mixed metals - InspectionNews

John Dirks Jr · #1 (**permalink**) 07-06-2008, 05:35 PM

I'm pretty sure I got this right but I just want to be sure. Would it be mixed metals causing the corrosion and leak in this picture?

Jim Zborowski · #2 (**permalink**) 07-06-2008, 05:42 PM

dissimilar metals would be the correct term

wayne soper · #3 (**permalink**) 07-06-2008, 06:24 PM

Yes, and possibly whacked that pipe with the hammer setting that fastener also.

Jon Randolph · #4 (**permalink**) 07-06-2008, 07:41 PM

I don't see evidence of a galvanic reaction, but there is a leak. Leak could be caused by wear due to pipe vibration against the clamp.

However, even if there are no signs of a curent reaction, it is possible. All galvanized needs to be removed and replaced with copper/brass/plastic - after the leak is repaired, of course.

Dave Hahn · #5 (**permalink**) 07-07-2008, 06:14 AM

Despite the sealants (paint) could be contact with the corrosive nature of the block/mortar. Not allowed to go "through" without protection, so don't know why it could lay against unprotected.

Brandon Chew · #6 (**permalink**) 07-07-2008, 10:38 AM

Copper is higher in the galvanic series than steel or zinc, so if there was galvanic corrosion due to dissimilar metals, the clamp should go before the pipe. I suspect the leak is due to another cause.

Jim Zborowski · #7 (**permalink**) 07-07-2008, 02:30 PM

Maybe some slight pipe movement. Both movement and isolation from dissimilar metals could be aleviated by use of clamps having rubber on them.

Patrick Martinez · #8 (**permalink**) 07-11-2008, 12:23 AM

John,

you got the nail on the head...Best correction method is to use, (at least), 10 mil tape, it isolates well and will help prevent the corrosion. Good Call,

Pat

Jerry Peck · #9 (**permalink**) 07-11-2008, 06:04 AM

Quote:

Originally Posted by Patrick Martinez

Best correction method is to use, (at least), 10 mil tape, it isolates well and will help prevent the corrosion.

"Best correction"???

The "best correction" is to use the proper clamps for the proper pipe.

Patrick Martinez · #10 (**permalink**) 07-11-2008, 05:08 PM

Yup, that too...Although you can use Galvy clamps on any piping system as long as the piping is protected....

Take Care all,

Pat

Jerry Peck · #11 (**permalink**) 07-11-2008, 05:52 PM

Pat,

My post was because you used the word "best", and when someone uses "best" instead of 'one way', that is usually their chosen wording because "best" means "best".

That said, and not to dwell on it any longer, the 2006 IRC states: (underlining is mine)

- SECTION P2605
- - SUPPORT
- - - P2605.1 General. Piping shall be supported in accordance with the following:
- - - - 1. Piping shall be supported to ensure alignment and prevent sagging, and allow movement associated with the expansion and contraction of the piping system.
- - - - 2. Piping in the ground shall be laid on a firm bed for its entire length, except where support is otherwise provided.
- - - - 3. Hangers and anchors shall be of sufficient strength to maintain their proportional share of the weight of pipe and contents and of sufficient width to prevent distortion to the pipe. Hangers and strapping shall be of approved material that will not promote galvanic action. Rigid support sway bracing shall be provided at changes in direction greater than 45 degrees (0.79 rad) for pipe sizes 4 inches (102 mm) and larger.
- - - - 4. Piping shall be supported at distances not to exceed those indicated in Table P2605.1.

I know 'logic' says you can use whatever you want, just slip some protection in there, however, we have all seen (I am sure) where that 'slipped in protection' was insufficient, moved out of place, etc., leaving *no protection*.

So, "logic" says the code says what it does for a reason, and that reason is what I just described above - to prevent galvanic action between dissimilar metals.

Thus, not only is "the best" answer, but "the real" answer, is to use compatible metals.