers distinct technical and financial benefits for process engineers:
- Fast & Easy Bolt Alignment: The non-welded outer backing ring rotates freely around the 304 collar, eliminating bolt hole misalignment during site assembly and dramatically reducing labor time.
- Significant Cost Reduction: Because only the weld-on collar makes direct contact with the corrosive fluid, you can pair a 304 stainless steel collar (30408) with an economical carbon steel loose flange.
- Superior Chemical Protection: Grade 30408 (304 SS) provides outstanding resistance against organic acids, alkaline solutions, and atmospheric corrosion in food, chemical, and water systems.
Target Applications & Industries
Our 304 stainless steel loose flanges with weld-on collars are widely installed across diverse industrial loops:
- Chemical Processing & Fine Chemicals: Corrosive chemical pipelines requiring high-grade 30408 wetted components and frequent system maintenance.
- Food, Beverage & Pharmaceutical Lines: Hygienic piping loops where quick disassembly and easy cleaning are essential.
- Water Treatment & Municipal Systems: Acidic wastewater and treated water transmission mains requiring cost-effective anti-corrosion flange setups.
Frequently Asked Questions (FAQ)
Q1: What is the equivalent standard for 30408 stainless steel?
30408 (S30408) is the Chinese GB/T material code corresponding directly to international ASTM A182 F304 / AISI 304 and European EN 1.4301 stainless steel.
Q2: Can I combine a carbon steel loose flange with a 304 stainless steel weld-on collar?
Yes, absolutely. This is the main design advantage of lap joint flanges. The fluid only contacts the 304 collar, allowing you to use a carbon steel loose backing flange to save up to 40% in material costs.
Q3: Does Oucang Valve supply full material test certificates (MTR)?
Yes. As a direct manufacturer, Oucang Valve provides EN 10204 3.1 Material Test Reports covering chemical composition and mechanical properties with every batch.
About the Manufacturer: Oucang Valve
Oucang Valve is an ISO-certified direct manufacturer specializing in forged steel pipe flanges, 304/316 stainless steel lap joint flanges, and heavy-duty industrial valves. Operating our own ring forging workshops, precision CNC maching centers, and spectrographic material labs, we offer complete OEM engineering and direct export for global industrial projects.
- Core Capability: Precision forged 30408 loose flanges, ASME/EN standard stub ends, PMI material verification, and fast global delivery.
- Quality Compliance: ASME B16.5, EN 1092-1, DIN, GB/T, JIS, and ISO standards.
- Factory Inquiry: Contact our engineering team for direct factory quotations, material test reports, and custom 2D/3D CAD drawings.
