Silver solder problems

Is it me, but I am having more than my fair share of porous joints with cad free silverflo 55. (630 - 660 deg C) Never had a porus joint with the old Easy flo #2.

These are copper joints using the new correct flux (Cup alloy type EF) and a mix of propane torch or oxy acetylene.

Pickling using 20% sulphuric acid.

Any ideas out there ?

I'm finding the new stuff is very sensitive to overheating and also if there is ANY movement/jiggling of the parts as heat is taken away and solder is hardening there will be microcracks and seep leakage. Wish I'd laid in 10 lb of EasyFlo #2 - it definitely was easier to use and was more forgiving than cad free solder.

JD

I thought it was just me. Have used easyflo #2 for 45 years and this new stuff IS different.

i have used silverflo 55 quite a bit on boiler work and dont have any problems, in fact i prefer it on boiler work to easyflo. sounds to me like you are overheating the silver solder in the oxy acetylene flame. you must let the copper heat and melt the silver solder.

cheers,

julian

When the cadmium is removed from the alloy there are two effects

1) the melting temperature increases (combatted by adding more silver and tin)

2) the molten alloy is less fluid

and in the case of easyflo2 an increase in the melting range from 10 to 30 deg C

So yes - it is different

Overcome these difficulties by

a) open your joint gaps to approx 0.15mm

b) consider putting a larger burner on your propane torch.

I suspect that oxy-acetylene has been used to create the extra heat. In using it the alloy is being overheated which is very easy to do. Overheating is the only way to produce porous joints.

Avoid overheating by watching the flux. When it becomes a colourless liquid you are approaching the melting point of the solder.

Do not heat the rod heat the joint. Let the rod get its heat from the joint not the flame. You might well find that a thinner rod helps you.

Remember what you are trying to do ...... ie braze. Remember the principles and don't deviate from them. You will be successful. If necessary seek help from your alloy supplier.

Professional boiler makers now tell us that they prefer the cadmium free alloy. Because it is less free-flowing it is easier to control and they use less!

The days of boilers being assayed are numbered!

Hi,

For what it's worth, I wouldnt use oxy acetylene for this purpose, the high temperature heat source is too concentrated, as CuP Alloys (sorry , but no signature) hints at, making it all too easy to overheat the solder. As he says, use a larger burner and build a wall of refractory to reflect heat back into the work, white refractory reflects more heat back.

I wouldn't use normal firebricks (and especially not cement blocks except as a backing) as their job is to absorb and store heat in furnaces and fires providing a heat mass to stabilise temperatures whereas proper refractory will absorb less heat and reflect it back into the job. I used to demonstrate this by holding a refractory brick while heating the other end red hot with a large brazing torch. Reverberatory furnaces used the principle of heat reflection into the metal for smelting iron, producing purer metal as there was no direct contact with the heat source. Materials which absorb heat would have been of little value.

Regards

Terry

Thanks for the info. Terry - you are spot on, but its near impossible to use refactory brick inside the firebox when trying to cure a leaking tube joint. When I use the propane torch in that confined area there are two problems.

1) The hot air exiting the box tends to extinguish the torch.

2) Its not just the leaking joint which gets melted, all the rest get a good burst of heat which can then cause expansion fractures on adjacent joints.

Ok, so I hear what has been said and will keep in mind for the future, BUT if you have a porous joint, what it the correct proceedure to rectify it ?

Hi again!

Problem heating inside enclosed spaces - use a Sievert propane cyclone burner. These draw in air further back down the neck tube, mixes it with the gas and produces a stable flame.

Prevent subsequent fractures by building up heat generally all around the leak. This reduces the expansion stresses.

Use plenty of flux and the lowest melting point alloy - the 55% cadmium free. It will melt at a lower temperature than the first run.

Allow to cool naturally.

keith

Hi SB5

CuP Alloys got there first. As far as the refractories go, you should still pack around the outside of the shell to concentrate the heat and insulate. It also slows down the cooling cycle helping to prevent stress cracking.

Just another small point, Citric acid makes a good pickle and you can buy it from the local supermarket (baking section), local pharmacy or winemaking suppliers. It is much less dangerous than H2SO4 but still try to keep fumes out of the workshop away from rust prone surfaces.

Best regards,

Terry

Food grade descaler makes excellent pickle as well.

Neil

You must bring the whole barrel up to temperature including the tubes otherwise you are going to strees all the other tubes if you just concentrate on the repair only.

speedy,

i dont really understand what could have gone wrong here, in the sense that a porous joint should have been noticed by your club boiler inspector as you submitted the part built boiler at each stage for inspection. a porous joint is pretty obvious and easily seen on inspection after pickling after the relevant braze up. a porous tube joint would be easy to spot. there is quite a well established proceedure for how to braze up an inner firebox and the tubes, depending on the method of fixing boiler stays, and each of the 2 methods avoids direct heat where the silver solder is applied, virtually eliminating the risk of incorrect penetration and overheating of the silver solder.

i agree with keith 100%. ive been using non-cadmium silver solder used by RN as a replacement for easyflo for years. i only use easyflo No.2 for very fine boiler fittings and the like these days.

cheers,

julian

Well there you go Julian. Where we live (France), we don't have boiler inspectors . Once a boiler has been completed to a recognised design, the whole boiler is presented for inspection and test, ratified by two independant club officials.

So back to my question - what do you do with a porous joint - pour more solder onto it, drill out and refabricate, try to scrub it off whilst molten or what ?

I would try to get it to flow again, then add some higher teperature soplder that won't overheat on top.

Neil

hi speedy,

i am very sorry to be pessimistic but if i was presented with a completed boiler with porosity in any joints i would refuse to pass the boiler at all on the basis that any hidden joint could have the same defect eg crown stays. i would have little confidence in full penetration of any joints without seeing both sides of the joint. on a speedy boiler i would especially want to see full penetration of the throatplate to barrel and also that the tapered barrel joint (potentially the most dangerous) was sound too.

i cut up a suspect boiler last year i had been given...good job i did because although the inner firebox looked ok the silver solder hadnt penetrated properly and the (hidden) water space side of the tubeplate joint was defective. it had passed a hydraulic test but wouldnt have lasted long in service and was lethal.

a porous joint has no strength.

suggest you put it down to experience (albeit costly) and have another go. there are many of us on this forum who will be glad to help to ensure your next boiler is sound and a success.

cheers,

julian

All,

I would tend to agree with Julian, he has made an excellent point.

At the club I belong to, if a member is building their own boiler, the clubs boiler inspector likes to see the boiler at various stages during its construction, so he can see the hidden internal joints. (and spot a potenhtial problem before the build is complete.)

Dave

Well, that has just about put the lid on that. Lets all pack up now. How I do love negativity.

On this forum it often goes that way. Now that all the naysayer inspectors / clubmen are safely back in their armchairs, there will probably be a few more constructive posts to help in more practical ways. Wait a bit and see. Keith from CuP alloys had some suggestions worth investigating.

JD

It can't be that bad that at worst you could drill out any rivets/screws used to jig it together and melt the whole bloody thing back to its component parts.

Where have you got the porous joints?

Joey

Jeff,Joseph and Michael - that's the positive support I was looking for - Thanks.

I believe that most of the bad joints (Riveted stays) have been cured and the last one is a bush / longditudinal stay on the 3/16" thick backhead. I don't see this as a problem as they are easy to get to, but previously there was one little 'tinker' of a leak on a tube at the fire box end which was only cured by bringing the whole firebox up to a reasonable temperature. Interesting that you say use the tenacity flux on these 'repairs'. Wil bear that in mind.

Thanks once again

Bob