How frequent should I run pigs? What is the best material for my prover sphere? How can we eliminate rust on flanges and bolts? Answers to these and more questions can be found in this section.
What is an effective pigging speed?
Many factors go into determining effective pigging speeds such as, the pigging objective (cleaning, batching, sweeping liquids etc.), what product you are running in and if you are running on-stream, etc.
Cleaning or utility pigs when run on-stream will have the speed dictated by the flow rates. We have seen that range from .2 mph to 20 mph. These are extremes and tend to be less effective. However, some good guidelines are as follows: Liquid lines 1-4 mph and gas lines 5-10 mph seem to be most effective.
How often should maintenance pigging be done?
We work with lines that are pigged every day, both liquid and gas, and those pigged once a year. Frequency should be based on the particular need of the line.
As a rule of thumb, the closer to production the line is, the more need there is for pigging. For example, crude oil lines that have potential for wax build up or known build up are often pigged weekly.
Some general guidelines are as follows:
|Crude oil lines near production||weekly or bi monthly|
|Crude oil lines away from production||monthly or quarterly|
|Wet gas||bi monthly or monthly|
|Dry gas||quarterly or semi annually|
|Product lines||quarterly or semi annually|
What should be used on a mandrel pig, cups or discs?
Discs, when sized properly, do a very good job of displacement, cleaning and sealing. However, on longer runs discs may wear out sooner than cups and potentially lose its sealing capabilities. Unlike cups, Discs are bi-directional and can be used when the pig will be reversed during operations such as hydro testing or when potential problems could require reversal.
Although cups are less aggressive than discs when it comes to cleaning, there are several advantages cups have over discs. Cups get longer wear or more mileage than discs and are capable of negotiating greater reductions in pipe ID and can maintain a seal in “out of round” pipe. Also, cups often make launching a pig easier, especially if low flow rates are present, because of the cups ability to feed into the reducer and maintain a seal.
NOTE: Recent years have seen the development of cups/discs combined in a cup configuration to try and achieve both benefits.
What is the proper size for spheres (balls) to be sized at when used for pigging?
Liquid lines 2% - 3% over the pipe id.
If multiple ID’s such as heavy wall riser and standard wall pipeline, we may go 1-2% over the largest ID.
Gas lines 0% - 1% over pipe id.
With multiple ID’s, we may use the same consideration as above.
What is proper sphere (ball) material for pigging?
In crude oil, we suggest neoprene unless you have sour crude, high chemical counts, or high pressure. Although not as tear resistant as urethane, neoprene is more resistant to UV rays and aging than urethane.
In natural gas and products, we suggest urethane. The hardness (durometer) can be varied and less susceptible to chemicals, H2s, and high pressure. The norm is to use higher durometer (hardness) to prevent penetration. In low-pressure gas systems, neoprene is sometimes used for the benefits mentioned above in crude.
What is the proper size for spheres (balls) to be sized at when used for liquid measurement?
The most common request from operators and measurement personnel that we encounter is 3% over pipe id. The next most requested is 2% over pipe id. These sizes account for at least 95% of sphere request. Both provide good seal and function. On larger provers, balls are sometimes sized larger to account for pipe tolerances.
What is the proper material and durometer (hardness) for Measurement Prover Spheres?
Neoprene and Urethane are the two primary materials used for prover spheres. Neoprene is typically used with crude oil and often for water draws. Neoprene provides a good seal and long life but because of the softness (50-53 durometer), we do not use Neoprene in high pressure situations or high chemical content.
Urethane is the most widely used product for prover spheres and can be formulated for various hardness. Twenty years ago, probably 70% of all prover spheres were 53 durometer urethane. As chemicals and additives became more prevalent, spheres began to be attacked and break down. Today, probably 70% of the spheres are of higher durometers, 58 green, 65 blue, etc. Urethane is used in provers for crude oil, refined products, LPG products, and water draws.
Can Trenton #2 tape be used below ground?
#2 Trenton can be used underground in the same manner as #1 is used with the correct primer. The correct primer is called Temcoat, and is similar to the primers normally used. It is a little thicker/heavier but application is the same—a thin layer worked into the wall of the pipe. It is good to use with cathodic protection on the line and allows a one tape system (#2 and Temcoat) to be used at the ground interface rather than the old two tape system of #1 next to the pipe with #2 on top of the #1.
Can something be done offshore to eliminate rusting flanges, bolts and piping?
Trenton #2 tapes (brown, aluminum, white) with the standard brown or white primer can eliminate much if not all of these issues above the splash zone. Trenton #2 Wax Tape is UV protected; it hardens to the touch and can be painted after 2-3 weeks. The space between flanges should be filled with primer or Trenton hot wax and then make an outer wrap on the flange. Many customers also wrap the studs and nuts and thus protect the whole flange. Miscellaneous piping can be wrapped in the same manner with Primer and #2 Trenton Wax Tape.
Can Pikotek VCS flange insulation gaskets (raised face) be used on both raised face and RTJ flanges?
The answer is yes. The VCS (Very Critical Service) gasket has a corrosion resistant core of stainless steel (316). The core has a high density composite reinforced material permanently laminated to the core. Together, this provides the structural backbone for additional sealing elements (Teflon-spring energized or Viton) and provides the structural strength and integrity found in conventional RTJ rings. See our Pikotek section to learn more.
Other Important Information
Here is the world's first patented pig. First patented in 1885, the Go-Devil was originally called "Pipe Line Cleaner". It was invented by John S. Klein for the National Transit Pump and Machine Co. out of Oil City, PA. We were fortunate to get our hands on one of the last ones that had leather cups on it (later replaced by rubber). Until recently, we still had a couple customers using them in East Texas. It was actually a pretty effective scraper on paraffin wax.