flange dismantling

When they talk aboutflange dismantling, many imagine a banal unscrewing of nuts. But in practice, this is often the most nerve-wracking part of the work, especially on old pipelines or after emergency situations. An error during disassembly can result in damaged seating surfaces, stripped threads, or worst of all, personal injury. The main misconception is that if the flange is new and from a trusted supplier, likeShanxi Hongkai Forging Co.,Ltd, then it will be easy to remove. The quality of the forging, of course, affects the service life of the connection, but not the process of its disassembly after years of operation.

Preparation is already half the dismantling

Before you take the impact wrench, you need to feel the connection with your eyes and hands. Old dirt, traces of many years of leaks, the degree of corrosion - all this tells you what you have to deal with. I always try to “stir up” first. connection manually, with a key using little force. If a flange, especially a large one, has sat “tightly”, it is better to immediately plan to warm it up or use special chemicals, rather than tearing the bolts.

Here it is important to understand exactly what product you are working with. For example, butt-welded flanges from the samemanufacturer of forged flangesfrom Shanxi, made according to GOST or ASME, after welding they create a very rigid assembly. It will be necessary to dismantle not just the bolted connection, but carefully cut off the flange itself if it is planned to replace the pipe section. And here you look at the steel grade and wall thickness.

The tool is a different story. Universal wrenches are often not suitable for nuts that have become stuck on over decades. You have to use special attachments, impact wrenches, but with an eye to the strength class of the bolts. To disrupt the edges means to complicate the work significantly.

Corrosion and “sticky” connections

The most common headache is when a bolt and nut turn into a monolith due to corrosion. Especially at sites with temperature changes or in aggressive environments. The standard approach is to apply a generous amount of penetrating lubricant a day before, or better yet, a few hours before work. But sometimes this doesn’t help either.

In such cases, controlled heating with a gas burner is used. It is important not to overheat the metal so as not to change its properties. For critical connections on high-pressure flanges, which are supplied byShanxi Hongkai Forging Co.,Ltd(they make products up to DN4000), heating requires special care. Sometimes it’s easier to carefully cut off the bolts with a grinder, but there is a risk of damaging the flange itself.

There was an incident at a chemical plant: they were dismantling old flanges on a line. After warming up, one bolt still burst, and a fragment damaged the sealing surface of the adjacent flange. I had to urgently look for a replacement. It’s good that the customer had them in stockforged flangesaccording to DIN from a reliable manufacturer - the situation was resolved quickly. This is to the question of why it is important to know where to buy a quality replacement.

Features of dismantling different types of flanges

Loose flanges (on a welded ring) - in theory, should be the easiest to remove. But in practice, the ring is often “welded?” to the pipe due to corrosion or scale. The main task here is to carefully separate the ring without bending it. Sometimes a wedge helps, sometimes a small hydraulic jack helps.

There is another problem with blind flanges (plugs) - they are often under residual pressure in the system. It would seem that the elementary rule is to relieve pressure, but in a hurry or due to inexperience it is violated. The result can be disastrous. Therefore, my ritual is to always check shut-off valves and pressure gauges, even if the system, according to the customer, is “deaf”.

Threaded connections are a separate hell. If the thread is torn off during installation or “licked?” corrosion,flange removalturns into a jewelry job of drilling out the remains. For such cases, the kit should always include left-handed drills and extractors. And again, if replacement is necessary, it is better to have a product on hand from a manufacturer that guarantees compliance with standards, be it EN, ASME or GOST. As, for example, in the catalogShanxi Hongkai Forging Co.,Ltd, where the range covers most standard sizes.

What happens after withdrawal

The most critical point that many people miss is inspecting the seating surfaces after disassembly. Risks, scratches, corrosion pits - all this needs to be cleaned out, otherwise the new connection will not be leak-tight, no matter how high-quality the new flange you install. I always use templates or at least a straight metal ruler held up to light to check.

Another nuance is the condition of the bolts and nuts. They are often changed all at once, and rightly so. But if your budget is limited, you should at least carefully check the threads and rod for cracks. Putting old bolts on new, precision forgings means negating all the benefits of a quality new product.

Sometimes after dismantling it turns out that a non-standard flange or a product with special characteristics is needed. That’s when the ability to order according to drawings, which is offered by many serious manufacturers, including the mentioned company, comes in handy. The main thing is to provide accurate data about the damaged node.

Conclusions that come with experience

Dismantling- this is no less important operation than installation. It cannot be approached on a residual basis. There is no universal instruction: each node requires its own assessment, its own set of tools and, often, its own trick.

The quality of the flange parts themselves certainly makes life easier in the long run. A dense, cavity-free forging from a proven plant is less susceptible to corrosion and holds the load better. But even the best flange, if installed incorrectly, will be a nightmare to disassemble.

Therefore, my main advice is: think about dismantling at the installation stage. Proper tightening, use of recommended lubricants, anti-corrosion coatings on threads is an investment in the fact that someday this unit will have to be disassembled. And it’s good if this is a planned job, and not an emergency shutdown of the workshop due to one stuck bolt.