Study guide
9.3 Pigging, Cleaning & Drying
API 1169 Pipeline Construction Inspector Exam
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1 Chapter 1: Introduction & Exam Overview
1.1 Current Exam Facts & Logistics 1.2 Eligibility Pathways & Application 1.3 Publications Effectivity Sheet & On-Screen References 1.4 Scaled Scoring, Passing Score & Results 1.5 Study Strategy, Recertification & Web Quiz
2 Chapter 2: Inspector Roles & Quality Management
2.1 Inspector Roles, Responsibilities & Authority 2.2 Quality Assurance Records & Documentation 2.3 Hold Points, Witness Points & Inspection Test Plans 2.4 API Spec Q1 Quality Management System
3 Chapter 3: Safety, Environmental & Qualifications
3.1 Safety Roles, Stop-Work & Site Safety 3.2 Environmental Controls, Permits & SWPPP/BMPs 3.3 Training, OQ & Personnel Qualification
4 Chapter 4: Front-End Construction
4.1 Survey, Staking & Alignment Sheets 4.2 Line Locating & One-Call (CGA) Coordination 4.3 ROW Clearing, Grading & Topsoil Segregation 4.4 Permits, Encroachments & Landowner Requirements
5 Chapter 5: Stringing, Bending & Welding
5.1 Stringing, Material Identification & Handling 5.2 Bending: Ovality, Wrinkles & Equipment 5.3 Welding Procedures, Qualification & API 1104 5.4 Consumable Control, Weld Docs & Repairs
6 Chapter 6: NDE, Trenching & Crossings
6.1 NDE Methods, Acceptance Criteria & Documentation 6.2 Trenching & Excavation Safety 6.3 Crossings, HDD & Drills 6.4 Cased vs Uncased, Bore Specs & Voids
7 Chapter 7: Coating, Padding, Lowering-In & Tie-Ins
7.1 Coating Procedures, Qualification & Field Joints 7.2 Padding & Lowering-In 7.3 Tie-Ins: Alignment, OQ & Material ID 7.4 Coating Repair, Holiday Inspection & Testing
8 Chapter 8: Back-End — CP, As-Builts, Backfill & Restoration
8.1 Cathodic Protection Installation & Test Leads 8.2 As-Built Survey, Redline Drawings & Weld Maps 8.3 Backfill & Buoyancy Control 8.4 ROW Cleanup & Restoration
9 Chapter 9: Hydrostatic Testing & Pigging
9.1 Hydrostatic & Pneumatic Testing (API RP 1110 / INGAA CS-S-9) 9.2 Gauge Plates, Deformation & Test Failures 9.3 Pigging, Cleaning & Drying
10 Chapter 10: Post-Construction & Turnover
10.1 Line-List Closeout 10.2 Final Completion Assessment & Punch-Out 10.3 Turnover to Operations & Documentation Packages
9.3 Pigging, Cleaning & Drying
Key Takeaways Explain This Topic AI
After the hydrotest and before turnover, pigs are run through the line to remove water and debris — cleaning pigs (brush or scraper), gauging pig, and drying pigs (foam) — using a pig launcher and receiver
Drying methods include air blow, vacuum drying, foam-pigging, and a methanol sweep for gas lines; the method is selected to meet the moisture specification for the service
Dewatering and drying are especially critical for gas lines because residual water forms hydrates (ice-like solids) with natural gas at operating pressure and temperature and accelerates internal corrosion
The inspector verifies the pigging sequence, the gauge plate condition after each run, drying to the specified moisture dew point or criterion, and the complete pigging and drying documentation
API does not publish official domain weights; pigging, cleaning, and drying fall under Back-End Construction (BOK area 4) with an unofficial practice estimate near 22%
Last updated: August 2026
Pigging, Cleaning & Drying
Quick Answer: After the hydrotest and before turnover, the pipeline is pigged to remove test water and construction debris, then dried to the moisture specification for its service. Cleaning pigs (brush or scraper), a gauging pig, and drying pigs (foam) are launched from a pig launcher and received in a pig receiver . For gas lines, drying is especially critical because residual water forms hydrates (ice-like solids) with natural gas and drives internal corrosion.
Why Pig After a Hydrotest?
A hydrotest leaves the pipeline full of water and any debris dislodged during the test — weld slag, dirt, rocks, tools, and scale. Turning the line over to service in that condition would carry that water and debris into the product stream, foul valves and meters, and — in a gas line — create hydrates and corrosion. Pigging, cleaning, and drying are the bridge between a successful hydrotest and a line ready for product.
