In this case
I think it's better
To face it -
We belong together
We belong together

("We Belong Together," by Ricki Lee Jones, 1981)

FORM AND FUNCTION OF PIPE FITTINGS

PTOA Readers and Students just learned in PTOA Segments #249 and #250 that the three technologies used to "join" metal pipe segments together are:

• Threaded/Screwed Connections.
• Flanged Connections.
• Welded Connections.

 

The same three technologies are used to join Pipe Fittings and Valves to metal pipe.

Each Pipe Fitting is intentionally selected to be part of The Piping Network because each Pipe Fitting has a specific job.

The jobs of Pipe Fittings are featured below ... but first ...

Can we talk?

Truth be known ... since the advent of the digitized world ...  exposure to the common Pipe Fitting hardware featured in this PTOA Segment and the Valve hardware featured in the next PTOA Segment has progressively dwindled through the Millennial, Gen Z, and Alpha Generation cohorts. The word "ignorant" aptly applies because the word means "lacking awareness." The fact is:

You Don't Know What You Don't Know.

Nobody does.

PTOA Readers and Students need to recognize this PTOA Segment for what it is: the opportunity to get "knowed-up" on the form and function of common Pipe Fitting hardware that the Process Operator will be surrounded by in any large, industrial processing facility.

Were we meeting in a brick-and-mortar classroom, Your Mentor would create a hands-on exercise wherein a random display of Pipe Fittings used in household plumbing would be spread out on a table. Your Mentor would be holding a secret list of Pipe Fittings.

As Your Mentor called out the name of a type of Pipe Fitting, each team of participants would be tasked to connect the Pipe Fitting to the next Pipe Fitting called out from the list.

During the exercise, each PTOA Reader and Student would have to ascertain if a Coupling Fitting, Union Fitting, Bushing, or other adapter hardware were required to make the connection.

The contraption created by the end of the exercise would be compared to an accurately completed version hiding behind Your Mentor's desk.

By the end of the exercise, PTOA Readers and Students would be more familiar with the form of the smaller, screwed/threaded versions of the Pipe Fittings featured below.

Albeit much larger than the household-plumbing sized Pipe Fittings used in the classroom, the industrial-sized versions of the Pipe Fittings look similar.

The specific function that each Pipe Fitting is selected to perform is also described below.

 

PIPE FITTING JOBS

Pipe Fittings that Change the Direction of Flow

The 45° Elbow Fitting, the 90°Elbow Fitting, and the Return Bend Fitting (U-Turn Fitting) make it possible to change the physical direction of flow.

Changing the direction of flow upward or downward ... or to the east or to the west ... or any variation in between ... makes it possible for a processing facility to fit on less acreage than would otherwise be required.

Changing the direction of flow also makes it possible to gain elevation. For example, the feedstock that flows into a tall reactor must be pumped up to the level of the Reactor Inlet (Reactors were featured in PTOA Segments #28 and #37).

What goes up in the real world must always come down!

The vertical Reactor Effluent piping must abruptly change direction so that the Reactor Effluent can suddenly flow horizontal, aka parallel to the ground. The 90°Elbow Pipe Fitting changes the direction of the Reactor Effluent flow.

Eventually, the horizontal, straight run pipe will become just another pipe in the pipe rack with its contents timely delivered to the next "process operation."

The next process operation might be the transfer of heat in a Shell and Tube Heat Exchanger (featured in PTOA Segments #30 through #36, and PTOA Segment #78).

The nearby photo shows a train of Shell and Tube Heat Exchangers connected via 90°Elbow Fittings and Return Bend Fittings.

Fin Fan Heat Exchangers are behind the Shell and Tube Heat Exchangers (Fin Fan Heat Exchangers were featured in PTOA Segments #38 and #74).  Tall Reactors rise above the Fin Fan Heat Exchangers.

The Piping Network will also change the direction of flow to intentionally provide allowable thermal expansion that would otherwise require much more acreage. The thermal expansion piping loops shown in the two nearby photographs would look very strange to the casual observer who does not understand their important job.

To recap:

In a large industrial processing plant, the PV Fluid Flowrate flows through many twists and turns in The Piping Network. Changing the direction of flow is the job of the 45° Elbow Fitting, the 90°Elbow Fitting, and the Return Bend Fitting (U-Turn Fitting).

As illustrated in the nearby photo, smaller 45° Elbow Fittings and 90°Elbow Fittings perform the same job of changing the physical direction of flow in low PV Flowrate/low PV Pressure process services.

 

 

Pipe Fittings that Change the Pipe Size (and thus change the PV Flowrate)

Sometimes the pipe size ... aka Pipe Diameter ... needs to be reduced or expanded.

