Welding ductile iron

[CandCQC]

I have a large ductile iron valve(48" waterway) that is in need of weld repair in the main external support rib of the valve. I am planning to use a 7018 rod and preheat to 550-750 F.and am hoping to achieve a PWHT of 850-1000 F for a period of 2-4 hrs. I have some concerns due to my limitations on PHT and PWHT. I will have to use a torch to heat the part. I can wrap the part with some weld blankets but I am afraid of a crack in the HAZ due to rapid cooling. I thought of using some type of ready heater to direct heat at the weld to try to keep the valve as hot as possible for as long as possible. Any ideas or direction to some reference material?

 

[pennpiper]

CandCQC,
Your stated situation and your question seems to have all the makings of a disaster in the making. It in complicated by the natural limitations implied by the background identifications, your being "Structural".

A "Structural" person asking a "Welding/Heat Treating" question about a very large "Piping" component. My "Identity" up there says "Mechanical" in fact it is "Piping".

You also did not say where in the world you are located, this may have a bearing on the issue.

If you are in the "USA" any repair on valves is governed by "Codes" and "Standards" and is subject to inspection and re-certification. Valve repairs (even of the type you describe) are normally handled by trained, experienced and properly certified people in companies that do this all the time.

I strongly recommend that you check with the proper authorities in your local area to confirm and conform with their requirements.

Also get some advice from professionals in the Valve Repair and Re-Conditioning field.

See:

http://www.comid.co.uk/html/services.html

See:

http://www.furmanite.com/Services/ServiceDisplayPage/tabid/54/obj/153/lang/1/Default.aspx

 

[dbooker630]

I'm not in the piping business but for automotive ductile iron applications requiring (and permitting!) weld repair, I use a high nickel (45-50%) as opposed to 7018. Huntington Ni-Rod FC55, Hobart 44G, or Crown 8-60 are good examples.

 

[pennpiper]

You said your valve is ductile iron but some of the same safety, inspection and testing issues will no doubt apply as for other materials so I add this reference:

RP 621 SCOPE

This Recommended Practice (RP) provides guidelines for the reconditioning heavy wall (API 600 type) carbon steel, ferritic alloy (up to 9% Cr), stainless steel, and nickel alloy gate, globe, and check valves for ASME pressure classes 150, 300, 400, 600, 900, 1500, and 2500. Guidelines contained in this RP apply to flanged and butt weld cast or forged valves.

RP 621 is available from Global Engineering Documents,

http://global.ihs.com,

for $95.00.

 

[gtaw]

Ductile iron pipe is essentially a cast iron that has been inoculated and heat treated to allow the excess carbon to precipitate and form nodules rather than platelets typically found in cast iron..

Welding allows the carbon to go back into solution and revert to a cast iron upon cooling. While the preheat is advisable, it is doubtful in my opinion that your post weld heat treatment will be adequate to allow the excess carbon to form nodules rather than platelets upon cooling to ambient temperature.

The use of high nickel filler metal will prevent the weld from cracking upon cooling, but the use of nickel filler metal is not going to benefit the heat affected zone. Underbead cracks would not be unexpected and can be predicted with a high degree of certainty.

I would consult with the valve manufacturer. They may be able to provide some insight on the proper way to facilitate a welded repair.

I have had excellent results repairing large castings with oxy-acetylene welding using cast iron rods, but that is a little different than welding ductile iron. Even with torch welding the final weld is cast iron, not ductile iron.


Best regards - Al

 

[CandCQC]

Thanks for the advice everyone!! Yes this is outside of our realm of normal work. We are located in Iowa and the I have advised our owners to relay our weld procedure to the customer for engineering evaluation. I know this part does not fit our shop but I dont get the liberty of making those decisions. I only have the option of expressing all concerns to upper management and between them and customer's engineering they will decide if we are to try this. Thanks again!!

 

[unclesyd]

Below is a recommendation from a DI producer on the welding of same using AL Bronze Electrode. I have use this method many times with excellant results.
One thing to remember is that when welding DI or CI you paint the metal on instead of "burning it in"


["AWS A5.15 Class ENiFeT3-CI, or AWS A5.6 (ASME SFA 5.6) Class Cu A1-A2. These electrodes shall be capable of producing suitable welds without preheating or postheating of the pipe and ring. A recommended semi-automatic welding wire, with appropriate weld specifications, is as follows:"}

AMPCO-TRODE® 10
A versatile aluminum bronze alloy available in covered electrode, spooled wire and 36” bare filler rod for joining like and dissimilar metals and for overlay of bearing, wear-and corrosion-resistant surfaces. Conforms to Class CuAl-A2 of Specifications ASME-SFA-5.6; ASME-SFA-5.7*; AWS-A5.6; AWS-A5.7*, AWS-A5.13*;

 

[racookpe1978]

OK.

To continue this topic (of weld repairs on cast and ductile orin) but on a non-pressurized, non-structural component.

Our church has some cast iron outside furntiure (older/antique matching garden tables and chairs) that they've asked me to weld repair rather than discard.

Can that level of repair (thinner components will be easier to pre-heat, less stress since its not a valve-body rib, non-pressure, non-fluid-bearing environment) be done with the high-nickel SMAW Hobart rods?

 

[gtaw]

I've always had better results using an oxy-acetylene torch and cast iron rod.



Best regards - Al