Can a Gasket selection cost a billion dollars?
A young engineer once asked what is “glass transition temperature”
Why are you paying so much attention to it?
What possible harm can it cause? Is it having any real importance?
Also, There is small surprise for you at the end of the article so stay tuned till the end .
I hope you would find this article and the small gift valuable !!
Why are you paying so much attention to it?
What possible harm can it cause? Is it having any real importance?
Also, There is small surprise for you at the end of the article so stay tuned till the end .
I hope you would find this article and the small gift valuable !!
The below story answers this interesting question
NASA one of the top engineering companies in the world had their space shuttle launch.
The space shuttle was named challenger.
A strange thing happened this time.
After 17 secs in air the space shuttle worth billions of dollars turned into scrap.
You might thing the cause of this accident could be something very complex.
However, scientist Feynman discovered and showed to the team of investigators that it was a simple gasket that caused the accident.
He dipped the gasket in Ice cold water for some time and then stretched the gasket; He showed that the gasket once stretched took a long time to regain back to its original shape.
When the gasket was cooled further, it broke into pieces when stretched
The space shuttle was named challenger.
A strange thing happened this time.
After 17 secs in air the space shuttle worth billions of dollars turned into scrap.
You might thing the cause of this accident could be something very complex.
However, scientist Feynman discovered and showed to the team of investigators that it was a simple gasket that caused the accident.
He dipped the gasket in Ice cold water for some time and then stretched the gasket; He showed that the gasket once stretched took a long time to regain back to its original shape.
When the gasket was cooled further, it broke into pieces when stretched
How can this happen?
It is a simple concept called glass transition temperature (Tg)
When we cool a plastic below its glass transition temperature it starts to behave similar to brittle substance like glass.
Hence the name given to this phenomenon is “glass transition temperature”.
When we cool a plastic below its glass transition temperature it starts to behave similar to brittle substance like glass.
Hence the name given to this phenomenon is “glass transition temperature”.
What had happened?
When the rocket was launched, the atmospheric temperature was very low.
Snow had accumulated on the rocket.
However due to stringent deadlines it was decided to launch the rocket.
As the rocket was launched the temperature inside the engine was very high.
This caused the metal parts to expand.
In the previous launches the gasket would come out of its place and seal the groove and thus prevent these combustible gases to leak out
This time since the rocket was launched during an extremely cold weather where the gasket was near it glass transition temperature.
Thus when the metal expansion happened the compressed gasket near its glass transition temperature took time to seal the grove
Thus these combustible gases escaped quickly thought the groove.
Thus, it was inevitable for the explosion to be prevented in presences of such combustible gases leaked, (also, the temperature was around 1000 Deg Celsius)
Within few seconds the space shuttle, worth billions of dollars got destroyed and the most unfortunate thing was that the entire crew died.
Snow had accumulated on the rocket.
However due to stringent deadlines it was decided to launch the rocket.
As the rocket was launched the temperature inside the engine was very high.
This caused the metal parts to expand.
In the previous launches the gasket would come out of its place and seal the groove and thus prevent these combustible gases to leak out
This time since the rocket was launched during an extremely cold weather where the gasket was near it glass transition temperature.
Thus when the metal expansion happened the compressed gasket near its glass transition temperature took time to seal the grove
Thus these combustible gases escaped quickly thought the groove.
Thus, it was inevitable for the explosion to be prevented in presences of such combustible gases leaked, (also, the temperature was around 1000 Deg Celsius)
Within few seconds the space shuttle, worth billions of dollars got destroyed and the most unfortunate thing was that the entire crew died.
Why is this incident very important to us in gasket selection?
Since the gasket they used in space shuttle engine was FKM Vitton.
This is a widely used O-ring in our Petroleum & chemical industry
Also, Hydrocarbons that we handle are one of the most dangerous substance ever handled by mankind.
Hence a small negligence on our part can lead to a catastrophic accident.
With Little more Engineering Knowledge, we can save lives of people at plant and Billions of dollars!
This is a widely used O-ring in our Petroleum & chemical industry
Also, Hydrocarbons that we handle are one of the most dangerous substance ever handled by mankind.
