Flanges are very practical for the pipe system that needs dismantle, and the Heat Treatment of Flange is also important. Here are a brief introduction about flange and its heat treatment.

Flanges and gaskets, fasteners collectively known as flange joints. Flange joints are widely in engineering design. It is an essential part of piping design and valve, and it is also a common part in engineering such as industry, heat, water supply and drainage, heating, ventilating, and control.

Forging flange sealing surface has three types:

Flat Face (FF), it is suitable for the low pressure, the medium non-toxic situation. Female and Malel Face (FMF), applies to the slightly high pressure occasion. Tongue and Groove Face(T and G). It is suitable for the flammable, explosive, the poisonous medium and the high pressure situation. GASKET is a kind of ring which can produce plastic deformation and have a certain strength of material.

For example, there is a long distance pipeline,the whole pipeline need to be connected by each pipe, also installed valve, sight glass and so on, then weld it up. But it is not convenient for repair or maintenance later because of its non-removability. So most of these pipes will be uses flange joints, To facilitate the maintenance and replacement.

The flange is weld connection to the pipe or in other ways. And then fix two relative flanges with fasteners (bolts), which form a complete pipe. Pipes and valves, sight glass are basically the same way to connect.

Heat Treatment of Flange

Heat treatment is necessary for Stainless Steel Fittings, Carbon Steel Fittings and Alloy Steel Fittings, and their treatment way are different. Metal performance will have different changes after process of heating, insulation, cooling, so as same flanges. Such as stainless steel flange superior performance, which get through the heating cooling on flange, At the same time, it is one of the important parameters in the heat treatment process.

The flange is in the process of heat treatment, the general annealing cooling speed is the slowest, the normalizing cooling speed is quicker, quenching cooling speed is faster. Flange are mutually connected and uninterrupted in the process. When heating, the workpiece connects to the air so oxidation often occurs. Decarbonization (the reducing of steel carbon content), The fittings have a very adverse impact after heat treatment. Flange and fitting usually should be controllable atmosphere or protective atmosphere. Coating or packaging methods can protect heating molten salts and in vacuum.

In addition, the heating temperature of the flange is one of the important technological parameters in heat treatment process, and controlling the heating temperature is the main problem to ensure the heat treatment quality. It is generally heated to a phase change temperature above to obtain high temperature tissue. Heating is one of the important processes of heat treatment. There are many heating methods for flange and fittings,firstly use charcoal and coal as heat source, and then apply liquid and gaseous fuel. Now a lot of manufacturers are using electrical applications, so easy to control, and no environmental pollution. Using these heat sources can be directly heating, or molten salt or metal, floating particles for indirect heating. At the same time, the performance of flange is different from the process of cooling, the main control cooling speed.

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The function of Spectacle Blind ASME B16.5 is isolating or connecting piping systems. It is a steel plate with a fixed thickness which consists of two discs. The two discs are connected by a flat steel, one is solid and the other is a hollow ring, which is the same diameter as the flange.

1. Spectacle Blind  2. Flange 3. Gasket 4. Bolt

Spectacle Blind ASME B16.5 is  independent of other facilities or devices in the piping system. Normally, it is located in the open position so that the fluid passes through the pipe. When the Spectacle Blind is in the closed position, the pipe and fluid are off.

The maintenance of the piping system is a reason for the Spectacle Blind rotate to the closed position. Spectacle Blind ASME B16.5 connected to a hole in the web, loosen and dismantle part of the bolts, Spectacle Blind can rotate between the flange, after replacing the gasket, the bolts can be reassembled and fastened.

Spade and Spacer

The spade and spacer are basically similar to the Spectacle Blind asme b16.5 , the difference is that the they are two separate parts.

The spade and spacer suits for piping systems that do not require constant maintenance, or for large-diameter pipelines. Depending on the pipe diameter and pressure rate, the spade may have a weight of hundreds of pounds. In order to reduce the unnecessary piping load, we usually select the separate parts spade and spacer instead of Spectacle Blind.

Spade and Spacer

1. Spade  2. Flange 3. Spacer 4. Bolt

As described above about the spade, the pipe is maintained with the replacement of spade and spacer. Loosen all bolts, temporarily remove some bolts, the spade and spacer can be replaced. After replacing the spacer, the bolts can be reassembled and fixed.

Because the spade is between the flanges, we cannot see whether it is a spade or spacer. Therefore, special markings are usually made on the handle, or there is a separate design. Customers usually provide their own technical datasheet.

The ASME B16.48 covers pressure-temperature rating, material, dimension, tolerance, mark and test from 1/2 “to 24” pipeline blind flange. These fittings and ASME B16.5 flange are partners. Spectacle Blind, Spade and Sapcer are made of steel plates or forgings and are approved for use by ASME B31.3. Usually it has the same physical and chemical properties as the flanges and piping materials.

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There are nine types of Fastener Surface Treatment, like Electro-Zinc, Phosphating, Oxidation (Blackening), Cadmium(Electro) Plating, Electrochromism, Silver and Nickel Plating, Hot-Dip Zinc,  Zinc Infiltration and Dacromet

Electro-Zinc 

Electro-Zinc is the most commonly used Fastener Surface Treatment for commercial fasteners. It is cheaper and good looking, colors are black or military green. However, its anti-corrosion performance is so so and the zinc coating layer is thin. Generally, electro-galvanized neutral salt spray test should be took within 72 hours. There are also special sealants, making the neutral salt spray test up to 200 hours. But it is expensive, and can only support galvanizing 6 times. Electro-Zinc processing is easy to produce hydrogen embrittlement, so more than 10.9 bolts do not need galvanizing.

