In the following article, we will learn about three types of pipes used in the oil, gas and petrochemical industries: seamless pipes, ERW pipes or electrical resistance welding, LSAW.
Seamless pipe is a pipe that is created by stretching and creating a hole in the middle of a metal billet, and seamed pipes are created by cutting the billet and welding the sheet.
Types of pipes used in industries
Seamless pipes
To produce seamless pipes, metal billets are heated and shaped so that they become tubular in cross-section, and then by creating a hole inside them, it becomes a tube without any seams or welds on it. Does not exist. The word “seamless” means the absence of any seam or welding line.
Application of seamless pipes
Seamless pipes have various uses in oil and gas industries:
- Drilling pipes, casing and tubing
- Pipes for transporting liquids such as oil and gas, acids and steam
- Pipes used for oil and gas refining and related products
- Pipes with utilities
The most common pipes used in the oil and gas industry
- All kinds of carbon steel pipes for high and low pressure applications with standard (ASTM A53, A106, A333 & API 5L)
- Pipes with MOLY-CHROME ASTM A335 GRADE P5 TO P91 financial alloy, which are used for high pressure and high temperature cases in refineries and power plants.
- Stainless steel pipes (ASTM A312 304, 316, 321, 347)
- Duplex or super duplex pipes (ASTM A790/A928)
- All kinds of nickel alloys (Inconel, HASTELLOY, Monel, Nickel 200, …)
- Non-ferrous pipes (aluminum, copper, brass, …)
Specific and common specifications of seamless and seamed pipes
Some characteristics are only used for seamless pipes, such as ASTM A106, but some are used for both seamless and seamed pipes. Such as: ASTM A53
Carbon steel pipes (A53, A333, A106, API 5L) have the largest consumer market because they can be used for most high and low temperature applications.
The main use of stainless steel pipes is in industries that have high corrosiveness or very high temperature and pressure.
The difference between seamless pipe and seamless tube
Seamless pipes should not be confused with seamless tubes, there are several differences between the two. A pipe is a cylindrical object in which fluids flow inside, while a tube is a cylindrical section that can have different shapes such as round, oval and square and can be used as structural/mechanical structures, systems instruments and structures under pressure such as boilers and super heaters.
Pipe pricing
Seamless pipes are usually 20 to 30% more expensive than seamed pipes due to their complex production method and the limited number of producers of this type of pipe. In the case of pipes with more specific sizes and specifications, such as 20-inch pipes and above, or special materials such as A335 p91, since the manufacturers and supply are very limited, their prices are relatively higher.
Considering this point, there cannot be the same method for pricing all carbon steel or stainless steel pipes according to their thickness and inner diameter, because all the above items must be taken into account to determine the price of the pipe, so that the cost estimation of the projects becomes difficult. don’t turn Apart from the above, price changes should be considered, especially in the case of alloy pipes that have chemical elements such as mobidium, chromium, copper, and nickel.
Dimensions and weight standards of petrochemical industry pipes
ASME B36.10 & B36.19 standards are about the dimensions and weight of pipes used in petrochemical industries.
The ASME B36.10 standard is about the weight and dimensions of all carbon steel and alloy pipes from sizes 1.8 to 24 inches.
The ASME B36.19 standard is about stainless steel, duplex and nickel alloy seamless pipes.
Seamless pipes are specified with standard sizes that are based on the approximate amount of fluid that flows inside them and the grade that is the same as the thickness of the pipe.
Direct weld or hidden seam pipes (ERW)
ERW pipes are produced using coils in such a way that at first the coils are opened, straightened, cut, finally it becomes a tube shape and their edges are connected through electric welding. You can also read the spiral tube article.
ERW pipes are available in sizes from 1.2 to 20 inches. The most common standard for carbon steel pipes is ASME A53 and the most common standard for stainless steel pipes is A312.
In recent years, due to technological progress in the field of welding, ERW pipes have become a suitable alternative for seamless pipes in terms of price and performance. Over the years, these new welding techniques have eroded the superiority of seamless pipes over ERW pipes and have made it possible to replace seamless pipes in at least some cases. Of course, seamless pipes are still superior to ERW due to their high resistance.
Production steps of ERW pipe
As mentioned earlier, ERW pipes are produced using coils, so that at first the coils are made, straightened, and cut, and finally they become the shape of the pipe, and their edges are connected through electric welding. These steps can be seen in the image below:
The most common type of welding in the pipes of the oil and gas industry is the “high frequency induction process” (ERW-HFI), which means high induction pressure on the outer surface of the pipe that welds the two ends of the coil completely and accurately.
LSAW Pipes (Direct Welded Butt Weld)
Steel pipes are produced by cutting, bending and welding steel sheets.
LSAW pipes compete with seamless and ERW pipes in sizes between 16 and 24 inches and dominate in sizes 24 inches and above. There are two types of LSAW pipes depending on the type of weld seam. The straight seam pipe that is formed is one or two straight welding lines and the spiral seam pipe.
The difference between LSAW and DASW pipes is that in DSAW pipes, welding is done inside and outside the pipe at the seam, but in LSAW pipes, welding is done only on the outside of the pipe.
The difference between LSAW and ERW pipes is that LSAW pipes are produced using steel sheets, but ERW pipes are produced using steel coils.
Production steps of LSAW pipe
The production of LSAW pipe starts with a sheet. These steps are as follows:
The question of whether to use seamed or seamless pipes for a project is a question that is asked more today than in the past. Both of these tubes have positive and negative points that should be considered when using them.
Pros and cons of seamless pipes
Seamless pipes are made from a steel billet and do not have any type of welding seam that creates a weak point and is susceptible to rust and corrosion.
Seamless pipes have more predictable and precise shapes.
The biggest weakness of seamless pipes is their high price compared to the size and grade of the welded pipes.
Since the manufacturers of seamless pipes are more limited, the production and delivery time of these pipes is relatively longer.
The thickness of the walls of the seamless pipe may vary along the length of the pipe. In these pipes, the acceptable tolerance for the wall thickness is +-12%.
Advantages and disadvantages of seamed pipe
- The price of seamed pipes is lower than that of seamless pipes.
- The thickness of the wall of the seamed pipes is almost the same throughout the length of the pipe because these pipes are produced from steel sheets or coils.
- The biggest weakness of seamed pipes is the existence of a welding seam, which creates a weak point along the length of the pipe. This point may have had a greater impact in the past years, but with the advancement of technology and the emergence of new welding technologies, this problem has also decreased compared to the past.
- In the end, it can be concluded that new seamed pipes using new welding technologies can compete with seamless pipes, and by using these types of pipes, you can save between 20 and 25% in costs.
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