IET
Decrease font size
Increase font size
Topic Title: Mechanical problems !!!!
Topic Summary: Galvanic corrosion & Disimmilar Metals
Created On: 17 June 2010 03:59 PM
Status: Post and Reply
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 17 June 2010 03:59 PM
User is offline View Users Profile Print this message



NGraham

Posts: 18
Joined: 14 March 2009

Help -

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
brass valve
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.
 17 June 2010 04:35 PM
User is offline View Users Profile Print this message



westonpa

Posts: 1771
Joined: 10 October 2007

There is a problem because brass, stainless and iron have been used. See below for a reasonable explanation:

http://www.engineeringtoolbox....-corrosion-d_906.html

They need to use metals that are closer to each other or alternatively use other materials, for example a plastic washer.

Regards.
 18 June 2010 01:09 PM
User is offline View Users Profile Print this message



NGraham

Posts: 18
Joined: 14 March 2009

Regards both the replies on the matter (thanks for taking the time), I also have looked at various galvanic tables leading up to my question that i posted.
All tables I have seen (in various formats, some quite clear, some not so) tend to suggest there is a problem with the materials used.

The contractor still disputes that and states there is no issue, yet he will not give written assurances or guarantees and cannot refer me to a relevant code of practice or installation guideline to which his installation complies (i.e. a CIBSE code or NHS Model Engineering Specification) .

I am trying to help him, as I do not want him to have to undertake the installation again, but I cannot accept what he is saying without written assurances.

The two replies to my post are typical of the responses I am getting from the contractor whereby it is becoming a debate over values in tables and no-one being able to provide definitive answers, only subjective (and sometimes opinionated) responses.

I was hoping someone had come across similar issues and could comment on a resolution.

I would like to conclude the matter and tell him to replace the connections for more suitable materials, but I still cannot confirm if his installation is correct or not and so cannot apportion cost.
 18 June 2010 02:04 PM
User is offline View Users Profile Print this message



westonpa

Posts: 1771
Joined: 10 October 2007

There is a problem but how quickly the iron, for example, corrodes will depend on flow and the liquid which forms the electrolyte, etc.

Suggest you post your question in the forums at http://www.ukplumbersforums.co.uk/

Regards.
 19 June 2010 12:11 PM
User is offline View Users Profile Print this message



seeker

Posts: 319
Joined: 10 March 2007

Originally posted by: NGraham

Help -



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

brass valve

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!
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.