HIP technology gives you several advantages such as superior material properties combined with flexibility regards to shape. This gives potential to save time and money on operations such as machining and welding. Elimination of welds in critical areas contributes to increased process safety. Typical material grades are: Duplex, Super Duplex, 6Mo and Inconel 625.
The PM/HIP Process
The production process from the melt to the finished product takes place in three stages. Powder is produced by inert gas atomization. The Powder is canned in sheet metal capsules, giving the product the desired shape. The capsules are consolidated into full density under high pressure and temperature by Hot Isostatic Pressing.
1 Melting and atomization
The melt which is produced in an induction furnace is tapped into an induction heated ladle where further alloying elements can be added in a protective atmosphere. When the melt is tapped from the bottom of the ladle it is discharged directly into the atomization chamber. The molten steel is broken up by jets of inert gas and the atomized melt solidifies into small spherical particles of high purity and low oxygen content and with a diameter less than 500 micron. The powder is stored in hermetically sealed vessels.
The powder is canned in capsules of mild steel which are produced by sheet metal forming and welding. The capsule is designed to give the fully dense of end product the desired shape. Compound products can be produced by designing capsules with separate compartments for different powders or enclosing parts of solid material together with the powder.
3 Hot Isostatic Pressing (HIP)
The capsules are placed in a HIP press where they are subjected to high pressure and temperature. The HIP parameters pressure, temperature and time are predetermined in order to give the material full density and the required properties.
Depending on the type of material and the application, the products may be heat-treated, machined and subjected to various types of quality control such as ultra-sonic inspection, dye penetrant testing, testing of mechanical properties, etc. The mild steel sheet used in the can remains on the product after HIPing. It is removed by machining or by acid pickling.
Product size and weight range
Maximum dimensions after HIPing are diameter 1 500 mm and height 2 850 mm. Maximum weight is approximately 20 metric tonnes.
Avoid HISC with HIP
SINTEF states that HIPed items are more resistant to Hydrogen Induced Stress Cracking (HISC).
DNV-RP-F112: DNV recommends HIP as manufacturing method for Duplex Stainless steel subsea equipment exposed to cathodic protection.