RENTECH BOILER SYSTEMS CHOSE ALGOR PIPEPAK SOFTWARE TO VERIFY COMPLIANCE WITH ASME PIPING CODE

A feed water piping line including a control station bypass section such as the one shown here was modeled and analyzed by Rentech Boiler Systems, Inc. using ALGOR's PipePak software.

Rentech Boiler Systems, Inc. in Abilene, Texas is a supplier of custom steam-generating pressure vessels for companies such as Dow Chemicals, Exxon, Mobil and Shell. Recently, to support the installation of a boiler at the plant site of Solar Turbines, Inc. (a Caterpillar subsidiary), Rentech chief engineer Don Morran used ALGOR's PipePak software for flexibility analysis of a feed water piping line, which carries water from a supply source to the boiler inlet. "Before water goes into the boiler, preprocessing operations heat the water and pressurize the piping," said Morran. "Analysis of the piping system was required to verify its structural integrity under pressure, temperature and site loadings and ensure compliance with the applicable ASME piping code."

Routing the Piping System

The piping system started at a de-aeration tank in which oxygen was removed from the water to prolong the life of the boiler. The piping was routed around existing features of the installation site including platforming, forklift trails, building barriers and property lines.

Almost immediately, the piping went into a control station equipped with a sensor that monitored the water level inside the boiler. The control station's valve regulated the flow of water to maintain a consistent level inside the boiler per the steam demand. Over time, due to repetitive motion, this type of valve tends to wear out. Hence, the piping system included a bypass around the valve so that it could be replaced while the boiler was still in operation.

Further along the piping line, the water was routed to a waste heat recovery system called an economizer, which heated the water under pressure with hot effluent gas from turbine exhaust, making the boiler operation more efficient and putting the plant's waste heat to productive use. The piping system then emptied into the boiler.

Modeling and Analyzing the Piping System in PipePak

Don Morran, chief engineer with Rentech Boiler Systems, Inc., uses ALGOR's PipePak software to examine analysis results for the feed water piping line model.

According to Morran, "The on-site project manager worked with a draftsman to provide me with a preliminary routing for the piping as an AutoCAD drawing." The geometry could have been imported into PipePak via a neutral geometry file (such as a .dxf file); however, Morran preferred to enter the data in the built-in spreadsheet. "Because I've been using the software for over 15 years, it's nearly as fast for me to enter the data in the spreadsheet. This gives me a feel for the piping system and enables me to make changes, if need be, as I go along."

Morran specified ASME B31.1-2001 as the applicable piping code by choosing from a menu of options. Specifying the piping code automatically set several other model parameters including the default load combinations.

Morran then used the spreadsheet to define the piping system geometry including pipes, bends, reducers, valves, anchors, supports, tees, flanges and weights. He specified pipe data including size, corrosion allowance, insulation and contents; material data including material properties and allowable stresses from the standard library; and load data including temperature and pressure loads for various operating and test conditions.

As Morran defined the model, he confirmed the entered data by reviewing a graphical display of the piping system in the built-in graphics environment, which provides a 3-D, full-color, OpenGL display of the piping system and a tree view listing all system components. "After entering 3 or 4 lines, I would render the model to ensure the geometry that I had entered matched what the draftsman had given to me for analysis," said Morran. "The display of the piping model included all of the details down to the valve hand wheels. It was almost like a photograph of the physical object."

After the model was defined, Morran used the software to check the geometry and entered data and validate that it was ready for analysis. The processor performed a finite element analysis (FEA) of the piping structure solving for all defined load combinations in just a few seconds.

The built-in graphics environment of PipePak displays the feed water piping line model. At left is a close-up, shaded view of the control station bypass section; at center is an HTML report, which lists system stress values in tabular format; at right is a close-up view of code stress ratios in the economizer section, which illustrates that all stresses in the model are below allowable values in compliance with the ASME B31.1-2001 power piping code.

Viewing Results and Verifying Code Compliance

Morran then used the software to view the analysis results. "First, I examined stresses throughout the entire piping line, and they looked satisfactory," he said. "Next, I examined the anchors at each end. In general, the end points should be as well supported as possible because experience has shown that reducing or eliminating stresses at the ends can prolong the life of a piping system. Therefore, I added supports at appropriate locations along the line in order to reduce the stresses at the ends." After reanalyzing the revised model, Morran concluded that stresses at the end points had been sufficiently reduced.

To verify that the piping structure complied with the ASME B31.1 power piping code, Morran displayed the code stress ratios for each load combination, which indicated that all stresses were safely below the allowable value. Morran said, "Displaying the ratios between code stress and allowable stress is a quick and easy way to indicate whether or not the piping system is in compliance with code requirements. It will show immediately if there is a problem and where it's located both numerically and by coloring. If the maximum code stress ratio is less than one, then you know your system meets code."

Morran used the software to automatically generate a report that summarized input, analysis results, equipment data and more. Morran said, "Probably two hours after the job hit my desk, the report was back in the draftsman's hands and he was drawing the additional supports that were specified during analysis. The ability to share model and analysis information with anybody who needs to see it, through reports and graphics displays in both electronic and hard-copy format, is a great time saver."

Click here for more on how Rentech Boiler Systems, Inc. used ALGOR software.