This publication is an indispensable tool for Company owners, Piping Contractors and all members of an organization who perform tasks related to cost estimating, bidding, cost control, budget planning and contract review. The Book provides solid Technical Support to make a reliable estimate of man-hours consumption in Piping. The content of the book is the result of the Author's work experience and details a calculation procedure that will help you to accurately estimate the direct labor required for the assembly of process piping on site, including its supports for the transmission of loads to the support structures and its protection against corrosion. A meticulous estimate is essential for the proper functioning of any Company and for the future monitoring of the use of man-hours in the course of the Project, in order to detect and correct deviations. The author of this Manual, has an expertise of more than 40 years in his professional work as Head of Work, Project Manager and finally as president of a Company of Constructions and Industrial Assemblies in different plants of Chemical Processes, Refineries, Pipelines, Gas Compressors and Thermal Power plants, exercising the direction of the works and the control of the resources used for their execution, particularly in the case of installation of piping. This Manual that gives the Reader is the fruit of that Technical Expertise. The direct man hours indicated in the 14 (fourteen) tables of this Manual have been verified by the Author during the course of the Piping assemblies of the different installations. In the Manual the author presents complete calculation examples of Piping installations, based on the man hours indicated by the tables to later apply the corrections or adjustments needed for each Project.