Pig Kicker line size

[Al Ashikuzzaman]

I am currently designing a new DN200 gas pipeline with a pig launcher arrangement positioned immediately after connecting to the existing pipeline. The pipeline is designed to operate at a maximum pressure of 85 bar and a minimum pressure of 40 bar. The maximum and minimum flow rates are 35,000 SCMH and 250 SCMH, respectively.

The design includes a DN50 kicker line for the pigging system. However, I have noticed that both DN50 and DN100 kicker lines are commonly used with DN200 pipelines, leading to uncertainty about the optimal kicker line size. My calculations indicate that to maintain a pigging velocity between 1–5 m/s, the system would require a flow rate of approximately 14,000 SCMH at 2 m/s and up to 36,000 SCMH at 5 m/s.

I am concerned that a DN50 kicker line may not supply adequate flow to achieve these velocities.

How should I specify the kicker line size and configuration to maintain pigging velocity within the range of 1–5 m/s under normal operating conditions?
Are there any relevant standards or guidelines that define the appropriate kicker line size for a DN200 pipeline?
Is there any other critical information I should consider in selecting the kicker line size for optimal pigging performance?

 

[akpipelineengr]

Those main line and kicker line sizes are in the range that I've typically seen. I've seen operators' specifications limit the kicker to no less than 1/4 of the main line diameter (so DN 50 for your DN 200 main line), and many installations are larger than that. You'll need to check fluid velocity and pressure drop in the kicker line. Pressure drop shouldn't control because kicker lines are typically short. Fluid velocity becomes an issue of integrity management and service life, if you have a particularly erosive or corrosive service.

 

[pierreick]

Hi,
You may find some tips in the doc attached.
Pierre

 

[georgeverghese]

From a process safety in operations perspective, if the operator were to divert the entire flow of 35e3 scmh through the kicker line while pressure is 4000kpag, this will result in a rho-v2 exceeding 500e3 in SI units, while the max permissible upper limit to prevent excessive vibration is 200 e3. For this inadvertent operation, a min kicker line size of DN80 is preferred (rho-v2 =90e3).

 

[LittleInch]

I am currently designing a new DN200 gas pipeline with a pig launcher arrangement positioned immediately after connecting to the existing pipeline. The pipeline is designed to operate at a maximum pressure of 85 bar and a minimum pressure of 40 bar. The maximum and minimum flow rates are 35,000 SCMH and 250 SCMH, respectively.

The design includes a DN50 kicker line for the pigging system. However, I have noticed that both DN50 and DN100 kicker lines are commonly used with DN200 pipelines, leading to uncertainty about the optimal kicker line size. My calculations indicate that to maintain a pigging velocity between 1–5 m/s, the system would require a flow rate of approximately 14,000 SCMH at 2 m/s and up to 36,000 SCMH at 5 m/s.

I am concerned that a DN50 kicker line may not supply adequate flow to achieve these velocities.

How should I specify the kicker line size and configuration to maintain pigging velocity within the range of 1–5 m/s under normal operating conditions?
Are there any relevant standards or guidelines that define the appropriate kicker line size for a DN200 pipeline?
Is there any other critical information I should consider in selecting the kicker line size for optimal pigging performance?

Askituzzaman,

There is in reality no real common thought process or indeed "optimum" size for such lines.

My personal preference in design is for a size no less than 50% of the mainline pipe size, which gives you velocities about 4 times the velocity in the main line and for the relatively short periods of time it is used this is fine. Many companies for reasons I've never really understood go for 25% and seem to think that the minute saving of a smaller valve and pipework is ok, whereas I don't.

The kicker line is though only in use for short periods when used as a launcher as as soon as the pig is know to have gone, most people open the bypass valve and close the pig trap and vent / drain straight away. Reception traps often operate with the bypass valve open to a certain amount ( you often see the requirement for "inching") This splits the flow through the trap and the bypass line and can help reduce the arrival speed of the pig into the trap. Personally I prefer to flow through the trap 100%, but I recognise others don't like doing that.

So do your number and try to keep the velocites "reasonable" if only there for a short time.

No one should object to a kicker line 50% of the pipeline ID or maybe 40% once you get above 24". I have seen some crazy ones where a 36" launcher has a 6" or even 4" kicker line connection. Looks crazy and if it looks bad it usually is.

So up to you really. For an 8" line I would definitely go for a 4" kicker line.

 

[Pipeline55]

Askituzzaman,

There is in reality no real common thought process or indeed "optimum" size for such lines.

My personal preference in design is for a size no less than 50% of the mainline pipe size, which gives you velocities about 4 times the velocity in the main line and for the relatively short periods of time it is used this is fine. Many companies for reasons I've never really understood go for 25% and seem to think that the minute saving of a smaller valve and pipework is ok, whereas I don't.

The kicker line is though only in use for short periods when used as a launcher as as soon as the pig is know to have gone, most people open the bypass valve and close the pig trap and vent / drain straight away. Reception traps often operate with the bypass valve open to a certain amount ( you often see the requirement for "inching") This splits the flow through the trap and the bypass line and can help reduce the arrival speed of the pig into the trap. Personally I prefer to flow through the trap 100%, but I recognise others don't like doing that.

So do your number and try to keep the velocites "reasonable" if only there for a short time.

No one should object to a kicker line 50% of the pipeline ID or maybe 40% once you get above 24". I have seen some crazy ones where a 36" launcher has a 6" or even 4" kicker line connection. Looks crazy and if it looks bad it usually is.

So up to you really. For an 8" line I would definitely go for a 4" kicker line.

Fully agree with Littleinch with additional context that for offshore where minimising size, weight and maintaining access in tight spacing is more critical a kicker line sizing of 30% of pipeline ID on 24” and above is permitted within my employer’s standards (major operator).

 

[georgeverghese]

If there are solids suspended in this gas, this may require larger kicker line sizes. Same goes if there are suspended liquid droplets in this gas.