If you are ever in the market for a high-grade pipe, you cannot do better than a seamless pipe. Even compared to other variants like ERW and LSAW, seamless pipes are a class apart. These products are built to last and are almost impervious to corrosion, erosion, or performance failure.
What Makes Them So Durable
Usually, in manufacturing welded pipes like SSAW or ERW, two extremities of steel coils or plates are fused electrically to produce a uniform-looking product. This quality makes their sizing more flexible and thus better suited for projects that require pipes with larger diameters.
Modern welding techniques like HFI make ERW pipes a worthy alternative to seamless pipes. But despite this, the latter is still the more durable product, owing to its pronounced lack of a welded area. This area joining two steel pieces is usually the most vulnerable to rust, corrosion, and leakage.
Seamless pipes avoid these pitfalls because they are made entirely from steel billets. These blocks of metals are heated and perforated to create a round hollow section that is uniform throughout. This uniformity ensures no vulnerable areas on the pipe, making them stronger than welded pipes.
ASTM Specification For Seamless Pipes
Seamless pipes mostly use ASTM A519 specification for manufacturing, as it is the usual standard for seamless carbon and alloy steel mechanical tubing.
- A crucial requirement of this specification is that it validates any form of production, granted that the pipe is seamless.
- Another essential factor is the inclusion of hot-rolled and cold-rolled tubing up to sizes 12-3/4 inches within the A519 specification.
In addition, this standard also includes specifications like:
- The steel in the mechanical tubing may be cast as ingots or strands.
- According to this standard, the pipes/tubes can be either round, square, rectangle, or a special furnished shape.
- The percentage of elements present must be specified via a heat analysis.
- In case of any welding, the process must follow the appropriate directions for the grade, the component condition, and the intended service.
- If secondary melting occurs, each element's heat analysis must be provided.
- The tubing must be covered before being shaped to stop the effects of dust.
Types Of Seamless Pipes
Following these requirements for carbon and alloy steel mechanical tubing and the complimentary specifications like ASTM A513, the resultant seamless pipe can get segregated into three broad categories. These following divisions are made based on the production and the resultant variety of products.
Hot Rolled Pipes
Hot rolled carbon and alloy steel making follow many of the ASTM A513 specifications for the production process. However, even with these set standards, applying huge amounts of heat is the characteristic step in hot rolled pipe production. Without meeting this criterion, a product cannot be termed "hot rolled."
Applying the correct heat to the steel billets is the defining step when making hot-rolled seamless pipes. The main difference between hot-rolled and cold-rolled pipes is that the former is carried out at the recrystallization temperature while the latter takes place at room temperature.
The recommended temperature for manufacturing hot rolled seamless steel pipes is 1000 degrees Fahrenheit, which is the range at which recrystallization occurs. If by any chance, the heat drops below 1000 degrees Fahrenheit, hot rolled pipe production will be halted, and the billet will have to get reheated to resume the process.
In addition, this heat must get increased by another 190 degrees Fahrenheit during the latter stages of the production to test the safety factor of the hot-rolled pipe.
Steel, like most metals, is naturally more malleable at higher temperatures, and this increased heat further improves the malleability of the pipe.
It is easier to shape the carbon and alloy steel at the recrystallization temperature, as they can be expanded in size or changed to a different shape with minimal ease. As a result, hot-rolled pipes tend to be bigger than cold-rolled pipes, with the average diameter being over 38 mm.
Advantages Of Hot Rolled Seamless Pipes
As a seamless steel product, hot rolled pipes do not have a welded area and are therefore less susceptible to corrosion or product failure. In addition, this pipe also passes through extremely high temperatures during the production process. This exposure to temperatures of 1000 degrees Fahrenheit provides hot rolled seamless pipes with several advantages, including:
- Exposure to high temperatures helps improve the strength of hot-rolled pipes. In addition, producers, to check the safety factor of the product, increase the heat well beyond the recrystallization range. A test like this lets you see what conditions a hot-rolled pipe can withstand and increases the product's overall durability.
- High temperatures make molding the carbon steel billets and ingots easier. Since the recrystallization temperature of these alloys is extremely high, the hot-rolled steel can be deftly shaped and expanded. This malleability is why the diameter of the average hot-rolled pipe is larger than that of cold-rolled pipes.
- Hot-rolled pipes are more malleable than cold-rolled products, allowing developers to experiment with their thickness and diameter.
- Despite being extremely robust and versatile, hot-rolled pipes are cheaper than cold-rolled products, making them more accessible to the public.
Uses Of Hot Rolled Pipes
Along with being more affordable than cold-rolled pipes, hot-rolled products also have a wide range of uses that include:
- Used for producing metal furniture like racks, displays, stands, lounges, and more
- Used in office goods like chairs, tables, desks, etc
- The automobile industry uses exhaust pipe material, seating frameworks, bus/train structures, and more.
- Common as guard rails for streets and highways
- Used to transport crude/refined oil and gas
Disadvantages Of Hot Rolled Pipes
Hot-rolled seamless pipes are not without their fair share of disadvantages. In this case, the same qualities make them, so users often end up acting as a hindrance. For example:
- The same heat that adds such durability to the hot-rolled seamless pipe also plays spoilsport in its shape. When the pipes begin to cool down, they do so erratically, without maintaining a uniform size or shape. The result is a product that may be irregular in its proportions and even have some residual stresses due to the uneven cooling.
- Soon after the production process, a flaxy film caused by the high temperatures covers the surface of the pipe. Also called mill scales, or scales, they are a collection of several iron oxides on the surface of the hot-rolled tube. Though they do not much affect the product quality, you still have to pass the pipe through a pickling/cold-drawn method to eliminate these scales. This extra step adds an unnecessary burden on your time and cost.
- The production of hot-rolled pipes characteristically involves exposure to tremendous amounts of heat. Be it an oil-fired soaking pit or an induction heater, this process uses a lot of fuel and energy, which may not be the case with cold-rolled pipe production.