TO POTECT AN AUSTENITIC ST ST. DURI
TO POTECT AN AUSTENITIC ST ST. DURI
(OP)
TO POTECT AN AUSTENITIC ST ST. DURING SHUTDOWN WE INTEND TO WASH IT WITH A 2WT% OF SODA ASH SOLUTION. WE ARE GOIUNG TO HAVE A WASHING SYS. CONSISTS OF A STORAGE AND MIXING TANK (5 M^3) AND A PUMP (30 M^3/H). DOES THIS DESIGN SOUND OK? COULD WE USE AN AIR OPERATED DIAPHRAGM PUMP? COULD WE USE SUCH PUMP AS A SELF PRIMING AND INSTAL IT ABOVE THE TANK? IS IT BETTER TO USE DRY SODA ASH OR TO USE SLLURY?
THANK IN ADVANCE TO YOUR ANSWERS.
THANK IN ADVANCE TO YOUR ANSWERS.





RE: TO POTECT AN AUSTENITIC ST ST. DURI
Do you have any H2S in your fuel gas system? If so, you may want to wash down the outside of the tubes also to prevent cracking.
Regards,
Bob
RE: TO POTECT AN AUSTENITIC ST ST. DURI
Is the washing also intended to clean off something corrosive?
Is this solution intended to leave a neutralizing residue on the surface?
What is the SS alloy?
Subject to my not knowing your environment, I would wash the SS with a warm citric acid solution, rinse with water, then final rinse with DI water. Any carbonate residue would attract moisture and dirt from the air, possibly leading to corrosion.
RE: TO POTECT AN AUSTENITIC ST ST. DURI
HAZOP at www.curryhydrocarbons.ca
RE: TO POTECT AN AUSTENITIC ST ST. DURI
Even if there isn't much sulfur present, we usually assume that there is a layer of sulfide scale that will form polythionic acid when there is O2 and moisture. So, you either have to keep the steel from being in contact with air during a turnaround...or you have to neutralize the weak acid.
By the way, I believe that it is usually recommended to do a hot H2 strip to get as much sulfide as possible off of the steel prior to neutralization. Other things to consider are:
1. The mix tank water should be at least 38 C to help dissolve the soda ash.
2. The mix water has to be low in chloride content (<50 ppm), and the soda ash shouldn't be >500 ppm Cl. Add 0.5 wt% sodium nitrate (do not exceed this) for added protection against chloride attack.
3. Add a wetting agent for better penetration of coke, scale and films.
4. Soak everything for at least 2 hours, and have a good circulation rate if you suspect you may have some air pockets.
Also, I remember taking to someone about cracking of ss fins on heater tubes due to the amount of sulfur used for odorizing natural gas...which stresses that it really doesn't take a lot of sulfur to cause a problem.
Regards,
Bob
RE: TO POTECT AN AUSTENITIC ST ST. DURI
Thanks, I gave you a star for being both helpful to 38621 and informative to me.
Ken
RE: TO POTECT AN AUSTENITIC ST ST. DURI
ALSO WE INTEND (TO BE ECONOMICAL AND HAVE 5 M^3 TANK AND NOT A 15 M^3 TANK) TO FILL THE TUBES VOLUME WITH 3 BATCHES OF SODA ASH SOLUTION 2 -3 WT% - IS THIS WISE? COULD WE THAN CIRCULATE THE SOLUTION INTO THE HE (14 M^3 TOTAL INC PIPES)BY THE DIAPHRAGM PUMP? HOW DO WE KNOW THAT THE SODA ASH SOLUTION LEAVE A THIN ALKALINE FILM ON THE ALL SURFACE ?
RE: TO POTECT AN AUSTENITIC ST ST. DURI
It was quite simple, ammonia cylinder + regulator + instrument tubing. close the vent stack(keep some opening for avoiding pressurisation of fire box).
This was quite simple, in 2 or 3 cylinders we could get the result.
Also how will you ensure that whole tubes are coated with soda ash solution, spraying in firebox with available openings is difficult.
Also you can keep instrument air positive pressure inside the firebox, to prevent moisture entering, once you have sprayed ammonia.
Hope you find this useful...
Regards,
SAA
RE: TO POTECT AN AUSTENITIC ST ST. DURI
HAZOP at www.curryhydrocarbons.ca
RE: TO POTECT AN AUSTENITIC ST ST. DURI
Regards ,,
RE: TO POTECT AN AUSTENITIC ST ST. DURI
RE: TO POTECT AN AUSTENITIC ST ST. DURI
This may be too late for the reply. However, I would like to confirm my understanding with all members.
The reference should be NACE RP 0170.
The clad material of 300 series S.S. should be nutralized. However, the service temperature of the vessel should be concerned. In case of service temperature less than 400 C, sensitization will not occur.