Hydraulic cylinder weld

By ArkWeld Date 12-13-2003 18:46

I recently did a repair on a hydraulic cylinder attached to a log splitter. The original weld appeared to be cold lapped and was leaking at the weld toes. I repaired it by running a slight weaving bead over the top of the original weld tying in the toes of the factory weld. This corrected the leak. About one month later the same cylinder began leaking at a location about 1 inch from the previous repair. As I ground down the end of my repair weld for a tie in for the new repair I noticed a center line crack in the weld that was under the surface. It had the appearance of a hydrogen crack. My assumption is that this was caused by an un-equal cooling rate between the out side and inside of the cylinder because it was filled with fluid when I made the original repair. I would appreciate any thoughts on this issue. Repair weld: SMAW 1/8 7018, 115 amps, oven stabilized approx. 280-300 degrees, no cylinder pre-heat. My business is known for high quality welds and I'm concerned I maybe missing something here. Thank You

By billvanderhoof (****)

Date 12-14-2003 06:41

The hydraulic oil has lots of hydrogen (of the same order as water) so hydrogen cracking is a reasonable finding.
Bill

By DEA Date 12-14-2003 14:03

I don't know about the welding part.(new to that)
But the seals and o'rings in a log spliter cylinder are only rated for 220 deg.Viton type are rated at 400deg.
I work in a hydraulic shop.
DEA

By bmaas1

Date 12-15-2003 03:58

Possibly the original crack was longer than was able to be seen. Possible hasn't surfaced yet.

Brian Maas

By CHGuilford (****)

Date 12-15-2003 15:35

As was mentioned, oil is a really good source of hydrogen in your welds. Not a good thing.
Also, you mentioned a weave in your repair weld bead. That could induce a good deal of shrinkage stress into the repair and adjacent heat affected zones. Plus the edges of the weave would tend to cool rapidly, possibly causing hardened spots that could crack again.

As I have mentioned in some previous posts. I would be very careful with repairs on hydraulic cylinders. You could cause the cylinder to become out-of-round and leak by the piston. You could also weaken the cylinder so that it could burst; probably not catastrophically but enough to cause risk of fluid injection. Being a log splitter, a burst cylinder wouldn't drop a load like a one used in a hoist would.

I tend to think a split cylinder should be replaced, but if I absolutely had to repair one by welding, I would try a 309L stainless filler metal. I'd grind in slightly, make sure the oil is drained, and flush the crack area with acetone or similar. I would use stringer beads and preheat would depend on wall thickness. As was also mentioned, the seals won't stand a lot of heat. I would treat the repair as very temporary.

For that matter, I wonder if a piece of neoprene would work as a patch. Cover the problem area, shape or cut a piece of metal to cover the neoprene snuggly, and use a number of large hose clamps to hold everything on. If that works, I would still treat it as temporary repair.

Chet Guilford

By Lawrence (*****)

Date 12-15-2003 16:43

I'm with Chet on this,

To do a consumate repair it is standard to route out 100% of a flaw and verify its removal. Doing that with a pressure cylinder presents all kinds of distortion/integrety problems.

I bet the time you have put into this project already is equal to or greater than the cost of a new part. The new part is verifiable while this repair is always going to be a question mark.

By billvanderhoof (****)

Date 12-16-2003 08:13

I'm guessing that this cylinder is the type where the head is welded to the barrel and that that is the failed weld. Since the weld is designed to be there a repair may be possible (if difficult).
Bill

By billvanderhoof (****)

Date 12-17-2003 06:55

For me a really good repair here would involve removing the whole weld, disassembling the cylinder washing the area to be welded with solvent, reassembling and rewelding. A new 4" bore 24" stroke cylinder from northern hydraulic is around $200 so you get to figure the economics. If this is a reasonably low hours machine an attempt should have been made to warranty the cylinder, but sometimes the customer just doesn't want to bother.
Bill

By ssbn727 (*****)

Date 12-16-2003 09:02

Hi ARKWELDER!
Replace it with a new one then try the repair the original one as suggested by Chet and Bill... Hey, It never hurts to have a spare on hand!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By HappyWelder (*)

Date 12-18-2003 16:57

What about metal fatigue?

If the weld was cold-lapped and exposed to cyclic loading cracks coused by fatigue would be a problem. It would also do You no good to remelt a portion of the crack because the crack would grow again. If the cold-lap extends all around the circumference (please excuse my violations of the english language) repairment of discovered cracks would amount to little because new cracks would start to grow everywhere.