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HIP FORMING OF SUPER DUPLEX ? 1

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C2it

Petroleum
Jun 27, 2007
504
Out of my comfort zone here ...

We have to engineer an offshore platform wellbay to accommodate around 1000 barG through to production and test manifolds. The production manifold will need to be approximately 500mm OD and around 100mm thickness. Around 10 branches of about 300mm OD and 70mm thickness will enter the manifold at around 1500mm spacing.The proposed material is super duplex stainless.

That's the easy bit. My question is ... how might we manufacture the manifold and branches ?

Hot isostatic pressing looks attractive because we could tailor the design to accommodate required pressure reinforcment, but ... it possible to use HIP with super duplex ?

If HIP is possible, are there significant welding problems with joining super duplex at this sort of thickness ?

Comments appreciated !
 
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Super duplex can be Hipped. The max thickness allowed by NORSOK standards is 8 inches. Any thicker than this and the cooling rate will not be quick enough to prevent embrittlement from intermetallic phases.

I would suggest you contact Bodycote, as they have done this kind of thing quite often. Get them involved with the design phase as it will be much cheaper to have their input from the get-go.

Not sure if this is going subsea and connected to cathodic protection (can't tell from the description), but Hipped super duplex also allows for higher stresses without the risk of HISC.
 
Review EEMUA 218 for manufacturing quality requirements. There can be significant problems with welding super duplex at any thickness, just like any other material really. The problems will be dependent upon the subsequent tests that have to passed.

Steve Jones
Materials & Corrosion Engineer


All answers are personal opinions only and are in no way connected with any employer.
 
Without seeing flow diagrams, I hesitate to offer solutions, but you might consider using block forgings with studded outlets, and then one of the types of compact flanged joints as the attachments/branches/outlets. I say this because this is the method the company I work for have used for 10K to 15K psi Inconel 625 applications. Another benefit of the building block approach is that it is easily modified, and components can be readily removed for maintenance. Company website is
 
Do you really mean you wish to join your manifold parts using diffusion bonding? Diffusion bonding is commonly done in a HIP chamber, but diffusion bonding does require more preparation than a simple HIP operation does. For example, diffusion bonding usually requires some method of fixturing the components such that the entire faying surfaces are forced into intimate contact by the chamber pressure. If the materials are weldable, a common approach is to seal the joint perimeter by welding. These weld areas, with their inferior material properties, can later be removed by machining. If the materials are not weldable, there are still other ways to fixture them.

Diffusion bonding is a "solid state" joining process, which means the resulting joint interface is of very high quality since the materials never undergo a phase change like that occurring with fusion welding processes. Since the materials being joined are never exposed to temperatures above their melting point, virtually any type of metal can be diffusion bonded, including super duplex stainless.

Hope that helps.
Terry
 
I believe the use of P/M-HIP fabrication method for this manifold has merit because of the benefits of near net shape and homogenous material in comparison to a casting, and machining costs associated with a forging blocks. The use of P/M-HIP will come down to cost benefit analysis. However, as mentioned above, the joining of these components will still be the challenge using conventional welding processes.
 
metengr-

Thanks for posting that paper. I work in aerospace and when the term HIP is used it is generally associated with densification of structural castings. Powdered metal components are not common in aerospace, so I failed to consider that this process is indeed an application of HIP.

A couple years back, I looked at using HIP for densification of a large structural titanium investment casting. One of the issues that came up was finding a domestic vendor that had a HIP chamber of sufficient diameter to accommodate the part. The only US sources I could find with large HIP chambers were Howmet and PCC. Thus if the part is large or bulky, the number of parts the chamber can process in each cycle may be quite limited. It can cost upwards of $10K to run a single batch of parts through a large HIP chamber. I also found that access to these large HIP chambers was sometimes limited. So processing cost and access to a HIP facility are a couple more things that C2it may wish to consider in his trade study.
 
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