Numerical methods for the stress analysis of pipe-work junctions
Pipe junctions arc a regular feature of piping and pressure vessel systems and are often
the subject of multiple loads. acting simultaneously and at irregular intervals. Due to the
nature and complexity of the loading. the subject has received a significant amount of
study from designers and stress analysts to resolve some of the difficulties in stressing
An extensive finite element (FE) analysis was carried out on 92 reinforced buttwelded
pipe junctions manufactured by the collaborating company. Spromak Ltd. After
comparing the resulting effective stress factor (ESF) data with ESFs for un-reinforced
fahricated tee (UFT) it was concluded that, for the majority of loads, reinforced branch
outlets appear better able to contain stresses than their un-reinforced counterparts.
The linear FE study was followed by the inelastic analysis of three reinforced branch
junctions. The purpose of the research was to investigate the potential use of such
analysis as a tool for estimating the bursting pressure of pipe junctions and satisfying
customer requirement for proof of a products performance under internal pressure.
Results obtained showed that small displacement analysis is unsuitable for estimating
the bursting pressure of a pipe junction, whilst the large displacement results were
similar to those obtained using a hand-calculation. Ultimately, the study concluded that
inelastic analysis was too expensive, offering little by way of insight into the problem
than could be found by using classical stress analysis techniques.
Following on from the study of reinforced branch outlets, this thesis described work
undertaken with British Energy Ltd. to extend their current capability of stress
prediction in UFT junctions using a FE based neural network approach. Upon
completion of training new neural networks, the PIPET program was tested against
new, previously unseen, FE data generated for this study with good results.
The program was further evaluated by comparing the output from PIPET with FE data
obtained from reviewed literature. For the pressure load case, a significant proportion of the data obtained from said literature was within the PIPET predicted stress ranges. with
the new version of PIPET tending to calculate slightly lower stresses than the original
program. However, whilst the pressure load case comparisons proved useful, the branch
bending cases showed less concordance with PIPET's predicted stress ranges.