Break on through to the other side
Break on through to the other side
Break on through
Break on through
Break on through
Break on through

["Break on Through (To the Other Side)," by The Doors, 1967)

 

WHY THERE WILL BE HUNDREDS OF FLANGED PIPE CONNECTIONS IN A LARGE PROCESSING FACILITY

PTOA Readers and Students just learned in PTOA Segment #249 that Welded Pipe Connections do not require maintenance and will never leak.

Flanged Pipe Connections and Screwed/Threaded Pipe Connections DO REQUIRE MAINTENANCE and DO HAVE THE POTENTIAL TO FAIL AND LEAK.

The logical question is ... Why install a Flanged Pipe Connection?

In a nutshell the answer is "access." Albeit the Welded Pipe Connection is continuous, leakproof, and maintenance free ... it does not allow access into Rotating or Stationary Equipment, valves, or pipe fittings.

• Flanged Pipe Connections provide a location to open up ... aka break into ... The Piping Network that ties the facility together.  Opening up the Flanged Connection is often called "busting open a Flange." Maintenance and Process Operations will argue over who has the responsibility to "bust open the Flanges" because it is hard work that is not done frequently. The lead photo in this PTOA Segment shows a technician spreading a set of mating Flanges after the bolts have been "busted open."
• Flanged Pipe Connections make it possible for major pieces of industrial hardware to be manufactured at their specialty foundries and then incorporated into The Piping Network at a processing facility months later.
• Flanged Pipe Connections make it possible to incorporate and repair a variety of flow control valves and pipe fittings into The Piping Network.

 

 

THE FLANGED PIPE CONNECTION

Fastening the Flanged Pipe Connection

A Flange is a rimmed ring with bolt holes which has been attached to a longer piece of pipe via cast or weld.

The pipe that is to be connected to the flanged pipe must also have a Flange.

The Flange ends of two different pipes are bolted together thus forming a longer pipe. A typical, large industrial complex will have several hundred Flanged Pipe Connections.

The ISA symbol for a Flanged Pipe Connection is two vertical parallel lines drawn over the bold, solid process line. The parallel vertical lines symbolize the mated Flange faces. The area between the vertical lines may or may not be vacant.

 

Three Popular Types of Flange Gaskets

Once again, brilliant PTOA Readers and Students can immediately identify that a strictly metal-to-metal interface would result in leakage.

A carefully placed Flange Gasket must be secured between the mating Flange faces.

The Flange Gasket type must be compatible with the highest PV Pressure the pipe will sense, the range of processing PV Temperatures that the pipe will experience, and the chemical composition and phase of the fluid that will flow through the pipe at those PV Temperature and PV Pressure ranges.  

Non-metallic Full Face Flange Gaskets (for example Rubber and Teflon) are typically used for low PV Pressure and low PV Temperature applications. One notable exception:  Graphite Flange Gaskets are also non-metallic and can be used for PV Temperatures that do not exceed 840°F (450°C).

Not all Flange Gaskets are flat.

Metallic Gaskets ... for example the RTJ ("Ring Type Joint") Flange Gasket ... are used when the process service requires high PV Pressures (like even up to 20,000 psi!).

The RTJ Flange Gasket looks like a thick round ring, not at all flat. Metallic RTJ Flange Gaskets are on the top row of the nearby "Types of Gasket" graphic.

The RTJ Flange Gasket is carefully set into the groove that has been fabricated into to each of the mating RTJ Flange faces.

Note that the RTJ Flange Gasket design/technology eliminates the need to stress about the bolt hole configurations.

As their name suggests, the Composite Flange Gasket has both metal and non-metal components.

The center area in the popular Spiral Wound Flange Gasket is made of metallic strips embedded between non-metallic fibers. This crucially important area provides the sealing surface between two Raised Face Flanges.

Composite Gaskets are popular in the processing industries because of the wide range of PV Pressures and PV Temperatures which they can accommodate.

The nearby graphic shows a yellow-coded Spiral Wound Flange Gasket. The notations written on the yellow outer ring surface specify which process service the Spiral Wound Flange Gasket is rated to accommodate.

