SS 304 limpet coil failure

Is it possible that the materials used in the limpet coil and their temperatures and pressures were not advised to the original equipment manufacturer [OEM] for the reactor?

If so, then an urgent request for advice from the OEM would be a good starting point.

300 series stainless cannot withstand chloride ion, only 400 series (and more exotic materials) can be used in brine system, especially at elevated temperatures (ie. steam heat to flush out cold brine as you switch from cool to heat).

You now have billions of small cracks throughout your system. It is like swiss cheese, and is destroyed most likely. While you might patch the leaks by something like rad leak stop in the short term, the pressure structure may fail catastrophically under pressure. Throw it out & start all over again. Next time, start by getting expert advise to design the system. Suggest process engineering firm.

Your system is inherently unsafe. 300 series stainless steel CANNOT be used in the high chloride service you describe. It will suffer aggressive stress cracking and suffer brittle fracture-probably without warning-though small leaks MAY appear first.

You should immediately discontinue using the equipments, decommission and scrap it, and reconstruct using a material suitable for the service.

Good evening Sangeetadixit.

I have my corrosion data at work. Will look at this in the morning.

The weldments failing first is not surprising. Usually the heat affected zones adjacent to the welds are more susceptible than the base metals being joined.

I'm not familiar with the use of nitrite inhibitors. I think that the question needs to be asked if the wedments were passivated after welding.

We'll talk in the morning

milo

Good evening Milo

As per equipment manufacturer ,the welding is done through special electrode technique.For control of failure during operation they recommended molybdate -nitrite inhibitor. Still within 2 Years of installation there is a failure in around 2-3 units.What is the procedure for passivation of weldment

Sangeeta

Sangeetadixit:

You have been given great advice by the others. 304 (18-8) stainless and Chloride are bad combination. pits, stress cracks, and corrosion are likely due to chlorides, which according to my reference (Carpenter Stainless Steels Manual) you can expect corrosion rates to be upwards of 50 mpy (mils penetration per year). This is in inches, mpy/39.4= mm/y

Passivation will not help you given the fact that your base grade is incompatible with your fluids. However the basic passivation technigue is clean degrease to remove oils weld flux and other soils; immerse in nitric acid, rinse and dry.

Another technique that is used is the A-A-A technique-

1) clean degrease

rinse

2) 5% Sodium hydroxide 160oF 30 minutes

rinse

3) 20% by vol nitiric acid + 22g/liter sodium dichromate at 120o F for 30 min.

rinse

4) 5% by Weight sodium hydroxide 160o F 30 minuts

rinse.

This allows the alkaline solutions to neutralize any acid being retained in nonmetallic inclusions.

Based on your description of duty cycle and materials involved, i would NOT want my daughter to work in your shop, or within a mile or so downwind.

milo "heed the others- you have bad troubles !"