Hence a small negligence on our part can lead to a catastrophic accident.
With Little more Engineering Knowledge, we can save lives of people at plant and Billions of dollars!
What are the Technical lessons we can learn?
Lesson 1: Check the upper as well as the lower temperature limit the gasket can sustain
We usually only check the Upper Temperature limit of O-Rings and Gaskets
Example: - PTFE has the upper temperature as 260 °C but there is also Lower temperature limit that must be checked.
This is sometimes called “Glass Transition temperature” or “Brittleness Temperature” or “Lower Temperature limit”
Below is a screen shot from ISO 23936-1:2009 (Yellow highlighted is “Brittleness Temperature” for PTFE )
We usually only check the Upper Temperature limit of O-Rings and Gaskets
Example: - PTFE has the upper temperature as 260 °C but there is also Lower temperature limit that must be checked.
This is sometimes called “Glass Transition temperature” or “Brittleness Temperature” or “Lower Temperature limit”
Below is a screen shot from ISO 23936-1:2009 (Yellow highlighted is “Brittleness Temperature” for PTFE )
Yes, PTFE has a very low brittleness temperature, but all materials do not have such a low glass transition or brittleness temperature!
Avoid selecting gaskets near upper or lower temperature limit.
Note :- When an O-ring is cooled near, but not beyond, it’s Tg (Glass transition temperature), the cold O-ring, once compressed, will take longer than normal to return to its original shape and in the meantime, gases can leak out.
Avoid selecting gaskets near upper or lower temperature limit.
Note :- When an O-ring is cooled near, but not beyond, it’s Tg (Glass transition temperature), the cold O-ring, once compressed, will take longer than normal to return to its original shape and in the meantime, gases can leak out.
Lesson 2: Checking Chemical Compatibility of Gasket/ O-ring
Few Examples of materials that must not be used for a peculiar Process service
1.Polyether-Etherketones (PEEK)
Hydrogen sulfide can attack PEEK, specifically in the presence of amines and elemental sulfur and at high partial pressures and temperatures in the range of 200 °C
Limited chemical resistance exists also against halogenated hydrocarbons
(Reference: O-Ring selection standard ISO 23936-1:2009 Page 10)
Now, My Personal Favorite the O-Ring used above in NASA’s Shuttle Motor FKM Vitton
Limited chemical resistance exists also against halogenated hydrocarbons
(Reference: O-Ring selection standard ISO 23936-1:2009 Page 10)
Now, My Personal Favorite the O-Ring used above in NASA’s Shuttle Motor FKM Vitton
2.FKM Vitton
This is an amazing O-ring material acceptable to many services but still there are few services where it is not compatible
FKM is not acceptable for Amines or hot water and steam.. (Reference API RP 551,Page 15)
Note that STEAM is used in majority of plants.
Refer the following statement from API RP 551 Standard, Page 15 with regards to FKM
“We cannot predict how an Elastomer will fail some swell, some dissolve, and some take a compression set. Explosive Decompression (ED) can also occur when an elastomer absorbs process vapor and the pressure is abruptly released. A seal can become damaged as a result and will be unable to hold pressure afterwards”
FKM is not acceptable for Amines or hot water and steam.. (Reference API RP 551,Page 15)
Note that STEAM is used in majority of plants.
Refer the following statement from API RP 551 Standard, Page 15 with regards to FKM
“We cannot predict how an Elastomer will fail some swell, some dissolve, and some take a compression set. Explosive Decompression (ED) can also occur when an elastomer absorbs process vapor and the pressure is abruptly released. A seal can become damaged as a result and will be unable to hold pressure afterwards”
3.Polytetrafluoro-ethylene (PTFE) -One of the safest Gasket
The temperature limit is 260 °C. At this temperature, the mechanical properties are very poor due to creep.
Stress corrosion cracking has not been observed with PTFE.
Refer the following statement from O-Ring selection standard ISO 23936-1:2009 Page 11 with regards to FKM
“No media used in oil and gas production, including functional chemicals (detergents, surfactants, emulsifiers, demulsifies and corrosion inhibitors), have been reported to attack PTFE up to the temperature limit.”
