An underground steam line for a military base in Alaska, approximately 1.6 km (1 mile) in length, used the units depicted in Figure CS-32, each unit being 9.14 m (30 ft) in length. As shown, the steam line for each unit was enclosed in a cylindrical conduit made of sheet steel and weighed approximately 356 kg (785 lb). The conduit was to serve as the return drain line and to provide insulation. Each length of steam line was supported within the conduit by means of three U-shaped legs, made by cold-bending hot-rolled steel bar stock. See section A-A' for a cross section. These legs were welded to the pipe about 2 m from each end.
The units were fabricated in California and were transported to Alaska by a sequence of truck, barge, and railroad. Because of an early winter, only one-half of the line was installed the first summer. Before work was resumed the following spring, someone decided to test the line and found that there were numerous holes in the conduit. The holes (slits in casing) were located where the edges of the U-shaped supporting legs contacted the outside conduit (casing) on the top of the casing. As the result of these holes, the project was delayed and a costly litigation ensued.
1. Why do you think these holes occurred?
2. Was it a design error? A fabrication error? A service error? A service environment error?
3. What error(s) caused the failures? When did the defects actually develop?
4. What action would you recommend to avoid this problem in the future?
5. What should be done about the part of the line already installed?

Transcribed Image Text:

Conduit 1.27 (0.05) wall Defects (slits in conduit) Weld 12.7 A' 254 508 (10" (20") 63.5 (2 1/2") Steam Return Section A-A of leg Leg one of three Steam line 6.4 (1/4") wal (Not to scale)