Problems in connecting carbon steel flanges to stainless steel pipes

As a supplementary note: if the valve is equipped with cast iron flanges, and the pipes are made of carbon steel or stainless steel, how should they be connected?

Method 2 is adopted: stainless steel is used for the paired flanges. There is no need for anti-corrosion treatment when connecting carbon steel flanges to stainless steel flanges. Since the pipelines are made of stainless steel, why are carbon steel valves chosen?

The material of the valve should be the same as that of the pipeline, right? Otherwise, won’t the valve corrode and get damaged soon? :o

In terms of connections, 1. carbon steel is used for the mating flanges, and welding is performed between the pipeline and the mating flanges made of different steel types. 2. The mating flanges are made of stainless steel. (No anti-corrosion treatment is required during connection.) Either one is acceptable. The question is: the valve can be made of carbon steel, so why must the pipeline be made of stainless steel?

What I mean is that the valve serves as the boundary point: carbon steel before the valve and stainless steel after it. So if the entire valve is made of cast iron, can the matching flange be chosen according to the pipeline? For carbon steel pipes, carbon steel flanges should be used, and for stainless steel pipes, stainless steel flanges should be used – is no additional treatment required?

The material of the flange should match that of the pipeline. As for the valve material, the materials for the valve body and the valve core are determined based on the requirements of the process medium (such as corrosivity and temperature).

If installation must be done in this way, it is recommended to use a swivel flange (with the flanged edge made of stainless steel and the flange itself made of carbon steel).

I think the matching flanges should be of the same material as the pipes, to reduce the difficulty of welding and prevent corrosion of the flanges. The valves are made of carbon steel while the pipes are made of stainless steel – why is that? Are the valves lined? If so, then the flanges on the valves should also be lined.

It is incomprehensible in principle; stainless steel valves should be preferred whenever possible. If selection is necessary, valves with stainless steel flanges can be used; it is recommended to employ insulating gaskets

The pipes should be made of stainless steel; the valves as well should be of stainless steel. Carbon steel pipes can be connected afterward, and the junction points should include valves. Please check the piping specifications again regarding the location of the breaks.

As asked on the 5th floor: The valve can be made of carbon steel, so why should the pipes be made of stainless steel? As a supplement: What are the operating conditions like?

It is recommended to use the second method; these days, insulating gaskets are used between carbon steel flanges and stainless steel flanges. The first method is very poor; firstly, welding different types of steel is difficult, and secondly, welding stainless steel to carbon steel has an even more adverse effect on the carbon steel than using the second method. As for other methods, it means not using stainless steel pipes.

The pipes are made of stainless steel, while the valves are made of carbon steel; it might be at the points where the pipe grade changes.

Since the electrodes of carbon steel and stainless steel are different, which can lead to galvanic corrosion, it is recommended that the material of the pipe flanges be the same as that of the pipes; stainless steel should be used. If possible, the valves should also be made of stainless steel. Otherwise, insulation treatment should be applied to the connection between the valves and the pipe flanges. If the medium is not highly corrosive, it can also be connected directly.

Published on 2009-2-2 14:54. View only this author’s posts. What I mean is that the valve serves as the boundary point, with carbon steel on the side before the valve and stainless steel on the side after it. So if the entire valve is made of cast iron, can the matching flange be chosen according to the pipeline? For carbon steel pipes, carbon steel flanges should be used, and for stainless steel pipes, stainless steel flanges should be used – is no additional treatment required? No special treatment is required.

1. Carbon steel is used for the mating flanges; welding is employed when joining pipes with flanges made of different steel types, while normal bolt connections can be used when connecting to valve flanges. (Normally, stainless steel flanges should be used for stainless steel pipes.) 2. Stainless steel flanges should be chosen for mating purposes; when connecting carbon steel flanges with stainless steel flanges, stainless steel bolts must be used. Attention should be paid to controlling the chloride ion concentration in the gasket material, which should not exceed 50 ppm. If ordinary carbon steel bolts are used, an insulating coating should be applied to the area where the stainless steel flange comes into contact with the carbon steel bolts, in order to prevent iron atoms from the carbon steel bolts from diffusing into the stainless steel and causing corrosion to the flange.

There is a problem with the design; such a situation should not occur. It is recommended to use stainless steel valves and matching flanges based on the operating conditions.

Flanges are generally used for connection, and welding of dissimilar materials is not recommended. The pipes are made of stainless steel, so why are the valves made of carbon steel? For the connection of different materials, flange connections are generally used, and valves are installed as necessary for control, to facilitate maintenance work.

For those upstairs who find this incredible, let me explain why it makes sense to use stainless steel pipes paired with carbon steel valves. Generally, the lead time for ordering valves is quite long. Some clients place orders before receiving the drawings from the design firm, but once they get the drawings and see that the pipelines are made of stainless steel, they are stunned. . . .