Pigging

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Pre-Commissioning Training #2

PIGGING

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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 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. Selecting a pigging tool without thoroughly accounting for all pipeline components and potential anomalies significantly increases the risk of a stuck pig incident—an outcome that must be avoided 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.

Basic flooding pig fitted with seals

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 ferrous debris such as: electrodes, 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. For instance, you won't use wire brushs for a coated line...

Brush pig - spring mounted

Different types of pigs for different operations

• Gauging:

Gauging is necessary to make sure the pipeline is free of geometrical 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

Smart gauge plate that recordstimestamps for each hit

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 pigs on which brushes, seals and gauging plates (at least two gauge plates in the pig train) 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.

ILI tool

Different types of pigs for different operations

• Pigging in risky / unknown conditions:

Pigging may be risky as the pig can get stuck into the line. To prevent that, for instance on the first run, a foam pig may be used. These are available in various densities of foam and can be used in applications where the passage of the pig may be hampered or restricted due to unknown factors such as high debris presence, multiple diameters, or even to dislodge a stuck pig.

Foam pig

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:

Different types of pigs for different operations

• Pigging using gel pigs:

Gel pigs are a mixture of chemicals injected into the pipeline that forms some kind of gel that you can use as an interface with the fluid. There are different types of gel pigs for different applications (it's their composition that changes their application). They can be launched without a launcher and can be useful for unpiggable lines.

Gel pig

It must be reminded that the use of gel pig is more time-consuming than the use of foam pigs etc. since you must perform some tests to find the right concentration of chemicals that will allow you to efficiently push the fluid!

Gel slugs

Gel slugs may also be used during precom operations, but they replace fluid, not pigs! Here are some examples:

• MEG gel for drying and dewatering. It improves the sealing capacity of mechanical pigs and mitigate the risk of water bypass backward if the pig is stalled, and gas bypass forward.
• Debris pick-up gel during cleaning operation

MEG gel

Keep in mind that these are only the usual operations that a pig performs. A lot of ways of using them exists and projects are constantly innovating (reeling with pigs, check valve pigs etc.)!

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 opened valves 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

VALVES

PIPELINE INTERNAL DIAMETER

BENDS

WYES

TEES

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 also be used during precom but also during production by propelling pigs with dead oil for instance).

PLR with hydraulic torque for ROV operations

PLR installed subsea with a quarter turn lever for ROV operations

Launching and receiving pigs

Launching and receiving pigs

To successfully perform Pre-Commissioning operations using a PLR, the engineer must know what he wants to do with it and the related characteristics he must gather prior to the operation (FCG: what flowrate? ; Hydrotest: valves pressure class ; Vertical or horizontal?...). He must also be aware of the environment in which the PLR is going to operate (internal pressure for hydrotesting, external pressure (collapse risk in deep water), valves to go through, debris expected, installation method, deck space, duration subsea & fluid (painting / external and internal coating) ...).

PLR coating ongoing

Launching and receiving pigs

Here are some guidelines to keep in mind during definition / specification of a PLR:

• Go for the best quality possible: no compromise with flowrate or pressure must be done to avoid risk when operating. PLR is indeed a costly item but that’s a few hundred thousands bucks in order to save millions.

• Keep it as standard as possible for valves / stabs. You want to optimize it while keeping it simple.

• Keep the number of different stabs and other consumables as low as possible on a field.

• Listen to other disciplines engineers even if you don’t accept everything they say since you’re the one operating PLRs.

PLR manufacturing

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 to track it will change! Indeed, the medium / distance separating us from the pig will have an impact on the feasability / 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. The sensitivity and effectiveness depends not only on the strength of the isotope but also on the pipeline depth and material condition / type around the pipeline (for instance, wet soils will shield a lot of radiation).

Isotope (it's very small!!)

Detector mounted on pipeline

Radio isotopes systems

Isotopes often have a half-life of many years. That could become a serious issue if the isotope mounted on a pig somehow falls out. Thus, an alternative is to use a short-life isotope that have a half-life of roughly 24h so it won't be a hazard for long in case it falls out the pig. However, it will be necessary to use a stronger initial source to have an adequate signal along the entire pipeline.

Isotope emergency container & tools

Isotope base container & tools

Acoustic pingers

Acoustic pingers are a common 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. Units are generally activated by a through water contact and can be provided with battery life up to a few thousand hours. These do not work well in gas pipeline in production since the signal loses its strength in gas atmosphere.

Pig with acoustic pinger

Diver held receiver

Pinger

Ping receiver

Electromagnetic systems

Those are usually used for land pipelines and increasingly for gas and buried lines. 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 detectable.

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. They may be used underwater but the magnetometer must be placed near the pipeline. One method that has been used is to place a system combining magnetics and pingers on or near the pipeline. The magnetometer is triggered by the pig and activates the pinger so the operator can detect it from far away.

Magnets

For better results, the pig body shall be made of stainless or other non-magnetic material to avoid reducing the strength of the magnetic field generated by the magnet. Magnets placed on standard utility pig bodies can be used but will be much less effective.

Pig fitted with magnets

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 standards

You will rely during the engineering of pigging operations not only on the company's applicable standards but also on international standards. You can keep those in mind for general pigging requirements:

DNV-RP-F115

DNV-ST-F101

API RP 17P

API Spec 5L

ISO 13623-2017

Pre-Commissioning of submarine pipelines

Petroleum and natural gas industries— Pipeline transportation systems

Recommended Practice for Subsea Structures and Manifolds

Submarine pipeline systems

Specification for Line Pipe

Pigging documents

Most Pre-Commissioning operations include some pigging. However, some procedures describes / specify how the pigging will be done, which pigs must be used etc.: - Piggability study: This document details the pigs to be used in accordance to the system design (valves, radii, pipeline features...). It must be very precise to ensure every characteristic is taken into account to ensure successful pigs runs. The study will be provided to potential subcontractors.

Example of conclusions of piggability study for a production system

Pigging documents

- Pigs & Pig Tracking Scope Of Work: This document will be sent to subcontractors to bid for the project. It details which operation must be performed, the pigging equipment to be provided as well as infos on personnel requirements, key dates, permits etc.

Extract from Pigs & Pig Tracking SOW

Pigging documents

The Pre-Commissioning subcontractor will often provide to you a document including all pigs drawings, pig specs, pig tracking equipment and its user manual etc. The pigs & pig tracking equipment are usually contracted by the precom subcontractor. The In-Line Inspection pig will be found separately from other pigs as some companies are specialized in ILI runs and ILI data analysies (NDT Global for instance).

Extract from ILI report

General checks

Refer to Pre-Commissioning department checklists to see general checks to be done before, during and after pigging operations and also for detailed PLR design:

CHECKLIST: PLR Design

CHECKLIST: Pigging of pipeline system

Some international standards (DNVGL for instance) also provide checklists regarding some of the pigging operations.

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

• Design for the piggability of the proposed design, out of roundness, bends, structures design, the PLR design, where can pig tracking equipment be fitted considering PLR design

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

• Welding for weld penetration, 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.