Avoiding Failure in a Hot Isostatic Press

A Hot Isostatic Press (HIP) is a thick walled vessel subject to cyclic stress from internal pressure and temperature profiles. It contains a furnace that heats a work piece to as much as 2900° F (1590° C). These furnaces are designed with a thermal barrier that keeps the inside wall of the vessel below 400° F (204° C). A break down of this thermal barrier can allow jets of hot gas to impinge on the vessel wall and allow hot gas to accumulate at the top of the vessel. Sudden heating of the wall will cause large, localized, compressive stresses and can result in yielding and cracking. The excessive local temperature can also cause a reduction in material properties. Any of these problems can lead to the failure of the vessel. This paper traces a case history of a vessel with these kinds of damage. The problem was first identified by normal, non-destructive, inservice inspection. Further inspection and testing was required to identify the extent of the problem and to verify complete removal of the affected metal. This included insitu metallography of the vessel surface, hardness testing and tensile testing of trepanned specimens. The final vessel configuration was analyzed at a reduced pressure for compliance to Section VIII, Division 2. It was then hydrotested and placed back into service, avoiding catastrophic failure.