post mid sem

7/30/2019 Post Mid Sem

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1.Name and define in brief about different types of pigs?Pigs are categorized as either "utility" pigs or "intelligent" pigs. See

Figure 11 .

Figure 11

Utility pigs have very few moving parts and they are primarily used for product

separation and cleaning. Different types of utility pigs include:

Spheres, Foam pigs, Gel pigs, Cup pigs, and Bi-di pigs

Figure 12 illustrates these various types of pigs.
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Figure 12

Selection of utility pigs depends upon the type of operation

2.Notes on Intelligent piggingIntelligent pigs

Intelligent pigs are more complex, and contain devices such as sensors,

recording packages and batteries etc. They are used for such purposes as

pipeline diameter gauging, leak detection, curvature monitoring, crack

detection, and corrosion monitoring.

Intelligent pigs provide early indications of unusual pipeline conditions, and

thus help prevent actual failures through the implementation of pre-plannedrepairs, thereby saving unscheduled downtime and unplanned costs. Figure 1

shows a typical intelligent pig and Figure 2a and Figure 2b show a table that

provides a summary of various commercially available intelligent pigs and

their application.
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Figure 1

Figure 2a

Figure 2b

One type of intelligent pig that has been gaining wider use is the magnetic flux


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pig. In this pig, a sensor records the magnetic flux leakage across the pipe wall

to detect any defects or reduction in pipe wall thickness. Figure 3 and Figure 4

explain the principle of magnetic flux pig operation.

Figure 3

Figure 4


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Another type of intelligent pig that detects metal loss is an ultrasonic pig.

Figure 5 Illustrates the principle of ultrasonic operation and Figure 6 shows a

typical ultrasonic instrument.

Figure 5

Figure 6


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4.Explain the pig receiver/ launcher and the accessories on them, functions of all

accessories installed and the precautions to be taken while designing/ constructing

them?

PIG TRAPS/LAUNCHERS/RECEIVERS

Pig traps are used for inserting pigs into a pipeline then launching, receiving, and

finally removing them without flow interruption. Pig traps are not generally

proprietary products and are usually made to a specification drawn up by the user.

However, pig trap closures are proprietary products and form a critically important

part of a pigging system. Safety is a major consideration in the selection of a

closure. All closures must have a built-in safety lock which prevents them being

opened while the trap is pressurized.


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The pig must fit loosely in the launcher/receiver so the barrel of the

launcher/receiver must have a greater diameter than the pipe itself. When the pigis received the fluid has to pass around the pig in the barrel, so it would be a good

idea to give the barrel a cross sectional area of about twice that of the line pipe, In

your case say 28 inches. That will ensure that the velocity of the fluid passing

around the pig is similar to the flow rate in the pipe when one or more pigs are in

the barrel. You can make the barrel diameter smaller, however I would size it so

that the flow velocity around the pig is less than 20m/s when flowing gas and


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4m/s when flowing liquid. Be generous with barrel length. It is common for the

barrel to hold a batch of pigs (say four or six pigs). Also, if you are going to use an

intelligent pig on this line you will be surprised how long they can be. Find out

what pigs you are going to use and make sure the barrel has adequate length.

The reducer between the line and the barrel is not a trivial issue. I would use an

eccentric reducer with the flat side on the bottom, at least on the launcher. A pig

is easier to launch when the barrel and the pipeline bottoms are on the same

level. If you use a concentric reducer it is difficult to raise the pig up at the end of

the barrel and stick its nose into the line. Also, it sits there at an angle and

sometimes jambs.

If your launcher already has a concentric reducer then design a sliding carriage

which you can use to locate the pig on the centre-line and slide it down the barrelinto the mouth of the pipeline. This arrangement will also require a rammer to

ram the pig into the mouth of the pipeline so that the carriage can be withdrawn.

A sturdy wooden pole will do. Do not use aluminum in the sliding carriage and

rammer because aluminum creates sparks when struck on rust. The barrel must

be fitted with a closure and it is normal to install a quick opening closure. These

are expensive pieces of equipment but make opening the barrel an easy task. The

closure mechanism MUST have a means of ensuring that it cannot be opened

when there is pressure in the barrel. This normally takes the form of a small valve

that accesses the barrel through the closure which must be open before theclosure can be opened. It would be very dangerous indeed to open a closure when

there is even a small pressure in the barrel so you MUST have a warning device.

