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Flanged Joints

Lap Joint Flanges (con’t)• Welding neck flanges are probably the best all around type of

flange. They are the strongest of all those shown. There are no flow problems associated with the assembly and the butt joint is the best method to insure a sound weld.

• Lap joint flanges are good for a combination of alloy pipe and carbon steel flanges. This combination reduces the cost and usually reduces the delivery time compared to waiting for solid alloy flanges.

• The gaskets used with flange joints must always be softer than the flange material because one or the other must be deformed in order to make a tight joint.

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Flanged Joints

Lap Joint Flanges (con’t)• The elastomers include rubber, nylon, plastic, etc. These

materials have a disadvantage in that they can cold flow when squeezed - - even at room temperature. Thus, it is difficult to maintain a tight joint. These materials also have a tendency to flow out ant must be reinforced with cloth or wire mesh if any significant pressure is involved. Some elastomers are good for no more than 100oF. At this temperature that will soften and some will actually begin to melt. Some elastomers are soluble in oil.

• The spiral wound metal gasket with asbestos filler requires special flange finishing. Tightening of joints using these gaskets normally requires special attention and will take more time to properly tighten.

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Expansion Joints

Expansion Joints• All metals expand with increasing temperature. Steel pipe is no

exception to this rule. Expansion must be considered to accommodate the change in length in the change from atmospheric temperature to operating temperature. Expansion joints are used to absorb the effect of the increased length with temperature. These can be bends or corrugated expansion joints. The attached piping must be properly anchored and guided to direct the expansion to utilize the expansion to utilize the expansion joint most effectively.

4

Blinds

Blinds are a piping item used extensively in the plant. A blind is used to provide positive isolation in between piping flanges and thus insure that any leakage that takes place will be to the atmosphere and not through the pipe.• Normally, blinds are used to prepare vessels or tanks for entry

and to isolate equipment and piping in order to provide complete safety in welding.

• Blinds are also used for hydrostatic testing but in this case they must be of special design in order to handle the test pressures that will be involved.

5

Spacers

Spacers are required when there is a blind of appreciable thickness to be used. It is ordinarily impossible to spring the flanges far enough apart to install a blind of thickness beyond ½ in.• Under the above conditions a spacer is required to take up the

space occupied by the blind when the equipment is returned to operating condition.

• Sometimes the blind and the spacer are attached to each other and in this case it is known as figure 8 or spectacle blind.