Penstock Pigging

Reasons for Pigging ■ Removal of the natural build up of deposits on

the internal bore of the pipeline.

■ Removal of sediment on any low spots

■ To improve pipeline performance (reducing head loss, increasing hydro power output)

■ Need for pigging is massively dependant of pipe diameter/roughness/length in respect to flow –undersized pipelines need lots of pigging

■ Peat – watercourses with high peat contact –classic for building up on inside of pipe

Corrugation Effect

■ Corrugation effect from the build up of peat or other debris within the pipe.

■ Increased resistance.

■ Increases head loss, that would be greater then the loss due to pure reduction in diameter alone.

How to Pig

• Selection of the best suited pig for the penstock

• Soft Pig

• Hard Pig

• Inserting the pig into the penstock pipe via a pig trap; bell-mouth or opening with a greater diameter then the penstock.

• Appling pressure to the pig, via water

• Removal of the pig through a pigging valve or removable pressure vessel; located at the bottom of the penstock pipe

Checks

■ Bends in penstock are known and pig is sized appropriately.

■ Pipe diameter is know for the entire length of penstock.

� Pipe diameter varies with different pressurise ratings (check SDR number).

� Pipes of different materials have different ID.

� Pipe internal shape has not been misshaped external forces i.e. wrong material used when burying the pipe.

Pig insertion

■ Bar and straps

■ Pig launcher

■ Brute force

■ Working below ground – gas meter and certification

Scheme Design

■ Design parameters

– Allow the controlled realise of water, hence controlling the pig position.

– Sealable chamber for the pig that can be depressurised

– Safe and easy removal of the pig.

Simple pigging branch leading to outfall

Simple straight through pigging arrangement

No pigging arrangement

What can go wrong?

Pig going through part open valve

Piggy

Clean pipe – head

loss minimised