Letter 20086

Which alloy for stack gas sampling?  

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I am involved in stack emissions testing for an environmental consultancy. We currrently test a number of processes, including cremators and incinerators, where we would typically sample for acid gases e.g HCl and HF, and also dioxins. In the past we have used quartz lined probes, but breakages have been the cause of many a headache in the past. I would like to move towards using inconel or hastalloy probes for sampling purposes (no more breakages!), but the choice available is a little bewildering to a materials non-expert like me. Which material would be the most corrosion resistant and best suited for the job? Stack temperatures can reach up to 1200 deg C and we would typically sample for 2 - 3 hours.

Many thanks for your help,

Ben Rose
Scientifics Limited - Manchester, England

Hi Ben,

All my stack testing was to determine cfm flows and multi point traversing, not long term environmental sampling ... which raises the point, WHY so very, very long??? Surely a sample can be drawn out in milliseconds or so. What does long term sampling prove, if anything?

What materials to use? Well, ask yourself one question ... what are the stacks made of?

If Dolomite, ah, then I'd opt for, say, Hastalloy C ... but for short STANDARD duration testing, use stainless.

Another thing, you won't really get much corrosion at elevated temperatures ... it's when there is moisture around + oxygen that things, metals anyhow, corrode.

I used to use ALNOR equipment ... this had an (optional) long stainless probe and electronics to determine velocities ... but after use then the probe, a pitot tube, might have been cleaned, perhaps ! But then we were testing at ambient temperatures.

... hope this helps you a little ...

Freeman Newton
- White Rock, B.C. Canada plastics background ,,, 40 odd years

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