Product Characterization, Pigging, and Pigging Frequency

FourQuest has extensive experience removing various debris types from pipelines; the types and amount of debris vary depending on the service of the pipeline.

For example, pipelines are typically limited to construction debris, corrosion, and water during construction. If a pipeline is in service, depending on the commodity, the following table shows typical types of debris.

Typical Pipeline Debris
Service	Type of Debris
Refined Products	Corrosion Product
Crude Oil	Hard and Soft paraffin (wax), asphaltenes, sand, hard scale, corrosion product
Multiphase	Hard scale, sand, wax, corrosion product
Injection Water	Hard scale, sand, corrosion product
Dry Gas	Corrosion product, compressor oil, black powder

Once the type of debris is characterized, a pig recommendation and application program can be established. Utility pigs are divided into two groups: cleaning and batch/seal pigs. Each group can be designed in many different forms. The following tables show pig selection depending on the cleaning and treating application:

The benefit of mandrel pigs is the ability to customize different parts to target desired contaminants. For example, light and heavy crude petroleum will develop not only corrosion product, but also hard and soft paraffin, asphaltenes, sand, and hard scale. Depending on ILI tool, lab, and visual inspection results, we can optimize the use of the mandrel pig. Some customizable applications are but not limited to:

1. Jetted Cups – These cups efficiently break up large volumes of accumulated pipeline wax and sand by directing bypass product through it’s jetted grooves. The debris is then suspended in the turbulent flow and transferred ahead of the pig.
2. Carver Disk – This disk has diagonal grooves which provides numerous edges to scrape the pipe internal wall removing wax, scale, and other pipeline debris.
3. Dual Body Configuration – To increase cleaning capabilities and reduce durations, using a dual body configuration utilizing a knuckle adaptor will double the cleaning power in a single run.

Determining the optimum pigging frequency involves a thorough understanding of the product(s) being shipped. The characteristics of deposition (heavy hydrocarbons or sediments) or water is analyzed in laboratory evaluation. By performing static and dynamic settling tests on pipeline products, a starting point is established to determine the frequency of pigging required based on the deposition rate.

Additionally, FourQuest studies the interface between batches of pipeline products, as often a unique “incompatibility” occurs between two products, causing rapid deposition due to a shift in the equilibrium of either product.

FourQuest relies on simulation programs to understand the dynamics of flow in the pipeline system and relates this knowledge to the results of settling tests to establish a starting point in pigging frequency.

Optimization of pigging frequency occurs from data collected during utility pigging runs. Basic parameters from cleaning runs that are used to confirm/adjust pigging frequency include:

• Pig speed – if the speed is not constant, there is a likelihood of debris accumulation in front of the pig
• Pig rotation – if the cups and disc are not worn evenly, there is a likelihood of debris accumulation preventing the desired “rifle” rotation of the tool
• Debris in front of the pig at receipt – the volume of debris can be assessed and calculated to reveal the thickness of debris removed. Further, the debris can be analyzed to confirm the baseline lab study of deposition. The hardness of debris will confirm the type of cleaning disc or cup that is best suited to minimize the number of pigging runs
• Debris packing during the pigging process – is a strong indication of heavy debris in the line and a soft durometer disc of cup which has floated over the debris. This is an indication to change the configuration of the cups/discs and the hardness of the urethane

FourQuest is always aware of the negative effects of deposition in a pipeline and specifically looks for precursors to corrosion in the deposits removed from pigging operations and the role it plays in under-deposit corrosion. Maintaining a clean operating surface in a system mitigates under deposit corrosion, improves throughput, and lowers pump energy costs. FourQuest recognizes that water in a pipeline system poses the greatest risk to corrosion and has worked extensively with clients in the interpretation of water analysis and interpreting its effect on corrosion:

Routine Water Chemistry Test – provides a baseline condition/characterization of water found in the pipeline and removed from pigging operations.

1. Physical Tests – conductivity, Alkalinity as HCO3/CO3/OH, Hardness CaCO3, pH, total dissolved solids (TDS)
2. Anions and Nutrients – Chloride, Fluoride, Nitrate, Nitrate + Nitrite, Nitrite, Sulfate
3. Ion Balance – Cations/Anions
4. Dissolved Metals – Aluminium, Antimony, Arsenic, Barium, Beryllium, Bismuth, Boron, Cadmium, Calcium, Chromium, Cobalt, Copper, Iron, Lead, Magnesium, Manganese, Molybdenum, Nickel, Potassium, Selenium, Silver, Sodium, Strontium, Thallium, Tin, Uranium, Vanadium, Zinc, Zirconium

Conductivity – The conductivity result is the electrolyte’s (water) ability to transfer ions between the cathode and anode in an electrochemical reaction. The higher the conductivity, the greater the ability to transfer ions, hence the stronger the corrosion reaction.

pH – The pH of water is analyzed to understand if a corrosive effect occurs as a result of acids in the water. This information helps characterize the risk of prolonged water presence in the pipe and its effect on metal loss.

Linear Polarization – Linear polarization resistance (LPR) is a quick, nondestructive testing technique commonly used in material corrosion studies to provide corrosion rate data. This information helps define the risk of prolonged water presence in the pipe and its effect on metal loss.

Microbial Analysis – BART provides detailed insight into various bacteria types that can be characterized by their quantitative presence and their effect on corrosion. Identifying bacteria types will result in understanding corrosion and mitigating attacks. Common BART Tests are:

• Sulfate Reducing Bacteria
• Heterotrophic Aerobic Bacteria
• Acid Producing Bacteria
• Iron Related Bacteria
• Slime Forming Bacteria