Progressive pigging is recommended for pipelines when large amounts of debris, such as wax or sand, has accumulated because of no pigging program or the use of inefficient pigs such as ball pigs or foam pigs.

The procedure consists of a series of inefficient pigs and progressively moving up to more aggressive and efficient pigs to control the amount of material moved in each pig run. The objective is to reduce the chance of creating a plug of debris in the line. The cost of repeated pig runs is a much less expensive alternative to digging up a plugged pipeline.

The biggest challenge is establishing how thick the deposit of material in the line is. If cut-outs have been done on the line it may have been established how thick the material is on the pipe wall. If the line produced paraffin and ball pigs were used it can be assumed that the deposit thickness would be pipe ID less ball OD divided by 2 if it is evenly distributed around the pipe wall.

If there is no way of knowing how thick the deposits may be it is best to assume a reasonable worst case even if the first few pig runs do not bring any material in.

The size and wall thickness of the line in question must be known to establish the starting point of the first progressive pig diameters.

The first pigs run are soft, un-aggressive pigs to prove the line is piggable and sweep soft loose material. The progressive pigs are a combination of hardness and increasing diameter. If the system is a liquid system, by-pass porting can help to keep loose material moving in suspension ahead of the pigs. This method is less efficient in gas systems as the gas cannot suspend the loosened material.

The number of steps or stages depends on how much material is in the line but obviously the more stages you use the less opportunity there is to create a plug.

The most important part of the procedure is to not skip any one stage as the missed stage may make the difference to creating a plug.

Pipetech will work with the customer to design a progressive pigging program taking into account the logistics and necessity to establish the number of stages.

This procedure is intended as a general description. Particular systems may require different approach or pig types.