Inconel / Kline

I can not answer why Inconel was used or not. I was not involved in the development of these vehicles. But Inconel is also used in aerospace engineering and they have to be very durable. Titanium will eventually become brittle. I've already seen titanium exhaust systems ripping. The material Inconel is actually known for longevity, so damage was new to me in that frequency.

 

Hi Guys

Im Glad everyone is enjoying their exhausts. I wanted to clarify some of the questions raised here about Inconel titanium and stainless.

Stainless is a great base material to build exhausts from, its durable, fairly corrosion resistant, cheap and easy to manufacture. However its certainly not lightweight, has a fairly flat sound, and does surface corrode at the high temperatures that exhausts are subjected to.

Titanium in various grades, is an amazing material. We work with grades 2 through to 7, each varies in its mechanical properties, 7 being one of the strongest. It has a very high tensile strength, low density, is corrosion resistant at temperatures up to 600c, easy to machine and weld with both manual and automatic processes.

The drawback with titanium as an exhaust material, is that prolonged heat exposure up to and above 600c degrees, results in a slow oxidization of the material, forming what is known as “alpha case”. This alpha case formation is accelerated in exhaust application due to the corrosive reactive nature of the exhaust gases. Alpha case is very brittle, and will easily crack under vibration and load resulting in exhaust failure. The way to avoid these failures, is to either, use for exhaust components that remain fairly cold, or to use extremely thick 2mm plus titanium, and or to add a passivating coating, ie, paint layer to the exhaust.

Inconel superalloy, has around the same strength to weight ratio of titanium, its significantly higher desnity, but has greater tensile strength. So exhausts made from 0.7mm wall will weigh roughly the same as 1.3mm wall titanium, and will be 35% lighter than a 2mm wall titanium exhaust. The property of Inconel that make it perfect for exhaust manufacture though, is its thermochemical stability. It remains completely inert up to 1200c degrees, and the tensile strength actually increases at high temperatures, this means that your Inconel exhaust get stronger during and after use, unlike titanium that will degrade over time.

Ferrari, Mclaren, Aston martin all use Inconel on their hypercar projects for the standard exhausts.

Here are some links

https://cars.mclaren.com/featured-articles/extreme-heat.html

https://www.roadandtrack.com/new-cars/first-drives/a21284763/ferrari-488-pista-first-drive-review/



Akra has also used Inconel on some of its exhaust range where titan couldn’t stand the heat, even with thick sidewall, and passivating coating, one example is the Aventador.

Our success rate with Inconel exhausts has been extremely high, we have on average less than 1 failure per thousand exhausts shipped, that’s over a 99.9 percent success rate. In the rare event of failure, we will replace the part free of charge, and often cover installation fees where applicable.

We are primarily known for our Porsche exhausts, if you go to 6speedonline, and search Kline Inconel, you will see we have hundreds of happy customers, and zero problems.

The main reason that Car manufacturers, and other exhaust manufacturers don’t use Inconel more often, is that its incredibly difficult to manufacture. We had to set up our own tube manufacture, machining, and pressing manufacture departments in order to offer Inconel exhausts.

For anyone interested, here is a video of some of the procedures we use at Kline Innovation.




Thanks, and all the best

 

Can’t beat that post ^ on the subject, and I agree. I’ve spent the last decade in the fuel cell industry and we use all the common super alloys (Haynes 230, I625, I600, I800, I601, SS 446, etc). For extended high temperature applications in a corrosive carburizing environment, nothing performs as well as Inconel.
‘Performs’ I mean fatigue strength, resistance to corrosion, high temp creep, thermal expansion, and brittleness.

When I bought my manifolds, I went with Inconel. Maybe overkill for a street car, but then so is a Ferrari.


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Ti-6-4 annealed has Ftu=130ksi and density of 0.16 lb/cu in
Inconel 600 annealed has Ftu=80ksi and density of 0.30 lb/cu in

--> Ti has much better strength to weight than Inconel

from MMPDS-01
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Know someone with an inconel manifold (and a massive GT42 sized turbo hanging of it) and has zero issues. Car gets used HARD and a lot. Mind you the company that made the manifold for him makes exhausts for F1 teams, NASCAR etc. Make of that what you will...IMO Inconel is a superior product, but can only be as good as the fabricator in the end.

