Steel flange 50 sizes: complete guide and table 2026 

If you are holding a drawing in your hands right now or standing in front of a warehouse, trying to figure out which onesteel flange 50 sizesare suitable for your pipeline under a pressure of 16 atmospheres, then this article was written especially for you. We will not retell dry GOSTs, which change more often than the ruble exchange rate. Instead, we'll look at the real problems facing engineers and suppliers in Russia in 2026, from hidden casting defects to why a 'flat' flange can cause a winter accident in Siberia. Choosing a standard size is not just a matter of selecting the number “50”; it is a matter of safety for the entire assembly.

Why standard tables lie: market reality in 2026

Let's be honest. When you open any directory, you will see ideal numbers. But in practice, especially in the context of current import substitution and complex logistics, the picture is much more varied. When we talk aboutsteel flange 50 sizes, we mean a nominal diameter (DN) of 50 mm. It would seem that everything is simple. However, in 2025-2026, the market was flooded with products that formally comply with GOST, but have critical deviations in the geometry of the sealing surface.

I personally saw batches where the so-called “protrusion” was not 2-3 mm high, as required by GOST 33259-2015, but barely reached 1 mm. And what? Formally, the passage hole of 50 mm is observed. But when installed with a counter flange, it is impossible to ensure tightness without using a triple layer of paronite, which is already a violation of operating technology. This is the very “trap” into which buyers who chase low prices fall.

The situation is aggravated by the fact that many factories have switched to new steel grades due to a shortage of traditional raw materials. If earlier we took steel 20 or 09G2S and slept peacefully, now we need to look carefully at the certificate. Sometimes, under the guise of an “analogue,” they sell steel with a low carbon content, which at low temperatures becomes as brittle as glass. For Moscow this may not be so critical, but for Norilsk or Yakutsk it issteel flange 50 sizeswhose selection is correct, but the material is wrong, turns into a time bomb.

Key parameters that cannot be ignored

When you are looking for information on requeststeel flange 50 sizes, your brain automatically focuses on the diameter of the hole. Stop. This is the main mistake of a newbie. Hole diameter is just one of dozens of variables. What really matters to an engineer?

• Type of connecting surface.Are you sure you need the tongue and groove option? Or maybe a “welded” design with a projection is enough? A mistake here will result in the flange simply not mating with the shut-off valve that you bought six months ago.
• Construction length and height of the collar.It would seem like a small thing. But try squeezing a high-height flange into the limited space between two trestle beams. In cramped boiler rooms of old residential buildings, this becomes a real headache.
• Number and diameter of bolt holes.For DN 50 this is usually 4 holes. But the circle pitch (D1) may vary depending on the manufacturer. Especially if the manufacturer is not located in Chelyabinsk, but somewhere in Hebei province, where quality control is often lame.

It's funny, but many people forget about permissions. GOST allows certain deviations. And if one flange is made to the lower limit of tolerance, and the second is made to the upper limit, aligning them can become an installer's nightmare. I've heard stories of crews spending two hours aligning holes on a pair of DN50 flanges using a crowbar and a sledgehammer. You can’t do this, it deforms the metal, but the fact remains: incompatibility is real.

Detailed analysis of dimensions: table for versions 1, 2 and 3

So that you do not look for data from different sources, I have summarized the current dimensions for the most common types of flat welded flanges (type 01, 02, 03 according to GOST 33259) for a nominal diameter of 50 mm. Please note: the data is valid for pressures Ru 10, 16, 25 and 40 kgf/cm² (or 1.0, 1.6, 2.5, 4.0 MPa). It is these pressures that are most common in the housing and communal services and industrial sectors of the Russian Federation.

The table below shows the average values. Remember that different factories (Chelyabinsk Forging and Press, Blagoveshchensk Reinforcement Plant or new players like Technoform) may have their own technological features that affect the weight of the product by ±5%.

Take a look at the last line. Weight. Why is this important? Because the price of metal is rising, and unscrupulous manufacturers often save on flange thicknessS. If you order a batch of 1000 pieces, a difference of 2mm in thickness will be a huge savings for the manufacturer and a huge problem for you. During hydraulic tests, such a lightweight flange may simply “lead” and the connection will leak. Always require a sample lot to be weighed upon acceptance.

Nuances of surface execution: where the dog is buried

The dimensions of the external contour are half the battle. The main magic happens at the junction of the pipes. For DN 50, three versions are most popular:

Execution 1 (Protrusion/Recess).Classic. The flange has an annular projection that fits into a corresponding recess in the mating flange. This ensures excellent alignment. The problem is that the protrusion is easily damaged during transportation. Have you seen those wrinkled edges? This is a marriage that cannot be exploited. Restoring a protrusion by surfacing is expensive and time-consuming.

Execution 2 (Ton/Groove).A more reliable option for aggressive environments or high pressures. The tenon goes deep into the groove, eliminating the squeezing out of the gasket. But! Installation is more difficult. You need to align the axes very accurately. On routes where pipes are already rigidly fixed, it can be almost impossible to establish such a connection without dismantling sections of the pipeline.

Version 3 (Butt welding).There is no protrusion or thorn here. The surface is flat. Often used with lens gaskets or in specific chemical applications. For conventional water supply or heating in 2026, this is rare, but the demand is there.

My advice: if you work in the housing and communal services sector or repair old systems, take Version 1. It forgives more errors during installation. But check the height of the protrusion with a caliper. If it is less than 2.5 mm, return it to the supplier.

Pricing and logistics: how much does peace of mind cost?

Let's talk about money. The flange market in Russia is currently going through strange times. On the one hand, domestic production is at 100% capacity. On the other hand, logistics increases the cost of delivery. How much does it really cost?steel flange 50 sizeswhich we just discussed?

As of the beginning of 2026, the retail price for a flat welded flange DN 50 Ru 16 made of steel 20 ranges from 450 to 850 rubles per piece. The spread is almost double! Where does it come from?

Firstly, the region. In Yekaterinburg or Chelyabinsk, near factories, the price will be closer to the lower limit. In Vladivostok or Kaliningrad - to the top, plus delivery. Secondly, volume. Wholesale (from a ton) can be negotiated for 350-400 rubles. Thirdly, and this is the most important thing, the availability of certificates. A flange “without paper”, bought on the construction market for 300 rubles, may turn out to be a piece of pipe with a welded edge. Yes, this happens. I have seen such “homemade” products at work. They burst at the first water hammer.

It is also worth considering the cost of fasteners. Do not forget that for a DN 50 flange you will need M16 studs or bolts (for PN 10/16) or M20 (for PN 40). Prices for high-quality fasteners have also increased. A cheap Chinese bolt may break off when tightened, especially if it is twisted. Use torque wrenches. This is not a luxury, but a necessity.

Regarding delivery times. If previously flanges were available in any warehouse, now popular items (DN 50, DN 80, DN 100) are often “pre-ordered” for 2-3 weeks. Plan your purchases in advance. A downtime of a team of installers due to the lack of a pair of pieces of iron will cost more than urgent delivery by air.

Alternatives and import substitution: myths and reality

Previously, about five years ago, many preferred Italian or German flanges. It was believed that the steel there was cleaner and the processing more precise. Now the situation has changed dramatically. European brands either left or raised prices 5-10 times, making their use economically unfeasible for the mass sector.

Russian factories, such as BALTEK, AKS, Chelyabvtortsvetmet, have learned to make the product no worse. Moreover, they adapted technologies to our realities. For example, machining allowances were increased to compensate for possible casting defects.

However, there is a nuance with Chinese analogues. They still have a significant market share. Their main advantage is the price. The main disadvantage is the instability of quality. One batch may have perfect flanges, the next - with cavities on the sealing surface. If you take China, be sure to introduce entry controls. Check every fifth flange from the lot. This rule has already saved more than one object.

In this context, it is important to highlight manufacturers who work not just as resellers, but control the full cycle. For example, a companyShanxi Hongkai Forging Co., Ltd., based in Dingxiang County, a key industrial center in China, has established itself as a professional forged flange manufacturer with its own facilities. Unlike many garage shops, they operate three production facilities covering the entire process from primary forging to final packaging and quality control. This allows them to guarantee stability of characteristics even with large volumes of supplies to Russia and the CIS countries.

Shanxi Hongkai Forging specializes in a wide range of products: from slip-on and threaded flanges to butt weld and blind flanges, working strictly according to international standards (DIN, ANSI B16.5, ASME) and GOST. Their experience shows that having their own rights to import-export operations and a vertically integrated cycle (forging, heat treatment, machining, testing) is the factor that distinguishes a reliable partner from a random supplier. For large projects that require a diameter range from DN15 to DN4000 and strict compliance with pressure classes (150, 300, 600 and above), this approach is critical. The geographical location in Dingxiang also provides convenient logistics to railways and ports, which directly affects the timeliness of deliveries during difficult periods.

