Control Valve

A control valve works to restrict the flow of fluid a pipe at the command of an automated signal. Control valve design are intended

·        For discrete  (on/off) control

·        Throttle fluid flow somewhere between fully open and fully closed (shut).

Control Valve are comprised of two major parts :

• Valve body : contains all the mechanical component necessary to influence fluid flow
• Valve actuator : provides the mechanical power necessary to move the component within the valve body

Pipe Fittings

1.      Flanged Pipe Fittings

A pipe “flange” is a ring of metal, usually welded to the end of a pipe, with holes drilled in it parallel to the pipe centerline to accept several bolts.

Solid Inclusion

Solid foreign substance entrapped in the weld metal

Slag Inclusion

Slag trapped during welding. The imperfection is of an irregular shape and thus differs in appearance form gas pore

Causes	Prevention
Incomplete slag removal from underlying surface of multipass weld	Improve inter-run slag removal
Slag flooding ahead of arc	Position work to gain control of slag. Welder needs to correct electrode angle
Entrapment of sl  ag in work surface	Dress work surface smooth

Cavities

a.      Gas Pore

A gas cavity of essentially spherical shape trapped within the weld metal.

This cavity can be present in various forms :

-         isolated

-         uniformly distributed porosity

-         clustered (localized) porosity

-         linear porosity

-         elongated cavity

-         surface pore

Crack

An imperfection produced by a local rupture in the solid state, which may arise from the effect cooling of stresses. Cracks are more significant than other types of imperfection, as their geometry produces a very large stress concentration at the crack tip, making them more likely to cause fracture.

Hystory of Welding

Welding has been found  since prehistoric times, as evidenced by the findings of grafting of silver gold copper relics years 4000-3000 BC. At the end of 19th century welding became popular since electrical energy can be developed to joint the metal.