The Potential Pitfalls of Computer-aided Pipe Design

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Tuesday, March 8th, 2016
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The development of computing software has had a profound impact upon the process of modern piping design, yet can also lead to bad habits and unsound practices if improperly used by engineers.

Jim E. Meyer, lead engineer for Louis Perry Group and facilitator for the American Society of Mechanical Engineers (ASME) course on the B31.3 Process Piping Code, notes that the code was devised over half a century ago, well before computers and other forms of hi-tech equipment were accessible tools for engineering professionals.

“The ASME B31.3 Process Piping Code, which provides minimum requirements for safe piping systems from design through to fabrication, examination and testing, was developed prior to the 1950s, in an era when we had no computers,” he said.

The revolution in computing technology that has taken place since the code’s inception has greatly facilitated the practice of pipe design, chiefly by speeding up the once time-intensive process of analysis.

“We use computers now because the math is just too difficult when the piping configuration consists of more than couple of bending legs,” said Meyer. “In 1973 a simple computer analysis might take three to five days, involving the punching of cards and getting the computer department to run the analysis, and a further two days to rerun it if there was a mistake or the piping had to be revised.

“Now that process takes 10 minutes to an hour.”

The speed with which analysis can be conducted means that engineers can practice pipe design more freely without the need to worry about expensive or time-consuming analytical process.

“40 years ago we were very careful to design a system which would not require many iterations because of the time involved,” said Meyer. “Now it is so fast it is easy to push the button for the analysis and just see what the computer tells us.”

Meyer points out, however, that excessive reliance upon computing software for analytical purposes can make some engineers lazy, or even lead to a deterioration of those critical design skills that play a key role in the engineering process.

“Computer software is used to meet the design requirements in the code – computers now let a piping designer layout the piping in a 3D model and import the geometry to piping analysis software, so sometimes an analysis can be completed without any real thought on the part of the engineer,” he said.

“If the analysis results say the system meets code requirements, many engineers will sign off without giving it any more thought, and as we rely more on computers, we are losing some good design practices.

“I try to make sure people understand the computer will give them an answer, but as engineers, their job is to make sure they understand the answer because it is based on a number of assumptions, many of which may not be valid for a given piping system.”

Even with computing software that can check whether criteria requirements are satisfied, engineers must fully understand various aspects of the piping process in order to ensure that the analysis itself is correct.

An outstanding example of this is the expansion joints for pipes, which if not correctly designed and built can be a source of potentially deadly explosions.

“Expansion joints, which are added for reasons including thermal expansion, thermal loads on equipment or general fit-up, can be modelled using available software, but this is very difficult and the answer must be checked carefully,” said Meyer.

“What many people forget or do not even know is that there is pressure thrust associated with an expansion joint, and modelling must take into account hardware that will affect how much thermal growth the joint can withstand.”

Failure on the part of engineers – even those who are qualified and highly capable – to fully understand this one key aspect of pipe design can have disastrous consequences.

“In 1974 a plant in the UK made a site modification without understanding this pressure thrust, and dozens of people were killed when the joint blew out because of the pressure thrust and a chemical cloud explosion,” Meyer said. “As I have become more involved in training, I am amazed how many times I come across engineers who have not been taught or do not understand the pressure thrust associated with expansion joints.”

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