Flange Gasket and Bolts - Piping Study

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dimentional standards for flange

dimentional standard for large flange

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Flange

A flange is a method of connecting pipes, valves, pumps and other equipment to form a piping system. Italso provides easy access for cleaning, inspection or modification. Flanges are usually welded or screwed.Flanges are available in round, square, and rectangular shapes. In some cases, flanges are usually in theshape of a ring or a plate to form a rim at the end of a pipe when fastened to the pipe.

TYPES OF FLANGES

TYPES OF FLANGES

The most used flange types are:

• Welding Neck Flange

• Slip On Flange

• Socket Weld Flange

• Lap Joint Flange

• Threaded Flange

• Blind Flange

Special Flanges:

• Orifice Flanges

• Spectacle Blinds (part of flange connection)

• Spades and Ring Spacers (part of flange connection)

• Long Welding Neck Flanges

• Weldoflange / Nipoflange

• Expander Flange

• Reducing Flange

MATERIALS FOR FLANGES


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MATERIALS FOR FLANGESThe most common materials used in flanges produced is carbon steel, stainless steel, cast iron, aluminium,brass, bronze, plastic etc.

In addition, flanges, like fittings and pipes, for specific purposes sometimes internally equipped with layersof materials of a completely different quality as the flanges themselves, which are "lined flanges".

The material of a flange, is basically set during the choice of the pipe, in most cases, a flange is of the samematerial as the pipe.

SOME COMMON FLANGE MATERIALS 1. ANSI FLANGESSize : 1/2" TO 54"Pressure Rating : 150#, 300#, 600#, 900#, 1500#, 2500#Material :Carbon Steel : A-105, A-350 LF2, etc.Alloy Steel : F-5, F-9, F-11, F-22, F-91, ETC.Stainless Steel : SS 304, SS 304L SS316,SS 316L, SS 316Ti, SS 321, SS 347, SS 304H, 317L, Etc.Duplex SS : F-51, F-55High Strength Steel : A694 Gr 52, 60, 65, 70,AISI 4130, 4140Nickel Alloys : Monel 400, Inconel 625, Inconel 825, Alloy 20, etc.Standards : ASME B 16.5, ASME B 16.47, API 6AType : SORF, WNRF, SWRF, BLRF, Threaded etcSpecials : Spacers, Spectacle Blinds, Drip Rings, RTJ, Tongue, Groove, Orifice, etc.2. DIN B.S. & UNI FLANGESSize : DN 10 to DN 800Pressure Rating : PN6 to PN64Material : 1.4404, 1.4307, 1.4571, 1.4541, 1.4462, 1.4306Standards : EN 1092-1, BS 4504, UN 2278 etc.Type : SORF, WNRF, BLRF, SWRF, Threaded, etc.Specials : RTJ, Tongue, Groove, Orifice, etc.

Flange Installation

Flange Installation

Center the gasket on the flange. This is extremely vital where raised faces are involved. Note: standard ANSI ring gaskets,

when cut properly, should center themselves with the bolts in place.

Use a torque wrench and well-lubricated fasteners with hardened flat washers to ensure correct initial loading.

Tighten bolts to compress gasket uniformly. This means going from side to side around the joint, in a star-like crossing

pattern.

All bolts should be tightened in one-third increments, according to proper bolting patterns. Retorque 12 to 24 hours after

start-up, whenever possible.

All applicable safety standards including lockout/tagout procedure should be observed.

Never use liquid or metallic based anti-stick or lubricating compounds on the gaskets. Premature failure could occur as a

result.

Note:

ASME PCC 1:2000 (R2005) :Guidelines For Pressure Boundary Bolted Flange Joint Assembly


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dimentional standards for metallic gasket

dimentional standard for non-metallic gasket


Gasket

GasketFlanged joints are made by bolting together two flanges with a gasket between them to provide a seal. Thegasket's function is to seal two different surfaces held together by one of several means, the most commonbeing screw-threaded devices such as bolts.

The charecteristics of Good Gasket

The charecteristics of Good Gasket

It will seal the fluid system.

A good gasket should be chemically inert to resists the system fluid to avoid chemical reaction with fluid system.

Should deform enough to flow into the imperfections on the gasket seating surfaces to provide intimate contact between the

gasket and the seating surfaces.

Withstands system temperatures without serious damaging the fluid system properties.

Should be resilient and resists creep enough to maintain an adequate portion of the applied load.

A good gaskets has sufficient strength to resist crushing under the applied load, and maintain its integrity when being

handled and installed.

Should not corrode the gasket seating surfaces.

There are limits on the degree of flange surface imperfection that can be sealed successfully with a gasket. Large nicks, dents,

or gouges must be avoided, since a gasket cannot properly seal against them.

The surface finish of a flange

The surface finish of a flange is described as follows:

1. Roughness : Roughness is read in millionths of an inch (or meter) as the average of the peaks and valleys measured from

a midline of the flange surface.

2. Lay - Lay : is the direction of the predominant surface-roughness pattern. Example: multidirectional, phonographic

spiral serrations, etc.

