Duramax Diesels Forum Truck of the Week
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Old 12-28-2008, 10:36 PM
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Default How To Chose Material

This will be to help you chose the correct material for what you are building. I will be quoting several articles. Well start with MS (mild steel) It is good for intakes, boost tubes and anything that isnt subject to high heat. It will work as a DP since there is no pressure but should be avoided to connect the exhaust on twins.

Next is SS (stainless steel) I will let Burnsstainless explain this one with the following post.
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Old 12-28-2008, 10:39 PM
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Quoted from Burns


Stainless steel is a material that we wish never was labeled "stainless" because it can do so much more than simply resist rust. The origins of stainless steel date back to the early 1900s when an English metallurgist developed a type of steel for making knives that would not rust. Technically, "Stainless Steel" is strictly a trade name applied to what are known as corrosion-resistant steels. It is a fabulous material that outperforms mild and alloy steels in so many different applications in racing that no other material can match it, and all racers should consider it as a vital element in their fabricating efforts. However, stainless steel does have some unique properties that the fabricator needs to know about before launching into a project. An interesting characteristic of many types of stainless steel is that they are non-magnetic, a quality that makes them very important in the aerospace industry. Compared to mild steel, stainless steel has superior high temperature characteristics. It is an excellent material for headers and exhaust systems, or any application where high heat is encountered.

Stainless steel is similar to mild and alloy steels; it is an alloy of iron that contains at least 12% chromium. This high chromium content retards corrosion giving the steel its "stainless" quality. There are many alloys of stainless steel, which are broken down into two basic categories:

Chromium-nickel grades
Straight chromium grades
The chromium-nickel grades are the more common stainless steels used in race car fabrication compared to the straight chromium types, due to the nickel content which provides excellent weldability and corrosion resistance. Also, this nickel improves some mechanical properties such as fatigue strength, toughness and ductility. People sometimes refer to stainless steels based on their chromium and nickel content: for instance, 18-8 stainless has 18% chromium and 8% nickel in it.

Stainless steel typically has a rather low carbon content, in the range of .08% to .15%, and sometimes as low as .03%. The carbon is needed for hardness, but it also can cause the stainless to become susceptible to corrosion at high temperatures. What happens is this: when chromium-nickel steel is heated to a temperature range of 800° to 1590°F, the carbon in the steel combines with chromium to form chromium carbides. This transformation is called carbide precipitation and reduces the corrosion resistance of the steel. The chromium is reduced in this heat-affected area and makes the steel subject to what is known as intergranular corrosion. Some stainless steels are known as low carbon grades to minimize this carbide precipitation; others, such as 321, are special alloys that reduce carbide precipitation by combining and stabilizing the chromium at elevated temperatures.

You may have heard Smokey Yunick talk about maintaining high exhaust velocity and increase scavenging by covering headers with a thermal wrap. In addition, there are companies that coat headers with a thermal barrier, typically some type of ceramic formula, in order to keep the heat inside the exhaust system. Stainless steel performs this function without the need for add-ons because it has a much lower coefficient of thermal conductivity, thereby keeping more heat inside and transmitting it to the header outlet. Radiated heat is perhaps the most important reason to wrap or ceramic coat the headers to protect the car and the driver from excessive, fatiguing high temperatures.

Typical 1010 carbon (mild) steel conducts 219% more heat per foot than do the types of stainless steel we use in header fabrication. By contrast, quite a bit more heat stays inside the stainless header tubes and does not get passed into the surrounding air. By not allowing the contraction of the cooling gases as they flow down the tubes, more exhaust velocity is retained which promotes better scavenging at the collector. This retention of velocity increases the overall header efficiency.

