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AL6XN ability to resist chlorides

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I am in the process of choosing a material of construction for a wastewater evaporator. My choices have been narrowed down to AL6XN, Hastalloy 276, or Titanium (in increasing order of cost respectively). I would obviously want the cheapest material of construction that will perform adequately. This material will be exposed to the following conditions.

temperature = boiling (212-225 degrees F)
pH range = 6-8 at all times
chlorides = 75,000 ppm to saturation
other halides (I-, Br-, F-) are also present in lesser concentrations
High levels of nitrates from neutralized nitric acid (10-20%) are present as well. Neutralization is performed prior to proposed evaporation with Mg(OH)2 as a buffer (pH 8.3)

I am fairly certain Titanium as a material of construction will give me many years of reliable service...but it is three times the cost of AL6XN. Is anyone out there familiar with the chlorides resistance capabilities of AL6XN? I've been told it will resist all the way to saturation as long as the pH is above 5. How about Hastalloy 276? I am considering a general corrosion test per ASTM G31, but doubt this will tell me much about the potential SCC, pitting, and crevice corrosion caused by the chlorides and other halides in my waste stream.

Thanks in advance,

Marty Verbic
- Urbana, Illinois

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After reviewing your requirements it appears to me AL6XN is not the material of choice for this application. AL6XN appears it would be susceptible to crevice corrosion attack if any deposits were left on the surface of the material.

I believe the materials of choice for this application from best to worst would be

1)Titanium #7 which would be totally immune to crevice corrosion attack at the specified pH range and temperature.

2)C276 immune to CC at the pH range and temperatures up to 250 deg F.

3)Titanium #12 immune to cc at pH of around 6.

4)AL6XN & Titanium grade 2 are both subject to CC at the ranges specified

Ken Kimbrel
- Springfield, Missouri