voestalpine Böhler Welding offers welding consumables and equipment for the manual, semi-mechanized welding of pipelines.

A broad range of products are available depending on the welding processes you want to use:

• A wide range of coated electrodes includes types for high-efficiency vertical welding with a cellulosic coating and low-hydrogen basic types that can be used both vertical down and vertical up.
• A wide range of products for semi and fully mechanized welding includes solid wires and rods, self-shielded and gas-shielded flux cored wires and submerged arc wire/flux combinations for double jointing.

The range covers standard applications:

• Carbon steel pipeline with high strength steel grades up to API X60/EN L415MB, high tensile grades up to API X100/ENL690MB,

Corrosion Resistance Alloy pipeline (CRA) from standard stainless-steel grades, duplex and super duplex stainless steel, nickel alloy 625 and clad pipes in alloys 316L, 625 and 825.

To prevent hydrogen induced cracking, it is necessary to preheat pipes before starting to weld and to maintain an interpass temperature during the welding of individual beads.

In view of the often difficult site conditions, preheating at 150°C (300°F) is generally recommended. This applies to all wall thicknesses up to 25 mm (1”) and weld metals up to class E9010 (FOX CEL 90). Lower preheat and interpass temperatures may be selected when welding thin-walled pipes.

The diagram below shows minimum required preheat temperatures, as a function of wall thickness and electrode type. This refers to both the preheating and interpass temperatures.

Cellulosic electrodes are mainly operated on direct polarity. The welding equipment must have a dropping characteristic and a high open circuit voltage. Terra MP 350 RC is the ideal choice for this application. Recommended joint preparations are listed here below.

The root pass is a critical part of any pipe weld that requires perfect penetration. Electrode diameter, travel speed and amperage must be selected to match the pipe diameter and wall thickness. 3.2 mm (1/8“) diameter electrodes are recommended for pipe diameters up to about 250 mm (10“) and wall thicknesses up to 8 mm (5/16“).  Choose 4 mm (5/32“) diameter electrodes for larger sizes.

Welding is performed in vertical-down direction, with the electrode in good contact with both beveled plate edges.

Line-up clamps should be removed only after completing the root pass around the entire circumference and, when welding larger diameter pipes, only after completing the hot pass has been completed.

The hot pass should be welded immediately after application of the root pass, but never later than 10 minutes. This is particularly important for high-strength line pipe grades to prevent underbead cracking in the base material.

To avoid slag inclusions, the root pass must be ground before the hot pass is started. The use of a relatively high welding current is advantageous because this achieves good penetration so that any remaining slag inclusions are re-melted and at the same time ensures that the root pass is thoroughly annealed.

Filler layers beads are sufficiently flat and free from undercut and slag inclusions when the electrode is applied with a slight circular or stepping motion, especially in positions 12 to 2 o‘clock, 12 to 10 o‘clock, 4 to 6 o‘clock and 8 to 6 o’clock. Weaving of max. 2xØ is recommended for all other positions.

The cover pass is executed with a slight weaving of the electrode. The weld should not overlap the groove edge by more than 1.5 mm (1/16“). If the cover pass is executed correctly, weld reinforcement is about 1 to 2 mm (1/16“).

In combination with basic vertical-down electrodes (BVD), root passes can be welded with either cellulosic or basic vertical-up electrodes. If root passes are welded with cellulosic electrodes in the vertical-down progression, hot passes shall preferably be welded with cellulosic electrodes as well.

The interpass temperature influences the metallurgical processes that take place in the deposit during solidification and cooling and thus to a certain extent also influences the mechanical properties of the basic vertical down weld metal. It is generally recommended to keep the interpass temperature in the range of 100°C-200°C (210°F-392°F) during the entire welding process.

Basic vertical-down electrodes can only be operated with direct current. Welding machines must have a dropping characteristic and a high open-circuit voltage. The Terra MP 350 RC is the ideal choice for this application. Filler passes are executed with electrodes of 3.2 mm, 4.0 mm and 4.5 mm diameter, depending on the pipe thickness. The high current ensures sufficient penetration and satisfactory economy of the process. Slight weaving is always recommended, as this prevents short-circuiting the arc.

When welding thick-walled pipe, it is recommended to apply two to three beads side by side, remove all the slag before applying the next bead and keep the arc as short as possible. The cap is deposited with a slight weaving technique, with a maximum weave of twice the electrode diameter.