Pipe Welding Methods Explained: Flat Head, Fillet, Autogenous, and Filler Wire Welding
The following is a detailed introduction to the common forms of welded pipe fittings (flat head welding, fillet welding, autogenous welding, wire welding):
1. Flat Head Welding
Definition:
Flat head welding refers to a welding method in which the end of the pipe fitting is processed into a flat head (a plane perpendicular to the axis of the pipe fitting), and then the end faces of two flat head pipe fittings are tightly connected by welding.
Features:
Welding preparation: The end of the pipe fitting needs to be cut or processed into a flat surface in advance, and the centering accuracy requirements are high.
Welding process: Arc welding (such as TIG welding, MIG welding) or gas welding is usually used. During welding, the molten pool is concentrated on the end face, and the penetration depth needs to be controlled to avoid burning through.
Weld form: A butt weld is formed, the weld is perpendicular to the axis of the pipe fitting, and the appearance is flat.
Application Scenarios:
Commonly used for pipe fittings with small nominal diameters (such as DN50 or less), such as instrument pipes and small-diameter water pipes.
It is suitable for pipeline systems that are sensitive to fluid resistance (such as clean pipelines and gas transmission pipelines) because the inner wall of the weld is relatively smooth.
Advantages and Disadvantages:
Advantages: Uniform force on the weld, low fluid resistance, and neat appearance.
Disadvantages: High requirements for pipe processing accuracy, and defects such as incomplete penetration and pores are prone to occur during welding.
Recommended Products:
For flat head welding, we recommend using our Tube to Tubesheet Orbital Welding Machine MWP Series.
Our Tube to Tubesheet Orbital Welding Machine provides a reliable and efficient solution for tube sheet welds in a variety of industries. It is designed to weld stainless steel tube sheets with a welding power of 400 Amp and a welding angle of 0-360°. It features a lightweight design of only 140 Kg and is powered by a voltage of 220 V/50-60 Hz. It provides a secure and reliable solution for tube sheet welds. Our machine is user-friendly, easy to operate, and allows for quick and effortless welds. The tube to tubesheet orbital welding machine can weld pipes with diameters ranging from 6 mm to 63 mm,
2. Fillet Welding
Definition:
Fillet welding is a welding method that forms a right-angle or sharp-angle weld at the angle between pipe fittings and pipe fittings, pipe fittings and flanges (or other components), usually a fillet joint.
Features:
Welding preparation: Pipe fittings do not need to be completely aligned, and can be welded directly at the angle, with low assembly accuracy requirements.
Welding process: Wire welding (such as manual arc welding, MIG welding) is used, the weld is triangular (fillet weld), and the weld leg size and fusion depth need to be controlled.
Weld form: It is a non-butt weld, which mainly bears shear force and lateral load.
Application Scenarios:
Widely used for the connection of pipe fittings with flanges, brackets, and branches, such as branch pipe connections in pipeline systems and steel structure pipe fittings welding.
Applicable to connection parts that are not subject to much force or are not the main load-bearing part.
Advantages and Disadvantages:
Advantages: simple assembly, high welding efficiency, strong adaptability.
Disadvantages: obvious stress concentration in the weld, lower bearing capacity than butt weld, prone to defects such as undercut and uneven weld leg size.
Recommended Products:
For fillet welding, we recommend using our Tube to Tubesheet Orbital Welding Machine MWP Series.
Our Tube to Tubesheet Orbital Welding Machine provides a reliable and efficient solution for tube sheet welds in a variety of industries. It is designed to weld stainless steel tube sheets with a welding power of 400 Amp and a welding angle of 0-360°. It features a lightweight design of only 140 Kg and is powered by a voltage of 220 V/50-60 Hz. It provides a secure and reliable solution for tube sheet welds. Our machine is user-friendly, easy to operate, and allows for quick and effortless welds. The tube to tubesheet orbital welding machine can weld pipes with diameters ranging from 6 mm to 63 mm,
3. Autogenous Welding
Definition:
Autogenous welding refers to a welding method that does not fill welding wire during the welding process, and only relies on the melting of the pipe base material itself to form a weld, also known as "no-filling welding".
Features:
Welding preparation: The gap between pipes (usually small) needs to be precisely controlled, and the base material composition needs to meet the weld performance requirements.
Welding process: The heat of the arc or flame is used to melt the edge of the base material, forming a molten pool and then condensing into a weld. The molten pool metal comes only from the base material.
Weld characteristics: The weld width is narrow, the excess height is small, and it is consistent with the base material composition.
Application Scenarios:
Applicable to thin-walled pipes (such as wall thickness ≤3 mm) or occasions where the weld composition is required to be completely consistent with the base material (such as stainless steel and aluminum alloy pipes).
Common in automated welding (such as full-position automatic welding of pipelines) or precision instrument pipe welding.
