SS Tank Cracks

Hi Tornado, they pass through the tank walls and are welded on the outside. The bars are only 12mm SS rod. I should have noted in my intial post that the walls move in and out a bit.

Does the tank contain any pressure above atmospheric plus fluid depth? If yes, cycling between high and low pressure would flex the walls, as you note; this might lead to a fatigue issue. (I'm kind of guessing at this point).

There may be weld issues such as too much/little heat, too small a fillet, incompatible electrode, etc. If the stays themselves are not breaking, they may be large enough, unless subject to corrosion. (Still casting about for ideas.)

What is in the tank, its concentration, temperature and pressure?

Guys, the tank is at atmosheric pressure, so no internal pressure. It is only 2 months old, so there is a bit of angst by the Engineering Dept. I want to help them.

The medium being heated is water for normal food processing operations. The gist of my question really is how to stop the vibration from thesteam sparge pipes as I believe that is the source of the problem. Am I wrong?

Not now, though if the tank had been holding 33%wt caustic soda at 95degC prior to that piece of knowledge being shared it might have been a different story, OK?

I think you are right. It could happen that the walls vibrate because the sheet is too thin and the bars are too rigid but with a too small circumference. If you send a sketch of the container it could be possible to give some hints how to make it stiff and increase the carrying capacity of the bars. It could be possible to weld a series of profiles on the walls and increase the stiffness so much that it will vibrate with only very small amplitudes and not be any more a source of problems. I doubt that it will be easier with holes changes. Have you by any chance a possibility to quantify the wall vibration amplitude and frequency? Or at least to indicate on the sketch where are the max amplitudes ? Their value can be estimated with a stick kept so that the wall does not touch it at max, the gap between the stick end and the wall can be optically estimated.

I am in Sydney at the moment, so unable to get dimensions etc. Will do that next week when I get back. In reply to previous reply, the tank is only a month old and has only been used for water.

Really looking for answers to try and eliminate or reduce the vibration caused by the steam injection.

Chloride can have a devastating effect on 'stainless' steel (sulphides and reducing agents similarly) my shortest failure was 24 hrs in a cylindrical domestic water tank 0.9% sodium chloride at 90°C with air sparge.

Problem is STRESS CONCENTRATION where/how you fasten to wall.

For anybody wanting to solve your problem we need to get drawing/photo of details of fastening.

If you cannot send/ describe that -- the best we can say " Hang the Tank with Cradle from tank bottom "

If the tank was manufactured by an outside vendor and being it's two months old, I would contact the manufacture and dump it in their lap's. That's the simplest solution. But if it was an in house design... you got some rework to do. DJ

Read this and get back to us. http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/heating-tanks-and-vats-by-steam-injection.asp

Does it crack on the weld or on the sheet around the welding ?

1. If it cracks on the weld, it is a problem of the material used for welding. It was probably welded with a MIG (wire) machine or electrodes. When thermal dilation is involved you should use always the same material (only TIG welding is recommended)

If it cracks around the welded area it is ether due to the vibration or difference in thermal dilation due to the difference of thickness of materials.

To reinforce the junction you can use a flange always welded with a TIG machine and stiffen the walls, as already suggested.

For the vibrations of the steam jet you can construct a damper (something like the silencer of a motobike) it works.

Hi, You've ruled out the the only real answer that of heat exchanger,but I don't see why,it would be an easy option to connect a coil to the existing feed pipe return it out through the side then through a simple condenser and either return it to the boiler or down the drain,you are already wasting the steam so what you do with it is irrelevant, but it is a re-usable commodity,it could be passed through a hot water tank for hand washing,or fed into the heating system which would be better than throwing it away.

I worked for a large toy car manufacturing company back in the 70s &80s and they had hundreds of die cast & plastic moulding machines all of which were cooled with water which was then pumped up to a cooling tower on top of the building, 30feet from the tower was a huge boiler heating water for the toilet blocks,the central heating etc, which was using about a 1000 gallons of fuel a week, when I pointed this out to the CEO we altered the system and saved around 75% on oil usage.

I tell you this because it sounds like you could make savings in your company.

Bazzer

I have similar hot water bath with steam heating arrangement. The tank walls made of 300 mm thick concrete. Steam pipes vigorously vibrate due to condensate (can not avoid ).

Your problem appears to be due to following reasons:

1. Steam inlet pipe is supported on tank wall, so pipe vibration is transferring to tank and affecting weld joints (weak areas). Let there be no rigid connection between steam pipe and tank walls ( support steam pipes externally). Steam pipe should enter from top of the tank, travel vertically down-wards and then horizontal sparge pipes on tank bed.

2. How long are the stay bars? Have you obsered any deformation on tank walls where stay bars are connected? From ambient temperature condition while welding stay bars (no water in tank) to operating temperture of 86 degC, SS stay bars can expand about 1.0 mm/m length. This can cause tremendous stress on weld joints leading to crack. Use suitable compansators.

You are quite correct steam pipes should enter through top of tank to avoid any interaction of tank walls which is badly designed and cannot support the stresses involved.

Large reinforcing patches on the tank walls might stop the problem but if going to that much trouble it would be cheaper to relocate the steam pipes.

I suggest you have a failure analyst/metallurgist examine the cracks to determine the cause. In the meantime, I suggest you change both the tank and weld metal to 304L stainless steel and explore design options to reduce operating stress, e.g. thicker material.

At that water temperature you will be getting chloride stress corrosion cracking.

There's plenty of reading on the net.

I have been involved in replacing a complete 304l hot water pipework with 2205 dulpex stainless in several plants.