I've taken apart some of my own test welds, and while most of them look
great (solder the length of the joint) every once in a while I do one that
I know is bad before it even cools, because the hot solder just keeps
rolling off the pipe instead of being sucked into the weld. When I take it
apart to confirm, I see that there is no solder in the weld, just a small
amount of black residue which I'm guessing is burnt flux.

Is that caused by something specific? Pipe too hot or too cold before
welding? Is it something that can be fixed if the weld is in place, or will
I have to always separate the joint and re-clean it, re-flux, and re-weld?
I'm thinking if the pipe is too hot, I should be able to let it cool and
then just try to scrape in some flux (it would get sucked in as the pipes
re-heat and it melts) and re-solder.

I'm thinking especially if this happens on a joint where I _can't_ tell it
is bad until it is too late (hard to reach valve installations, etc) that
it would be nice to be able to just fix it in place- I'm working on a
really old house and trying to put valves in-line in a couple of places I
can barely reach, and I'm not sure I'll be able to see well enough to be
certain that it is ok, and getting a valve back out to clean it will mean
taking apart 2 joints, doubling my chances of any errors when putting it
back (versus just fixing one weld).

Any advice welcome (other than "hire a pro", I wish I could afford ti but I
can't). Thanks!
Keith

Hire A Pro Mate!

On Mon, 08 Aug 2005 06:41:01 GMT, Keith wrote:

I've taken apart some of my own test welds

"Keith" wrote in message
. 63.158...

I've taken apart some of my own test welds,

Just for the technical correctness, they are solder or sweat joints, not
welds. Welding is a different process.



and while most of them look
great (solder the length of the joint) every once in a while I do one that
I know is bad before it even cools, because the hot solder just keeps
rolling off the pipe instead of being sucked into the weld. When I take it
apart to confirm, I see that there is no solder in the weld, just a small
amount of black residue which I'm guessing is burnt flux.

Sounds like a dirty joint. Are you cleaning the joints first with steel
wood, emory, wire brush, etc.,? Then using hte proper flux?


Is that caused by something specific?

As mentioned, not clean enough, or, yo are overheating, burning up the flux
and then adding some carbon to the mix.



Is it something that can be fixed if the weld is in place, or will
I have to always separate the joint and re-clean it, re-flux, and re-weld?

Take it apart and start over. It will never get better unless you clean it.


I'm thinking if the pipe is too hot, I should be able to let it cool and
then just try to scrape in some flux (it would get sucked in as the pipes
re-heat and it melts) and re-solder.

No, there will be contaminants the the flux will not get rid of.


I'm thinking especially if this happens on a joint where I _can't_ tell it
is bad until it is too late (hard to reach valve installations, etc) that
it would be nice to be able to just fix it in place- I

I'm thinking it would be nice too, but it just does not work that way.

I'm working on a
really old house and trying to put valves in-line in a couple of places I
can barely reach, and I'm not sure I'll be able to see well enough to be
certain that it is ok, and getting a valve back out to clean it will mean
taking apart 2 joints, doubling my chances of any errors when putting it
back (versus just fixing one weld).

Make another cut and put in a coupling to put it back together. That way,
only one joint is taken apart, but still two to put it back. One being
easier though.



Any advice welcome (other than "hire a pro", I wish I could afford ti but
I
can't). Thanks!

Practice. Do the easy joints first and get the timing right. By the time
you get to the difficult joints, you will have more experience. Double
check your technique of where to heat the joint, how hot to heat it, how
much solder to use. Rule of thumb is the length of solder is about equal to
the diameter of the joint.

if you get both side clean and flux your joints will flow right. are
you sanding the pipe and brushing the inside of the fitting to get it
bright copper,if not it wont flow,bad flow is also caused by not getting
both sides hot enough

Plenty of good advice on the joints. When there is any doubt about leaks, I
generally pressurize the pipe with air, spray on soapy water and check for
bubbles. Once you get water back in it makes it pretty hard to unsolder
sometimes. Blowing the water out of the pipes with air also helps when
soldering or unsoldering.
Don Young
"Keith" wrote in message
. 63.158...

I've taken apart some of my own test welds, and while most of them look
great (solder the length of the joint) every once in a while I do one that
I know is bad before it even cools, because the hot solder just keeps
rolling off the pipe instead of being sucked into the weld. When I take it
apart to confirm, I see that there is no solder in the weld, just a small
amount of black residue which I'm guessing is burnt flux.

Is that caused by something specific? Pipe too hot or too cold before
welding? Is it something that can be fixed if the weld is in place, or
will
I have to always separate the joint and re-clean it, re-flux, and re-weld?
I'm thinking if the pipe is too hot, I should be able to let it cool and
then just try to scrape in some flux (it would get sucked in as the pipes
re-heat and it melts) and re-solder.

I'm thinking especially if this happens on a joint where I _can't_ tell it
is bad until it is too late (hard to reach valve installations, etc) that
it would be nice to be able to just fix it in place- I'm working on a
really old house and trying to put valves in-line in a couple of places I
can barely reach, and I'm not sure I'll be able to see well enough to be
certain that it is ok, and getting a valve back out to clean it will mean
taking apart 2 joints, doubling my chances of any errors when putting it
back (versus just fixing one weld).

Any advice welcome (other than "hire a pro", I wish I could afford ti but
I
can't). Thanks!
Keith