9. Apply water pressure of 1 1/2 times the maximum allowable working pressure. To avoid rapid shock and strain, bring this pressure up in 10 equal increments, inspecting for leaks and deformities at each increase.
10. Inspect tube ends, boiler seams, pressure fittings, and connections. Make the corrections and repairs wherever possible. In case of unusual conditions, DISCONTINUE the test IMMEDIATELY and NOTIFY YOUR SENIOR PETTY OFFICER. Do NOT exceed the test pressure. NEVER apply more than 10 pounds of pressure above the maximum working pressure on a low-pressure boiler. Consult the ASME code for testing procedures for other than welded steel boilers.
11. Secure pressurizing connections at the required test pressure. Continually inspect the boiler tubes, seams, fittings, and connections. If the boiler and fittings are tight, the pressure should NOT drop more than 1.5 percent in 4 hours. If loss of pressure is over 1.5 percent, find the leak(s) and make the repairs.
Following all hydrostatic testing, steam pressure is raised to lift safety valves and to determine the fitness of the boiler for use.
Q1. Most cases of major boiler damage is caused by what operating condition?
Q2. What could happen if "loose packing" is used on a gauge glass?
Q3. What are the four reasons for using blowoff or blowdown valves?
Q4. What is the purpose of a hydrostatic test on a boiler?
Learning Objective: Recognize and understand methods for renewing, repairing, and cleaning boiler tubes and sheets.
For any boiler retubing job, it is absolutely essential to use tubes that conform in every way to the tube requirements of the particular boiler. Boiler tubes are NOT identical. They differ in such important characteristics as composition of the metal, outside diameter, wall thickness, length, and curvature.
Much of the required information on sizes, thickness, and number of tubes per boiler is given in the manufacturer's technical manual. Some of the information is under the heading of "Tube Data." More detailed information is usually given on the drawings included in the manual.
Generating tubes are usually made of low carbon steel. They may be either seamless or resistance-welded. Seamless tubes were once definitely preferred for naval use. However, improved methods of manufacturing the welded tubes have led to - - an increased use of welded tubes in naval boilers. Repair ships, tenders, and other naval activities that use, handle, or issue plain carbon steel tubes have been instructed to make no distinction between the seamless and the welded tubes, but to stock, issue, and install them interchangeably without regard to the method of manufacture.
Superheater tubes usually are not made of plain low carbon steel. On boilers where the superheated steam temperature reaches 850F or higher, the superheater tubes may be made of carbon- molybdenum steel, chromium-molybdenum steel, or an 18-8 chromium-nickel (stainless) steel.
To find detailed information on the composition of the metals used for generating tubes and superheater tubes in any particular boiler, check the manufacturer's technical manual. The information may be given on the drawings, or it may be included in the text.
Once you have found information on the composition of the metals used for boiler tubes, your next problem is to understand it. Do you know what it means when you see "mild steel" on a blueprint? Can you identify metals by their chemical symbols? Do you know what an "alloy steel" is, or anything about the different kinds of alloy steels? Do you know anything about the various systems of classifying steels? Do you know why different steels are used for different kinds of tubes? Answers to these questions are necessary before you can make much sense out of the information you are likely to find on blueprints on the composition of boiler tubes.
Although we all have a general idea of what we mean by the word metal it is not easy to give a simple, accurate definition. Chemical elements are metals if they are lustrous, hard, good conductors of heat and electrcity, malleable, ductile, and heavy. In general, these properties of hardness, conductivity, 2-7Continue Reading