Category: Gaskets

What is a Gasket?

A gasket is meant to form a mechanical seal that fills the space between two or more mating surfaces. Its goal is to prevent leakage from, or into, the joined objects while under compression.

Gaskets allow for less-than-perfect mating surfaces on machine parts. They can fill irregularities and increase the likelihood of sealability — especially in high-pressure applications and flanges that have a high differential temperature range (cyclic flanges).

There are many different types of gaskets used in the oil and gas (petrochemical) industry and other heavy industry. They include both standard ANSI/ASME pipe flanges (an example is ASME B16.5 flanges) and gaskets used in heat exchangers.

What Nachos Can Teach You About Proper Gasket Assembly

What most people don’t know is that the gasket stress is what we care about the most! Not the bolt load.

We use this analogy when training people: “What is the purpose of the chip in chips and queso? It’s the vehicle that gets the queso to the mouth.”

That is the purpose of the bolt: To be the vehicle to gets the gasket stress correct.

What are the Most Common Types of Gaskets Used in Oil and Gas?

Here are the 8 types of gaskets you will see the most often:

1. Envelope Gasket (Double Jacketed Gaskets)

Envelope Gaskets can be either double jacketed gaskets, or they can have PTFE (some call it Teflon but that is a trademarked name) on the outside of a stainless steel metal core. However, they don’t have a lot of compression or recovery, and do not hold up to radial sheer (slipping of the flanges on the gasket during high-temperature fluctuations).

2. Flat Metal Gaskets

These gaskets usually have a stainless steel core without any filler material, and are used in low criticality applications. They also don’t have a lot of compressibility or recovery.

3. Non-Asbestos Sheet Material Gaskets

Non-asbestos sheet material is typically found with full-face flanges and have elastomeric properties, although they can be just graphite gaskets in few cases. One can have high chemical resistance sheet gaskets such as a PTFE/ePTFE gasket that has great compressibility and a little bit of recovery if you don’t overstress them.

Normally, these gaskets are used with low pressure and low temperature, but they can be also put in put in flanges where chemical resistance is needed. Most gasket manufacturers stock a wide range of elastomeric, non-elastomeric, PTFE/ePTFE, graphite gaskets, and compressed sheet material in both sheets and rolls.

4. Ring Type Joint

Ring Type Joint gaskets are also called RTJ gasket, ring gasket or ring joint gaskets. They come in oval or octagonal shapes, which can be used in API 6A applications.

RTJ gaskets were traditionally found in high pressure and high-temperature applications, as sheet material elastomers can not hold up in those types of applications. But today RTJ gaskets are being phased out of high pressure and high-temperature applications, as spiral wound gaskets with inner rings are now the preferred gasket.

However, if you are using ring type joint gaskets, know that they are typically made of a soft stainless steel gasket material, and should be replaced after every use due to the plastic deformation that it sees in the flange. If you don’t replace it, you are jeopardizing the sealability of the gasket.

5. Kammprofile Gasket

You’ll also see Kammprofile spelled “camprofile gasket,” and they are sometimes called grooved metal gaskets. These types of gaskets are commonly found in heat exchangers in the oil and gas industry.

They are much more reliable than jacketed gaskets (double jacketed gaskets). Kammprofile gaskets are typically made of a stainless steel metal core with a flexible graphite filler material.

The area (a.k.a cross-section) of the gasket can be easily changed to achieve good gasket stress while withstanding a high bolt load. Kammprofile gaskets are also really great for radial sheer which is seen when the flanges slip on each other (really the flexible graphite filler) during flange expansion and contraction (due to temperature).

This gasket material is a solid metal gasket, and the metal core can be made of stainless steel or other exotic materials so that it can be put in high pressure and high-temperature flanges.

To learn more about Kammprofile Gaskets, click here.

6. Spiral Wound Gaskets WITH an Inner Ring

These types of gaskets are the best metal gaskets for all pressure ratings of pipe flanges, especially ASME B16.5 flanges.

I would argue that they are also great for heat exchangers due to their sealability tolerances with imperfections in flanges, and because they can be made for high pressure and high-temperature applications.

These spiral wound gaskets have a stainless steel inner ring, a carbon steel outer ring, and the metal core is made of stainless steel windings. The filler material is typically flexible graphite, but you can also have an elastomeric filler material such as PTFE if chemical resistance is needed.

Spiral wound gaskets are more also flexible than Kammprofile gaskets so they tend to also have more compressibility and recovery, but they are harder to place in a flange at larger diameters so it is advisable to move to Kammprofile gaskets.

To learn more about Spiral Wound Gaskets, click here.

7. Spiral Wound Gaskets WITHOUT an Inner Ring

These types of gaskets should not be used in typical pipe flanges, and especially not in high-pressure rated pipe flanges (such as 600 pounds or greater).

The reason: Spiral wound gaskets without inner rings can buckle under high gasket stress, such as what you’ll see when there is a lot of bolt area and little gasket area.