You've probably seen Indy cars with their enclosed engine compartments and thermal clam-shell enclosures around their turbocharger headers. They must thermally wrap their exhaust pipes just so the radiant heat off the tubes won't cause fires or melt any critical systems. In this case headers made out of mild steel would completely fail and break apart due to the severe heat retention, let alone scale and send death particles into the turbocharger, ruining the turbine blades. 321 stainless steel has excellent high temperature fatigue resistance in this enclosed application and does a darn good job of living in this hostile environment better than any other material except the ultra-high nickel content steels ( such an Inconel ), which are hard to find, very difficult to work with and extremely expensive.
These many characteristics, such as superior heat retention properties, high temperature fatigue resistance, and to a lesser extent, the cosmetic value of a non-rusting finish, combine to make stainless steel an ideal choice for headers and exhaust systems. Such a system will produce more horsepower and last "'til the cows come home". It is an excellent solution. Now that you are sold on the merits of stainless steel, there are a number of things you need to know about the different types available before you launch into a header and exhaust system project.

A three-digit numerical classification system is used throughout the industry. The racer needs to be familiar with only one of these three-digit series within the system - the 300 series. They offer the fabricator a wide array of choices, from ornamental quality up through the highest-temperature and closest-tolerance aircraft quality.

Within the 300 series of stainless steels, there are four types that are suitable, available and cost effective for the racer. These are 304, 316L, 321, and 347.

321 and 347 are known as stabilized grades of stainless. These are alloyed with either titanium (321) or columbium (347), both of which have a much stronger affinity for carbon than does chromium at elevated temperatures. This eliminates carbide precipitation leaving the chromium where it belongs for corrosion protection...remember our discussion of intergranular corrosion? Both 321 and 347 are top choices for exhaust headers, especially turbocharger systems and rotary engines. Since 321 is much more available than 347, that leaves 321 as the first choice, with no sacrifice in needed qualities.
316L is an extra low carbon (ELC) grade of stainless that has only .03% carbon, making less carbon available to precipitate with the chromium. It is used extensively in marine exhausts where salt water corrosion mixed with diesel exhaust particulates and electrolysis create such a horrible environment that even other grades of stainless cower and run away!

304 is the most inexpensive and available stainless in the 300 series. It is suitable for normally-aspirated header applications, and has been successfully used by many racing teams. It does not have the high temperature fatigue resistance that 321 does, but is considerably less costly and much more available. Most 304 tubing these days has the dual designation of 304/304L.

Practically speaking, there are overlapping applications of 304 and 321 stainless in header construction, but knowing you've got the insurance of the aircraft-grade 321 for the job is definitely worth consideration of the extra cost... if your application requires it.

Stainless steels come in both tubing and pipe sizes. Since certain pipe sizes are almost identical in dimension to tubing sizes, pipe may sometimes be substituted for tubing, and vice versa. Numerous wall thicknesses are available, but for headers, normally .049" (18-gauge) to .065" (16-gauge) is used.

Different specifications are used to meet particular requirements for the military (MIL), the American Society of Testing Materials (ASTM), and the Society of Automotive Engineers (SAE). Examples of what to look for when you order stainless tubing are as follows:

ASTM A-554 304 stainless is a welded mechanical tubing used primarily for ornamental purposes. It is not fully annealed and is work-hardened slightly in manufacturing. It has good column strength and good bendability.

ASTM A-269 304 stainless is a general service commercial specification that is higher quality and is fully annealed for better ductility. It is available in both welded seam and seamless, and is a good spec for the racer to use. We have not seen any difference in longevity between welded seam and seamless stainless tubing in header use, but there is a substantial cost difference. The column strength is not as good as A-554, but it has excellent bendability with a higher cost due to the full annealing.

MIL-T-8808/8606\MIL-T-6737 321 stainless are military specifications for aircraft tubing. Suffice it to say that some MIL-specs are not necessarily better or even as good as some ASTM standards. There is no particular magic here.

