Welding Thrust Flanges onto Ductile Iron

By peterR Date 09-17-2004 18:48

Hi,

we have designed a valve chamber for use as thrust restraint for use with HDPE pipe. HDPE exerts huge forces on the thrust flange. The original design was in Steel (to be fabricated).

The contractor wants to do this in Ductile Iron, with a thrust flange being welded onto ductile Iron Pipe.

I asked him to supply me with information regarding the weakening which will (or will not) happen as result of welding ductile.

As far as I am aware, local weakening may happen as result of some of the carbon in the ductile going into solution, and then not solidifying back into spheres, but rather as flakes, thereby giving rise to the possibilty of a tensile or shear failure.

On a typical 24 inch pipe, what part of the cross section would be affected by a weld attaching a thrust flange to it? For this it seems one would have to assume that the weld would be equal to the wall thickness of the pipe, since the flange is thicker.

Any ideas - or should I just stay away from allowing these welds to happen.

By Cain

Date 09-23-2004 12:30

Here is my brief experience with welding DI castings......

I have welded on DI castings before, but was told the weld would not be considered a structural/load-bearing weld. You mentioned this in earlier, regarding the carbon. We welded on castings to rework cosmetic issues, to fill voids and/or other flaws.

The filler was expensive, high nickel, as well as the weld procedure. We had to spend a lot of time cleaning! Preheating and PWHT was also exhausting, we had to preheat the entire component to 650 F and sustain this temperature for1 hr per inch of thickness. We then welded, and immediately began the post weld heat treat process at 650 F while decreasing the temperature at a rate of 50 F per hr until ambient temperatures were reached. We obviously had to use an oven.

In my humble opinion, I would stay away from this material, regarding welding, and use an alternate material with better weldability. There is a lot of money and effort spent on making a non-structural weld.

Good Luck!

By peterR Date 09-23-2004 12:39

Thanks Cain for your view on things.

The work will not be done in ductile.

Peter