There are instances when a spiral wound gasket without a stainless steel inner ring or carbon steel outer ring can be used for groove flanges such as male/female flanges, but we will typically see that they will compress enough to not allow for recovery.

8. Corrugated Metal Gaskets

These gasket types can be made to have a minimum of 0.5″ cross-section and have been used to change gasket area. They are better than metal jacketed gaskets for heat exchangers, but should not be used in standard piping flange gaskets.

How to Identify a Gasket: A Color-Coded Chart

Most piping flange gaskets in the oil and gas industry today are spiral wound gaskets made of stainless steel for the metal core material with either PTFE or graphite filler material. ASME B16.20 offers a Color Coding Chart that is part of the standard for inspection purposes.

The color coating on the outer ring (which is typically carbon steel) is painted on the outside of the ring so that an inspector can identify the windings material.

Typically 316 stainless steel is used as the standard in petrochemical applications, as it is better for high-temperature applications. While 304 stainless steel could be used, most End Users in the petrochemical industry err on the conservative side for the 316 stainless steel which has a green color on the carbon steel outer ring.

The most common filler material is flexible graphite, and that is indicated by the grey stripe on the green outer ring.

The ASME B16.20 color chart above indicates what the gaskets are made of. NOTE: there is no marking for gaskets that do not have a stainless steel inner ring, so it is prudent that ALL spiral wound gaskets have an inner ring.

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What are Spiral Wound Gaskets?

A Spiral Wound Gasket is the most common metallic gasket used in industrial plants. A properly selected and installed spiral wound gasket can withstand high temperatures and pressures, preventing leaks throughout their intended lifespan. 

A spiral wound gasket consists of three elements:

1. Outer ring. Made of carbon steel, this outer ring is sometimes called the centering ring or guide ring. It’s used to center the gasket when you insert it into a bolted flange joint. 
2. Inner ring. The inner ring is pivotal for the gasket because it prevents windings from buckling inside the pipe. When a gasket buckles, parts of it get sucked into the pipe. From there, pieces of the gasket will typically flow through the pipeline until they get caught on something. Often, they’ll get wrapped around rotating equipment like a pump. The mess that results is known as a “bird’s nest.” Inner rings help you avoid this problem. 
3. Sealing element. As you might guess from the name, the sealing element creates the seal that prevents leaks. A sealing element encompasses both windings and filler material. Most spiral wound gaskets in oil and gas refineries will use a flexible graphite filler material rated for high temperatures. A flexible graphite filler also allows the gasket to be more tolerant of flange distortion and joint misalignment. Polytetrafluoroethylene (PTFE) is another common filler material. PTFE is not rated for high-temperature applications, however. Meanwhile, most winding materials in refineries will be stainless steel and monel. 

Spiral Wound Gasket Markings

Spiral Wound Gaskets have several different markings on them. Each tells you something specific and important about the gasket itself. Starting from the top…

ASME B16.20 

At the top of a spiral wound gasket, you ought to see a marking that states “ASME B16.20.” this indicates the gasket is made to the ASME B16.20 standard, which is the standard governing metallic gaskets for pipe flanges (which includes spiral wound gaskets).  

Manufacturer

First, the manufacturer’s name is usually positioned on the right-hand side of the gasket. This tells you who made the gasket. 

Winding Material and Filler Material

Indicates what the gasket is made of. Gasket color also tells you a lot about these materials — more on that in a moment. 

Diameter and Pressure class 

These markings tell you the size of the gasket, along with the load the gasket can handle. 

There are different pressure classes: 150, 300, 400, 600, 900, 1500 and 2500. Higher numbers indicate the ability to tolerate greater pressures. 

Spiral Wound Gasket Color Codes

Colors play an important role on spiral wound gaskets. The color of the outside rim, and the color of the stripe along the rim, both are important indicators of the material within the gasket. 

1. Outside rim colors indicate the gasket’s windings materials
2. Rim stripe colors tell you the gasket’s filler materials 

For example, the following outside rim colors indicate specific windings materials: 

• Yellow means 304 stainless steel gasket material. That means the inner ring and metallic windings are made of 304 stainless steel.
• Green is 316 stainless steel. 
• Turquoise is 321 stainless steel. 
• Blue is 347 stainless steel. 
• Orange means that it’s made out of Monel. 
• Black is Alloy 20
• Silver is carbon steel
• Brown is Hastelloy B
• Beige is Hastelloy C
• Gold is Iconel
• Red is Nickel
• Purple is Titanium

NOTE: If you work in the oil and gas industry, most of the time you will see one of three colors: Yellow (304 stainless steel), Green (316 stainless steel), or Orange (monel). Monel is an alloy of nickel and copper that, in addition to tolerating high-temperatures, also is resistant to corrosion. 

