An equipment manufacturer required CADE to conduct the validation design of a flexible pipe connection, between a reactor and a steam generator, to meet the requirements of the end user. This connection had to join the output of two pieces of equipment working at high temperatures and consider the displacement of one of the outputs when reaching a high temperature.

Initially, the manufacturer had proposed a helicoidal design, aimed to absorb the pressures generated by displacement and minimize stress on the connection. Once CADE performed the first Creep analysis, it was determined that the generated stress levels were too high in this first design, even in a state of rest, mainly due to the high weight of the pipe.

Then, a second design was proposed, also based on a spiral concept, although considering a much more horizontal and lighter geometry. However, the system was still too rigid to absorb the stresses generated by the displacement.  Finally, CADE was required to design and analyze (by means of Finite Element Analysis) an alternative solution for such connection.

CADE’s design solution

After studying different diameters and lengths, CADE staff defined a new geometry for the design, as well as the location of the supports and the manner the pipe should work.

Taking into account the displacement of one of the outlets when reaching a high temperature, it was proposed to place a tensioned pipe in the form of a flexible arch, which when heated it would return to its natural position. In this way, the highest stresses are generated when cold, which is when the pipe is forced into a more extended position, but they are reduced when the system heats up when it starts operating.

flexible pipe connection initial proposal

First proposal

flexible pipe connection proposal

Alternative proposal

flexible pipe connection final design

Final design

Applicable norms and codes

To deliver a final valid design, API-350 ed.2015 regulation on “Calculation of Heater-tube Thickness in Petroleum Refineries” was considered.

Furthermore, said standard was complemented with the prescriptions of ASME API 579-1 / ASME FFS ed. 2016 Part 10 regarding “Assessment of Components” operating in The Creep Range“.


  • Stress analysis
  • Creep analysis
  • Fatigue analysis
  • Fatigue-Creep combination by Fitness For Service
  • Stability analysis (buckling prevention)


CADE provides advanced engineering, simulation, and consulting services for the design and validation of critical equipment, piping systems and/or special structures.

Author: Javier Martinez Carillo


Parque Científico y Tecnológico

Paseo de la Innovación 3, 02006 Albacete – España

Tel. +34 967 19 01 72


Santiago Bernabéu, 3 Entreplanta
28036 Madrid – España

Alfonso XII, 62

28014 Madrid – España

Do you want to subscribe to our newsletter

We will keep you informed

I guess you are interested in what we do

If you please, contact us and tell us about your project to inform you what we can do for you

Can we call you?

We inform you about our engineering solutions