Originally posted by: NGraham
I am an M&E (mainly electrical biased) project manager dealing with an installation on a hospital and have encountered a problem which myself and numerous others are struggling to resolve. Not being a member of CIBSE i cannot utilise their forums.
A contractor has carried out live tap-ins on a chilled water system using the following materials:
stainless steel tapping tee,
black iron nipple
all being fitted on to a non-metallic chilled water main.
A potential risk has been highlighted by the site based facilities maintenance company whereby they view the installation as having a high potential to suffer from galvanic corrosion due to the use of dissimilar metals.
The installation Contractor is adamant that there is no such problem.
Rather than continue to trawl the internet and read the various articles on the subject (believe me there are lots of articles) I was wondering if anyone has any experience of this or has access to a relevant person within their organistaion who could make considered comment and advise if the installation is indeed at risk. (First look at relevant galvanic tables suggest there could be a problem)
We are trying to avoid having to pay for the services of a mettalurgist at present as no-one is certain if we do have a problem and as such no-one will sanction payment for a report.
Any help (or pointers in the right diection) would be appreciated.
Is the chilled water for drinking? If so the black iron nipple would be a no-no.
There will be some corrosion between the stainless steel and the iron and is likely to create "seizure" of the screw where the two are in contact, however in my limited experience it is unlikely to be such that the wall of the BI nipple becomes eroded to the point of leakage before the elapse of a significant period of time.
Ordinary Brass will also suffer some galvanic effect and it may be prudent to employ Dezincification Resistant (DZR) Brass or Gunmetal. You may be able to find help in the library of one of the process industry trade magazines. Some (many) years ago I used to be on the list for "whats new in process engineering" (I don't know if its still published) and it was a mine of useful inforation such as you need here.
I would simply insist on a written statement from the contractor and without it refuse to accept the job as satisfactory (unless he has installed in compliance with a design brief or drawing supplied by others). No written back up - no job acceptance, the ball is in his court!