×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Effect of pH on Black Iron pipe for steam

Effect of pH on Black Iron pipe for steam

Effect of pH on Black Iron pipe for steam

(OP)
What kind of effect will a pH drop in RO product water have on regular black iron pipe used to move 125 psi steam?
The original pH was 6.5.  It's dropped to 5.4 - 5.7.

Would this much of a pH drop accelerate the rusting/breakdown of black iron pipe used to move regular cold water?

RE: Effect of pH on Black Iron pipe for steam

Depends mostly on what /how much ,species is causing the pH . I assume RO water is pretty clean , then a very small addition can cause a large pH swing. And, yes a pHof 5.5 could be aggressive.  
I once worked at an R&D facility with a distribution system for distilled water; the pH could be below 5, yet people who knew about it said it was no problem for corrosion tests, it still had very low impurity levels.

RE: Effect of pH on Black Iron pipe for steam

(OP)
blacksmith37,

Without paying an outside lab to do a complex analysis of the water, this is only a guess.  I know that the RO membrane is blocking alkalis.  But it isn't able to block lactic acid, so eventually the pH will drop because the alkali's are coming out.

Like you said, the pH of 5.5 could just be because the water is so pure that it is easy to drop.

I guess there's more information to provide to get a better answer on this.  Unfortunately I won't have it until I send the water samples out.

The old RO was letting a bit of the alkalis through too, and so the water came out much closer to what the feed was.

RE: Effect of pH on Black Iron pipe for steam

I'm missing something:  If the pipe is carrying steam, then it must be pure water (regardless of source water pH) since all the impurities (acids) would be left behind when boiled, right?

And, if the black iron is transferring condensate, then where would the acidity come from?   

RE: Effect of pH on Black Iron pipe for steam

some acids (ie formic) can carry overhead since a lot of them have boiling points only slightly above water.

ports394 - grab a sample of the condensed water and let it dry out in open air.  check to see if there's some stuff left behind.  that might be your acid.

-Mike

RE: Effect of pH on Black Iron pipe for steam

Probably the biggest acid producer in such cases would be CO2.   

RE: Effect of pH on Black Iron pipe for steam

(OP)
Right... CO2 + H2O is carbonic acid.. but i thought that was extremely unstable and it broke down when it wasn't under pressure.

RE: Effect of pH on Black Iron pipe for steam

Don't most use an amine in the boiler water to regulate the condensate pH?  Most condensate is pretty pure once it is formed, and it will dissolve most anything because it does become acidic without treatment.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources