flanges 65 mm

When they say “65 mm flanges?”, many people immediately imagine a standard, almost common size. But in practice, there are so many nuances and pitfalls associated with this conditional DN65 that it makes your head spin. A common mistake is to assume that since the diameter is small, there won’t be any problems with it. In fact, it is precisely in such seemingly simple positions that the main difficulties with the selection of material, pressure and, most importantly, with the quality of the forging itself lie.

Why DN65 is a different story

Let's take, for example, standard flanges according to GOST 33259. For DN65, the nominal pressure is a whole range: RU6, RU10, RU16, RU25, RU40. And this is where the fun begins. Flange geometry, thickness, diameters of holes for studs - everything changes depending on the pressure. An inexperienced buyer can easily get confused, especially if the specification simply states “65 mm flange”. And then during installation it turns out that the holes do not match or the thickness is not enough.

I personally came across a situation where 65 mm flanges on RU16 were required for repairs at one of the facilities. They brought the batch, everything seemed to be in accordance with GOST. But during pressure testing they began to leak along the sealing plane. The reason turned out to be microcracks in the material - a consequence of poor-quality forging. The workpiece was apparently overheated and then cooled incorrectly. It was a lesson: size is only half the battle. It is the manufacturing technology that is critically important.

That is why I now always look not just at certificates, but at the reputation of the manufacturer. For example, the Chinese company Shanxi Hongkai Forging LLC. (their website ishttps://www.hkflange.ru). They position themselves as a manufacturer of forged flanges in one of the main forging centers in China. What is important is that they work in accordance with GOST, ASME, EN. For DN65 this is fundamental: if a factory can make it to different standards, it means they have a clear understanding of the differences in geometry and tolerances.

Material: from St20 to 12Х18Н10Т

We sorted out the size, but then the question of material arises. For 65 mm flanges, carbon steel St20 for non-aggressive environments, alloy steel 09G2S for low temperatures, and stainless steel type 12Х18Н10Т for chemistry can be used. An error in the choice of material is a guaranteed emergency failure of the unit in the future.

I remember a project where the technical specifications required flanges made of 09G2S steel. The customer saved money and took cheaper ones from St3sp. The system worked outside; in winter the temperature dropped to -30. As a result, the cold brittleness of the material made itself felt - cracks appeared in the transition zone from the collar to the disk. I had to urgently change the entire batch.

On the websiteShanxi Hongkai Forging Co.,Ltdit is clear that they focus on meeting international standards. This is a good sign. For sizes such as 65 mm, it is important that the chemical composition of the material and mechanical properties are not “approximate”, but strictly according to the regulations. This is especially true for impact strength at low temperatures for steels of type 09G2S - a parameter that is often checked only according to the passport, but in reality it can “float”.

Flange type: butt weld, flat, loose

For DN65 all main types are used: butt welded (GOST 33259), flat welded (GOST 33260), free on a welded ring (GOST 33261). The choice depends on the installation and operating conditions. Loose flanges, for example, are good for hard-to-reach areas where bolt holes need to be precisely aligned. But their cost is higher, and you need to order a set at once - a flange and a ring.

I had an incident with a 65 mm flat welded flange. It was placed on a pipeline with frequent thermal cycles (heating and cooling). Due to the rigid connection and the difference in the coefficients of thermal expansion of the pipes and the flange, cracks appeared in the welding zone. We converted it to a butt weld flange and the problem disappeared. It has a smoother transition and better stress distribution.

Manufacturer who makes a wide range including all these types likeShanxi Hongkai Forging Co.,Ltd, usually has more experience and can give competent advice. Their website indicates a range right up to DN4000, but this just means that for small sizes they most likely have streamlined and accurate production. It's the little things that are most often defective at non-core factories.

Quality control and real tests

How to check the quality of a 65mm flange? Dimensions using a caliper, holes using a plug gauge. But the most important thing is a visual inspection of the surface, especially in the area of ​​the collar and chamfer for welding. There should be no shells, sunsets, or sharp transitions. The color of the tarnish after heat treatment should be uniform.

Once we received a batch where on several flanges65 mmthere was a barely noticeable little mark - a mark from the mold, indicating possible internal tension. The sample was sent for ultrasound testing. The flaw detector showed discontinuity of the metal. The manufacturer, of course, replaced it, but time was lost. Since then, for critical objects I have insisted on selective ultrasonic testing or even Brinell hardness testing.

In the description of the company ?Shanxi Hongkai Forging Co.,Ltd. It is said about manufacturing according to customer drawings. This is an important point. Sometimes standard DN65 requires non-standard holes or an unusual grade of steel. The possibility of such an order indicates the flexibility of production and the presence of our own design bureau, which for me, as a practitioner, is a big plus.

Bottom line: what to look for when ordering

So, let's draw a line under this size.Flanges 65 mm— this is not just a consumable. This is a complete unit on which the tightness of the system depends. The first thing is to clearly define the standard, pressure and type. Secondly, do not skimp on the material, demand a certificate with specific numbers in chemistry and mechanics. The third is to select a supplier with a clear emphasis on forging technology rather than sheet metal stamping.

Sites likehkflange.ruare useful precisely because they make it clear about specialization. When you see that a company is a manufacturer of forged flanges and forgings, working in accordance with GOST, ASME, EN, this inspires more confidence than just a trading house with an extensive catalog. Because forging is about the solidity and reliability of the workpiece, which is critically important for a flange.

Overall, DN65 is a good test for a supplier. If he can make a high-quality flange for this size according to different standards and from different materials without problems and lengthy approvals, it means that his processes are streamlined. And this, ultimately, saves nerves and time on site. Everything else is just details that are resolved on a daily basis.