In general the hardness of a pig, also known as the durometer of a pig, is directly related to how aggressive the pig is. The durometer of a pig is measured on the Shore A scale.
Typically, in day to day maintenance pigging, it is best practice to pig with as hard a pig as possible without having operational issues. The amount of differential pressure available dictates how hard the pig you are using can be.
Below is a guideline* of differential pressure required vs. pig hardness. This guideline* will cover a variety of operating parameters but it should be noted that it is possible to move a harder pig with less pressure in a liquid system than in a gas system. The size of a pipeline also plays a role in the amount of pressure required to move a pig due to the surface area. For example the amount of force available with 30 psi of differential pressure in a 2” pipe line is much lower than 30 psi of differential pressure in a 16” pipe line.
- Purple 65A: 10 – 40 psi
- Green 75A: 40 – 75 psi
- Light Blue 85A: 75 – 150 psi
- Orange 95A: 150+ psi and typically used in liquid systems only