Like the metallic RTJ Flange Gasket mentioned previously, the Spiral Wound Flange Gasket design/technology does not need to be concerned with bolt hole configuration.  The Spiral Wound Flange Gasket is placed upon the raised sealing region of a Raised Face Flange.

The raised surface of a Raised Face Flange is shown being cleaned in a nearby photo. Note that the Spiral Wound Flange Gasket will only cover the raised sealing surface on the Raised Face Flange, not the full face and bolt holes of the Full Face Flange shown above.

 

The Gasket Must Be Rated to Successfully Seal at all Process Service Extremes

As was stated above, the use of Flange Gaskets in Flanged Pipe Connections is more complicated than Welded Pipe Connections and leads into the subject matter of Flange Gasket housekeeping. The life of every Process Operator literally depends upon maintaining good Flange Gasket housekeeping.

The totally preventable 1986 Challenger Space Shuttle explosion is perhaps the most infamous example of an incompatible Gasket/seal for the intended service.

Two of the Challenger's O-Rings that were tasked with providing the seal in a set of solid rocket boosters were not compatible with the severely cold ambient temperatures. A design engineer had warned of the potential for incompatibility, but his concerns were overridden by members of the launch team.

The seal material contracted which allowed hot exhaust gas to escape from the resulting gap.

 

Keeping Track of Fresh and Spent Flange Gaskets

The Challenger may be the most infamous example of a mismatch between Gasket/seal and process service requirements, yet the same ignorance has been the root cause of many process industry catastrophes.

Like the seven Challenger astronauts, the welfare of every Process Operator depends upon the integrity of the leakage-preventing seals working throughout the processing facility.

Beware! During the maintenance interval called a Turnaround, more than likely contract labor will be responsible for busting the Flanges open, removing the spent Flange Gasket, and inserting the fresh Flange Gasket prior to bolting the Flanges together.

Never assume that a contract laborer has received the training required to properly select, handle and install Flange Gaskets. The contract laborer may not even be aware that Flange Gaskets cannot be reused, even when the spent Gasket shows no wear or tear.

The Flange Gasket that has been used has been intentionally deformed by compression; a Flange Gasket should never be reused and must be replaced every time the Flanges are separated.

Turnaround Planners can remove some of the anxiety regarding proper Flange Gasket selection by providing a Turnaround Flange Gasket List.

A Flange Gasket can be checked off the list and deemed responsibly replaced after the same type of spent Flange Gasket has been swapped out for the fresh Flange Gasket.

During a typical Turnaround in a large industrial complex, dozens of Flanges will be "busted open." One glance at the Flange Gasket List ... or the visually superior Flange Gasket Board ... will confirm that a new and proper Flange Gasket has been installed for all Flanges that have been opened during the Turnaround.

 

Reassembling the Flange Pipe Connection and Bolt Patterns. 

The reassembly of a Flange Piping Connection begins with loosely threading the bolts into the correct bolt hole.

The Full Face Flange Gasket has bolt holes that make it easy to position the Gasket between the Flange faces.  The metallic RTJ Flange Gaskets and composite Spiral Wound Gaskets are more frustrating to position; typically, the bottom bolts are hand threaded into their respective bolt holes which help support the Flange Gaskets prior to fastening.

A Torque Wrench is typically used to finish the fastening job of bolts and nuts. Besides making the fastening effort easier, the Torque Wrench helps to ensure that an equal amount of torque has been gradually applied to each bolt. Gradually applying the total magnitude of torque specified will ensure that the compression of the Flange Gasket is equalized throughout the fastening procedure.

The bolting procedure used for fastening is not random! Bolt Patterns are specific to the design of the Flange and the type of Flange Gasket. The nearby schematic enumerates the procedure to properly bolt up Full Face Flange Pipe Connections with four, eight, and twelve bolts.

Flange Blinds, Spec Blinds, and Blind Lists

During a Turnaround in a large processing facility, only the Process Units due for inspection or which otherwise have hinted that maintenance is necessary will need to be shutdown.

