Pigging - Basic Precom

Pre-Commissioning Training #2

PIGGING

What's a pig exactly?

During their work, Pre-Commissioning engineers regularly use PIGs, but what's a PIG exactly?? In fact, a PIG (Pipeline Inspection Gauge as it seems...) is a nifty cylindrical tool that precom engineers send through the pipeline pipeline for multiple purposes.

Bi-Directional pig

Pigs can be:

Be of steel bodied kind:

Made of foam:

Pigs can be:

With electronics (or not...):

Made of gel:

Pig body

The material used for the body of the pig itself is very important and will depend of the pipeline! For a cladded line, you can use pigs with a body made in 316L (stainless steel). For a carbon steel line, you can use carbon steel pigs...

The importance of choosing the right pig

Pigs will be specifically designed for each system and for each purpose. The effect of choosing a pig that does not consider all aspects of the pipeline components and any anomalies introduces a considerable risk of a possible “stuck pig” situation that you want to avoid at all costs!!

Different types of pigs for different operations

Some of the many Pre-Commissioning operations, along with the type of pig used during them, are now detailed.

Pig (tool sent in the pipeline and used during most precom operations)

• Flooding:

For the flooding of the line, you use a pig with a standard set of seal disks fitted on their body.

Umbilical in underdesk basket on Normand Maximus

Different types of pigs for different operations

• Cleaning:

To perform this operation, you may use a pig which is fitted with brushes to allow internal cleaning of the pipe. Cleaning magnets may also be fitted to the cleaning pig in order to pick up and hold to remove ferrous debris such as electrodes or welding rods, old construction debris, corrosion product etc.

Pig fitted with cleaning magnets

Be careful, the material of the brushes shall be chosen considering the internal material of the pipeline

Wirebrush foam pig

Brush pig - spring mounted

Different types of pigs for different operations

• Gauging:

Gauging is necessary to make sure the pipeline is free of defects (ovalities, buckles…). To do that, a pig fitted with a circular aluminum gauging plate, usually 95% of the nominal ID or 97% of the smallest ID of the pipeline, is used (DNV standard). The plate is designed to bend should it encounter a buckle or restriction in the pipeline internal diameter. There are smart gauge plates which can create a timecode when it’s damaged to allow personnel to locate the flaw.

Pig fitted with Propipe multihit smart gauge plate

Gauge plate

Gauge plate fitted on a foam pig

Different types of pigs for different operations

• Multipurpose pigging:

Most of the time, the operations described above are performed in a single pig train run using a mandrel pig on which brushes, seals and gauging plates are fitted.

Multipurpose pig

Multipurpose articulated pig

Different types of pigs for different operations

• Caliper run (caliper pigs are detailed in the In-Line Inspection module):

Caliper pigs are sometimes used to inspect the line. This type of device would normally include electronic sensors that accurately measure and record the internal diameter of the pipeline along its entire length. Upon recovery of the pig, the recorded data can be downloaded and analyzed to confirm the presence of geometrical anomalies and their location.

Different types of pigs for different operations

• Multi-diameter pigging:

These can be designed to negotiate multiple known diameters in pipelines. A highly effective sealing capability can be maintained using these devices as part of an engineered solution. All diameters must be known to ensure sealing characteristics are maintained. For a valve bore:

What a pig may encounter

Ok, we get it, precom engineers like to send lots of pigs into pipelines. But what can a pig encounter during its run in the pipeline? (hover pictures for infos!)

There is numerous others things a pig might face during its run (poorly closed hydraulic devices etc.).

Pipeline design for pigging activities

Pipelines to be pre-commissioned should be designed to ensure a trouble-free pigging operation. A pipeline needs a consistent open bore from start to finish if it is to be pigged successfully. Obviously, this is never the case (it wouldn’t be funny otherwise...) so during the designing of a piggable pipeline, the following should be considered: Length of pig run Bend radius and degree of bend Valve type Tees Wyes Pipe inside diameter Dual diameter lines Distance between all items Internal material etc.

PLET Design Drawing

Pipeline design for pigging activities

Keep in mind that each project may require additional consideration regarding the pipeline design. Furthermore, each project contains a “Piggability Design Report”. This document is essential to all pigging activities since it will confirm the feasibility of a given operation. Here is an example of some distances to check before operating.

A pig will be designed to negociate ALL pipeline specs, whether they are a few meters from each other or a hundred kilometers away.

Launching and receiving pigs

As we do not send pigs by hand in the pipeline, we use a Pig Launcher & Receiver (PLR)! A PLR is used either topside or subsea during operations where a pig needs to be sent / received through the system when the preloading of a pig isn’t possible. This equipment will be manufactured according to the dimension of the pig (ID, length...), the number of pigs, ROV accessibility etc. You can use a temporary PLR (for precom for instance) or permanent PLR (that can be also be used during precom but also during production by propelling pigs with dead oil for instance).

