function dP = pipeLoadDelta(t,d,P,Leff,E,Sy)
% pipeLoadDelta  Difference between applied and critical loads for a pipe in compression
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% Synopsis:  dP = pipeLoadDelta(t,d,P,Leff,E,Sy)
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% Input: t = pipe wall thickness
%        d = pipe diameter
%        P = applied load
%        Leff = effective length of the pipe
%        E = elastic modulus of the pipe material
%        Sy = yield stress of pipe material
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% Output:  dP = Pcr - P = amount by which the critical buckling load exceeds
%               the applied load for the pipe.
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% Note:  The user is responsible for insuring that all input variables
%        have consistent units