Historically, companies have relied on stick electrodes for welding chrome-moly tube and pipe, in part because of the mechanical and chemical properties these filler metals provide and also because they are the accepted standard specified for such applications. However, with greater demands to increase productivity and stay competitive, some companies are considering a wire welding process as a means to get ahead. Specifically, they are turning to the use of T-1 or T-5 gas-shielded flux-cored wires, both of which have undergone significant advancements in recent years and offer greater consistency than similar products in the past.

Like any filler metal, including stick electrodes, flux-cored wires for chrome-moly have distinct advantages and disadvantages. They are undisputedly faster than welding with stick electrodes, but depending on the specific chrome-moly tube or pipe application, they may or may not be the right fit for the job. Following is information about the main types of flux-cored wire for welding chrome-moly tube and pipe to help you make the decision for yourself.

What You Should Know About T-1 Wires
Flux-cored wires referred to as T-1 have a rutile (also called acidic) slag system. Filler metal manufacturers generally offer T-1 wires in multiple product classes to match the chemical and mechanical properties of various chrome-moly tube and pipe. These include flux-cored wires with B2, B3, B6, B8 and B9 product classes, which contain from 1.25 to 10.5 percent chrome and 0.5 to 1 percent molybdenum. See Figure one for specific product class information.

A T-1 wire’s rutile (or acidic) slag system results in an easy-to-remove slag and makes the wire well suited for welding on multi-pass applications, as there is minimal clean up required in between passes. These types of wires also create low amounts of spatter, which reduces the need for post-weld cleaning.

Typically, T-1 flux-cored wires for chrome-moly have a stable arc and weld very smoothly, making them very welder-friendly and readily usable by welding operators of varying skill sets-a factor that is appealing for companies who need to train employees on the flux-cored process. They operate on 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 and efficiency. They also create well-shaped, uniform and smooth weld beads, and are available in lower hydrogen versions. In the past, T-1 flux-cored wires were only available in H16 or H8 versions, meaning they had 16 or 8 ml of diffusible hydrogen (respectively) per 100g of weld metal. Today’s T-1 flux-cored wires are available with as little as 4 ml of diffusible hydrogen per 100g of weld metal (signified by an H4 classification).

Additionally, many T-1 flux-cored wires are also able to weld out-of-position, allowing them to be used for welding tube and pipe applications within an existing piping system. Steam piping, heat exchangers and other high temperature, corrosion resistant applications are common examples that can benefit from these wires. This ability to weld out-of-position provides a distinct advantage over other chrome-moly welding processes, such as submerged arc welding, which can only weld 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. One such disadvantage is that T-1 flux-cored wires tend to create welds with slightly higher oxygen content than other filler metals-typically 600 to 1200 ppm (parts per million). 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. The welds also lack toughness particularly when exposed to cooler temperatures, so they may not be suitable of applications such as the cold start of a power plant that has been shut down or in a piping application subject to extremely cold weather. As rule, T-1 flux-cored wires for chrome-moly also have higher weld metal hardness compared to a stick electrode or submerged arc wire, for example, which makes them more prone to cracking.

Given these advantages and disadvantages, your specific application will determine whether a T-1 flux-cored wire is the right choice for your chrome-moly application. For example, if you require an all-position wire and do not need to maintain toughness, these wires might be a good option. However, if you have a cooler temperature application, you will likely want to consider an alternative.

T-5 Wires: A Viable Alternative?
T-5 flux-cored wires are a potential alternative to T-1 wires, specifically for applications requiring good toughness, as they feature a lime-fluoride (also referred to as basic) slag system that is 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 only 400 to 700 ppm (parts per million) as compared to the 600 to 1200 ppm in a T-1 weld deposit. This lower oxygen level ensures greater toughness in both high heat and lower temperature applications. Newer versions of T-5 flux-cored wires, including those featuring an AWS (American Welding Society) classification of E81T5-B2M H4 (among others) have even lower levels of oxygen in the final weldment-as low as 200 ppm or below.

As a rule, T-5 flux-cored wires provide low diffusible hydrogen levels, ranging in the 4 to 8 ml per 100g of weld metal, and are therefore good at resisting cracking. They also feature lower weld metal hardness than T-1 flux-cored wires and are resistant to porosity, making them a particularly good option for casting weld repairs that may contain moisture. T-5 flux-cored wires are also good for welding tube and pipe applications in a shop environment, where welding operators can weld in the 1G position (flat) while the tube or pipe rotates.

Conversely, these wires do not work well in an existing, installed piping system with the exception of welding on castings or elbows where the pipe extends at a 90-degree angle and can be welded in a flat or horizontal position. That is because their basic slag system features a low melting point that creates a weld puddle that is usually too fluid to use out of position. In addition to being limited mostly to welding in the flat positions, T-5 wires are notoriously challenging to weld, especially for less experienced welding operators as the fluid weld puddle can be hard to control. T-5 wires also tend to have a less stable arc and generate higher spatter levels than T-1 wires. In many cases, they are not as efficient for multi-pass welding due to their difficult-to-remove slag, which requires more chipping between weld passes than a T-1 wire.

Typically, filler metal manufacturers 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. B3 product class flux-cored wires contain 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 provide good toughness properties, but they can be difficult to use and are typically 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, that they are more readily able to weld out of position, particularly vertical up and vertical down. These wires operate with mixed shielding gases (Argon and CO2) as opposed to straight CO2, which provide a stable arc similar (but not as steady) as a T-1 flux-cored wire. As a result, these wires often are easier to train welding operators to use, but they still provide the toughness desired with a traditional T-5 wire. Usually, they have impact properties of more than 37 joules at -50 degrees Celcius in the ‘as welded’ condition. In the PWHT condition, they can offer toughness greater than 47 joules at -40 degrees Celcius. These newer T-5 wires typically have greater slag coverage as well, which helps provide good quality welds and is relatively easy to remove. One disadvantage to these newer wires, however, is that unlike other T-5 wires they operate on DC current, negative polarity (DCEN) and will require you to change power sources and/or dedicate a power source to operating them. Also, the weld puddle on these newer type of wires tend to behave differently than other T-1 or T-5 wires, which may require additional welder training to use them properly.

With these newer wires, as well as the traditional T-5 flux-cored wires or T-1 wires, it is important to find products with a low X-factor. X-factor is a formula that measures a weldment’s resistance to temper embrittlement. Temper embrittlement is the brittleness or loss of toughness that occurs when the weldment is held (or slowly cooled) through a temperature range of approximately 850 to 1,100 degrees F and is particularly important when welding chrome-moly. For all types of flux-cored wires for welding chrome-moly, the X-factor should be below 15.

Making Your Choice
Determining whether your application can benefit from a T-1 or T-5 welding wire will depend on several factors, including whether you can change the specifications for your particular chrome-moly application. In some circumstances, it may simply not be an option to change from the stick welding or submerged arc process, or it may not be in the best interest of your particular application. But in some cases, T-1 or T-5 flux-cored wires may offer just the advantage you need to improve productivity and gain that competitive edge. And, remember, you can always consult with a trusted distributor or filler metal manufacturer to help you determine the best choice for you and your company.