Reason it's not in main stream products is cost.

 

Note: above strengths are at room temp. At 1000F the tensile strengths are approximately equal (77% of Ftu for Inconel and 49% for Ti), thus Ti still has almost 2:1 strength to weight advantage (all else being equal)

 

Keep in mind that Inconel is just Special Metal's trade name for a family of nickel alloys. There are a number of them, I've mostly dealt with 718 which is significantly stronger than 600 (Ftu of ~180ksi at room temp, 140ksi at 1200F) . I don't know what alloy Kline is using, or if you could even make a manifold out of 718.

 

Tensile strength of titanium alloys after annealing :

Grade 1 34.8KSI

Garde 2 49.9KSI

Grade 3 75.4 KSI

Grade 4 79.8 KSI

Grade 7 49.9 KSI

Grade 9 89.9 KSI

Grade 5 170 KSI


Tensile strength Inconel alloys :

625 160 KSI

718 180KSI

After annealing\ageing at typical exhaust operating temperatures 8 hours use

625 190 - 210 KSI

718 200 - 220 KSI


So before ageing Inconel 625 is roughly double the tensile strength of Titanium grades 3,4, and 9. Is roughly triple the tensile strength of Titanium Grade 2 and 7, and is roughly 5 times greater tensile strength than Titanium grade 1.

Grade 5 Titanium is significantly stronger than other grades of Titanium, but still significantly less than annealed and age hardened Inconel. Also Grade 5 titanium is virtually impossible to rotary draw bend (mandrel bend) at any radius, due to lack of yield, and high galling resistance, and completely impossible to rotary draw bend at 1D and 1.5D CLR radius, required for manifolds, and complex design exhausts.

Aside from this, G5 titanium is not particularly thermochemically stable at elevated temperatures, and would have a short service life compared to say G4 or G7 Titanium.

The vast majority of Titanium exhausts on the market, are grade 2, or grade 1. There are a couple high end brands using G4,7,9. There are no legitimate grade 5 titanium exhausts on the market.

We typically use Inconel 625 for exhaust parts that are in contact with gas discharge, i.e. tube etc, due to its thermochemical stability, and Inconel 718 for structural points, due to its increased tensile strength.

 

The 718 180 ksi is a solution treated-aged condition. This is HIGHER than annealed.
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Please post data that shows an increase in strength when annealed and/or at high temp.

 

We do our own metallurgic testing in our materials lab to ensure quality conformity. but here is chart for an equivalent material and process from an independent source. cold rolled sheet, age hardened at 1325f degrees.

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The table shows room-temp values. The material DOES NOT get stronger when used at temp.

 

Finally, some subject matter experts in the thread!

 

if you read the table description carefully, it says

"properties of cold rolled sheet, aged at 1325f degrees for 8 hours, then 1150f degrees for 18 hours."

then the first two data entries are

cold rolled (ie no age hardening) = 155 KSI

cold rolled, aged(ie age hardened at high temperature as in the table description) = 209 KSI

this clearly shows that after being age hardened at high temperature, that an increase in tensile strength is achieved, within the range that we have previously mentioned.

we previously stated that after age hardening on the car, that the tensile strength of 718 is 200-220KSI. 209 falls exactly in that range. as does the repeat data.

 

All that says is that tempering a metal at high temperature yields increased mechanical properties over an annealed condition. Nothing new there. Different methods and temperatures can yield different results. The graphs that I have posted are for solution treated and aged material per a particular AMS that is used in the aerospace industry. Not surprised there are other tempers that yield higher strengths, especially at room temp. Your table provides no data with respect to performance at elevated temperatures, whether it be static strength/oxidation resistance/stress corrosion resistance/durability.

In your previous post (#27) you stated

This is not true. Period. The material gets weaker when exposed to high temperatures.

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=NINC34
Strength at RT 199 ksi
Strength at 1200F 160 ksi

 

The original statement “the tensile strength actually increases at high temperatures, this means that your Inconel exhaust get stronger during and after use, unlike titanium that will degrade over time” was an offhand, light description, intended to highlight an interesting phenomenon, that after a wearing in period at operating temperatures, the exhaust will display increased tensile strength.

