Lang factors were produced long ago out of a study of some 14 plants only out of which three of them costing more than $2.5 million, small by modern standards. Lang factors, as well as the classification of the plant types as owg has well described, have been largely superceded and replaced with other cost estimating techniques, that include the selection of new more expensive metallurgies other than carbon steel, keeping, however, the factoring method but with factors adjusted down for higher equipment costs.
There are estimates that use factoring for individual pieces of equipment based on FOB costs plus an addition for transportation to the site. Others classify the plant sections into various categories such as battery limits (BL) that include site preparation as a miscellaneous item which depends also on the other sections, such as Storage Area, Utilities, Services, Indirect Costs, and Miscellaneous.
Because of the many uncertainties involved at the various stages of cost estimating, 15 to 50%, to cover for contingencies, are sometimes added, especially if the estimate is based on very preliminary flowsheets.