Pig Types and Their Post-Hydrotest Roles
Pig Type Construction Purpose in Post-Hydrotest Sequence
Cleaning pig (brush) Poly body with wire or nylon brushes Remove weld slag, scale, and loose debris from the pipe wall
Cleaning pig (scraper/cup) Poly body with urethane cups and scraper blades Scrape stubborn deposits and push free water ahead
Gauging pig Pig carrying a gauge plate sized near pipe ID Confirm the bore is clear and round after the test (see 9.2)
Foam pig (swab) Open-cell polyurethane foam cylinder Push remaining water out and absorb moisture; repeated runs dry the line
Sphere Inflatable elastomeric sphere Batch and displacement duties, often in liquid lines
Smart pig (ILI tool) Instrumented pig with sensors Not typically a post-hydrotest tool; used for in-line inspection of in-service lines
The post-hydrotest pigging sequence typically runs: cleaning pig(s) → gauging pig → foam (drying) pigs , repeated as needed until the receiver shows no debris and the foam pigs return dry.
Pig Launcher and Receiver
Pigs are introduced through a pig launcher at one end of the section and removed through a pig receiver at the other. Both are pressure-rated vessels with a barrel larger than the pipe ID so the pig can be loaded or removed, kicker lines to drive the pig, and isolation valves. The inspector verifies:
The launcher and receiver are correctly installed and isolated before opening.
The pig is loaded in the correct orientation (cups/blades pointing in the direction of travel).
The receiver is depressurized and vented before the pig is removed.
No one stands in front of the open receiver barrel — a pig can exit with significant force if the receiver is inadvertently pressurized.
Drying Methods
Once the free water is pushed out by pigs, the line must be dried to the moisture specification for the service . The four common methods are:
Method How It Works Typical Use
Air blow (dry air purge) Forced dry, filtered air is blown through the line until the outlet dew point meets spec General service; simple and widely used
Vacuum drying The line is evacuated with a vacuum pump; water boils off at low pressure Lines with long or complex profiles where air flow is uneven
Foam-pig drying Repeated foam pig runs absorb residual moisture until the pigs return dry Supplement to air blow or vacuum; polishing step
Methanol sweep A batch of methanol is pushed through the line to absorb water, then displaced Gas lines, especially where hydrate risk is high and dew-point drying is insufficient in the available time
The acceptance criterion is usually a dew point (e.g., a specified dew point at line pressure) or a moisture content limit in the project specification. The inspector verifies the criterion, the method, and the recorded dew-point or moisture readings.
Why Gas Lines Demand More
In a gas line, residual water combines with natural gas at certain pressures and temperatures to form hydrates — ice-like crystalline solids that can block valves, restrict flow, and damage equipment. Water also drives internal corrosion , particularly in the presence of CO2 or H2S. For these reasons, gas-line drying specifications are typically far more stringent than liquid-line specifications, and a methanol sweep is often used in addition to air blow or vacuum drying to suppress hydrate formation during commissioning. The inspector confirms the drying method and acceptance criterion match the service (gas vs. liquid) and the project specification.
Dewatering to Moisture Spec
"Dewatering" covers both removing the bulk test water and drying the residual moisture. The sequence is:
Bulk removal — run cleaning and foam pigs to push the free water out through the receiver.
Drying — apply the selected drying method (air blow, vacuum, foam, methanol sweep) until the outlet meets the dew-point or moisture criterion.
Verification — record dew-point or moisture readings at intervals until the criterion is met and stable.
Documentation — record the pigging sequence, pig runs, debris observed, drying method, and final moisture readings in the turnover package.
Inspector Verification and Documentation
The API 1169 inspector's post-hydrotest pigging and drying responsibilities are to verify:
The pigging sequence was followed (cleaning → gauging → drying).
The gauge plate condition after each gauging run (see 9.2).
The drying method and acceptance criterion match the service and project spec.
The final moisture or dew-point readings meet the criterion and are stable.
The pigging and drying records are complete and included in the turnover package.
The launcher and receiver were operated safely (isolation, venting, no personnel in front of the open barrel).
A line is not ready for turnover until it is clean, dry to spec, and documented. A common field finding is a line turned over with foam pigs still returning damp — the drying criterion has not been met, and the turnover is premature.