What is Welding Flange?

What is Welding Flange

Welded flange is disc-shaped fitting used for pipe or equipment connection, which is fixed on the end of the pipe or equipment interface by welding, and uses bolts and sealing gaskets to achieve a sealed connection. It is divided into flat welding flange (suitable for medium and low pressure environment) and butt welding flange (suitable for high pressure and high temperature scenarios), which has the advantages of strong sealing, high pressure resistance, flexible installation, etc., and is widely used in petroleum, chemical industry, water supply and drainage and other fields, especially suitable for systems that require frequent disassembly or high sealing requirements. Welding is carried out in accordance with relevant standards and flaw detection to ensure quality and safety.

Features of Welded Flanges

The characteristics of welded flanges can be summarized as follows:

1. Structural design

It is disc-shaped, with bolt holes on the edge, which are connected with the mating flange through bolts, and a sealing gasket is installed in the middle to ensure tightness.

It needs to be welded with pipes or equipment in advance to form a rigid monolithic structure.

2. Connection

Relying on welding fixation, it is divided into two processes: flat welding (direct welding) and butt welding (groove welding), the latter has higher strength.

3. Categorical characteristics

Flat welded flange (SO): suitable for medium and low pressure environments (PN≤16) with low cost.

Butt welding flange (WN): suitable for high-pressure, high-temperature or corrosive media, with high fatigue resistance.

4. Performance advantages

Strong tightness: Low risk of leakage after welding, suitable for scenarios with high tightness requirements.

High pressure and high temperature resistance: Especially the butt welding flange can withstand complex working conditions.

Flexible installation: easy to install in sections and later maintenance.

5. Material adaptability

Carbon steel, stainless steel, alloy steel, cast iron and other materials are available, and can be flexibly selected according to the corrosiveness, temperature and pressure of the medium.

Application of Welded Flanges

1. Construction and Municipal Engineering

Application Scenarios:

Fire pipes, heating systems, water supply and drainage networks, ventilation equipment connections

Material Selection:

Ordinary carbon steel (Q235B/A105): low cost (about 5-15 yuan/piece), suitable for DN50-DN300 low-pressure pipeline.

Hot-dip galvanized carbon steel: outdoor or humid environment (such as underground water pipes), resistant to rust but with a lifespan of about 8-10 years.

2. Food and pharmaceutical industry

Application Scenarios:

Beverage production lines, pharmaceutical reactors, dairy equipment

Material Selection:

304 stainless steel (polished Ra≤0.8μm): FDA compliant, weak corrosion resistant.

316L Stainless Steel: Used when in contact with highly salty media such as soy sauce.

3. Chemical and petroleum refining

Application Scenarios:

Reactor interface, oil pipeline, acid medium transportation

Material Selection:

316L Stainless Steel: Resistant to chloride ion corrosion (e.g. seawater, hydrochloric acid), temperature resistant to 400°C.

Duplex 2205: High pressure hydrogenation unit (PN40+), yield strength ≥ 450MPa.

Hastelloy C-276: Handles extremely corrosive media such as aqua regia and high-temperature chlorine.

4. Energy & Electricity

Application Scenarios:

Nuclear power plant circulating water system, thermal power plant steam pipeline, wind power tower connection

Material Selection:

Carbon steel (20G): steam pipe (≤540°C), heat treatment is required to relieve stress.

316L stainless steel: seawater cooling system for coastal power plants (Cl⁻ concentration> 20,000ppm).

Nickel-based alloys (e.g. Inconel 625): Creep resistance at high temperatures and pressures (>600°C).

5. Aerospace & Military

Application Scenarios:

Aero engine fuel lines, missile propellant delivery systems

Material Selection:

Titanium alloy (TA2): lightweight (density 4.5g/cm³), low temperature resistance (-253°C).

Hastelloy C-276: Extremely corrosive environments (e.g. hydrazine fuels).

6. Other special fields

Ship Engineering:

The desalination plant uses 316L stainless steel flange (DN200-PN16) to resist corrosion in the marine environment.

Environmental protection industry:

The aeration pipeline of the sewage treatment plant is made of carbon steel lined flange (DN300-PN10), which is acid and alkali resistant.

New Energy:

The high-pressure hydrogen tubes for hydrogen fuel cell vehicles use aluminum alloy flanges (DN8-PN70) in accordance with ISO 13984.

Apply the selection key principle

Medium corrosiveness: Corrosion-resistant materials (e.g., 316L> 304> carbon steel are preferred.

Temperature and pressure: stainless steel or alloy for high temperature (>300°C), butt welding flange for high pressure (>PN25).

Industry standards: Chemical industry follows HG/T 20592, food food complies with FDA, nuclear power implements ASME BPVC III.

Cost balance: Carbon steel is suitable for non-corrosive scenarios (cost of 5% of the system), and the alloy material needs to calculate the full life cycle cost

The Price of Welded Flanges

The price of welded flanges is significantly affected by factors such as material, specification, pressure level and purchase volume. Carbon steel flat welded flange (the unit price of small batch starts at about 4 yuan, and bulk purchase can be as low as 2.5 yuan; Stainless steel 304 flat welded flanges start at about 10 yuan, and large diameter or high-pressure models can reach 80-189 yuan. Special materials such as duplex steel and Hastelloy flanges are expensive, and they can reach more than 1,000 yuan each.

The core influencing factors include the material (carbon steel< stainless steel < alloy), specification (the larger the caliber, the higher the pressure level, the more expensive the price), the type of process and the procurement channel.

When purchasing, it is necessary to clarify the material, specification and sealing surface form, and give priority to the manufacturer that has passed the ISO certification and request the test report. In 2025, the market shows that carbon steel flanges will rise slightly by 5%-8% due to steel fluctuations, and 316L stainless steel will increase by 12% due to nickel prices. Some manufacturers have launched 3D printing customization services, with MOQs as low as 10 pieces and a unit price of about 6-8 yuan. It is recommended to compare prices through multiple channels and pay attention to long-term maintenance costs to avoid low-cost and inferior products.

Supplier of Flanges

LTZC has been focusing on flange manufacturing for 20 years, providing carbon steel, stainless steel, high-pressure flanges and customized products, covering all categories of butt welding, flat welding, threading and blind plates, and strictly complying with ASME, DIN, JIS international standards. We have passed ISO 9001 and API 6A certifications from raw materials to finished products to ensure the stable performance of our products in high-pressure scenarios such as petrochemical, energy, and shipbuilding.

Own factory + intelligent warehousing, support 72-hour emergency delivery, can be matched with bolt gasket one-stop procurement. In the past 20 years, it has served 500+ enterprises around the world, saving more than 15% of costs for customers such as PetroChina and European Energy Group. If you need a flange, find LTZC - fast, economical and stable.