There are as many uses for stainless steel as there are projects in the shop. There is nothing else that transmits an image of quality and skill to the majority of fabricators than a cleanly constructed stainless steel project. Whether it is a set of headers, intake stacks, or even a stand for one's dyno engine cooling fan, stainless steel has such great mechanical properties that its use should be considered for many projects beyond exhaust systems
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Old 12-28-2008, 10:41 PM
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Quoted from Burns
Inconel


InconelŪ refers to a family of trademarked high strength austenitic nickel-chromium-iron alloys that have exceptional anti-corrosion and heat-resistance properties. These alloys contain high levels of nickel and can be thought of as super-stainless steels. Inconel alloys are used for a variety of extreme applications including navy boat exhaust ducts, submarine propulsion motors, undersea cable sheathing, heat exchanger tubing and gas turbine shroud rings.

For many years, Inconel has been used for Formula One and Champ Car exhaust systems. More recently, several Winston Cup racing teams have utilized Inconel for producing ultra-light, high-durability exhaust headers.

Burns Stainless recommends Inconel 625 alloy for exhaust systems due to its excellent strength, corrosion resistance and fabricability. This alloy also exhibits high creep and rupture strength; outstanding fatigue and thermal-fatigue strength; as well as excellent weldability (though the guy welding it might have a different opinion!). Inconel 625 contains molybdenum and columbium, which stiffens and strengthens the nickel-chromium matrix without precipitation hardening treatments. Some hardening however does occur when heated to intermediate temperatures (1200 F to 1600 F) increasing room temperature strength. Also, this alloy retains over 75% of its room temperature strength at 1200 F. This alloy is available in a wide variety of forms including tubing, sheet, bar, plates and castings. Burns Stainless typically stocks welded and drawn Inconel 625 tubing. The tubing specification is SAE AMS 5581, Nickel Alloy, Corrosion and Heat Resistant, Seamless or Welded Tubing.

Inconel 625 can be welded using conventional stainless steel TIG welding techniques. Inconel Filler Metal 625 rod is used to weld Inconel to Inconel as well as to dissimilar metals including stainless steel. Inconel weldments are high strength and are highly resistant to corrosion and oxidation. Many welders describe that welding Inconel as "dirty". In other words, the weld pool appears to be under a "skin" and is not well defined. In addition, the weld pool is somewhat "sluggish" as compared with steel or stainless steel. These characteristics tend to result in a "coarse" appearing weldment as compared to stainless steel. Welding Inconel is not necessarily more difficult to weld than stainless, just different. By following the welding procedures outlined in the header construction tips article, successful welds with Inconel 625 are possible.
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Old 12-28-2008, 10:44 PM
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Even tho everyone thinks 409 is junk because it is magnetic, it is still better for pre-turbo exhaust than 304

409 is a titanium stabilized ferritic stainless steel which means that it is a steel alloy containing chromium. It contains less nickel and more carbon than 304 stainless steel. Ferritics are best suited for high temperature applications that require corrosion resistance and high strength. The principal use of 409 stainless steel is automotive exhaust systems and most catalytic converter shells are made of 409.

More workable and stable than 304, 409 will accept bending and heat cycling better than 304. It resists both atmospheric and exhaust gas corrosion. It is magnetic due to its higher carbon content. Through chemical reaction, it oxidizes to a slight brownish hue which aids in corrosion resistance. While it does not polish well, it offers the advantages of higher strength, lower cost and longer life due to its heat handling qualities.
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Old 12-29-2008, 01:31 AM
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Do you have any tips for working with Hardox. While may not be good for anything engine related it would be good for say a custom set of skidplates.

This comes from destroying my own skidplates and having some of this around, it is pretty damn expensive.
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Old 12-29-2008, 01:44 AM
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Originally Posted by specialagentPK View Post
Do you have any tips for working with Hardox. While may not be good for anything engine related it would be good for say a custom set of skidplates.

This comes from destroying my own skidplates and having some of this around, it is pretty damn expensive.
Hardox is for abrasion, not impact. I would just use MS. But here is a link on how to work with it.

http://www.ssabox.com/templates/ifra...____10183.aspx
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Old 12-29-2008, 04:03 AM
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Originally Posted by Turbo Buick 6 View Post
Hardox is for abrasion, not impact. I would just use MS. But here is a link on how to work with it.

http://www.ssabox.com/templates/ifra...____10183.aspx


Ahh ok we used it to line our endumps and figured if we couldn't drill through it it would be better for doing a skidplate than steel.