But please note the standard does not hold any responsibility of compatibility but it gives us a good guideline in selection.
Stress corrosion cracking has not been observed with PTFE.
Refer the following statement from O-Ring selection standard ISO 23936-1:2009 Page 11 with regards to FKM
“No media used in oil and gas production, including functional chemicals (detergents, surfactants, emulsifiers, demulsifies and corrosion inhibitors), have been reported to attack PTFE up to the temperature limit.”
But please note the standard does not hold any responsibility of compatibility but it gives us a good guideline in selection.
Hence stay safe and refer following Standards for gasket selection: -
1) ISO 23936, Non-metallic Elastomers for Oil and Gas Production
2) EN 682, Non-metallic Elastomers for Oil and Gas Production,
Also consult with manufacturer and material engineer in case you find something that needs further clarification!
2) EN 682, Non-metallic Elastomers for Oil and Gas Production,
Also consult with manufacturer and material engineer in case you find something that needs further clarification!
Lesson 3: - Avoid startup of a plant at extreme weather conditions
Also, during initial startup of plant it is better to not start activity at extreme conditions since the probability of such accidents increases like unaccounted thermal expansion at high temperature or glass transition temperature is unchecked etc.
Like the one happened above in NASA’s space shuttle launch
Like the one happened above in NASA’s space shuttle launch
In conclusion check the following 3 aspects of gaskets: -
1. Check the Chemical compatibility with the process.
2. Check maximum temperature gasket can sustain and then maintain a safety margin.
3. Check minimum temperature gasket can sustain and then maintain a safety margin.
A small Gift :- Free E-book and Courses
We as engineers have tremendous responsibility when it comes to engineering safety and being well grounded in the fundamental concepts of engineering.
This article is an excerpt from my Free E-book on diaphragm seals.
The below E-book covers all these concepts of Erosion, Gasket selection, Fill fluid vaporization, gold plating ,full vacuum etc.
I am really humbled and glad that engineers from 150+ companies including the likes of ADNOC, SABIC, DOW chemicals, Bechtel, Fluor, Worley, Technip, Emerson, ABB, Yokogawa etc have found it valuable and interesting.
I hope you would find the E-book valuable and interesting.
Click here Button to get access to your free resources
More Free Stuff ?
It’s been years learning about this incredible branch of engineering called Instrumentation. The more I learn about it the more interesting it gets.
During this course of learning I have stumbled across great E-books, whitepapers and free certification courses on Green Hydrogen , SIL (safety integrity Level ) course and Free SPI online learning tool to name a few.
Thus I thought to compile this list and add links to such amazing E-books, whitepapers and courses in a single place
After subscribing to the newsletter below you would receive access to Member only page which has access to all these resources for free.
I am super excited to share all this with you
Click below Button to get access to your free resources
1. Check the Chemical compatibility with the process.
2. Check maximum temperature gasket can sustain and then maintain a safety margin.
3. Check minimum temperature gasket can sustain and then maintain a safety margin.
A small Gift :- Free E-book and Courses
We as engineers have tremendous responsibility when it comes to engineering safety and being well grounded in the fundamental concepts of engineering.
This article is an excerpt from my Free E-book on diaphragm seals.
The below E-book covers all these concepts of Erosion, Gasket selection, Fill fluid vaporization, gold plating ,full vacuum etc.
I am really humbled and glad that engineers from 150+ companies including the likes of ADNOC, SABIC, DOW chemicals, Bechtel, Fluor, Worley, Technip, Emerson, ABB, Yokogawa etc have found it valuable and interesting.
I hope you would find the E-book valuable and interesting.
Click here Button to get access to your free resources
More Free Stuff ?
It’s been years learning about this incredible branch of engineering called Instrumentation. The more I learn about it the more interesting it gets.
During this course of learning I have stumbled across great E-books, whitepapers and free certification courses on Green Hydrogen , SIL (safety integrity Level ) course and Free SPI online learning tool to name a few.
Thus I thought to compile this list and add links to such amazing E-books, whitepapers and courses in a single place
After subscribing to the newsletter below you would receive access to Member only page which has access to all these resources for free.
I am super excited to share all this with you
Click below Button to get access to your free resources