Old Cast Iron Materials Testing 1

[ivanlocke]

I've got a water distribution manifold chamber - 2 48" pipes coming in, each with 3 48"x36" crosses and a 48"x36" tee at the end. It was probably built about 1915 - all cast iron. We are looking at replacing some of the valving and adding a couple of 90s to tie the two 48s together. While we are doing this though we wanted to look at the existing material to see how it is holding up. What kinds of things would I be looking at? Embrittlement? Would there be fatigue in this kind of application? I have not seen the pipes/fittings, so I don't know the level of corrosion, but if corrosion does not seem to be a problem is it worth looking at other things?

Thanks for any help.

 

[NickE]

Hmmm... Guessing grey cast iron.... What kind of pressure is the water at, is there any hammering (water hammer) going on, What temp range does this system see (environmental/process), you could maybe do some UV dye or Ultrasound to see if theres any macro-faults.

does it leak?

nick

 

[Metalguy]

Don't think embrittlement would be likely, but you could look for fatigue cracks. After all those years, they and corrosion would be the things I'd look at.

 

[ivanlocke]

Thanks for the replies.

The water is at about 110psi. Water temperature would range from just above freezing to 60 degrees and environment would be that found in vault, 0 to 100 degrees - maybe a bit less range since its in ground. Should not be too much water hammer as there are surge relief valves in the line, although there may have been significant hammer in the past.

What would embrittlement be due to?
In replaving the valves we would be removing some of the existing material which could be used for sending to a lab. This would all be from straight areas of pipe. For the fatigue I would assume I want to look at the crosses themselves where there would be higher stress.

 

[Simon55]

Considering the age and the likelihood of them being grey cast iron, there is also a possibility for graphitic corrosion. This is very hard to detect via NDT, but may show up on the valves if they are of the same material.

 

[aybee]

plain cast irons are by nature Brittle in respect that they have little or no ductility to begin with and I dont think that they are prone to developed embrittlement but am willing to be told otherwise then learn something.It may be amalleable grade in which case its less prone to sudden failure Cast irons are also by nature fairly corrosion resistant. You dont say how thick the stuff is which has a bearing on tendency to fracture. If it has lasted since 1915 and by the sound of it did not always have surge relief and operated down to freezing it must be fairly robust. You dont say how you intend to add the new stuff to the old if its welding then thats a new ball game you will need tensile tests to get a match for the consumable and it will be imperative to do weld procedures on old -new material with slow slow cooling after welding. If you take a sample and impact test it it will give you some confidence

 

[stanweld]

As long as you are making repairs to this system, you may wish to replace the old cast iron as well. Nothing lasts forever! Damage may occur to the old pipe during your planned modifications

If you wish to keep it, visually examine for corrosion and MT or PT inspect for cracking.