Reducing the pipe diameter to a smaller diameter is the job of the Reducer Fitting.

Increasing the pipe diameter to a larger diameter is the work of the Expander Fitting

Fred ...

Does the PV Flowrate back up when the fluid flows through a Reducer Fitting? HECK, NO!

The most brilliant PTOA Readers and Students will recognize that a fluid flowing through a Reducer Fitting looks a lot like the first half of the nearby Venturi Meter graphic. The Venturi Meter graphic was used to explain the PV Pressure↔Fluid Velocity Swap featured in PTOA Segment #159.

The decrease in pipe size (aka, decrease in the pipe's diameter) causes the Velocity Factor of the fluid's PV (Volumetric) Flowrate to increase while the PV Pressure of the flowing fluid decreases. The Velocity Factor of the PV (Volumetric) Flowrate was featured in PTOA Segment #235.

In summary, no fluid "backs up" in a Reducer Fitting.

Does the PV Flowrate suddenly lurch forward upon entering the larger diameter pipe of an Expander Fitting? HECK, NO!

The situation is illustrated by the last half (right side) of the nearby Venturi Meter graphic. While flowing through an Expander Fitting, the Velocity Factor of the PV (Volumetric) Flowrate decreases while the PV Pressure of the flowing fluid increases.

The nearby Process Flow Diagram of a Centrifugal Pump shows the thimble-shaped ISA Symbols for a Reducer Fitting and an Expander Fitting installed at the Pump Suction Line and Pump Discharge Line, respectively.

The two non-slanted sides of the thimble represent the variance in the process line diameter. For a Reducer Fitting, the process flow enters the fitting at the longer vertical side and exits the shorter vertical side of the thimble.  For an Expander Fitting, the process flow enters the shorter vertical side and exits the longer vertical side of the thimble.

Brilliant PTOA Readers and Students are already familiar with the common, real-life application of a Reducer Fitting and an Expander Fitting.  

The Typical Pump Installation Set-Up featured in PTOA Segment #164 and also shown nearby included a Reducer Fitting at the Centrifugal Pump's Suction and an Expander Fitting at the Centrifugal Pump's Discharge.

 

Pipe Fittings that Branch the Flow from One Flowrate into Two or More 

Sometimes the fluid flowing in a pipe needs to be split up into two or more flowrates.  Branched Flow Pipe Fittings are used to split up an incoming flow into one or more Process Streams.

The nearby graphic shows the basic (straight) Tee Pipe Fitting in the upper left corner. The basic Tee Pipe Fitting is used to split the incoming flow into two outgoing streams.  The basic Tee Pipe Fitting will have the same diameter pipe at the inlet and two outlets. The PV Flowrate of the two outgoing streams will be equivalent.

The basic Reducing Tee could have a larger diameter pipe for the incoming Process Stream and smaller diameters for the two outlet Process Streams.

Reducing Tees come in a variety of configurations. The two outlet streams are not always the same diameter.

The Y Pipe Fitting (labelled "Wye" in the nearby graphic) also splits an originating inlet flow into two outlet flows. One of the flows will be at a 45° or 60° angle from the two other horizontal flows. A strainer situated in a Centrifugal Pump's Suction Line is a Y Pipe Fitting.

The Cross Pipe Fitting is used to split the incoming Process Stream into three separate outlet flow Process Streams, two of which are at 90°angle from the originating Process Stream flow.

A "straight" Cross Pipe Fitting has equal diameters in all flowing directions.

The Reducing Cross Pipe Fitting is identified by its two 90° angled outlets that have a smaller diameter.

 

Stopping Flow with Pipe Cap Fittings and Plugs

Sometimes the PV Flowrate must be stopped.  A Pipe Cap Fitting stops a fluid from flowing. The nearby graphic depicts the ISA symbol for a Pipe Cap Fitting.

Pipe Cap Fittings are welded onto the pipe and never removed.

PTOA Readers and Students learned the concept of "Pipe Header" while learning about the Supply Header and Return Header of a Cooling Water System in PTOA Segments #39 through #41.

The ends of every Pipe Header must be capped.

In the nearby snippit of a Fuel (Gas) Header P&ID, the header is drawn as a vertical lined that is capped on both ends.

Capping the two ends of the Fuel (Gas) Header forces the flow through the five separate fuel supply lines.

The Fuel (Gas) Header P&ID snippet hints at the problem with Cap Pipe Fittings.

Process Operators must be aware that a capped pipe creates a dead leg in The Piping Network! A "dead leg" is an area where no flow occurs; the contents in The Piping Network are stagnant.

The real-world piping will be much different than the P&ID snippit shown for the Fuel (Gas) Header.

