Metallurgical Principles and Practice of Engineering (PE) Study Guide: Question #44

It Is the Policy of The Minerals, Metals & Materials Society (TMS) to Encourage the Professional Registration of Metallurgical Engineers.
A continuously operated 2,500 psig boiler suffers from a superheater tube failure after 3 years. The tube is composed of ASME SA 209 T1 (0.15C-0.50Mn- 0.30Si-0.50Mo) steel. The tube was inspected and shown to have a normal microstructure prior to its installation into the boiler. This tube steel has an oxidation limit of 900°F (482 °C). The scale thickness of the tube was 27 mils (0.027 in.) thick at the time of failure. Assume that the tube failed by creep rupture. Log X = 0.00022 P - 7.25 for ferritic steels where X =scale thickness, mils; P = Larson Miller Parameter. Assume the LMP constant related to the steel is equal to 20.

After the boiler tube failure, it was decided to replace the original tube material of this superheater section with low-alloy steel containing 2 ¼% Cr and 1% Mo. How will the alloy additions alone NOT improve the service life of the superheater section over the original carbon steel alloy?

(A)	By increasing the average microstructural grain size
(B)	By improving the high-temperature oxidation resistance
(C)	By increasing the strength of the alloy at equivalent temperatures
(D)	By preventing graphitization in the microstructure

The information on this page is maintained by the Nellie Luther (natale@tms.org).

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