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Welding to N80 Casing
3

Welding to N80 Casing

Welding to N80 Casing

(OP)
Looking to use N80 casing pipe ~8"x1/2" thick in a structural application. From published specs, Fy ranges from min 80 to 110ksi, Fu is minimum 100ksi.

Casing would be used as soldier piling for earth retention and will be installed by drilling using flush-threaded connections. This application is very restricted in terms of headroom and access otherwise I would do something different.

I'd need to weld studs and plates to connect wood lagging and ground anchors.

Normally, these connections are not that demanding when attaching to A572-50 rolled sections - typically 3/16 fillet SMAW (all-around on the 5/8" UNC allthread studs). Studs are typically spaced 9" vertically apart. In this application, I'd likely need to have pairs installed on one side of the pipe at a few inches spacing horizontally. Plates would get a 3/16 fillet weld on each side for about 9in/side.

I have some telling me that this welding could embrittle or even crack the casing, and others saying they've never had brittle issues with this kind of casing.

I will be cross-posting in the petroleum fora. All answers appreciated.

JTD

RE: Welding to N80 Casing

Are you welding N80 to itself or only to the A572-50? If the latter you could use an E7018 type filler metal. While I developed WPS's for these material nearly 20 years age, I don't precisely remember the details. I believe the preheat was 250 F min. No PWHT.

RE: Welding to N80 Casing

The per-heat will be important because of the range of alloys that can be used for N80.
Some of it can be rather high hardenability so watch out.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Welding to N80 Casing

(OP)
Clarification: I want to weld ~36 ksi 5/8" dia. all-thread studs (all around 3/16 fillet) and ~1/2" to 3/4" thick grade 50 plates (2 parallel 3/16 fillet welds, each about 9 inches long) to these casings.

@weldstan, @EdStainless: I will speak to my people about preheat.

I have seen suggestions elsewhere to use cellulosic E80 electrodes for the initial pass. Can you comment on this?

Please let me know if you think that there are other things we should consider to use SMAW process.

RE: Welding to N80 Casing

I would not use the E8010 type because it will increase the propensity for hydrogen cracking and therefor require higher PWHT temp.

RE: Welding to N80 Casing

When welding alloy steels, it is a capital error to select a filler metal based solely on matching the alloy content of the filler metal with that of the base metal. The blending of high carbon from the base metal with alloy elements in the filler metal is a recipe for excessive weld hardness/strength.

In this situation all that is required is for the weld strength to match that of the lower strength base metal. 70 ksi class fillers are often more than adequate.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Welding to N80 Casing

(OP)
Following up, I have looked at the provisions in AWS D1.1 and other references, specifically an FAA document here, discussing estimation of preheat temperature. I have no need for interpass temp as all my work will be single-pass fillet welds.

Based on carbon equivalent, I estimate that a preheat of 300F is warranted. Thanks to all who replied.

RE: Welding to N80 Casing

I strongly advise a minimum 2 passes. I have seen far too many failures with single pass fillets.

RE: Welding to N80 Casing

I would second weldstan's comment, in a manner of speaking.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Welding to N80 Casing

(OP)
3/16 fillet - which can easily be done in a single pass - is more than sufficient for the intended use as verified by using these details for literally years now. Unless there is something intrinsically made more problematic by the high-strength base metal that cannot be overcome with the preheat?

RE: Welding to N80 Casing

Dilution with the N80 will produce a harder weld deposit more susceptible to hydrogen cracking. The second pass provides some tempering of the root pass.

RE: Welding to N80 Casing

(OP)
I will take your caution under advisement and have our CWI scrutinize the work closely.

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