Yet, even the schematic as shown hints that a dead leg of stagnant fuel gas would be present between each capped end of pipe and the nearest supply line. No fuel gas flows through this volume of pipe.

This stagnant gas must be properly purged during a Turnaround before opening the line up to air.  A well-designed Piping Network will have a "bleed valve" for purging stagnant gas from the dead leg.

Plug Pipe Fittings are used to stop flow through a normally closed opening that will be accessed occasionally.  Otherwise stated, Plug Pipe Fittings are removed occasionally to allow flow into or out of the pipe in question.

For example, the angled Process Stream in a Y Pipe Fitting (labelled Wye in the nearby graphic) may be plugged during normal operations. The plug could be removed during a Turnaround to allow a specialty chemical to be injected.

The nearby photo shows a Plug Fitting inserted in the process line near the vicinity where the technician is working.

 

Pipe Fittings That Connect Two Pipes Together

The job of the Union Fitting and the Coupling Fitting is to connect two same-sized pipe sections together.

PTOA Readers and Students recently learned in PTOA Segment #249 that Pipe Sleeves are connected to Pipe via Welded Pipe Connections and Fillet Welds.

A Coupling Fitting is simply a threaded Sleeve that connects two pipes with the same diameter (Note: a pipe fitting that connects two pipes with differing diameters is either a Reducer Fitting or an Expander Fitting).

A Union Fitting is used to connect two pipes when it is known that one member pipe will need to be maintenance without disturbing the other member pipe.

The Union Pipe Fitting has three pieces which are visible in the nearby Union Pipe Fitting cutaway photo.

Two separate pieces of threaded Pipe are joined together with a surrounding ring. The ring has an inside flange at one end (the upper connection in the cutaway photo) and screwed/threaded connection to the other end (the lower connection in the cutaway photo).

 

 

The nearby photo shows a disconnected Union Pipe Fitting.  A pipe wrench placed on the ring was used to disconnect the two pipes. The ring will be placed back into position and tightened up when the pipes are reconnected.

The Nipple Pipe Fitting is a short piece of pipe with both ends being male threaded (threads on the outside of the fitting). Two pipes ...with the same diameter and female threads (threaded on the interior pipe wall) are screwed/threaded onto each end of the Nipple Pipe Fitting.

The Bushing Pipe Fitting (shown by itself below) connects pipes with different diameters/sizes.

The larger diameter, male threaded side of the Bushing Pipe Fitting is threaded into a female threaded pipe.

A smaller diameter pipe with male threads is screwed into the female threads on the inside of the smaller diameter of the Bushing Pipe Fitting.

 

 

DO IT YOURSELF QUIZ

Test Yourself!

How many of the non-labelled Pipe Fittings in the nearby photo can you identify by form and function?

The next PTOA Segment features the form and function of Valves.

 

TAKE HOME MESSAGES: Pipe Fittings are classified according to the job that they perform.

Pipe Fittings that change the direction of fluid flow include the 45° Elbow Fitting, the 90°Elbow Fitting, and the Return Bend Fitting (U-Turn Fitting).

Pipe Fittings that change the pipe size (and hence, fluid velocity) include the Reducer Fitting and the Expander Fitting. The ISA Symbol for both the Reducer and Expander Pipe Fitting looks like a thimble. The non-slanted sides of the thimble determine whether it is a Reducer Fitting (the fluid enters the tall side and exits the short side) or an Expander Fitting (the fluid enters the short side and exits the tall side). A Reducer Fitting is on the Suction side of every Centrifugal Pump. An Expander Fitting is on the Discharge Line of every Centrifugal Pump.

Pipe Fittings that branch the inlet flowrate into two outlet flowrates are the basic (straight) Tee Fitting, the Reducing Tee Fitting, and the Y Pipe Fitting (aka "Wye"). The basic (straight) Cross Fitting branches an inlet flowrate into three outlet flowrates, all with the same diameter. The Reducing Cross Fitting has two smaller diameter outlets at 90° angles from the inlet flow.

Pipe Fittings that stop flow include the Cap Pipe Fitting and the Plug Pipe Fitting. Cap Pipe Fittings are permanently placed; for example, Cap Pipe Fittings are attached to either end of a pipe header. Process Operators must be aware that dead legs of stagnant fluid are created when a pipe is capped. Plug Pipe Fittings are temporary; the Plug Pipe Fitting is removed when temporary access to the pipe is warranted. 

Pipe Fittings which connect two pipes together and have the same diameter include the Coupling Pipe Fitting, the Union Pipe Fitting, and the Nipple Pipe Fitting. The Bushing Pipe Fitting connects two pipes with different diameters together. 

©2024 PTOA Segment 0251

PTOA PV FLOWRATE FOCUS STUDY AREA
PIPING NETWORK HARDWARE

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