I'm trying to develop a test that needs to heat air up to 900C. I was using a Dalton Cartridge heater but since I'm not using it as a immersion heater, they keep burning up around 400C.

Test Details;

Material_Heated: 409SS pipe 1.5mm wall 26mm OD
Volume_Flowrate: 8.6PSI with no air flow
Flows_Through: no flow - pipe is air tight
Dimensions: 409SS 1.5mm wall 26mm OD 24.5in long
Not_Insulated

Start_Temperature: 25C
Target_Temperature: 900C

Application_Factors: Sample is DRY with no air flow but is pressurized to 8.6PSI. Target temps are 600C, 750C & 900C for 1 hour soak at each temp.

Any help is appreciated.

You say "not insulated", the heat loss is going to be considerable at 900°C, I'm not sure what kind of wattage you will need. 900°C is fairly high (1652°F) for most cartridge or strip type heaters.

If I were doing this I think I'd buy a replacement heating element (something like these: http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=HE )for an electric ceramics kiln and a pile of insulating bricks and build a crude oven, but I live near a kiln manufacturer and I already have a pile of kiln bricks so I may be biased.

You might go to http://www.mcmaster.com/ and look up part number 3540k33 and see if it, or others on that page might work, you might want a longer model and wrap it around your tube, the rated max. temp. is 1700°F (926°C) which would seem to meet your requirement, but remember the heater will have to be somewhat higher than your sample because of thermal resistance and losses, but they might work, at least for a while. If you are at the McMaster site, you might also check out the 93315K51 insulation (or others on that catalog page)

is there a chance it might catch on fire? And to what degree of heat would the heater have to be (let's say it's a real powerful industrial size heater).
I find it ridiculous that a jacket hung over night in front of a heater can catch on fire...but the safety inspector at work threatened to write me up for violating safety hazard. I know it's not the safest thing to do, but realistically, could this happen?