Iranian-made seam tracking system

Submerged arc welding (SAW) in pipe production: why is the seam so hard to follow by eye?

Submerged arc welding (SAW) is the main process for welding large-diameter water, oil and gas pipes, in both spiral and longitudinal (straight-seam) mills. It deposits weld metal at a high rate, penetrates deeply and suits thick plate and long, continuous welds. Yet the very feature that makes it right for mass pipe production makes the operator's job hard: the arc and the weld pool are hidden under a blanket of flux, so the operator cannot see where the weld is actually being made. He can only watch the seam ahead of the nozzle and correct every shift of the seam by hand.

On a production line the seam never stays put. In a spiral mill, variations in strip width and edge shape and forming errors keep moving the seam; in a straight-seam mill, edge deviation along the pipe and plate unevenness do the same. An operator staring at one spot for hours will sooner or later tire, and weld quality ends up depending on his attention rather than on the process.

Common submerged arc welding defects caused by drifting off the seam

• Lack of fusion: when the nozzle moves away from the centre of the seam, one edge of the joint is not fully melted and the bond stays weak.
• Incomplete penetration: the root of the joint is not filled; a defect that shows up in non-destructive tests such as ultrasonic (UT) and radiographic (RT) inspection.
• Misaligned inside and outside welds: on pipes welded from inside and outside, the two welds must overlap to cover the full wall thickness; drift in either one reduces that overlap.
• Changing nozzle height: when the nozzle rises or falls relative to the plate, the wire stick-out changes, which affects welding current, penetration depth and bead shape.

Each of these defects means weld repair, line stoppages, extra time and cost, and sometimes cutting out part of the pipe. Many of them share one root cause: at the moment of welding, the nozzle was not exactly on the seam.

How does a seam tracking system work?

The RasaAndishan weld seam tracking system is a laser seam tracking system. A laser sensor ahead of the welding nozzle scans the cross-section of the seam and finds its centre, and the controller continuously corrects the position of the welding head so that the nozzle always stays on the seam. The nozzle height is adjusted automatically as well. The operator is freed from chasing the seam and can supervise the welding process and its quality instead.

What does a seam tracking system add to your welding line?

• The welding nozzle stays on the seam for the whole shift, without interruption and without fatigue.
• Weld quality no longer depends on the operator's moment-to-moment skill and focus; it stays consistent from the first hour of the shift to the last.
• Seam deviation and the repairs caused by the nozzle leaving the seam are reduced compared with manual control.
• Automatic nozzle height adjustment keeps welding conditions stable.
• Instead of being tied to a hand wheel, the operator becomes the supervisor of the process.
• The know-how is local, with direct support from the Iranian manufacturer.

Which model suits your line?

The system is built in three models; the comparison table further down this page lists the features of each side by side:

• RA⁠-⁠ALSTS⁠-⁠5000: the most complete model. Besides seam tracking it offers gap control, stick-out control, a welding supervisor, dual seam type processing and an industrial panel and components. It uses the LS200 sensor, detects seams as shallow as 2 mm, operates from ⁦-40⁩ to ⁦+85⁩ °C and carries a 3-year warranty.
• RA⁠-⁠ALSTS⁠-⁠2000: seam tracking and welding supervisor; LS100 sensor, minimum detectable seam depth 6 mm, operating temperature ⁦-40⁩ to ⁦+85⁩ °C and a 1-year warranty.
• RA⁠-⁠ALSTS⁠-⁠1000: seam tracking; LS100 sensor, minimum detectable seam depth 6 mm, operating temperature 0 to ⁦+70⁩ °C and a 1-year warranty.

Track record

In February 2016 (Bahman 1394), automatic pipe welding with the RA⁠-⁠ALSTS⁠-⁠1000 laser seam tracking system was carried out at the Mahshahr pipe plant. Initial non-destructive ultrasonic and radiographic tests on the pipes produced this way showed high weld quality. The industrial version of the system was later built under the trade name RA⁠-⁠ALSTS⁠-⁠5000. Read the project report.

Beyond pipes

The system is not limited to the pipe industry. It is also used in car manufacturing, steel-building fabrication and any other industry that needs to detect the exact position of a seam, gap or ridge. To learn more about the process itself, read our article on submerged arc welding.

Ask us before you choose

To choose the right model for your line, send us the line type (spiral or straight-seam), the welding method, the plate thickness and the joint shape, and contact us.