welding job that requires you to follow them. For exam- ple, when a job is assigned to a Naval Construction Force unit, it is accompanied by a set of drawings and specifications.  When  there  is  welding  required  for  the job,  the  specifications  normally  require  it  to  be  accom- plished according to a specific code requirement. For instance, if your unit is tasked to fabricate a welded steel structure, the specifications may require that all welding be accomplished according to AWS D1.1  (Structural Welding Code).  The unit is then responsible for ensuring that the welders assigned to the job are qualified to produce  the  welds  according  to  this  welding  procedure specification. As shown in figure 3-37, a welding pro- cedure specification is simply a document that provides details  of  the  required  variables  for  a  specific  welding application. For an NMCB, the welding procedure specification is normally prepared by the certified welding inspector at the local Naval Construction Training Center. Using the Structural Welding Code,  along with the project drawings  and  specifications,  the  welding  inspector  de- velops  a  welding  procedure  specification  that  meets  the requirements of the job. The importance of this docu- ment is that it assures that each of the variables can be repeated by qualified welders. Once a welding procedure specification has been developed  and  qualified,  welders  are  then  required  to perform  a  Welding  Performance  Qualification  test.  Af- ter the test is complete, the weld specimens are tested according to the requirements of the Welding Procedure Specification. You may use either destructive or nonde- structive tests. One example of a destructive test is the guided-bend test. An X-ray test is considered nonde- structive. Testing is discussed in greater detail later in this training manual. NOTE: When you are assigned to do a welding job, make a thorough examination of the drawings and speci- fications.  Look  carefully  at  the  notes  on  the  drawings and  Section  5  (metals)  of  the  specifications.  If  specific codes are cited, inform the project supervisor so that you can  receive  the  training  needed  to  perform  the  required welds. DRAWINGS Drawings or sketches are used to convey the ideas of an engineer to the skilled craftsman working in the shop. As a welder, you must be able to work from a drawing in order to fabricate metal parts exactly as the engineer  has  designed  them. READING  DRAWINGS To read a drawing, you must know how engineers use lines, dimensions, and notes to communicate their ideas on paper. In this section, we briefly discuss each of these drawing elements. For a more thorough discus- sion, refer to publications, such as  Blueprint   Reading and Sketching, NAVEDTRA 10077-F1, or to  Engineer- ing Aid 3, NAVEDTRA  10696. Figure 3-38 shows many of the different types of lines that are used in drawings. You can see that each line has a specific meaning you must understand to interpret a drawing correctly. Let’s discuss a few of the most important types. A  visible line (sometimes  called object line) is used to show the edges of an object that are visible to the viewer. For example, if you look at one of the walls of the room you are in, you can see the outline of the walls and (depending on the wall you are looking at) the outline of doors and windows. On a drawing,  these  visible  outlines  or  edges  can  be  shown using  visible  lines  that  are  drawn  as  described  in figure 3-38. Now look at the wall again. Assuming that the wall is wood frame, you know that there are studs or framing members inside the wall that you cannot see. Also, the wall may contain other items, such as water pipes  and  electrical  conduit,  that  you  also  cannot  see. On  a  drawing,  the  edges  of  those  concealed  studs  and other items can be shown using  hidden  lines  (fig. 3-38). These lines are commonly used in drawings. As you can imagine, the more hidden lines there are, the more difficult it becomes to decipher what is what; however, there is another way these studs and other items can be “seen.” Imagine that you “cut away” the wallboard that covers the wall and replace it with a sheet of clear plastic. That clear plastic can be thought of as a cutting or viewing plane (fig. 3-38) through which  the  previously  concealed  studs,  piping,  and conduit  are  now  visible.  Now  those  items  can  be drawn  using  visible  lines,  rather  than  hidden  lines.  A view  of  this  type  is  called  a  sectional  view,  and  a drawing of the view is called a  section   drawing. Section  drawings  are  commonly  used  to  show  the internal components of a complicated object. Many times, you will see lines drawn on the visible surfaces of a section drawing. These lines, called section lines, are used to show different types of materials. 3-21