Pipes are for transporting hydrocarbons and other commodities, with associated safety systems, valves, tool launchers or receivers, manifolds, corrosion protection systems or other accessory equipments:
Duplex Pipe was originally developed in Sweden back in the 1940's. Duplex Pipes were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids. Called Duplex Pipe because of its mixed microstructure with about equal proportions of ferrite and austenite, duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The chemical composition based on high contents of Cr and Mo, improves inter-granular and pitting corrosion resistance, respectively.
Additions of nitrogen can promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels. The first-generation grades were alloys of chromium, nickel and molybdenum and while they provided good performance characteristics, welds had low toughness due to excessive ferrite, which limited the use of Duplex pipe steel to a few specific applications.
Monel is a series of nickel alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements. Compared to steel, Monel is very difficult to machine as it work-hardens very quickly. It needs to be turned and worked at slow speeds and low feed rates. It is resistant to corrosion and acids, and some alloys can withstand a fire in pure oxygen. It is commonly used in applications with highly corrosive conditions. Small additions of aluminum and titanium form an alloy (K-500) with the same corrosion resistance but with much greater strength due to gamma prime formation on aging. Monel is typically much more expensive than stainless steel.
Monel is used in the section of Alkylation units in direct contact with concentrated Hydrofluoric acid (HF). Monel drill collars are also used in surveying oil wells. Monel collars are used in drilling directional wells which require the well to be steered. Their use permits faster and more accurate surveys, reduce hazards, and decrease the cost of drilling directional or controlled oil wells. The reduced cost comes from the ability of real time surveys from a MWD (measurement while drilling) tool which has magnetometers built into them. The magnetometers if not surrounded by non-magnetic material (Monel, inconel, Cu-Be, or non-magnetic stainless) will be unable to read the earth's magnetic field without interference and will give an incorrect reading.
Inconel alloys are oxidation and corrosion-resistant materials well suited for service in extreme environments subjected to high pressure and kinetic energy. When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where aluminum and steel would succumb to creep as a result of thermally-induced crystal vacancies.
Inconel's high temperature strength is developed by solid solution strengthening or precipitation strengthening, depending on the alloy. In age hardening or precipitation strengthening varieties, small amounts of niobium combine with nickel to form the intermetallic compound Ni3Nb or gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures. The formation of gamma prime crystals increases over time, especially after three hours of a heat exposure of 850oC, and continues to grow after 72 hours of exposure.
Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low-oxygen, high-salinity, or poor-circulation environments. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.
Seamless stainless steel piping, or seamless steel pipe, is formed by drawing a heated solid billet, or cylindrical bar of steel, over a piercing rod to create a hollow shell. Rollers are then used to produce the proper diameter and wall thickness. This type of stainless steel piping can withstand pressure better than welded pipe because it does not have any seams to create weak spots. It is often used in the chemical and petroleum industries
Welded stainless steel piping is created by rolling a flat steel plate and welding the seam. After welding this seam, it can be removed from the outside or inside surface of a pipe using a scarf blade. The weld seam can also be heat treated to make the seam less visible. Welded pipe can be cheaper to manufacturer than seamless pipe. Welded stainless steel piping is used in a variety of applications that require corrosion resistance.
The first methods for producing steel pipe were introduced in the early 1800s, and they have steadily evolved into the modern processes we use today. Large diameter steel pressure pipes for water and wastewater applications are typically made with carbon steel and installed as buried assets. Steel pipe can be made using three main methods:
The primary benefit of steel pipe is its strength. These pipes don't crack under most impacts and can operate under high pressure. Under abnormal loads, steel will bend, rather than break.
There are several types of manufactured processes such as seamless pipe and welded pipe. It can be either stainless steel, carbon steel, duplex, Inconel, Monel or etc. For welded type, there are several welded pipe process but commonly used in pipeline system such as spiral submerged arc welded, longitudinal submerged arc welded, and electric resistance welding.
Seamless steel pipe (SMLS) is made from a solid round steel billet, which is heated and pushed or pulled over a piercing rod or form until the steel is shaped into a hollow tube. This steel pipe can be made in a variety of thickness from 0.375 to 4 inches. Seamless steel pipe is preferred for a variety of applications because it can withstand pressure better than other types of steel pipe and is easily available. Seamless steel pipe is available as new or secondary pipe. It is extremely versatile and is manufactured to meet a variety of structural and pressure applications.
Seamless steel pipe is most often used in the construction industry for structural or load-bearing purposes. This structural pipe is extremely durable and therefore it is also used in a variety of applications that require heavier wall thicknesses than are available in welded pipe. Seamless steel pipe can be used for a variety of types of applications.
Spiral welded pipe production by submerged arc method is based on using tandem welding technique for joining inside and outside coil edges, which have been trimmed and beveled by carbide milling for high quality weld structure.
Welding of hot rolled steel coils takes spiral form after passing through pre-forming and forming rolls. Excellent exterior weld quality at high production speeds is provided by double submerged arc welding process. Manufactured pipes are cut to the desired lengths at the exit of the pipe machine. Pipe ends are beveled by means of carbide machining for accurate on-site welding. Spiral welded steel pipes are widely used in Oil, Natural Gas, Water and other flammable & nonflammable liquid conveyance and distribution pipelines, steel structures for construction and other general purposes by means of their wide size range.
Electric resistance welding (ERW) refers to a group of welding processes such as spot and seam welding that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material combined with the time and the force used to hold the materials together during welding. Some factors influencing heat or welding temperatures are the proportions of the work pieces, the metal coating or the lack of coating, the electrode materials, electrode geometry, electrode pressing force, electrical current and length of welding time.
Small pools of molten metal are formed at the point of most electrical resistance (the connecting or "faying" surfaces) as an electrical current (100–100,000 A) is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are limited to relatively thin materials and the equipment cost can be high (although in production situations the cost per weld may be low)
Longitudinal edges of steel plates are first beveled using carbide milling equipment. Beveled plates are then formed into a U shape using a U-press and subsequently into an O shape using an O-press. Longitudinal edges of the plates are then tack welded followed by internal and external welds. Pipes manufactured by this process are subjected to expanding operation in order to relieve internal stresses and obtain a perfect dimensional tolerance.
Longitudinally welded steel pipes are used in onshore and offshore oil and gas pipelines requiring critical service, high performance and tight tolerances. LSAW pipe are also used in conveyance of flammable & nonflammable liquids, and as structural members in construction projects.