Mooring System Welding/Material Question

[chaoscreature]

This is my first post on Eng-Tips so please take it easy on me!

I have an application where we need to weld a strong flange onto the end of a mild steel pipe (ASTM A106 Grade C). The flange is 24" OD x 1.53 Wall thickness and 6 inches deep. The Pipe is also 24" OD x 1.530 wall, but is much longer. The flange material had the following requirements:
80,000psi min yield
100,000psi min tensile
Charpy Impact of 25 ft-lbs minimum @ -15 deg C.

http://www.eng-tips.com/threadminder.cfm?pid=725&page=2

Weldable without extensive PWHT. We can preheat and maintain interpass temps, we just can't bring the whole weldment up to a very high temperature after welding. We can also blanket cool.

The weld joint is a single 30 degree bevel on the pipe side and a 25 degree J-Groove on the flange side, both with a 1/4" land. I can't change the joint geometry at this point. we will be FCAW-G the inside of the pipe, SAW weld the outside and then backgouge and re-fill the inside to achieve CJP. The weldment will be X-Rayed, pull tested to 1 million pounds and then wet particle tested for cracks. Part of our welding procedure requires that we perform Charpy impact testing as well in the center of the weld pool, right at the weld toe, and 5mm outside the weld toe. I am proposing that we weld with Lincolnweld 880 flux and LAC-Ni2 wire. I have no idea what pre-heat or interpass we should try to maintain... but I have been told we want to be below 500F to maintain toughness in the A106.

The material I have chosen for the flange is double normalized and tempered AISI 3310, because of it's high nickel and low carbon content (and it's available).We have not purchased the material yet.

I just wanted to throw this out here and see what you all think. Please let me know if you think this is a workable plan or if you have some other suggestions.
Sorry this was a bit of a ramble, but everything here is theoretical and not proven yet and I need some heads to bounce this off.
Thank you in advance!

 

[SJones]

By the wording of the title, will this assembly be submerged with cathodic protection?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[chaoscreature]

We are not going to be using cathodic protection. While in service the units are slathered with copper grease, the majority of the oxidation occurs while the units are on dry land.

 

[metengr]

Your proposed weld plan on first glance would appear acceptable. I would use a preheat of 200 deg F for the SA-106 material and limit the interpass temperature to 500 deg F.

 

[chaoscreature]

Follow up to this post,
Does anyone here have any real world welding experience on 3310/3311, 4320 or a similar alloy in the Quenched and Tempered condition? We want to increase our load capacity by increasing our mechanical properties. To meet our mechanical requirements we will most likely need to temper around 900 deg F.
For reference 3310 is a 0.10% Carbon, 0.5% Manganese, 1.5% Chromium, 3.5% Nickel steel.