We have demonstrated this with empirical data, from the largest supplier of nickel alloys to the aerospace industry

Given the level of scrutiny into the exact phrasing/wording of that statement, I will amend it to

the tensile strength actually increases after exposure to high temperatures, this means that your Inconel exhaust precipitation hardens, during the process of heat cycling, and is stronger after use, unlike titanium that will degrade over time.

I am happy that we have established, with accord, that the tensile strength of Inconel 718 is around 200KSI, and the material exhibits excellent mechanical properties.

I don’t really feel that further discussion in this thread is really constructive in nature, and therefor will simply refer you to matweb and special metals for further data.

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=NINC34

http://www.specialmetals.com/assets/smc/documents/inconel_alloy_718.pdf

The latter of which is the lead supplier of nickel based superalloys to the aerospace industry, which is the go-to material of choice for aerospace, and motorsport, exhaust applications.

If anyone has any questions, you can email me any time, [email protected]

Wishing you all a great weekend!

 

I’ve enjoyed the exchange around material traits but personally still don’t buy the fluff piece that “the main reason that car manufacturers don’t use Inconel more often, is that its incredibly difficult to manufacture. We had to set up our own tube manufacture, machining, and pressing manufacture departments in order to offer Inconel exhausts.”

No offense to your company, but I find it hard to believe that between Ferrari, McLaren, Mercedes, Bugatti, Porsche, Lamborghini (hell all of vw group) and so on have not figured out manufacturing with all the resources at their disposal and years upon years of experience in inconel racing applications while only 1 tiny company (by comparison) somehow figured a magical way to mass produce relatively inexpensive aftermarket inconel exhausts.

Does not add up brah...

 

Well.....Kline has added it up and has done it successfully.

Automotive companies that you mention has the ability and can manufacture it in their cars but my assumption is that it is the matter of cost and marketing.
Most people don't know what inconel is ...but say the word titanium or carbon fiber and they go nuts. ooohhhhh!!!
I mean,....people who owns Mercedes, Porsche, Lamborghinis, Ferraris, McLarens, Bugattis, etc....most wouldn't care that the exhaust system is steel, let alone stainless steel, or inconel.
Majority don't even push their cars to even matter. If it's not a selling point it won't be put into cars....Titanium has a better selling point than Inconel.

 

Tubi in Maranello manufactures race exhaust for challenge cars and F1. They also manage prototypes and one off exhaust for Ferrari. I’ve toured the shop.

Tubi manifolds for the F430 are Inconel 600. Their heat shield is also Inconel 600. But not all their exhaust manifolds are Inconel 600.

My thinking is that it is cost and difficulty to weld that keeps Inconel out of mainstream, when not absolutely needed to meet the new car warranty life.

Interestingly, combustors on jet engines for helicopters are transitioning from Inconel to a CMC composite material using 3M’s Nextel fibers. It’s more expensive, but lighter and has much better high temp creep resistance.

We may soon see composite exhaust in an automotive application.





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Sorry but this is not accurate at all.

LaFerrari, Mclaren P1, Porsche 918, Senna, Pagani Huayra / Zonda, and Koenigsegg Agera all have inconel exhausts.

So does the Ferrari 488 Pista, which is a segment first and indicates lower price tier's may begin receiving inconel exhausts soon too.

 

And here I was getting excited about this brand exhaust. AND nothing for my 360.....

Oh well. The search continues!!!

Kevin

 

I know that BMW M3 (E92) performance exhaust was Inconel. It was like...$4k.

 

Not all of those did at launch, later iterations yes and also possibly as customer atelier specifications. I should've done a better job being accurately descriptive; but was going for a broad stroke comment that inconel isn't mainstream.

 

we seem to have no Kline Inconel Clients complaining here, and there are plenty of them

 

That's right. You had Inconel from Kline and were satisfied. Other damages of owners were not documented here either. Kline speaks of a complaint rate of less than 1% and always replaces these cases. I will soon get the exhaust system from Inconel for my F430 and look forward to it. I will tell you.

 

Not every owner who has purchased a kline EXHAUST product is on fchat or social media, and most of those who are on fchat, at least in our section, seem to have only purchased non-critical, cosmetic bits like extended exhaust tips. I only know of 1 other person (aside from RichardCH who has historically been a vocal promoter/sponsor of kline) on here who has purchased an actual exhaust component from them, the other guy is SkyHye who got cats. I think ShineKen got a valve controller? which again isn't a main exhaust component...