Selection of a Piping Material for a

Corrosive Environment

developed by Kenneth Kauffman

 

Background:

You have been hired by Kauffman Enterprises to offer your expertise in materials science for a chemical reactor being designed by the company. Your job is to determine the best combination of materials possible for the job described below.

 

The reactor vessel being designed will be operated at 525˚C and will contain concentrated hydrochloric acid. Since hydrochloric acid is highly corrosive and has a high vapor pressure, the vessel must be sealed for the safety of the employees of the chemical plant. The reactor itself will be made of a special stainless steel material and has already been ordered. However, there will need to be a significant amount of piping attached to the vessel and an analysis to determine the best alternative must be done. That is your job. Kauffman Enterprises is supplying you with five potential materials for the piping. This is based on a preliminary analysis done by one of the design engineers at the firm. You are to provide a recommendation to the firm as to which material would be the best for this job. You should also provide recommendations as to how these pipes should be added to the reaction vessel and any concerns that may arise from that. Consider what you know about fluid mechanics.

 

Data provided by Kauffman Enterprises:

 

Material
Cost/foot of pipe
Brass
$2.65
Bronze
$3.25
Copper
$2.76
Aluminum
$1.24
Stainless Steel
$4.65

   

 

Kauffman Enterprises has specifically asked that you take into account the expansion of the pipes and also the ability of the piping to resist corrosion (you will have to do some out of class research on this topic). Any other recommendations you have should also be included. Be creative, but support your conclusions with references or data. Follow the lab report format outlined in this lab manual. You should compare your results with the accepted standards. However, you should use your results in all of your calculations AND THEN PROVIDE AN ESTIMATE OF YOUR ERROR. Explain how you came up with your estimate and provide recommendations as to how the builders can compensate for any error that may be found in your measurements.

 

Procedure:

The procedure for testing the coefficient of thermal expansion is relatively simple. Place the sample inside what is basically a heat exchanger. Seal both ends of the vessel with rubber stoppers and measure the length of the pipe. Mark where this length is on the millimeter scale on the edge of the instrument. MOVE THE POINT OF THE METER SO YOU DON'T DAMAGE IT. Apply steam to heat the sample. Determine the change in length and the change in temperature. Determine the coefficient of linear thermal expansion. (more detailed instructions are given at the end of this section).

 

Each group will be in charge of the collection of the data from a different sample. The class will do an example run with Stainless Steel to demonstrate the method. You will have to share data with all of the groups and should collaborate with your group members, but the report is individual.

 

Note:

You can use your textbook as a reference for much of the information you are being asked to gather. However, it should not be your only reference. What are some alternative resources you can utilize? Make sure you include a properly formatted reference section in your report. Your report should contain an extensive description of the corrosion properties of each material as well as the key points relating to thermal expansion.

 

Coefficient of Linear Expansion

Procedure:

 

1.   Check the steam generator to insure that there is adequate water in it.  Be sure to check to see if it is still hot from previous experiments before handling it.  Once the steam generator is filled, plug in the hot plate to heat the water.

 

2.   Measure the initial length of the rod.

 

3.   Insert the rod into the apparatus.  Be sure that the jacket is secured to the apparatus.

 

4.   Attach the cold water supply to the water inlet of the jacket.  Attach the drain hose if it is not already attached.  Turn on the water and allow the water to cool the rod.  When the temperature of the water has become constant as indicated by the thermometer, read the temperature.

 

5.   Slowly rotate the micrometer screw until the point of the screw makes contact with the rod.  The lamp will begin to light indicating that contact has been made.  Take five independent readings of this length.  Do not over-tighten the micrometer screw or the equipment will be damaged.

 

6.   Back off the micrometer screw at least two turns.  Connect the steam generator to the apparatus and let run for several minutes.

 

7.   Read the temperature and take five independent readings of the length.

 

8.   Repeat the procedure for the remaining rods.

 

9.   Calculate the coefficient of linear expansion using the formula:

                                            a =

where:

a             =  the coefficient of linear expansion (Units are "per degree Celsius")

DL           = Change in length

Lo           = Original length

Dt            = Change in temperature

 

You may want to include the following in the Background section of the report.

 

•  What is the significance of the coefficient of linear expansion and what role does it play in engineering design?

 

•  When is it desirable to join two metals having like coefficients of linear expansion?  Different coefficients?

 

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