Hot-worked seamless pipes for PUF
Seamless pipes, as the term implies, are manufactured without welding seams. The absence of joints enables them to be used at higher pressures of the transported medium.
For example, in critical high-pressure heating networks or when technical liquids and gases are transported instead of water. However, for most regular heating networks using electric-welded pipes is sufficient.
In contrast with electric-welded pipes, seamless pipes are divided in just two categories: hot-rolled and cold-formed.
All you need to know about cold-formed pipes: specified under GOST 8733/8734, very expensive, however, include small diameters, thin and intermediate-size walls (as opposed to hot-rolled).
Hot-worked pipes, GOST 8732/8731
Hot-worked or, as they are sometimes called, hot-rolled pipes, are essentially general application seamless pipes. Similar to electric-welded pipes, they are manufactured according to a schedule and specifications drawn up as a GOST standard.
Their major difference from electric-welded pipes consists in the manufacturing method and limited range of potential suppliers.
Pipes are categorized depending on diameter, wall thickness and length. GOST 8232 advises steelworkers to produce items 4 to 12 meters long. Generally, we work with 8 to 12 m pipes, and the average length is assumed to be 10.5.
In terms of the outside diameter, common items are exactly the same as with welded pipes: 57, 76, 89, 108, 133, 159, 219, 273, 325, 377, 426, however, in this case 530 mm is the last size.
Hot-rolled features
The first feature is a limited selection of diameters and wall thicknesses, especially small, thin and intermediate ones.
The second feature is that large diameters do not allow intermediate and thin walls due to the manufacturing technology.
Below is the list of most commonly used wall thicknesses:
32, 38, 45, 57, 76 – 3,5 мм;
89, 108 – 4,0 mm;
133 – 4,0 и 4,5 mm;
159 – 5,0 и 6,0 mm.
219 – 8,0 mm;
273 – 7,0 и 8,0 mm;
325 – 9,0 mm;
426 – exclusively 9.0 mm or higher;
530 – 25 mm or higher.
The third feature is the steel grade: either 20 or 09г2с.
The fourth feature is the variation in pipe length, which, in contrast with electric-welded pipes, amounts to as much as 4 meters, as opposed to 0.4 m. As a result, at the time of ordering a pipe, we cannot prepare a shell of appropriate length in advance, or use a ready shell from stock. We have to wait for the pipes to arrive at the warehouse, then measure each pipe and produce a shell of individual length for each. Hence, the lead time for seamless orders is longer than that for electric-welded pipes.
The fifth and the most annoying feature is the variation in wall thickness, again due to the manufacturing technology, which we cannot do anything about.
See for yourself
Steelworkers ship pipes in tons, not in meters. Let’s say, we receive an order for 219х8.0 mm pipe insulation. To order the pipes, we need to convert meters into tons.
Theoretically, one meter of the 219х8.0 pipe weighs 41.63 kg. Hence, we need to order 18,735.5 kg to receive 450 meters of pipe (theoretical weight of one linear meter multiplied by the total length, i.e. 41.63x450).
Say, we have re-checked the calculation, made the payment and picked up exactly 18,735.5 kg of 219х8.0 pipe. However, having measured the pipes, we find that we have only 400 meters instead of 450.
Where have we made a mistake?
We have not taken into account the wall thickness variation of the 219х8.0 mm pipe, which is as high as +12.5%, i.e. as much as one millimeter! Thus, a meter of the pipe now weights 46.61 kg instead of 41.63 kg.
The total weight of the ordered and delivered pipe, 18,733.5 kg, divided by the linear meter weight of 46.61 kg, gives us exactly 400 meters instead of the expected 450.
The steelworkers have met their obligations; we ordered 18.7 ton, and they have shipped exactly this amount. In the certificates, the pipe is sized 219х8.0, while the actual size is 219х9.0, and this complies with GOST. Now we have to order an additional 50 meters.
On the other hand, if we decide to be on the safe side and calculate the ordered weight taking the variation into account, we may find ourselves with an extra 50 meters that have to be laid aside.
SAVERHOT is an official dealer of major Russian steel plants, so we always keep between 2,500 and 4,000 tons of pipes in stock at our warehouse. We continuously replenish our stock with commonly used items. The data on availability are always relevant as they are updated from the ERP system in real time.
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