This paper discusses the design of a removable hardened test pit lid for conducting high pressure pneumatic testing under extreme temperature variations. The high pressure extreme temperature (HPET) pit configuration requires a robust lid to contain the energy release that could occur through testing a variety of oil services items placed within a frangible thermally insulated enclosure. The insulated and hardened enclosures include an inlet and outlet for airflow. These energetic release scenarios represent postulated test item failures resulting in significant fragment and shock loads within the insulated enclosure. A 618in3 gate valve charged with 20,000psi of compressed nitrogen under a temperature range of −100°F to 600°F was used to produce the worst-case energy release in the event of a catastrophic failure within the test pit.
In order to assess the structural response of the hardened pit lid, two sets of computational fluid dynamics (CFD) analyses were performed. A 2-dimensional axisymmetric CFD model of the gate valve was used to estimate the fragment velocity of its blind flange. A 3-dimensional CFD model of the test pit, insulated enclosure, and blast lid was used to estimate the applied blast loads. The test pit enclosure was assessed using non-linear dynamic finite element analysis using single-integration hexahedral continuum elements. The braces were modeled with layered shell elements and the bolts were explicitly modeled with beam and spring elements. All of the materials are modeled using a plasticity-based piecewise linear hardening constitutive model, with rate dependency and softening, fit to each material yield, tensile, and elongation limit.
