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Prepared and presented by:
Akram Megdad / Sr. Mech. Inspector
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Pipe Flanged joints are considered to
be weak joints in the piping system andmany considerations should be taken to
avoid failure.Lack of proper installation and inspection
could result in a little leakage
OR
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Types of flanged joints.
Methods of connecting flanged joints.
orces acting on the flanged joints.langed joints installation and inspection.Summary.
In this presentation I will talk about ?
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Methods of Connecting Pipe Flanges
A flange is used to connect a pipesection to a piece of equipment,
valve, or another pipe in a way thatwill permit relatively simple
disassembly. Such disassembly may
be required for maintenance,inspection or operational reasons.
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Methods of Connecting Pipe Flanges
There are three general methods used to join or connectlengths of pressure piping,
these are:
3 By the use of flanges.
1 By the use of threaded pipes and screwedconnections.
2 By the use of welded joints.
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Typical flange Joint Assembly
Flange assembly consist of :
Two flanges.
A gasket to provide a
seal between the flanges.
Bolting to keep
the assembly
together.
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Flange Types
There are several standard types of pipe flanges. Twoitems must be specified to completely define a flangetype.
Flange Type Attachment Method Face Type+
A flange type is specified by stating the type of attachmentand face.For example,"A weld neck flat-faced flange" The
type of attachment defines how the flange is connected to apipe section or piece of equipment (such as a pressure-vessel
nozzle). The type of flange face or facing defines thegeometry of the flange surface that contacts the gasket.
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Flange Attachment Types
Threaded Flanges
A threaded flange has pipe threads machined into its bore asthe flange is screwed to matching threads on the pipe end.Threaded flanges are used only for small-diameter piping
systems, up to 50 mm (2 in.) NPS (nominal pipe size) atlocations where pipe disassembly may be required formaintenance, field modifications, or to match specialty
fittings and valves.For hazardous services, a threaded flange may only be usedup to 38 mm (1-1/2 in.) NPS. However, based on SAES-L-009, Metallic Flanges, Gaskets, and Bolts,welded slip-on-type flanges are preferred over threaded flanges in screwed
piping systems.
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Flange Attachment Types
Threaded Flanges
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Slip-on FlangesA Slip-on Flange has an oversized bore, it is slipped overthe pipe OD and projects slightly beyond the pipe end,the flange is then fillet welded to the pipe OD, and also
between the flange bore and the pipe end.Based on SAES-L-009, Saudi Aramco requires that an ASMECode SectionVIII, Division 1, flange analysis to be performedif a Slip-on Flange is used for any of the following cases:
1 - Severe cyclic conditions.
2 - Design temperature greater than 230C (450F).
3 - ANSI Class 400 or higher rating.
4 - Pipe size over 600 mm (24 in.).
Flange Attachment Types
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Slip-on Flanges
Flange Attachment Types
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Socket-Welded FlangesA socket-welded flange is similar to a slip-on flange except ithas an oversized bore that is partially machined into the end
opposite the face, the pipe is inserted into the "socket" and theflange fillet is welded to the pipe OD, the diameter of the
smaller bore is the as the I.D. of the matching pipe. This type offlange is often used with high pressure systems that use smaller
diameter pipes (< 4 inches).Based on SAES-L-010, Limitations on Piping Joints, the
maximum size of socket-welded joints in hazardous services shallbe 38 mm (1-1/2 in.) NPS for new construction.However, as with threaded piping systems, SAES-L-009indicates that welded slip-on-type flanges are preferred over
socket-welded flanges in socket-welded piping systems.
Flange Attachment Types
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Socket-Welded Flanges
Flange Attachment Types
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Blind Flanges
A blind flange is a flat metal
plate without an opening orbore that is used to blockflow in a piping system.
It is used when a pipe end
or equipment nozzle mustbe blocked from flow.
Flange Attachment Types
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Lapped Flange
A lapped flange is not physically connected to the pipe, it isslipped over a pipe stub that has a flared end and the pipe
stub is welded to the major pipe section, the flared pipe end
has a machined face where the gasket is seated, the boltingholds the flanges and gasket joint together.Based on SAES-L-009, Saudi Aramco prohibits the use of lap-
joint flanges in severe cyclic conditions. Their use is alsolimited to special applications suchas :
To avoid welding dissimilar materials.
To facilitate lining up the bolt holes in underwater flanged joints.
The use of lap joint flanges is the exception rather than therule, the main advantage of a lapped flange is cost and then
only in high-alloy piping systems.
Flange Attachment Types
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Lapped Flange
Flange Attachment Types
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Welded-Neck Flanges
A welding-neck flange is normally referred to as the highhub flange and it is the strongestof the standard flange
attachment types, it is designed to transfer stress
concentration at the base of flange, the end of the flange isbutt-welded to the end of the pipe, the flange bore is sizedto match the pipe bore. A welding-neck flange is the most
widely used in refinery services because of its greaterstrength and ability to be used at high temperature and in
cyclic service.
Based on SAES-L-009, this is the preferred flange type inmetallic piping systems, 50 mm (2 in.) NPS and above.
Flange Attachment Types
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Flange Attachment Types
Welded-Neck Flanges
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Forces Acting on the Flanged Joints
PRESSURE
THERMAL
DYNAMIC
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Forces Acting on the Flanged Joints
PRESSURE
The flange rating should be adequate forthe required pressure and temperature
range to avoid over pressure on theflanged joints.
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Forces Acting on the Flanged Joints
THERMAL
Thermal expansion
will cause highbending moment andcould lead toalignment difficulties,leaks and fires.
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Forces Acting on the Flanged Joints
DYNAMIC
Dynamic forces should be taken in consideration to assurethe flanged joints integrity such as:
Processes related.
Controlled and unpredicted forces.
Piping lay out and configuration.
Modification to piping lay out.
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Flanged joints Installation and Inspection
Alignment
Surface finish
Gasket centering Bolting procedure
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Flanged joints Installation and Inspection
Alignment
Flanged Joint misalignment caused by:
Low quality fabrication.
Field measurements mistakes.
And this will lead to:
Gasket damage.
Uneven load distribution.
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Flanged joints Installation and Inspection
Surface finish
The surface finish should be the right one for theright gasket type.
No scratches, specially in radial direction.
Clean from foreign objects.
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Flanged joints Installation and Inspection
Gasket centering
Check gasket dimensions for precision.
Gasket should be exactly centered.
Avoid touching the bolts.
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Flanged joints Installation and Inspection
Bolting procedureUse the proper equipment.
Follow the right bolting sequence
to provide even load distribution.
Apply the required torque, No more No less.
W hat happens when bolts are over torqued ?
Cracked flanges.
Squeezed gaskets.
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Flanged joints Installation and Inspection
Over torque cracked flange.
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SummaryRecognize that f langed joints are a cr itical
and potential hazard.Proper design material selection properinstallation careful inspection shall leadto the highest quality and save pipeflanged joints.
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Prepared and presented by:
Akram Megdad / Sr. Mech. Inspector