Explosion analysis – Stressfield Oy

Customer

Metso Flow Control Oy

Background

As part of the risk assessment for a high-pressure valve testing facility, Metso Flow Control Oy wanted to simulate the case of valve failure and the results of the blast impact and detached fragments on the surrounding walls.

Analysis objectives and methods

The goal is to determine the required thickness of the steel plate in the test facility safety walls. The penetration of any fragment or rupture of the safety wall is not allowed in the analyses.

Case 1: Impact analysis of detached fragments

The wall material model used in the FEM-analyses is strain rate dependent non-linear material with strain failure criteria (element erosion). The Johnson-Cook material model is used in the analyses with the parameters chosen conservatively. The used value of the true failure strain is chosen according to EN 10025-2.
The detached fragment material is modelled with a kinematic hardening plasticity model without strain-rate effect. No failure criterion is applied in the fragment material model.

Case 2: The minimum wall thickness is evaluated also by the explosion analysis.

The wall material is modelled with a plasticity model and the tangent modulus is set to zero for ideal plasticity. The failure criterion is applied so that effective plastic strain for eroding elements is 0.2.
The same material model is also applied on the test facility I-beams.

Solver: The analysis type is explicit dynamic analysis using LS-Dyna.

Loads

Case 1: Given the maximal specified test pressure, and the detached fragment properties, the initial velocity of the fragment was calculated analytically and used in the impact analysis. The flight path of the impacting fragment is chosen to be normal to the wall.

Case 2: The load model “ConWep” (Conventional Weapons Effects, LS-dyna) is used to generate the colliding pressure wave. The explosion energy is calculated according to the compressed gas energy for ideal gases. In the FEM analyses, the same explosion energy is generated using the equivalent amount of TNT.