high yield corrosion resistant steel 1

Hi,

I would suggest a Duplex steel such as 2205.

JLAU

Duplex 2205 has yield strengths on the order of 75-85 KSI. Martensitic (400 series) stainless steel such as 440C can be heat treated to the strengths you desire. However, they are not as corrosion resistant as 316 and will be very brittle in that temper.

Please consider CA6NM or 17/4 PH stainless steel which have higher yield strengths and good corrosion resistance. If you could have indicated the end application a better solution could be provided.

Thank you for your responses.
The application is for use in a condensing natural gas boiler. Do you know of any sources that compare the corrosion resistance of the 17/4PH and CA6NM against 316? Another possibility is a Nitronic, but I haven't seen any with high yields and I haven't seen any data on their corrosion resistance.

Phil

Hey Pesy,

A 13-8 PH steel will get to around 205 ksi yield (17-4 peaks around 180), but the problem you run into is susceptability to other forms of corrosion/degradation at this strength level. Many HSLA steels, PH steels, and maraging steels become increasingly sensitive to SCC and hydrogen embrittlement (in both fresh and seawater) once the yield strength reaches about 190 ksi. As stated previously, more information on your application would help narrow the scope of the selection field. Andy

Need information on end use, including the following:

What is the corrosive medium that the alloy has to resist?
Gas? Liquid? At what temperatures? Is any stress involved?
Does fatigue resistance matter? What other service conditions? Steady or intermittent exposure?

This is being used in a condensing boiler, as mentioned above. This means withstanding a dilute sulfuric acid at up to 500 F. The killer though, is that it goes through wet-dry cycles as the unit turns on and off. During the dry cycles, the water evaporates from the flue gas and the sulfuric acid gets concentrated. We know from past experience that 316 is fine for the corrosion, but we'd like to make the piece very thin so that it is flexible. Since it's gonig to be thin, we need a high yield to withstand the hoop stress . We're not sure of the exact numbers yet, but ther higher the yield, the thinner the material. We're thinking around 180ksi will suffice.

The metal will be under 0 stress. We are designing this to be able to withstand an explosion, hence the need for strength. Under normal conditions, there is no stress, and in the case of the explosion, the metal would be at room temp.

Phil,

Is the hoop stress in the boiler a result of the medium it contains only? (i.e. not internally pressurized) If this is the case, is your desire for high yield strength just an effort to contain the potential explosion?

How are you limited for space? If you have lots of space available, then how about making the boiler out of thin 316, and then build a seperate explosion containment chamber around the boiler. All you would need then is material designed for withstanding explosive force, and corrosion would not be an issue. Andy

Based on what you have told us, I like Andy's suggestion of a separate containment.

Two further thoughts:

1. Since you need to be "thin", I wonder whether total weight has to be kept to a minimum. If so, you might use a rotationally cast cylinder for your containment to increase specific hoop strength.

2. Would suggest you visit and download paper # 1318 "Corrosion Resistance of Nickel Containing Alloys in Sulphuric Acid" This contains service experience as well as detailed selection charts.