Thanks for the link.
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Old 12-29-2008, 04:38 AM
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Ahh ok we used it to line our endumps and figured if we couldn't drill through it it would be better for doing a skidplate than steel.

Thanks for the link.
If your talking about for your truck, I really don't think it would be worth the hastle since it is so dificult to work with. Your not scraping that much that your wearing it out....correct? just need something a little more rugged
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Old 12-29-2008, 06:11 AM
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Yea out at the gold mine the rocks are attracted to the truck and I have wrecked 2 trans pans and destroyed the plastic skidplate under the engine.
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Old 12-29-2008, 06:15 AM
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Yea out at the gold mine the rocks are attracted to the truck and I have wrecked 2 trans pans and destroyed the plastic skidplate under the engine.
Maybe you can scoop up some gold with a new skid plate
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Old 12-29-2008, 08:57 PM
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I like the tech descriptions above..... good info.

Here is a good one... My 304SS Kooks headers are magnetic where they are mandrel bent, but not on the straight portions. Working the metal made them slightly magnetic.

304L from my understanding has a higher nickel content than regular 304, which makes it suitable for a food grade metal. Supposedly it has a tighter grain structure to better resist bacteria from accumulating in its "pores". I'm told it is used for silverware, beer kegs etc.

Feel free to elaborate or correct me if i described this incorrectly. Just wanted to post some trivia..... It's been real long since I had any metallurgy classes in college.
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Old 12-29-2008, 09:15 PM
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Quote:
Originally Posted by Lonnie View Post
I like the tech descriptions above..... good info.

Here is a good one... My 304SS Kooks headers are magnetic where they are mandrel bent, but not on the straight portions. Working the metal made them slightly magnetic.

304L from my understanding has a higher nickel content than regular 304, which makes it suitable for a food grade metal. Supposedly it has a tighter grain structure to better resist bacteria from accumulating in its "pores". I'm told it is used for silverware, beer kegs etc.

Feel free to elaborate or correct me if i described this incorrectly. Just wanted to post some trivia..... It's been real long since I had any metallurgy classes in college.


The "L" after 304 or 316 or whatnot stands for low carbon. Although austenitic (300 series) has very low carbon, the "L" series is even lower. I would have to look but it very well may have a higher nickle content

304 is excelent for NA headers, but should not be wrapped. When they are subjected to a harsh environment there are better alloys to pick.
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Old 12-30-2008, 10:12 PM
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I looked into it a little further & the 304L does not have more nickel, only less carbon.... my mistake.

From what I could find, the 304L is often considered food grade & the 316L is frequently labeled as medical grade. I've heard some reference to 304L as medical grade, but I think this was just a sales pitch.

So.... I guess my down pipe & front pipe should be 316L or 321 due to the
higher heat & further downstream, I could use 304 for the rest???

I have noticed quite a bit of 304SS headers that I've put on cars turned a greyish color near the engine & start to look bad, whereas the lower part of the headers & the rest of the exhaust only turn a slight gold color.
I had considered JetHot coating on my 304SS Camaro headers to keep them looking good.

My Camaro exhaust is 409 and is turning grey already & it will likely never get wet.
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Old 12-31-2008, 02:34 AM
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Quote:
Originally Posted by Lonnie View Post
So.... I guess my down pipe & front pipe should be 316L or 321 due to the
higher heat & further downstream, I could use 304 for the rest???
304 will work for this since it isn't pre turbo and doesn't have near as much stress on it.....but you are correct, 316 would be better and 321 would be even better


but just remember that 304 is fine since MS seems to be up to the task
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Old 12-31-2008, 11:59 PM
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As crazy as it sounds, I just want it to stay looking nice. Actually I would like to polish the entire exhaust.
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