Hot Isostatic Pressing (HIP)
HIP combines very high temperature (up to 2,000°C) with isostatically applied gas under very high pressure (up to 30,000psi) – comparable to the Mariana Trench 11,000m deep in the Pacific Ocean. HIP is used to eliminate porosity in castings and consolidate powder metallurgy materials to give fully dense components. Further, dissimilar materials can be bonded together to manufacture unique, cost-effective parts.
HIP technology allows the engineer to optimise conventionally formed parts and also to design components unobtainable by other manufacturing routes, whilst simultaneously improving microstructural homogeneity and material properties.
Bodycote provides two major HIP routes for customers: HIP Product Fabrication, for the manufacture of components through powder metallurgy and diffusion bonding; and HIP Services, providing porosity removal through HIP densification.
Hot Isostatic Pressing (HIP) – PM Near-Net Shape
Imagine a component with no weaknesses, no cracks due to welding, optimised weight and material properties, and a superior lifetime – all achievable without expensive machining and deliverable in weeks rather than months.
Oil & gas operations require specialised equipment that must be reliable, cost effective and safe to the environment. The HIP powder metallurgy near-net shape process allows the designer flexibility to manufacture parts with complex geometries that require minimal machining compared to conventionally forged billets and preforms. Such design flexibility can significantly reduce expensive materials and, for example, eliminate up to 80% of the welds needed for subsea manifold systems.
The homogeneous microstructure attained through PM and HIP gives components increased wear and corrosion resistance which meets the stringent demands of the offshore industry. Large scale parts such as petrochemical valve bodies may be formed directly to shape by the HIP of encapsulated stainless steel powders. Large and complex components such as valve bodies, pump housings, swivels, tees, hubs and manifolds can be produced in one piece by HIP Product Fabrication, providing a cost-effective manufacturing route.
The flexibility inherent in the PM HIP design means that combinations of material can be used to give desired properties, enabling the production of components from metallic compositions that are difficult or impossible to forge or cast.
Bodycote’s Powdermet® process provides:
- Design flexibility
- Short delivery times
- Reduced welding and machining
- Isotropic mechanical properties
- Mechanical properties equivalent to wrought
- No hydrogen induced stress corrosion
- Ultrasonic inspectability
- Bonding of dissimilar materials without the need for temperature-limiting adhesives
- Weight optimisation
Hot Isostatic Pressing (HIP) – Densification
Casting is the ideal near-net shape process. The properties of cast components will, however, be limited by the unavoidable shrinkage of solidifying metal.
Even the best castings may have a small amount of residual shrinkage or gas porosity; defects that are liable to impair their service performance and reliability. Impact resistance and fatigue properties, in particular, are extremely sensitive to small amounts of porosity.
The HIP process exposes the casting to the simultaneous application of heat and high pressure argon gas within a specially designed and controlled pressure vessel. This combination of thermal and isostatic pressure provides the conditions by which internal porosity can be effectively eliminated.
During HIP processing, micro and macro porosity are removed by a complex combination of plastic yielding, creep and diffusion effects as material moves uniformly to fill voids from all directions. Diffusion bonding of the void surfaces during the final stage of densification ensures that defects are completely removed. The HIP treatment is conducted at a temperature at which excessive grain coarsening is avoided and a HIPed casting can challenge those properties expected from forged or wrought equivalents.
Hot Isostatic Pressing (HIP) – Diffusion bonding/HIP cladding
It is possible to bond different materials together to give an optimum combination of material properties and to save on expensive materials.
HIP can produce multiple diffusion bonds in a single process cycle. Unlike other joining techniques there is minimal change in the properties of each material, for example good corrosion resistance may be combined with high thermal conductivity. A diffusion bond is formed when two mating surfaces are processed under conditions of temperature and pressure that allow atom interchange to occur across the interface. Optimum bonding requires that surfaces to be joined are uncontaminated and that the variables of temperature, time and pressure are closely controlled to ensure uniformity.
HIP cladding is commonly used to coat premium materials with superior properties, such as corrosion and wear resistance, onto more economical substrates, so that a part may be designed cost effectively. Bi-metallic compounds can be produced by binding powder – powder, powder – solid, solid – solid.