Meanwhile, rim stripe color tells you the gasket has one of the following filler materials:

• Pink indicates mica paper
• Gray indicates graphite
• White indicates PTFE
• Light Green green indicates ceramic

NOTE: If you work in the oil and gas industry, most of the time you will see Gray, indicating graphite.

Why Spiral Wound Gaskets are in use

Spiral Wound Gaskets have been around since 1912, but they were not used regularly in industrial piping until the 1990s.  

On July 12, 1989, the EPA issued a final rule banning most asbestos-containing products. That included gaskets.  At the time, asbestos gaskets were used in applications under lower temperatures and pressures because they weren’t at risk for blowout under those conditions. Ring Joint Gaskets were used in the high-temperature (~500+ degrees Fahrenheit) and high-pressure applications. 

In the early 1990s, the petrochemical industry went in search of a type of gasket that would be  as effective as asbestos. Spiral wound gaskets were a strong option because they allowed the use of materials capable of handling the demands of the oil and gas industry. 

After about 5 years, the industry moved to make spiral wound gaskets the standard in ASME B16.20. 

An amendment to ASME B16.20 in May 2008 made the use of inner rings within spiral wound gaskets standard. The standard states:

“…Inner rings shall be furnished with all spiral-wound gaskets having PTFE (polytetrafluoroethylene) filler material. Inner rings for flexible graphite filled spiral wound gaskets shall be furnished unless the purchaser specifies otherwise. For all filler materials, inner rings shall be furnished in spiral wound gaskets for: a) NPS 24 and larger in Class 900 b) NPS 12 and larger in Class 1500 c) NPS 4 and larger in Class 2500 Inner rings are required for these gaskets due to high available bolt loads, which may result in outer ring damage.” 

The reason ASME B16.20 requires inner rings is because the flange faces create enough gasket stress that the additional compression causes the metal windings and filler material to push against the outer ring (also known as the guide ring).  

The outer ring is a solid piece of carbon steel. and the stainless steel windings are shaped in a “Chevron V” (refers to the shape, not Chevron the company). The shape aids in pushing the winding material to project into the inside diameter of the pipe. This will interfere with the process. If additional compression (roughly 22ksi gasket stress) is met, the metal windings will completely fail. Often, a “birds nest” (where the metal windings fall into the pipe and get tangled up) results.  The bad part about that is that they will travel until they reach some sort of rotating equipment and/or valve.   

Spiral Wound Gaskets are incredible gaskets for both piping (preferred gaskets in ASME B16.5 and B16.47 flanges). While the Kammprofile gasket gets a lot of attention for heat exchangers, spiral wound gaskets are also great for them.

Compressibility and recovery are what make spiral wound gaskets the best metallic gaskets for most flanges. They are now the metal gasket that has taken favor over Ring Type Joints for even high-pressure flanges including ASME B16.5 2500 series flanges.  

Installing Spiral Wound Gaskets: Things to Know

The outer ring is not a compression stop

While some manufacturers call the outer ring a compression stop, it  IS NOT.  If your gasket has enough seating stress to compress to the outer ring, you essentially have a flat metal gasket, which gives you little to no recovery for when your plant cycles and the flange faces move apart due to thermal expansion. 

Flange faces do not come down on the sealing element as flat as most people think. 

Flange faces actually rotate a little bit. What do we mean by rotate? If you look at the flange faces of a raised face flange the raised face is actually pivot point to a lever. The end of the lever is where the nuts are actually clamping down together. 

So what you do is you rotate your flange — i.e. you “bird mouth” your flange a little bit. Now they should bird mouth equally, but sometimes they don’t. One flange face typically bends to the other. 

This leads to what we call dishing. Some people have called it cupping, but the technical term is dishing. That’s when the outer ring bends down. 

Now there are a lot of conspiracy theories on this. Some people say, “Oh, It gets caught up in the bolt threads.” That’s not what happens at all. 

What happens is since the flange is rotating, it rotates maybe a degree or two. Depending on the length of your outer ring, that determines how much deflection you see at the end of it.

More on what to do when you see “dishing”

So let’s discuss some practical applications of when you see dishing. Let’s take a 2″ 300 and a 2″ 600 gasket. What gasket do you go grab when you need to assemble one of those flanges? You grab the same gasket. But what’s the difference between those two flanges? 

Well, the difference is the fact that a 300 has got 1/16″ raised face wall. The 600 has got a ¼” raised face, so what you’ve effectively done is quadrupled the height of your raise face, which makes it even a longer lever, which we will see more dishing on the 600 than you will on the 300.

Another place that we see this is on the 2500 and 1500 series flanges. That outer ring is so long that just one degree of rotation is exaggerated even further on those gaskets. So when this happens, an inspector will come by and say, “Hey, you over-torqued that flange. You need to go back and retorque it.” And as the assembler, we do that, and what happens? The exact same thing. This is a mechanical interaction. It is going to keep happening. Flange rotation is where the flange rotates, pushes on that outer ring just a little bit and you see dishing.

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