Electro-Zinc Application

The hydrogen must be plating before passivation because the passivation film will be destroyed in 60 ℃ and above.Therefore, it has poor operability and high processing cost. In reality, the general production plant will not take the initiative to hydrogen, unless the customers have mandatory requirements. The fastener torque-preload force of electroplating zinc is poor in consistency and unstable, so it is not used in the connection of important parts generally. However, the method of coated lubricating material can help to improve the consistency of torque-preload.

Phosphating 

Phosphating is cheaper than zinc plating but its corrosion resistance is worse. After phosphating,the fittings should be oiled. Therefore, the performance of corrosion resistance has a great relevant with the anti-rust oil.  For example, after general phosphating coating and oiling, neutral salt spray test only needs 10-20 hours. But if the anti-rust oil is high-grade, it can reach 72-96 hours. However, the price is higher. Lubrication performance of zn-Series Phosphating is better than manganese system phosphating, while manganese system phosphating has better corrosion resistance, and wear resistance.

Phosphating Application

Its working temperature is 225 degrees Fahrenheit to 400 degrees (107 to 204°), and industrial fasteners need phosphating oil treatment more often. Because of its torque a p reload consistency is good, the assembly can meet the design expected tightening requirements, so in industry it uses more often, especially in the connection of important parts, such as the connecting rod bolts, nuts, cylinder heads, main bearings, flywheel bolts, wheel bolts and nuts, etc. The surface of high-strength bolts may have hydrogen embrittlement problem after phosphating.

Oxidation (Blackening)

Blackening oil is a popular fastener surface treatment for industrial fasteners because it is the cheapest and looks good before the oil runs out. Because there is almost no rust-proof ability, it will soon rust without oil. In the presence of oil, the salt spray test can only reach 3-5 hours. Black Fasteners Torque-preload consistency is also poor. If you need to improve, you can apply grease to the thread when assembling and then spin.

Cadmium(Electro) Plating

The corrosion resistance of cadmium coating is very good, especially in the marine atmosphere environment, the corrosion resistance is better than other surface treatments. Electroplating cadmium processing process of waste liquid treatment costs, high cost, the price of zinc electroplating is about $number times. Therefore, in the general industry is not used, only for a specific environment. For example, for the oil drilling platform and the HNA aircraft used fasteners.

Electrochromism

Chromium coating is a very stable fastener surface treatment in the atmosphere, not easy to change color and loss of luster, high hardness and wear resistance. Chrome plating on fasteners is generally used as a decorative function. It is rarely used in industrial areas where corrosion resistance is high, because good chrome plated fasteners are as expensive as stainless steel, but only when stainless steel is not strong enough to be replaced with chrome fasteners. In order to prevent corrosion, chrome plating should be first plated with copper and nickel. Chromium coating can withstand the high temperature of 1200 degrees Fahrenheit (650 ℃). But it also has the same hydrogen embrittlement problem as electroplating zinc.

Silver and Nickel Plating

Fastener Surface Treatment of Silver coating can be anti-corrosion, and can be used as a solid lubricant fasteners. For cost reasons, the NUT is silver plated, bolts are not used, and sometimes small bolts are silver plated. Silver loses luster in the air, but can function under 1600 degrees Fahrenheit. Therefore, people use its high temperature and lubrication characteristics, to work at high temperature fasteners to prevent the bolt, nut oxidation bite dead. Fasteners Nickel-plated, mainly for both anti-corrosion and good conductivity of the place. such as vehicle battery extraction terminals.

Hot-Dip Zinc

Hot-dip zinc is coating fittings with liquid zinc. Its coating thickness is 15 to 10μm which is difficult to control. But it has good corrosion resistance, and very common in engineering.

The pollution during hot-dip galvanizing is serious, such as zinc scrap and zinc vapor. And due to the thickness of the coating, it is difficult to rotate the internal and external thread of fasteners. Luckily, there are two ways to resolve this problem. One is to attack the internal thread after plating to solve the problem, and it also reduces the antiseptic performance. The other is in the nut tapping, so that the thread is larger than the mark of 0.15 to 0.75mm (M5-M30), and then hot dip zinc.

Hot-Dip Zinc Application

Currently there is a loose thread, the United States “in the” internal thread can solve this problem. Because the internal thread and the outer thread are not fastened when the gap is large, so accommodate the thick coating can be used. It does not affect the rotation, while the anti-corrosion performance and strength also remain intact and unaffected. Because of the temperature of hot dip zinc, it can not be used for fasteners above Grade 10.9

Zinc Infiltration

Zinc infiltration is a zinc powder solid metallurgical thermal diffusion coating. Its uniformity is good, the thread, the blind hole can obtain the uniform layer. The coating thickness is 10~110μm and the error can be controlled at 10%. Its adhesion to the matrix and anti-corrosion properties in the zinc coating (galvanized, hot dip zinc, dacromet) is the best. Its processing process non-polluting, the most environmentally friendly.

Dacromet

There is no hydrogen embrittlement problem, and the torque-preload force is good for consistent performance. If you do not consider the environmental problems of hexavalent chromium, it is actually the most suitable for high strength fasteners.

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