Pigging System Design

1. Pigging Overview

Pipeline pigging is the practice of using pipeline inspection gauges (PIGs) or cleaning devices to perform maintenance operations without interrupting product flow. The term "pig" originated from the squealing sound early devices made when traveling through pipelines.

Pigging Frequency

The frequency of pigging operations depends on pipeline service, product characteristics, and regulatory requirements:

Piggable Pipeline Requirements

Not all pipelines are designed for pigging. A piggable pipeline requires:

• Consistent internal diameter (no internal diameter reductions >5%)
• Full-opening valves (ball or gate) throughout
• Long-radius bends (minimum 3D, preferably 5D)
• No dead legs or branch connections that could trap pigs
• Pig launcher at upstream end and receiver at downstream end
• Pig signaler/detector at launcher and receiver

2. Pig Types

Pipeline pigs are categorized by their function and construction. Selecting the appropriate pig depends on the pipeline geometry, product, and operational objective.

Utility Pigs

Utility pigs perform cleaning, batching, and displacement functions:

Inspection Pigs (Smart Pigs)

Inline inspection (ILI) tools, commonly called smart pigs, collect data about pipeline condition:

Pig Sizing

Pig diameter selection depends on pipeline size and type:

• Foam pigs: 1-2% oversized (compressible)
• Disc/cup pigs: Cups 2-5% oversized, body at nominal ID
• Smart pigs: Sized to specific pipeline ID by vendor
• Spheres: Typically 2% oversized when inflated

3. Launcher Design

The pig launcher (also called a pig trap or scraper trap) is a pressure vessel that allows pigs to be inserted into a pressurized pipeline. Proper launcher design is critical for safe and efficient pigging operations.

Launcher Components

Launcher Sizing

Launcher barrel dimensions depend on the largest pig to be run:

Closure Types

Launcher closures must be rated for full pipeline MAOP and designed for safe opening:

Launcher Orientation

Launchers can be horizontal or vertical, but horizontal is most common for ease of pig loading. Key orientation requirements:

• Eccentric reducer with flat side down (allows liquids to drain)
• Closure door accessible for safe operation
• Adequate clearance for pig handling equipment
• Drain at lowest point of barrel
• Vent at highest point

4. Receiver Design

The pig receiver (scraper trap) captures pigs at the downstream end of a pigged section. Receiver design is similar to launchers but with additional considerations for debris removal.

Receiver vs. Launcher Differences

Receiver Components

Receiver Barrel Sizing

Receivers require additional length compared to launchers:

• Minimum length: 2 × longest pig length
• Recommended: 2.5 × pig length for debris accumulation
• Multi-pig runs: Size for number of pigs between inspections
• Smart pig runs: Confirm tool length with ILI vendor

5. Material Specifications

Pig launcher and receiver materials must meet or exceed the pipeline design requirements. Material selection depends on pipeline pressure class, temperature, and service conditions.

Barrel Pipe Grade Requirements

Launcher and receiver barrels are typically one pipe grade higher than the mainline due to the larger diameter operating at the same pressure:

Closure and Fitting Materials

6. Piping and Valve Layout

Proper valve arrangement is critical for safe pigging operations. The piping layout must allow isolation, pressurization, depressurization, and bypass flow.

Launcher Valve Arrangement

Typical launcher valve configuration (upstream to downstream):

Receiver Valve Arrangement

Typical receiver valve configuration:

Pig Signaler (Passage Indicator)

Pig signalers detect pig passage at the launcher and receiver. They provide confirmation that the pig has left the launcher or arrived at the receiver.

7. Operational Procedures

Safe pigging operations require following established procedures for both launching and receiving. Never deviate from written procedures without proper authorization.

Pre-Launch Checklist

Launch Procedure

1. Load pig into barrel, oriented correctly
2. Inspect and lubricate closure seal
3. Close and secure closure door
4. Close drain and vent valves
5. Slowly open equalizing valve to pressurize barrel
6. Verify pressure equalization
7. Open launcher outlet valve fully
8. Open kicker valve to propel pig
9. Verify pig departure via signaler
10. Close kicker valve after pig departs
11. Resume normal flow configuration

Receive Procedure

1. Verify receiver inlet valve is open
2. Open bypass valve to maintain flow
3. Monitor for pig arrival via signaler
4. After pig arrival, close receiver inlet valve
5. Open vent valve slowly (stand clear)
6. Verify pressure gauge reads zero
7. Open drain valve, collect liquids/debris
8. Open closure following manufacturer procedure
9. Remove pig and debris
10. Inspect pig for wear, damage, or deposits
11. Document pig condition and debris recovered

8. Safety Considerations

Pigging operations involve significant hazards including high pressure, flammable gases, and heavy equipment. Proper safety measures are essential.

Primary Hazards

Personal Protective Equipment

• Safety glasses with side shields
• Hard hat
• Steel-toe boots
• Flame-resistant clothing (FRC)
• H₂S monitor (if applicable)
• Hearing protection (as required)
• Gloves appropriate for task

Minimum Safe Distance

Documentation Requirements

Maintain records of all pigging operations:

• Date, time, and personnel involved
• Pig type, size, and serial number
• Pipeline section pigged (launcher to receiver)
• Pig travel time
• Debris recovered (type and quantity)
• Pig condition after run (wear, damage)
• Any abnormal observations

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