difference AISI 316 L and 316 Ti with smoke 1

[Mac001]

I'm working at a heat recovery exchanger connected in line with an CH4 engine .
the fisrt exchanger will have inlet temp 440° and outlet temp 120°C
The inlet temperature will be 120°C and outlet 50°C.

I'm selecting the tubes material and i'm considering AISI316L
but a some source insist for AISI 316 Ti.

What the real difference in such a corrosion enviroments between these materials ?

thank you in advance !!

 

[JasonLouie]

I'm not sure about the corrosion environment, but 316Ti is probably asked for because of the high temperature. 440°C is in the sensitization range and the Ti in the 316 will bond with the carbon to prevent sensitization (this prevents intergranular corrosion). Another philosophy would be to use the 316L grade. Having less carbon will lower the amount of chromium depleted and hopefully prevent sensitization.

On the other hand, you still need to look at the stress tables and ensure that 316L has the required strength at your design temperature. If the strength is not there, then 316Ti will be required.

Someone else will have to comment on the corrosion environment...sorry.

 

[ApC2Kp]

Mac001,

There are differences between the two materials, and there are differences between the corrosion concerns in the two environments. The high temperature in first exchanger might suggest the 316Ti, but some might use 304 or 430Ti for internal scaling and external oxidation resistance. Your engine exhaust pressure is probably low to where strength is not major requirement.

The low temperature of 2nd exchanger results in condensing of water from exhaust. The wet conditions might be handled by stainless steels if condensate is drained and controlled to low concentrations by the liquid flushing out the acids. There will be carbonic acid, and other acids depending on the other trace compounds in fuel and intake air. The CH4 methane could contain mercaptans as odorant, and result could be weak sulfuric acid in the condensate. Engine combustion temperatures could generate NOX to result in nitric acid with condensate. A coastal salt spray air environment could result with intake air chlorides for attack in both the exchangers. Local neighbor processing plants with bleach operations, or even a municipal swimming pool chlorination system could provide enough chlorine vapor in the local atmosphere to destroy a stainless steel exchanger.

You didn't mention the exchangers other side fluid condtions. Are you heating water, or making LP steam? Do you need to heat a secondary fluid for building heat? The actual tube wall temperatures could be much lower than the hot gas temperature.

 

[Mac001]

The heat recovery will work with water up to 95°C ( in the first exchanger)and 45°C ( in the second) ..
the working temperature of the tubes will be very low, in counterflow will be approx 200-250°C

The plant will be located in Germany in an industrial zone , but i don't know other details...

 

[ApC2Kp]

Mac001,

The water being heated will need to be controlled to limit chlorides (150 ppm?) to avoid CSC. Otherwise, a higher SS or duplex SS is advised if there are excessive chlorides.

 

[Mac001]

What would happend ,if I would use Cu/ni instead of AISI 316 for the tubes and I would clad the plate with AISI 316?

 

[Mac001]

I mean For the condensing unit .. tubes in Cu/ni and plates cladded with Cu/ni