The Tube & Pipe Journal - September 2010

Product
Class
Description
T1 and T5 Flux-cored Wire Classifications and Descriptions

welders across a broad skill range, even those with little flux-cored arc welding (FCAW) experience. The wires operate with either 100 percent CO2 shielding gas or a blend of argon and CO2 (usually in a 75/25 percent mixture) and provide a high deposition rate. They also create well-shaped, uniform, and smooth weld beads and are available in low-hydrogen versions. In the past T-1 flux-cored wires were available only in H16 or H8 versions, meaning they had 16 or 8 milliliters of diffusible hydrogen, respectively, per 100 grams of weld metal. Some of today’s T-1 flux-cored wires are available in an H4 version; as the designation implies, they have as little as 4 ml of diffusible hydrogen per 100 g of weld metal.

Additionally, many T-1 flux-cored wires also are useful for out-of-position welding, allowing their use on existing piping systems. Steam piping, heat exchangers, and other high-temperature, corrosion-resistant applications are common examples that can benefit from these wires. The ability to weld out-of-position provides a distinct advantage over other processes, such as submerged arc welding, which are suitable for use only in the flat position or while the tube or pipe rotates.

That said, T-1 wires do have disadvantages that limit the chrome-moly applications on which they can be used. First, T-1 flux-cored wires tend to create welds with slightly higher oxygen content than other filler metals—typically 600 to 1,200 parts per million (PPM). Compared to stick electrodes or T- 5 flux-cored wires (to be discussed later), this higher oxygen content reduces the toughness of the T-1 weld in both the as-welded and post-weld heat-treated (PWHT) conditions. Cool ambient temperatures aggravate this characteristic, so T-1 wire is not the best candidate for applications such as the cold start of a power plant that has been shut down or a piping application subject to extremely cold weather. As a rule, T-1 flux-cored wires for chrome-moly also have higher weld metal hardness compared to a stick elec-

1.25% Cr, 0.5% Mo High-temperature service; typically used for welding P11

2.25% Cr, 1.0% Mo High-temperature service; typically used for welding P21 and P22

4 – 6% Cr, 0.50% Mo High-temperature service; typically used for welding steel that contains 5% Cr and 0.50% Mo

8 – 10.5% Cr, 1.0% Mo High-temperature service; typically used for welding P91 and P92

trode or submerged arc wire, which makes them more prone to cracking.

position welding, making these wires unsuitable for repairs on an existing, immovable piping system. Also, controlling the puddle is challenging, so T- 5 isn’t the best choice for less experienced welders. They also tend to have a less stable arc and generate more spatter than T-1 wires. In many cases, they are not as efficient for multipass welding due to their difficult-to-remove slag, which requires more chipping between weld passes than a T-1 wire.

Typically, suppliers offer T- 5 flux-cored wires for chrome-moly applications in two product classes: B2 and B3. The wires in the B2 product class contain 1.25 percent chrome and 0.5 percent molybdenum and are well-suited for welding P11 chrome-moly pipe that is subject to high-temperature service conditions. The B3 product class contains 2. 25 percent chrome and 1 percent molybdenum. They are typically used for welding P21 and P22 chrome-moly pipe and are also good for high-temperature applications.

Ultimately, the challenge of T- 5 wires is that they can be difficult to use and usually are limited to flat and horizontal welding positions. In recent years, however, new versions of T- 5 flux-cored wires have emerged, including the E81T5-B2M H4 wire mentioned previously, along with those classified as E91T5-B3M H4. These wires have slightly different characteristics than traditional T- 5 wires—namely, they

Figure 1

T- 5 WIRES: A VIABLE
ALTERNATIVE?

T- 5 flux-cored wires are a potential alternative to T-1 wires, especially for applications requiring good toughness, as they feature a lime-fluoride (also referred to as basic) slag system capable of providing clean welds with low sulfur and oxygen content. Specifically, T- 5 flux-cored wires have a high capacity for absorbing oxygen, resulting in an oxygen level of about 400 to 700 PPM, which is substantially less than the 600 to 1,200 PPM in a T-1 weld deposit. This lower oxygen level improves the toughness regardless of the application’s temperature.

Newer versions of T- 5 flux-cored wires, including those with an American Welding Society classification of E81T5- B2M H4 (among others), have even lower levels of oxygen in the final weldment. Some are less than 200 PPM.

In general, T- 5 flux-cored wires also have low diffusible hydrogen levels, 4 to 8 ml per 100 g of weld metal, and therefore have good crack resistance. They also are porosity-resistant, making them suitable for casting weld repairs that may contain moisture.

Like T-1 wires, T- 5 wires have drawbacks. T- 5’s basic slag system has a low melting point that creates a weld puddle that is usually too fluid for out-of-