A Flange Blind is used to seal off the piping boundaries of the maintenance area. A Full Face Flange Blind looks like a solid disc of metal with the bolt hole pattern that matches the Flange faces into which it will be set. A Raised Face Flange Blind and RTJ Blind will not have bolt holes.

The Flange Blind will be inserted between the smooth mating surfaces of two Flanges, thus prohibiting any gas or liquid movement between the maintenance area and the non-maintenance area of the Turnaround.

The point of blinding a part of the Piping Network off is to make certain the location of hazardous fumes and/or inert gases is known and managed during what are non-normal operations (aka, a Turnaround).  Re-installing a Flange Gasket which has been used and thus deformed does not ensure the Flange Blind isolation will be effective.

Thus, even though one side of the Flange Blind is simply subjected to atmospheric pressure during the Turnaround, fresh Flange Gaskets must be inserted when the Flange Blind is inserted and once again when the Flange Blind is removed and the process line is prepped for Start Up.

Spec(tacle) Blinds are installed on Process Lines that are frequently blinded off during a Turnaround.  A Spec Blind has one open side and one solid side, thus appearing like old time eyewear called spectacles.

During normal operations, the open side of the Spec Blind is in place. During a Turnaround, the solid round of the Spec Blind is rotated into place.  Spectacle Blinds require fresh Flange Gaskets every time a rotation occurs.

Blind Lists

Imagine the outcome from weary Process Operators who have spent weeks working long Turnaround hours ... not to mention the top management big wigs impatient to get the facility operating and making money again ... when the Start-Up is stymied because a Flange Blind was not removed, or a Spec Blind had not been rotated into the open position!

Turnaround Planners should coordinate Flange Blind Lists with a check off procedure to verify that every Flange Blind has been properly removed and every Spec Blind has been properly rotated prior to Start Up.

Wow, Fred!  There really IS a lot more maintenance and housekeeping involved with Flanged Pipe Connections! Good to know!

 

TAKE HOME MESSAGES: The Flanged Pipe Connection involves considerably more maintenance and housekeeping compared to the Welded Pipe Connection. There are still hundreds of Flanged Pipe Connections in a processing facility because they allow pieces of equipment to be incorporated into the Piping Network and allow access into the Piping System.

Flange Gaskets are used to seal the metal-to-metal interface between two Flange faces. The Flange Gasket must be rated to withstand the PV Pressure and PV Temperature range extremes as well as be chemically compatible with the process service.

There are 3 types of Flange Gaskets used to seal the 3 types of Flanged Pipe Connections:

• Non-metallic Full Face Gaskets are used to seal Full Face Flanges in low PV Pressure, low PV Temperature service. They have a bolt pattern which must match the bolt pattern of the two mating Full Face Flanges. 
• Metallic RTJ Gaskets are shaped like a ring of metal. The ring sets into a groove which has been etched into both mating faces of RTJ Flanges. RTJ Flanges are used in high PV Pressure service.
• The sealing surface of Composite Spiral Wound Gaskets are made partially of metal and partially of non-metal fibers. These popular Flange Gaskets set on the raised face of a Raised Face Flange and do not have bolt holes. Raised Face Flanges have a wide range of PV Pressure and PV Temperature service.

Process Operators should verify that the Flange Gasket is rated for the extremes of the process service. 

A Flange Gasket should never be reused because every spent Flange Gasket has intentionally been compressed and thus deformed.

Flange Gasket Lists and Flange Gasket Boards assist with Flange Gasket management during a Turnaround.

Reassembly of a Flanged Pipe Connection involves torquing the bolts in the specified Bolt Pattern which ensures that the Flange Gasket is uniformly compressed.

Before a Turnaround maintenance interval can begin, the active part of an industrial process must be isolated from the areas of the plant which need to have maintenance. Blind Flanges and Spec Blinds are used to isolate the boundaries of the Turnaround.  Blind Lists help with Blind Flange management during a Turnaround.

©2024 PTOA Segment 0250

PTOA PV FLOWRATE FOCUS STUDY AREA
PIPING NETWORK HARDWARE

 

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