The launcher/receiver must have an isolation valve between the barrel and the

pipeline. That valve MUST be a full bore valve to allow the pig to pass unrestricted

into or out of the barrel. I am sure all of the valves on your pipeline will be full

bore so that pigs can pass unrestricted through the pipeline. Also, it is very

important that this valve have high quality sealing. It must be either a soft seated

ball valve or a ball valve with metal to metal seating where the seats are groundand lapped-in to affect excellent sealing. This valve is the only barrier you have

between the line contents and yourself when the closure is open, and if it leaks

you will not only have fluid all over the show, but you may also find it impossible

to open or close the closure because you cannot get rid of the pressure or the

flow.


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For the same reason, the barrel must have a good drain valve if it is a liquid system

or a good vent valve if it is a gas system. You need those to depressurize the barrel

before opening it. Be generous with the sizing. It is very common for the barrel

isolation valves to leak with time. Your colleagues may well need the gooddraining capability twenty years down the track.

Each barrel is attached to the pipeline through a TEE. The line runs straight

through the tee into the barrel, and the fluid is diverted around the barrel through

the branch of the tee. Generally the tee is an equal tee however it is also common

for the branch to reduce a size or two. The problem with this tee is that when a

pig passing through it could attempt to travel down the branch and not the

straight run, so it could jamb in the tee. To prevent that ALL TEE's on a pipeline

with a branch size more than say 40% of the pipe diameter is barred. Barringmeans that steel bars are welded across the branch of the tee flush with the

inside of the pipe to guide the pig through the tee and to prevent it moving into

the branch. There are a number of ways of doing this. The simplest and cheapest

is to weld bars in there. That must be done with care to ensure that the welding

does not affect the metallurgy of the tee or introduce cracks or imperfections. You

may even have to heat treat the tee after welding. Another way is to weld a short

stub of pipe onto the branch and to design plates that weld into that sub that

protrude out into the tee where they act as bars. This whole assembly is heat

treated after manufacture and then simply welded on the branch of the tee.Another way to do it is not to cut the line at the tee at all but to install a tee that

wraps around the pipe. The branch of the tee is accessed by cutting slots in the

pipe in the branch area.

The tee must be located on the pipeline side of the barrel isolation valve and if it

has a wall thickness greater than the line pipe, the inside diameter must be

transitioned at a slope of about 1 in 4 down to the line pipe inside diameter. If this

were not done the ledge created between the two pipe sizes could jamb the pig.

It is common practice to install a pig signaler (called a pig sig) downstream of thebarrel isolation valve and the tee. This means that on the launcher the pig sig sits

downstream of the tee and one the receiver it sits on the piece of pipe between

the isolation valve and the reducer into the barrel. They are placed at that location

because both the tee and the valve are capable of jamming the pig, so if the pig

sig activates there is absolutely no doubt that the pig is either on its way or safely


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in the receiver. Make sure you put a short length of pipe between the reducer and

the barrel isolation valve. That pipe gives space for the nose of the pig in a

launcher, and is a good place to locate the pig sig in a receiver.

The only other thing required is the bypass line around the barrel isolation valve.This is called the kicker line. It generally tees off from the branch line from the

main tee I described above, and connects to the launcher or receiver barrel. You

would not tee off the main line with the kicker line because that would require a

second barred tee. It is not critical where it stabs into the barrel but it would seem

a good idea to stab into the closure end of the launcher (to get behind a pig to

push it) and into the reducer end of a receiver (to push the pig to the closure end

of the barrel). The kicker must have at least one isolation valve with the same

excellent sealing capabilities as the barrel isolation valve for the same reasons as

the barrel isolation valve. It is generally sized for a maximum flow velocity of say4m/s for liquid and 20m/s for gas. Also, the kicker line valve is used to throttle the

flow from full pipeline pressure to zero pressure. Use a valve (or a valve

combination) that is good not only for sealing but also throttling. I like to use a

high quality plug valve for this service. Put a few kinks in the kicker line for

thermal expansion if the pipeline fluid is hot.

The only other major issues needing attention is the support of the launcher and

receiver. Most are designed with two saddle supports. Design those as vessel

supports to support the launcher or receiver. Also, keep thermal expansion inmind when tying the supports to the foundations.

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