Pigging is used in the pipeline after certain time when the efficiency of the pipeline drop due to foreign particles store/scaled inside the pipeline. The use of proper pigging program helps maintain the integrity and optimum efficiency of pipeline which safe pipeline asset of the operating company and safe our environment.
The maintenance of the pipeline is very important because build-up deposit can create conditions for corrosion inside the pipeline which reduce life of the pipeline.
Pipeline Pigging for following reasons
- Commissioning and decommissioning of plant.
- Cleaning the wax removal
- Corrosion and scale control inside the pipeline
- Inspect ion of the pipeline at regular interval
- During the batch product changing or sweeping tout the liquids.
Pipeline Design for pigging operation
All Valves/ESDV Valves: – Valves specified for pigging purposes should be full bore, with specified minimum internal diameter, limited or zero bypass and compatible with product. Valves shall facilities uninterrupted passage of pig.
Barred Tee:- Barred tee shall be installed on branches larger than 50% of pipeline diameter if sphere or foam pigs are indented to be used.
A minimum of two guide plates should be used to prevent the pig from entering the branch pipe. Guide plates shall be welded across the tee branch pipe along with flow direction to prevent pigs from becoming the stuck at junction or from being wrongly diverted with the flow. Guide plates elements shall be smooth and from sharp edges to prevent damage to pipeline.
Thermal relief and pressure gauges:- Thermal relief valve shall be provide at trap locations in which the anticipated shut-in pressure of the product could possibly exceed the design pressure of the trap.
Pressure gauges with dial of 100 mm to 150mm diameter shall be located at 12’O’clock positions on the barrel to be visible to trap operator
Passage Indicator:- Pig passage indicator shall have a mechanism that provides a position indication that a pig has passed and can be installed , removed or replaced without pipeline shutdown.
Pig passage indicators shall be bidirectional, installed flush with the internal pipe wall and retractable/replacement under pressure. Pig passages indicators shall be considered on both sides of the main trap valve.
On Pig launcher one sited upstream of the mainline valve and one sited downstream of the mainline valve as a distance at least the length of the longest pig anticipated to confirm the pig has lift the trap and valve.
On Pig receiver one sided on the trap neck piping and separated upstream from the mainline trap valve by a distance that equal to the length of the longest pig anticipated to confirm receipt of the pig and the pig ha cleared the valve.