12" PLR with hydraulic torque for ROV operations

PLR installed subsea with a quarter turn lever for ROV operations

Launching and receiving pigs

Pig tracking

Why do we track pigs in the first place? Tracking devices can be fitted to pigs. These are useful in a number of ways, for example to confirm launch or receipt of a pig, and also to allow the localisation of a stuck pig.

Vocabulary point: -"signalling" : indicating when the pig has reached a certain point in the pipeline -"locating": determining the position of a pig, usually when it is stationnary -"tracking": following the path of a pig continuously or at least locating it at a series of predetermined points

Where can a pig be located?

Depending of where you expect to localize the pig, the method used track it will change! Indeed, the medium / distance separating us from the pig will have an impact on the faisability / efficiency of each method. The method used to track pigs should be specified during the early stages of the project. Here is where pigs will usually be located.

In a buried offshore pipeline (rock dumping)

Topside

Subsea

In a buried onshore pipeline

General overview of tracking systems

Let's start with a general overview of the various methods we can use to localize our precious pigs in the pipeline. There are four main methods used to hunt them wherever they are:

• Magnet based systems
• Acoustic pingers
• Electromagnetic systems
• Radio isotopes systems

Here is a summary of the fields where those systems are the best (or not) at:

Launching and receiving pigs

Regarding their accuracy, here is how these different methods rank.

Trackers accuracy

And now, the crucial cost comparison.

Cost comparison

Radio isotopes systems

These are used to localize pigs. They are very reliable, precise, small but expensive. Licensed operators are required to install and retrieve the isotope and it must be accounted for at all times. When isotopes are used, the pigs are located using radiation detectors.

Isotope (it's very small!!)

Detector mounted on pipeline

Acoustic pingers

Acoustic pingers are the most common and cost effective method of pig location in subsea lines. A transmitter of some sort is mounted in the pig and pings are detected by receivers installed in a workboat. Hydrophones may be used by ROVs or divers.

Pig with acoustic pinger

Hydrophone for ROV

Transmitter

Ping receiver

Electromagnetic systems

A coil is placed on the pig. The unit attached to the pig contain a battery and a transmitter. The transmitter creates an alternative electromagnetic field which penetrates the pipe wall and surroundings. The receiver comprises a search coil, which displays the received signal on a meter, and an amplifier, which amplify it and makes it audible.

Transmitter

Receiver

Working principle of EM system

Magnets

Pigs can be tracked using magnetism. Magnets are installed in the pigs and sensors in the system detect the change in the magnetic field as the pig passes. The magnetometer is triggered by the pig and activates the pinger so the operator can detect it from far away.

Magnetometer

Examples of systems combinations

Main pig suppliers

Here is a quick insight at what the market of pigging equipment looks like for Pre-Commissioning in Saipem SA: (hover logos for some infos!)

The pigging market is quite big and changing so stay informed about it for new opportunities!

Pigging interfaces

During pigging operations, precom engineers are communicating with numerous internal / external interfaces. Here are a few of the many times a precom engineer will have to communicate with other entities (press the + button for more infos on internal interfaces!):

Now that you have a clearer view of what pigging during precommissioning involves, let's practice with some exercises!

• ROV for the study of the accessibility of ROVs to PLRs for example.

• INMET for the deployment and the recovery of the precom auxiliary equipment, especially PLRs that need to be installed either topside or subsea. INMET may be contacted for the valve management plan (all valves must be open when the pigs pass) and the deck layout of the pigging spread. Pigs may also be preloaded in units prior to their installation. Finally, precom department must look at the level line of the layout planning from INMET to verify if there is any declivity which could influence pigging direction.

• Flexible for pig design in hoses

• Structure design for the piggability of the proposed design, the PLR design.

• Equipment for piggability given the valve design, ensure flow rate when pigging.

• Welding for the presence of welding tools, paper plugs etc. in the pigged pipeline

• ROV for the study of the accessibility of ROVs to PLRs, possibility to carry a signal receiver...

• INMET for the deployment and the recovery of the precom auxiliary equipment, especially PLRs that need to be installed either topside or subsea. INMET may be contacted for the valve management plan (all valves must be open when the pigs pass) and the deck layout of the pigging spread. Pigs may also be preloaded in units prior to their installation. Finally, precom department must look at the level line of the layout planning from INMET to verify if there is any declivity which could influence pigging direction.

• Flexible for pig design in hoses

• Structure design for the piggability of the proposed design, the PLR design, where can pig tracking equipment can be fitted considering PLR design

• Equipment for piggability given the valve design, ensure flow rate when pigging.

• Welding for the presence of welding tools, paper plugs etc. in the pigged pipeline

• Survey for frequency management system (prevent that tracking equipment / ROV use similar frequencies to communicate...)

• Painting / Coating to check if tracking equipment won't be impaired by coating etc.