Advantages and Disadvantages:
Advantages: High welding efficiency, no need for filler wire, reducing welding material consumption; weld composition is consistent with the parent material, and has good corrosion resistance.
Disadvantages: Sensitive to welding parameters (such as current and speed), prone to defects such as lack of fusion and burn-through; thick-walled pipes require multi-layer welding, which can easily lead to a decrease in weld performance.
Recommended Products:
For autogenous welding, we recommend using our Closed-head Orbital Welding Machine MWF Series.
Our Closed-head Orbital Welding Machines, namely MWF-12, MWF-18, MWF-40, MWF-80, MWF-120 and MWF-168, and the MWA-200 TIG welding power source are high precision pipe to pipe welding machines with high welding capacity and power rating. With programmable welding memory and cooling system, they are among the best orbital welders in the market. The control system is computerized to ensure accuracy and a high level of welding precision.The closed-head orbital welding machine can weld pipes with diameters ranging from 4 mm to 168 mm and wall thicknesses ranging from 0.8 mm to 3 mm.
4. Wire Welding (Filler Wire Welding)
Definition:
Wire welding is a welding method in which welding wire (or welding rod) is filled into the molten pool during the welding process, and the welding wire is melted and fused with the parent material to form a weld. It is one of the most commonly used welding methods.
Features:
Welding preparation: Welding wires of different compositions can be selected according to the material and performance requirements of the pipe fittings to adjust the mechanical properties or corrosion resistance of the weld metal.
Welding process: The welding wire is used as a filler metal and needs to be fed synchronously with the arc (such as MIG welding, TIG filler wire welding) or manually (such as manual arc welding). The filler metal can fill the weld gap or increase the weld thickness.
Weld characteristics: The weld metal is composed of the base metal and the welding wire, and the weld performance can be optimized by the welding wire composition.
Application Scenarios:
Suitable for welding pipes of various wall thicknesses, especially thick-walled pipes (multi-layer and multi-pass welding is required) or occasions where the weld performance needs to be improved.
Widely used in industrial pipelines (such as high-pressure pipelines, high-temperature pipelines), pressure vessels, steel structures and other fields.
Advantages and Disadvantages:
Advantages: The weld performance can be adjusted by the welding wire, and it has strong adaptability; the filler metal can fill larger gaps and reduce the assembly precision requirements.
Disadvantages: Additional consumption of welding materials is required, and the cost is high; welding process parameters (such as wire feeding speed and arc voltage) need to be accurately matched.
Recommended Products:
For wire welding, we recommend using our Open-head Orbital Welding Machine MWG Series.
This Open-head Orbital Welding Machine includes MWA-400 TIG welding power source and MWG-90, MWG-170, MWG-230, MWG-325 orbital welding heads, which is suitable for medium wall thickness carbon steel, stainless steel material pipe welding. It is designed as a compact structure and easy to use at work site with good weld surface and fast speed. The open-head orbital welding machine can weld pipes with diameters ranging from 19 mm to 325 mm and wall thicknesses ranging from 1 mm to 10 mm.
5. Comparison of Four Welding Forms
| Welding Form | Filler Material | Joint Type | Typical Wall Thickness | Application Scenario | Key Requirements |
|---|---|---|---|---|---|
| Flat Head Welding | Wire can be filled or not | Butt joint | Thin wall mainly | Small diameter pipeline, clean system | End surface flatness, centering accuracy |
| Fillet Welding | Wire must be filled | Fillet joint | Unlimited | Branch pipe connection, flange welding | Weld leg size, fusion depth |
| Autogenous Welding | No wire | Butt joint | Thin wall (≤3 mm) | Thin parts, consistent composition demand scenario | Precise control of welding parameters |
| Wire Welding | Wire must be filled | Butt/Fillet, etc. | Unlimited | Thick wall parts, performance optimization demand scenario | Wire composition matching, wire feeding stability |
6. Selection Suggestions
Based on the wall thickness of pipe fittings:
Thin wall parts (≤3 mm): give priority to autogenous welding or flat head welding without wire to reduce heat input.
Thick wall parts: use wire welding (multi-layer and multi-pass) to ensure weld strength by filling metal.
According to performance requirements:
Corrosion resistance or high consistency of composition: choose autogenous welding or welding with wire matching the composition of the parent material.
Complex force or high strength requirements: flat head welding or wire welding of butt joints is preferred to avoid stress concentration of fillet welds.
According to assembly accuracy:
High-precision assembly (such as automatic welding): flat head welding or autogenous welding can be used.
Low-precision assembly (such as on-site installation): fillet welding or wire welding is more flexible.
In practical applications, it is necessary to combine process assessment (such as welding process specification WPS) and standard specifications (such as ASME B31.3, GB/T 12469, etc.) to select the appropriate welding form.