3. Waviness : Waviness is measured in thousandths or fractions of an inch. Basically, it is the departure from overall

flatness.

Typical roughness readings can be from 125 to 500 micro-inches for serrated flanges and 125-250 micro-inches for


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non-serrated flanges. Fine finishes, such as polished surfaces, should be avoided. Adequate "bite" in the surface is required to

develop enough friction to prevent the gasket from being blown out or from extruding or creeping excessively.

The lay of the finish should follow the midline of the gasket. For example, concentric circles on a round flange, or a

phonographic spiral. Every effort should be made to avoid lines across the face, such as linear surface grinding, which at

180º points will cross the seal area at right angles to the gasket, allowing a direct leak path.

Waviness is seldom a problem under normal conditions. There are two areas that must be watched, however, since excessive

waviness is very difficult to handle.

The first area is glass-lined equipment where the natural flow of the fused glass creates extreme waviness. Often the answer

here is to use thick and highly compressible gasketing.

The second area of concern is warped flanges. If warpage is caused by heat or internal stresses, re-machining is generally

sufficient. However, warpage due to excessive bolt loads or insufficient flange thickness results in what is generally called

bowing.

The solution is to redesign for greater flange rigidity. Sometimes backer plates can be added to strengthen the design without

replacing the parts. Another step would be to add more bolts. When this is done, usually smaller bolt diameters are possible,

thus adding more bolt stretch and better joint performance.

dimentional standards for bolts

dimentional standard for nuts


BOLTS

Bolts

The design of bolt over a nut acts like a spring load.The bolt is a spring. It is an elastic member that hasbeen stretched to develop a load. The more load spring provided by the bolt, the better the retention ofstress on the gasket to maintain a leak proof joint. It must not be over-elongated (over-strained), or theelastic limit of the steel will be exceeded. The bolt then deforms and, with continued loading (stressing),may rupture.

To avoid such problems with bolt tightening, the use of a torque wrench is recommended. The equipmentdesigner normally specifies the torque required for a product. This ensures that the maximum available loadis applied consistently to the gasket. The load will be better retained by using a bolt with a longer grip,thereby ensuring a leak proof joint.Collapse all | Expand all

The Assembly of Flange Gasket and Bolts

The Assembly of Flange Gasket and Bolts.The assembly of flanges, bolts and gaskets form a family. The proper installation of all the three is veryimportant to have perfect leak proof sealing in a flanged joint.Improper installation of the assembly can lead


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flange leakage which is unsafe .


Factors that should be considered during installation of Bolts

BOLTS

Wrong bolt type used for flanged joint connections.

Improperly torqued bolts.

The material of the bolts should be compatible with the material of flange for thermal expansion.If the bolts were

incompatible and had a higher thermal expansion factor than the flanges. This will inevitably lead to the improper sealing

,joint loosening and flange leakage.

Improper bolt tightening sequence

If you are to reuse a bolt make sure it is clean and guages out.

Use a thread lubricant that everyone is happy with.

Use correct studs, washers & nuts.

Use correct bolting procedure. Always use correct torque indicating tool.

Repeat procedure after system is at working teperature/pressure.

Improperly torqued bolts.

Factors that should be considered during installation of Flange

FLANGE

Poor pipe alignment prior to bolting flanged fittings together.

Presence of dents,burrs on the face of the flange.

Improper use of tools for installation

Flanged Joints. Before bolting up, flange faces shall be aligned to the design plane within 1 mm in 200 mm (1/16 inch/foot)

measured across any diameter; flange bolt holes shall be aligned within 3 mm (1/8 inch) maximum offset.

Use of flange in steam service is very criticle and not recommended.The bolts have to be re-torqued following the first

thermal cycle.

Make sure you have the proper tools and they are in good condition. Avoid using open end wrenches, crescent wrenches, or

12 point box ends or sockets to be used for tightening bolts. In some critical areas no slip-joint pliers.

Poor pipe alignment prior to bolting flanged fittings together.

Check flange faces for damage. Use taper drift to align bores. Check facing gap with a feeler gauge, not by eye. Start

tightening up from the wide side.

Factors that should be considered during installation of Gaskets

GASKETS

Gasket creep temperature should be taken into account during selection. The gasket creep will occur in spiral wound as well

as sheet gasket due to the temperature. There are several WRC bulletins on use and selection of proper gaskets .

Some elastomer/aramid sheet gaskets in steam service,they became brittle and broke apart . Use spiral wound.graphite

gaskets which work best but B16.5 has recommendations on gaskets/bolts/weld necks if you're using 150 class flanges.

Never reuse a spiral wound gasket no matter how good it looks. You can check the effectiveness of the flange makeup

procedure by checking the thickness after use.


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Wrong gasket type used.

Never tape across a gasket, either ring or spiral wound.

Wrong gasket type used.

Never re-use old gaskets. Check on the side of the flange for spex, this should be specified in vendor drawings.

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Flange Gasket and Bolts - Piping Study

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