Frequently Asked Questions

We primarily work with ASME BPV codes such as Section VIII Division 1 & Division 2 and the UK national code PD5500. We also have extensive experience with the European harmonised standard EN 13445.

The time required to design a pressure vessel can vary significantly depending on the complexity of the vessel, the intended service, whether all aspects of the design are covered by design-by-rule methods provided in the applicable design code, and the availability of the required design data. For a simple vessel design, design calculations could be completed and a substantiation report provided in as little as two weeks. A larger project with a design taken from initial concept to full substantiation with preparation of fabrication drawings, where material selection is required, limited information on loadings is available, transient thermal behaviour is exhibited, and fatigue assessment is required could take in excess of six months.

FCL provide pressure vessels design services for various industries including: Petrochemicals; Oil & Gas; Nuclear; Marine; Green Technology; Pharmaceuticals and Transport.

Design-by-analysis refers to the use of computer-based simulations or mathematical models to evaluate the adequacy of a design. Typically, the component geometry is defined in  a computer aided design (CAD) model, appropriate material properties and loading/constraint conditions are applied to simulate the component and the expected loading, and a detailed analysis is performed using computer aided engineering (CAE) software to evaluate the deflections, stresses and/or temperatures arising in the structure for assessment against defined limits.  

In the case of pressurised equipment, design-by-analysis methods are typically applied when aspects of a design fall outside the scope of the chosen design code. Common examples are large rectangular openings, nozzles located in the knuckle regions of dished ends and special flange designs. Design-by-analysis methods may also be applied to assess temperature gradients in components subject to transient thermal behaviour, or to provide an accurate prediction of fluctuating stress levels where cyclic service requires a fatigue life assessment.

FCL primarily uses ANSYS for finite element stress and thermal analyses. We have decades of experience using this software to produce 2D axisymmetric, 3D shell or 3D solid models of varying levels of complexity, and always seek to achieve a high quality mesh with the necessary refinement in areas of interest to produce accurate results. We also have substantial experience in using Creo Simulate (and legacy versions of this software released as Pro/MECHANICA Structure and Thermal), which utilises P-element technology to provide high levels of convergence with relatively coarse meshes.

API 6A (ISO 10423) flanges do not have specified limits on external loads and these should instead be established by those responsible for the design of the flanges.  Work was carried out in 1987 by Stress Engineering Service (PRAC-86-21), for API, to determine the capabilities of API flanges under combinations of loading. This work was subsequently summarised in API 6AF, which presented a series of rating charts to be used for API 6A 6B and API 6A 6BX flanges. The charts presented therein indicate the limit on bending moment that can be accommodated for a given combination of bore pressure and axial loading.  Charts are organised by flange rating and bolt make-up stress. However, these charts, while helpful indicators, cannot account for factors such as the risk of HISC or modifications to the flange geometry to suit the attached piping. As such, bespoke calculations should be calculated to address these factors and establish external load capacities for the specific use case.  Finglow specialises in carrying out flange design on this basis.

By using design methods in ASME Section VIII Division 2, PD 5500 and API 6A in combination with DNV-RP-F112 as necessary.  Stress limits for the combined loads are calculated based on the material of construction of the flange for the operating and test conditions.

API 6A (otherwise known as ISO 10423) is a flange standard, similar to ASME B16.5 and B16.47. Within API 6A, Type 6B flanges cover low pressure (below 5ksi) and smaller sizes (up to 21¼″, depending on rating) while Type 6BX flanges cover increased pressures (up to 20ksi) and a flange size range from 1 13/16″ up to 30″. The key difference between 6B and 6BX flanges is that 6B flanges are designed to make-up via a metallic ring joint, and not for fac