IEM PI Section A – Design experience related 1

(For PI section A, candidate will have to write an essay, which the question was earlier prepared by interviewers based on candidate’s Report on Training and Practical Experience. The following were predicted questions, by Mr. BAY based on his submitted report to principal interview and his trial exercise prior to sitting of PI.)

Design Experience Related Question

What are the design principles/ criteria of pipe rack? What are the design horizontal forces, pipe shoe, fix shoe and free shoe? How to cater the vibration?

Introduction

Pipe rack, which is normally steel structure, to support pipes which the pipes are subjected to internal hydrostatic pressure or gas at high temperature. Structural engineers are to design the pipe rack to withstand both vertical and reactive actions from pipe to pipe rack both horizontally and longitudinally. 

 Design principle/ criteria

1)      Pipe stresss analysis and reactive force to pipe rack

It is piping engineer to conduct a pipe stress analysis. From the analysis, piping engineer to decide the pipe size, pipe loops and type of pipe shoe at strategic location. The type of pipe shoes are guide shoe, slide shoe and fix shoe (stopper). It is deemed highly necessary that piping engineer to provide the reactive force at these shoes especially at stopper to structural counterpart.  

Structural engineer will have to pay attention to type of shoes and the magnitude of the force. The force, especially at stopper, is a main concern for structural design of the pipe rack. Engineer to determine the bracing and size required.

2)      Type of pipe shoe

As per earlier paragraph, engineers need to pay attention to the type of pipe shoe. Guide shoe allow pipe to move longitudinally and slide shoe allow pipe to move both horizontally and longitudinally. As these shoes allow movement of the pipes, the reactive force exerted by pipes at these shoes are pretty much less severe compared to reactive forces exerted at stopper.  

For practical practice, slip forces at both guide and slide shoe can consider 10~20% of the operating weight of the pipe. The force at stopper is better referred to piping engineer for design value.

3)      Braced frame structure

Like all structural design, the horizontal force affects the lateral stability of structure. For pipe rack, the longitudinal and horizontal forces from pipes especially at stopper are to be taken care by design the appropriate structural system. It is always to adopt the braced framed system for an economical design. If the condition is not permitted, moment frame structure could still be designed with more attention to the steel connection design both the steel structural and footing. 

 How to cater the vibration?

Vibration of the pipe rack is caused by reactive force at stopper shoe. As the design and location of type of pipe shoe are prepared piping engineer, structural engineer is to design the pipe rack accordingly.