Alloy tubes are tubular and contain a higher percentage of alloying elements such as molybdenum (Mo), chromium (Cr), nickel, etc. than standard carbon steel tubes. Alloy steel tubes are used in the energy industry for high and very low temperature service (cryogenic), or for very high pressure applications.
Alloy steel tubes are suitable for butt-weld fittings and forged fittings and flanges. All these materials have similar chemical and mechanical properties and can be joined or welded.

Alloy steel products offer much higher performance than carbon steel products. Although they cost less than stainless steel grades, they have much lower corrosion resistance than stainless steel, but higher than carbon steel pipe.
Alloy steel pipe is used for applications requiring moderate corrosion resistance, good durability and economical cost. Simply put, alloy pipe is preferred in those areas where carbon steel pipe may fail. There are two types of alloy steel - high-alloy steel and low-alloy steel. Low-alloy steel constitutes pipe with an alloy content of less than 5%. High-alloy steels, on the other hand, have an alloy content between 5 percent and about 50 percent. Similar to most alloys, seamless alloy steel pipe has a working pressure capacity about 20 percent higher than welded pipe. Therefore, in applications where higher working pressures are a prerequisite, it makes sense to use seamless pipe. Although stronger than welded pipe, the cost is much higher. In addition, welded products have a greater risk of intergranular corrosion in the heat affected weld zone. The obvious difference between alloy steel welded pipe and seamless products is the transverse weld seam along the length of the pipe. However, today, with advances in technology, the seams present on alloy steel ERW pipe can be greatly reduced by surface treatment, making them invisible to the human eye.

The addition of molybdenum ("Moly") increases the strength of the steel and its elastic limit, enhances the wear resistance, impact quality and hardenability of the steel. It also improves resistance to softening, making chromium steels less brittle and preventing pitting.
Chromium is also a key element in stainless steel alloys, preventing oxidation at high temperatures and improving the corrosion resistance of steel. It improves the tensile, yield and hardness properties of low-alloy pipes at room temperature.
Other alloying elements that are present in varying degrees in all grades of pipe are
Aluminum: to reduce oxygen in the steelmaking process
Boron: Used to produce fine grains and increase the hardness of the steel
Cobalt: used to enhance the heat and wear resistance of steel
Manganese: to improve the hardenability of steel
Nickel: to improve toughness, hardenability and impact strength at low temperatures
Silicon: to reduce oxygen and improve hardenability and toughness
Titanium: prevents chromium carbide precipitation
Tungsten: Refines the grain size and increases the hardness of the steel, especially at high temperatures
Vanadium: gives the steel enhanced fatigue resistance
Low-alloyed steels have less than 5% total alloying elements; high-alloyed steels have a higher percentage of these elements.