Joint Efficiency Factors

When vessels are designed to other international standards, the standard should always be consulted to determine the rules for joint efficiency, as different codes treat it in different ways. For example, welded-joint efficiency factors are not used, as such, in the design equations given in BS PD 5500 instead, limitations are placed on... 

These stress values are the basic values multiplied by a joint-efficiency factor of 0.85. 

BD = head blank diameter, inch c = corrosion allowance, inch D = inside diameter of shell or head, inch E = joint efficiency H.Fac = head blank diameter factor OD = outside diameter of head, inch P = internal design pressure, psig R = inside radius, inch R = crown radius of torispherical head, inch S = allowable stress, Ib/in ... 

There are various methods of making the attachment weld of the skirt to the shell. The preferred method is the one in which the center line of the shell and skirt coincide. This method will minimize stresses at the juncture. Probably the most common method, however, is to make the OD of the skirt match the OD of the shell. Other methods of attachment include lap-welding, pedestal type, or a shear ring arrangement. The joint efficiency of the attachment weld also varies by the method of attachment and is usually the governing factor in determining the skirt thickness. This weld may be subject to cracking in severe cyclic service. 

E = joint efficiency El = modulus of elasticity, psi C], = seismic factor (see Procedure 3-3)... 

E =joint efficiency, 0.35-1.0 F = summation of all vertical downward forces, lb Fa = allowable compressive stress, psi f = vertical reactions at support points, lb hj = depth of contents to point of evaluation, ft Ki,K2 = rankines factors, ratio of lateral to vertical pressure... 

Evidence suggests that the failure behavior of thermoplastics is much the same as for thermoset composites. High joint efficiencies can be obtained with suitable consideration to the joint design, fastener type, and environmental factors. In addition to mechanical and adhesive joining, thermoplastic composites can also be heat welded depending on the concentration and type of fillers within the composite. 

C = Attachment Factor E = Joint Efficiency, Cat A seam only F = Total force exerted by stud(s), Lbs P = Design Pressure, PSIG S = Allowable Stress, head. PSI Sb = Allowable Stress, bolt, PSI Z = Factor dependent on D/d ratio... 

In the case of an opening which is Ifwated entirely within the spherical portion of a torispherical dished head, the thickness to be used in Eq. 13.28 is calculated by Eq. 7.77 with a joint efficiency of 1.00 and a shape factor of 1.00. 

D = diameter of shell to which head is attached K = stress intensity factor obtained from Eq. 9.6 S = allowable stress E = joint efficiency... 

Relevant shell design provisions for tensile stress failure exist in all specifications, where allowable stresses and efficiency factors for welds are specified. If overmatched butt-welded joints are used, efficiency factor is usually equal to unity. 

Common practice consists in investigating the influence of one experimental variable (hereafter we will refer to it as a factor while keeping other factors at a fixed value. Then, another factor is selected and modified to perform the next set of experiments, and so forth. This one-factor-at-a-time strategy has been shown to be inefficient and expensive it lacks the ability to detect the joint influence of two or more factors (z.e. it cannot address interactions) and often needs many experiments. An increase in efficiency can be achieved by studying several factors simultaneously and systematically by means of an appropriate type of experimental design. In such a way, the experiments will be able to detect the influence of each factor and also the influence of two or more factors because every observation gives information about all factors. 

D0 = orifice diameter, ft Ej = efficiency of joints, expressed as a fraction f = Fanning friction factor... 

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