Installation of 304L stainless steel pipe

[thedecimalinch]

We have 1000's of stainless steel pipework to be installed some of which will be lagged. Nearly all of it will be welded apart from connections to the equiptment. What flushing will be required? Will we need to use chemicals at all at any stage. After installation is there any kind of passivation or anything like that or is it simply flushing with water and that is it? Any advice would be appreciated as I am not a pipeing guy you see.
We also have quite a bit of carbon steel too some of which will be gunited with cement as will be under ground.

 

[Metalguy]

Too many unknowns. What is flowing? Chloride content? Constant flow? Temp? Cl- of lagging?

For now, do not let the initial fill water to stay stagnant in the pipe w/o lots of high-flowrate flushing.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[thedecimalinch]

It is mainly cooling water. I am not sure about the lagging. The cooling water will go up to 70 degrees celcius

 

[Metalguy]

You have to get a lot of info about the water and flow conditions. Is the water in a closed loop? Is it treated? With what?

Wet lagging with a lot of cl- will probably ruin that pipe at that temp. Hopefully whoever designed it knew what they were doing.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[EdStainless]

There are risks for both the inside and the outside of the pipe.
If the lagging contains Cl-, or could allow the absorption/penetration/trapping of salts then you are at high risk for external corrosion. Perhaps even stress corrosion cracking. In many applications it is common to coat the outside of stainless pipe in order to protect it from environmental chlorides.
On the inside the biggest risk is from stagnant water. Stainless likes to be kept full and flowing, otherwise impurities concentrate and you may get severe localized corrosion. The safest thing to do is to flush the system right before it is put into service. Never let water stand partially full in the pipes.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[thedecimalinch]

/hi thanks for the replies. some the carbon steel lines are open loop and all are treated with NAOH. The stainless lines are closed loop and none of them are treated.

I was hoping to get some input from a construction point of view. ie after installation do you have to use chemicals for passivation etc? Or just use water for flushing?

 

[stanweld]

Has the Engineer/Owner not provided detailed requirements for cleaning? If not, ask.Assure test water or rinse water is low chloride (< 50 ppm recommended). Heed the advice of EdStainless; I have seen a number of recent cases of leakage when test water was allowed to stagnate or when the Engineer did not account for non-flow periods. Perforation of the stainless piping occurred in as little as 2-months.

 

[EdStainless]

I hope that you don't really mean that the water in the SS piping is not treated. If that is so then biological growth will take over and you will have some serious issues.
There shouldn't be a big need to passivate such a system. Conventional cleaning should be fine. You had better not be putting anything into these lines during construction other than a bit of dust.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[rmw]

Are you near the sea or in a marine environment? Under lagging chloride build up and 70C are not a good combination.

rmw

 

[thedecimalinch]

Hi we are not really near the sea no around 100km away. Ihave been on sites before and the SCC was immense!

So basically a good flush out with water will suffice then?