EM Pig Tracking for Newbies - A Summary of Factors Affecting the Choice of Transmitter
To conclude our EM Pig Tracking for Newbies Series, here is a summary of the factors affecting the choice of EM transmitter, presented as a handy series of questions to give you a head start when you are selecting an EM pig tracking system.
In order to help you find the right transmitter for the job, a series of basic questions need to be answered. Some seem obvious and others not so much. We hope that providing a series of questions for you it will help you to save time and sometimes perhaps avoid designing an unpiggable line.
1. What is the pipe size?
This relates to the maximum circumference of the transmitter to be used which relates to max battery size and max coil size as well as the distance the signal has to travel before intersecting the pipe wall itself.
2. What is the pipe material of construction?
This relates to the amount of likely interference with the electromagnetic signal produced by the transmitter.
3. What is the pipe schedule or wall thickness
If the pipe wall material is a ferrous material the wall thickness further describes the amount of interference with the Electromagnetic signal produced by the transmitter.
4. If subsea, is this a Pipe in Pipe application? If so, provide answers for both pipe sizes involved to questions 1-3.
5. Is there a pipe coating?
In relation to EM transmitters this is primarily related to stack up distance between the transmitter and the closest position for a receiver.
6. If there is a coating, what is it made of and how thick is it?
See question 5.
7. What is the burial depth?
This relates to the closest position for a receiver to pick up the signal.
8. If offshore, how deep is it?
This relates to environmental pressures the transmitter could see.
9. What is the minimum bend radius in the line?
This relates to the maximum length that the transmitter can have. This will determine maximum number of batteries that can be employed again relating to life of the transmitter and max power of the signal.
10. How long is the pipe run that will be pigged? (Distance)
Along with speed this helps to establish maximum battery life required.
11. What type of transmitter do you need?
a. Will the transmitter be run immediately upon loading launcher and run to the end?
b. Is there a wait time such as a preloaded subsea launcher? How long will that be? Will you need a delayed transmitter start and what technology works best?
12. What is the pipe pressure maximum?
This will relate to materials of construction of the transmitter.
13. What is the flow media?
This will relate to materials of construction of the transmitter and elastomers.
14. What is the flow media velocity?
This helps to determine battery life requirements.
15. What is the maximum distance between tracking positions?
This will help the client to determine locating period.
16. What is the estimated wait and pinpointing time to locate a stuck pig?
This relates to maximum battery life required.
17. What is the temperature of the flow media, maximum/minimum?
This helps to determine chemical reactions potential and transmitter body materials and elastomers.
18 What is the maximum line pressure during the pigging run or hydrotest if the pig is required to be in the line during hydro?
This determines materials of construction and special mods/testing if required.
1. What type of pig is it? Foam, urethane or mandrel?
This determines if the pig body itself could be an interference problem as well as determining if the weight of a given transmitter could be problematic.
2. What is the length of the Pig? Is there a limit due to minimum bend radius or preloaded launcher max length?
Again, this relates to the maximum length of the transmitter therefore the maximum battery life possibilities.
3. What is the maximum cavity diameter in which to load the transmitter?
Maximum diameter limitation will determine maximum coil and battery types thereby transmitter power and battery life.
4. If a Mandrel pig, is the mandrel transmitter cavity section carbon steel, stainless steel or other?
If the mandrel is carbon steel the mandrel itself will reduce the transmitter signal before ever encountering the pipe wall. Stainless steel grades will greatly diminish or eliminate that effect.
5. What is the mounting system to be used to mount the transmitter?
6. Is there sufficient clearance for the pig to mount 1/2 of the transmitter extending out of the main body?
5 and 6 relate to the possibility to safely mount the transmitter in a foam or Urethane pig as well as extending the main body ½ way out of the pig to allow one lobe of the EM transmitter field to be able to transmit at full strength if in a carbon steel mandrel pig.
The Transmitter Application
1. Does the application require a Dual Rate function?
Do you need to use the transmitter as an alarm feature with a Smart Gauge Plate or other device where pulse rates change on a change of condition?
2. Is there a requirement to uniquely identify several pigs in a pig train?
In this instance rather than use different pulse counts with a 22Hz transmitter, which is not optimal for a given pig speed, you can use multifrequency transmitters with a multifrequency receiver.
3. Are their hazardous area certification requirements for the transmitter? ATEX/IECEx/UL/CSA?
This limits the available models and manufacturers.
As you see, just to get started in evaluating an application for an EM transmitter, there are a lot of things that need to be known to properly assist someone new to the business or with some unique requirements. I hope we have helped to “organize” some of these questions for you.