SAW welding, Submerged Arc Welding, is an efficient welding process especially suitable for welding thick plates. The process is not sensitive to welding defects, and it is also a safe process for the operator.
In this article, PEMA Welding Engineer Jari Tervolin defines the SAW welding process, discusses its benefits, and explains why it is such a suitable process in the wind energy industry.
User-friendliness, quality, and efficiency in one process
In the SAW welding process, the welding flux protects the arc and molten puddle from the air. A part of the flux melts, solidifies, and forms a slag on the weld bead. After welding, the rest of the welding flux is recovered and recycled, and the slag is removed. The welding flux also improves arc stability and electrical conductivity. Additionally, the alloying elements of the flux improve the welding metallurgy.
Thanks to the protection of the flux, high current, and deep and wide penetration, the weld quality is excellent, and SAW process is not sensitive to welding defects such as lack of fusion, lack of penetration, porosities, or spatters.
“SAW process is really the best fit for thick plates, simple and long welds such as circumferential and longitudinal welds. The process has high efficiency, quality, and operational reliability”, explains Jari Tervolin, PEMA Welding Engineer.
Besides the good weld quality and high reliability and functionality, SAW welding process is also an ergonomic and safe process for the operator: the welding flux does not only protect the arc and molten puddle, but it also protects the operator – there is no need to wear a mask. The SAW welding process does not expose the operator’s eyes or skin to radiation, and there are no harmful welding fumes.
SAW welding process in the wind energy industry
Above mentioned straight and thick plates can be often found in, for example, wind energy towers. Even though SAW welding is not the only suitable process in the wind energy industry, in most cases, it is the best solution. SAW welding process is especially suitable for welding longitudinal and circumferential welds due to its deep and wide penetration and high deposition rate. Furthermore, SAW welding can be carried out with multiple wire electrodes.
“SAW welding process is a very suitable process in the wind energy industry. When the thickness of the plates is typically over 10-12 millimeters, like in circumferential and longitudinal welds of wind energy towers, SAW welding process enables the best efficiency and welding quality”, explains Tervolin.
Additionally, SAW welding process can be integrated with welding robots, which enables welding of diverse workpieces. The process performance and deposition rate can also be enhanced with different variations, discussed in the next chapter.
Enhancing SAW welding process with the long stick-out tandem process and tiltable welding head
Tandem arc SAW process, with long stick-out and specially developed tiltable welding head, enables increased deposition rate and narrower groove by filling welds with large tubular production.
When the wire stick-out is longer, Joule heating (I2 x R) pre-heats the wire more, causing it to melt faster, and the deposition rate increases without increasing the heat-input.
Pemamek has also developed a tiltable welding head for semi-narrow gap grooves, which enables better tolerance for wire positioning and the shape of the welded pass. It enables the grooves to be narrower, and multiple pass welding can be finished with a smaller number of passes. The increased deposition rate and increased size of the weld pass can be handled better with PEMA tiltable semi-narrow gap welding head.
Milling machines enable various benefits
Milling is crucial for all sectors that have heavy welding in their production: it increases production efficiency, saves welding time, and significantly improves the welding quality.
Pemamek’s milling machines are designed for circumferential and longitudinal welds – with milling, a semi-narrow groove decreases groove volume, so a smaller amount of weld passes is required, and consumables can be saved. Also, deformations and tensions are lower. Automatic depth controlling enables the groove to remain constant. After the inside weld has been welded in wind tower manufacturing, the outside is milled a little bit over the inside weld and the root is opened so back gouging can be avoided.
“Semi-narrow groove significantly decreases groove volume and total welding time, and back gouging is not needed anymore. A defect rate can be also decreased using the milled semi-narrow groove“, says Tervolin.
Welding preparation with PEMA milling
- Only oxy-cutting for inside bevel → Saves time
- Outside milling → Reduces in defect rate
- Welding of semi-narrow groove → Less welding