boiler corrosion pitting

TO cowtown chemical-I am supprised that no one has answered your questions for you by now. The answer(s) arequite simple but the methods (wet test proceedure can be mis-leading) .The commonly used colorometric wet test is generally for sulfite as SO(sub3)and the types of (forms of or compounded sources of sulfite reducing material can vary.Generally,sulfite feed is considered to be as sodium sulfite ,i.e. 8lbs of sodium sulfite to 1lb oxygen. In practice ,10lbs is added to react with 1lb oxygen due to a number of limiting factors, to numerous to be covered here.The main thing you need to remember is that Sodium,mol wt 23 + sulfur,mol wt32 and oxygen, mol wt16 When combined to form Na(sub2)SO(sub3) is NOT the same as sulfite,SO(sub3) that you read as your wet test result. Otherwise you could be looking at 37% error in your test results.
Let me know if you need more help.
John White
polynox_chem@msn.com

ATTENTION: COWTOWN CHEMICAL! FROM:countryham...I've thought about your Questions since sending you my reply.My response to your questions,although valid in answer to your question, WILL NOT SUFFICIENTLY RESOLVE YOUR PIT PROBLEM BECAUSE IT LACKS AN EXPLANATION OF CHEMICAL STOICHIOMETRICS AND APPLICABLE KINETICS OF THIS REACTION! THE REACTION IS KINETICALLY KNOWN TO BE ONE OF &quot;SECOND ORDER&quot;,i.e.,a slow reaction,even at boiler water temperatures.The reaction rate doubles every 10 degrees C. rise And further doudles every 20% increase in sulfite concentration (note that I did not say sodium sulfite concentration).Furthermore,as the oxygen concentration is lowered,to 0.8ppm,the reaction becomes &quot;oxygen limiting&quot;,i.e.,the reaction rate becomes slower and slower.In addition,industral handbooks show &quot;typical&quot; reaction curves that are grossly inaccurate.In you particular case,YOU MUST ADD AN EXCESSIVE AMOUNT OF SULFITE TO RESOLVE YOUR PROBLEM AND IT SHOULD BE ADDED AS FAR BACK FROM THE BOILER AS PRACTICAL---PREFERABLY IN THE STORAGE SECTION OF THE DEAERATOR.THE REACTION WILL CONCIEVABLY TAKE UP TO 10 MIN. FOR COMPLETE OXYGEN SCAVENGING BECAUSE THE LOWER THE OXYGEN CONCENTRATION,THE SLOWER THE REACTION. THE ONLY WAY YOU CAN COMBAT THE SLOW REACTION PROBLEM IS TO INCREASE THE SULFITE RESIDUAL WITHIN THE BOILER TO MINIMUM LEVELS OF 25-30ppm SULFITE.IF I KNEW HOW MANY CYCLES YOU WERE RUNNING I COULD HAVE HELPED YOU MORE. GOOD LUCK<-countryham

Cowtown: If you are getting 1.5 ppm boiler feed water, you need to check the operation of your Deaerator. The industry standard for BFW out of the DA is < 7ppb. I don't have a clue about the reaction kinetics mentioned above, but if it is oxygen limited, you should probably reduce the O2 level. Again, your O2 inlet to the boiler should not be more than 7 ppb.