PRINCIPLES OF NAVAL ENGINEERING 



When the primary service rating is for 

 steam, and when no other service is indicated, 

 the service designation may consist of numerals 

 only. For example, the number 600 marked on 

 the body of a valve would indicate that the valve 

 is suitable for steam service at 600 psi. If the 

 valve is designed for water at 600 psi, the serv- 

 ice designation would be 600 W. Service desig- 

 nations are also used in combination; for exam- 

 ple, 3000 WOO indicates a product suitable for 

 water, oil, or gas service at 3000 psi. 



Some abbreviations that are commonly used 

 for material identification in the MSS system 

 include the following: 



AL Aluminum 



B Bronze 



CS Carbon Steel 



CI Cast Iron 



HF Cobalt- chromium- 

 tungsten alloy (hard 

 facing) 



CU NI Copper-nickel alloy 



NI CU Nickel-copper alloy 



SM Soft metal (lead. Bab- 

 bitt, copper, etc.) 

 CR 13 13-percent chrom- 

 ium steel 



18 8 18-8 stainless steel 



18 8SMO 18-8 stainless steel 



with molybdenum 



SH Surface-hardened 



steel (Nitralloy, etc.) 



Some examples of MSS standard identifica- 

 tion marking symbols are given in figure 14-30. 



PACKING, GASKETS, AND INSULATION 



Packing and gasket materials are required 

 to seal joints in steam, water, gas, air, oil, and 

 other lines and to seal connections which slide 

 or rotate under operating conditions. There are 

 many types and forms of packing and gasket 

 material available commercially. To simplify 

 the selection of packing and gasket materials 

 commonly used in the naval service, engineer- 

 ing personnel use a packing and gasket chart^ 

 showing the symbol numbers and the recom- 

 mended applications of all types and kinds of 

 packing and gasket material. 



The chart is identified as NavShips Mechanical 

 Standard Drawing B-153. 



The symbol numbers used to identify each 

 type of packing and gasket consists of a four- 

 digit number. The first digit indicates the class 

 of service with respect to fixed and moving 

 joints; the digit 1 indicates a moving joint (mov- 

 ing rods, shafts, valve stems, etc.) and the digit 

 2 indicates a fixed joint (flanges, bonnets, etc.). 

 The second digit indicates the material of which 

 the packing or gasket is primarily composed- 

 asbestos, vegetable fiber, rubber, metal, etc. 

 The third and fourth digits indicate the different 

 styles or forms of the packing or gaskets made 

 from the material. 



Pressure, temperature, and other service 

 conditions impose definite restrictions upon the 

 application of the various kinds of packing and 

 gasket materials. Great care must be taken to 

 see that the proper materials are selected for 

 each application, particularly when high pres- 

 sures or high temperatures are involved. 



Insulation is used on most shipboard piping 

 systems. Insulation is actually a composite 

 covering which includes (1) the insulating mate- 

 rial itself, (2) the lagging or covering, and (3) 

 the fastenings which are used to hold the insu- 

 lation and lagging in place. In some instances, 

 the insulation is covered by material which 

 serves both as lagging and as a fastening de- 

 vice. 



Insulating materials commonly used in the 

 Navy include magnesia, calcium silicate, dia- 

 tomaceous silica, asbestos felt, mineral wool, 

 fibrous glass, and high temperature insulating 

 cement. Cork, although light in weight and easy 

 to handle, is not fire-retardant and in burning 

 it gives off a dense, suffocating smoke; hence 

 cork is used only in certain applications and 

 only after it has been treated with a fire- 

 resistant compound. 



Lagging may consist of cloth, tape, or sheet 

 metal. Lagging serves to protect the relatively 

 soft insulating material from damage, to give 

 added support to insulation that may be sub- 

 jected to heavy or continuous vibration, and 

 to provide a smooth surface that may be 

 painted. 



Lagging is secured in place by sewing or 

 by using fire-resistant adhesives, insulating 

 cement, or sealing compounds. The method 

 used to fasten the lagging in place depends upon 

 the type of insulation used, the type of lagging 

 used, and the service requirements of the 

 piping or surfaces to be insulated. 



388 