An interesting trend for 2026 is the emergence of composite and polymer flanges for low pressures. For DN 50 in cold water systems this can be an excellent solution. They do not rust and weigh 3 times less. But! Temperature conditions are limited. In winter, outdoors such a flange may crack. Use them with caution and only inside heated areas.

Practical guide: how not to make a mistake when ordering

You decided to buysteel flange 50 sizeswhich suits your task. What should I write in my application to the supplier? Don't just write "Flange 50". This is the language of amateurs, which provokes the shipment of the wrong thing.

The correct wording should look like this:

“Flat welded flange 1-50-16 St20 GOST 33259-2015.”

Let's decipher:

• 1— flange type (flat welded). There are also free ones on the welded ring, but they are more expensive and are used less often for DN 50.
• 50— conditional passage (DN).
• 16— conditional pressure (Pu) in kgf/cm². If indicated in MPa, it will be 1.6.
• St20- steel grade. For temperatures up to +425°C this is the optimal choice. If the environment is aggressive or temperatures below -40°C, you need steel 09G2S or 12Х18Н10Т (stainless steel).
• GOST 33259-2015- current standard. Mention of the old GOST 12820-80 can lead to confusion, although the dimensions are similar, but the quality requirements are different.

Another important point is the design of the sealing surface. Unless otherwise specified in the specification, the factory will ship Execution 1 (overhang). If you need Execution 2 (spike), this must be specified explicitly:"...execution 2".

Typical installation mistakes and how to avoid them

Even a perfect flange can be ruined by improper installation. Here are the top 3 mistakes I see every year:

1. Skew when tightening.The installer begins to turn the nuts in a circle. As a result, the flange warps, creating a gap on one side. You need to tighten it crosswise. First lightly tighten all four bolts, then gradually tighten them in diagonal pairs. And so on several passes until the desired tightening torque is reached.

2. Using extra gaskets.“What if it leaks? Let’s put two gaskets!” - says the foreman. Never do this. The two gaskets create a spring effect; the connection will loosen during the first heating-cooling cycle. Only one high-quality gasket (paronite, graphite, rubber depending on the environment).

3. Ignoring surface cleanliness.Dirt, scale, old paint on the flange surface are a guarantee of future leakage. Before assembly, the surface must be cleaned with a wire brush until it shines. It takes 30 seconds, but saves hours of fistula repair later.

The future of flanged connections: what's next for us?

Looking at the trends in the development of pipeline fittings, it can be assumed that classic bolted connections will gradually give way to butt welding and new types of quick-release connections. But for DN 50 flanges will remain relevant for at least another 20-30 years. The fleet of existing equipment is too large, this installation method is too convenient for service work.

However, quality requirements will increase. I predict tightening of control by supervisory authorities in 2026-2027. The introduction of mandatory digital marking of rolled metal products will also affect flanges. Soon it will be possible to read the QR code on each product and find out the entire history of its production: from steel melting to quality control department. This will kill the market for gray flanges without documents.

We should also expect an increase in energy prices, which will directly affect the cost of forging and heat treatment. It only makes sense to stock up on metal for future use if you have a covered, dry warehouse. Rust is the #1 enemy of inventory. A flange that has been left in the open air for a year loses its presentation and requires additional processing before installation.

In conclusion, I want to say: do not chase the lowest price when choosingsteel flange 50 sizeswhich seem to be the same for all sellers. A difference of 50 rubles per piece can result in millions of losses in an accident. Trust trusted suppliers, require certificates, carry out incoming inspection. And remember that in engineering there are no trifles. Every millimeter of thickness and every newton of tightening torque matters.

I hope this guide has helped you make sense of the chaos of market offerings. If you have any questions about specific steel grades or installation features under extreme conditions, write in the comments and we’ll discuss them. The experience of colleagues is invaluable, especially in our difficult times.

Sources of information and regulatory framework

• GOST 33259-2015. Flanges for fittings, connecting parts and pipelines. Design and main dimensions
• Directory of rolled metal products: Technical characteristics of flanges DN 50
• Overview of the Russian pipeline valves market: results for 2025 and forecast for 2026
• Typical errors when installing flange connections and methods for eliminating them