I need some help on estimation point of view.

To do man hour calculations for Welding, Bolting, Tie-in, Demolition of existing lines etc etc, is there any standard Norms to make the assumptions, like

Eg:
For Shop welding - 1 joint per 3 meters
      2.5 man hours for inch dia welding...
      50% for Fitter Fabricator, 25% for Welder, 25% for Rigger/Helper

For Field welding - 1 joint per 4 meters
      4 man hours for inch dia welding...
      50% for Fitter Fabricator, 25% for Welder, 25% for Rigger/Helper

For Field Bolting - 1 bolting per 5 meters
      2.5 man hours for inch dia welding...
      50% for Fitter Fabricator, 50% for Rigger/Helper

Is there any standard set of norms which I can use to calculate the number of joint, inch dia welding, man hours required for the same.

Please let me know anything related to this...

Regards,

Sabir