LOADS ACTING ON PRESSURE VESSEL:

1) GENERAL LOAD: 

Those are load acting on entire cross section of vessel that responsible for bursting and collapse of vessel.
 - Pressure loads ( due to design, operating , hydro test pressure of fluid, hydro static head of fluid)
 - Moment loads(due to wind and seismic loads, transportation and erection )
 - Compressive and tensile loads ( due to dead weight of vessel and its attachments like ladders ,  platform,      cleats , nozzles, lifting lugs, trailing lugs, )
 -Thermal loads( due to temperature difference of fluids)

2) LOCAL LOAD:

Those are load acting on localize part of vessel ( due to reaction from supports and  nozzle loads )
 -Radial loads (inwards and outwards)
 -Shear loads (longitudinal and circumferential)
 -Torsional loads


Class of stresses are define by type of loading which produces them and the hazard they represent to the vessels

• Primary stresses:

• Secondary stresses

General layout of pressure vessel:

TYPE OF STRESS OCCURS IN PRESSURE VESSEL:

1)  Circumferential stress

 It is stress which usually is defined as the total circumferential force exerted along the  entire radial thickness as shown in figure.   It is also known as hoop stress.  Due to this stress failure of pressure vessel is lengthwise.   It means entire vessel fails along length. It is given by equation    

                                                     
                                                                 σC=Pd/2t

               

 2)   Longitudinal stress:

 It is stress which usually is defined as the total longitudinal force exerted on ends of               vessel as shown in figure.   Due to this stress, failure of pressure vessel is perpendicular to its axis that divided vessel into two parts.   It is given by equation

                                         σL=Pd/4t

3)  Radial stress 

 This is force exerted into entire body of pressure vessel due to its internal pressure of fluid    contains by vessel

Note : From above definition of stress we can say that circumferential stresses are almost double of longitudinal stresses. so that failure is critical due to circumferential stress then longitudinal stress.