def pipe_collapse_unity(p_e, p_c, gamma_m, gamma_SCLB, p_min=0
    ) ->'pipe_collapse_uty':
    """Calculate pipe collapse unity value.
    Local buckling – system collapse (external over pressure only).
    Reference:
    DNVGL-ST-F101 (2017-12) 
        sec:5.4.4.1 eq:5.10 page:95 $p_{lt}$
    """
    pipe_collapse_uty = (p_e - p_min) * gamma_m * gamma_SCLB / p_c
    return pipe_collapse_uty
