Man hours calculation - Fast Pipe Welding Time Calculator Tool

Pipe Welding Time Calculation: Fast Estimation of Man-Hours

It must be understood that a quick calculation with a good approximation of welding man-hours is crucial to making correct decisions in project management.

This guide divides pipe welding into two main categories to help estimate the time required:

Categories of Pipe Welding for Man-Hour Estimation

1. Piping with Quality Control by Hydrostatic Testing Only
2. Piping with Quality Control by Hydrostatic and Non-Destructive Testing (e.g., Radiographic Testing [RT], Ultrasonic Testing [UT])

 Estimating Pipe Welding Man-Hours

In modern piping projects, contractors use detailed engineering methods, such as isometric drawings and pipe models, to facilitate efficient construction in the workshop and easy assembly on-site.

Piping Works and Spool Fabrication

Each isometric line is divided into sections called spools, which are fabricated in the shop. After manufacturing, these spools are transported to the construction site for adjustment, positioning, and final welds.
Typically, with well-planned engineering, 70-90% of the welds are performed during prefabrication, significantly reducing costs and man-hours.
This also helps meet construction deadlines by minimizing the impact of adverse weather conditions on-site.

Benefits of Shop vs. Field Welding

It is well-established that welds made in the shop are faster and offer better quality control than those performed in the field.

Welding times vary depending on several factors:

• Material Type: This guide focuses on carbon steel pipes.
• Pipe Thickness: Thicker pipes require more time for bevel preparation and welding because more material needs to be filled.
• Pipe Diameter: Larger diameter pipes are more challenging to handle and weld.

Standard Welding Times for Carbon Steel Pipes

Type 1: Welding with Hydrostatic Testing Quality Control Only

• For a standard 4-inch carbon steel pipe:
  • Field Welding: 0.70 man-hours per inch of welding
  • Prefabricated Welding: 0.40 man-hours per inch of welding
• With a crew (helper, journeyman, and welder) working 10 hours per day:
  • Approximately 42 inches per day can be welded in the field.
  • Approximately 75 inches per day can be welded in the shop.

Note: These times apply under standard working conditions without economic incentives for higher performance. For more detailed insights, see "Estimator's Piping Man-hours Tool."

Type 2: Welding with Hydrostatic and Non-Destructive Testing Quality Control

• For the same 4-inch carbon steel pipe:
  • Field Welding: 2.0 man-hours per inch of welding
  • Prefabricated Welding: 1.0 man-hours per inch of welding
• With a crew working 10 hours per day:
  • Approximately 15 inches per day can be welded in the field.
  • Approximately 30 inches per day can be welded in the shop.

Note: These times also apply under standard working conditions. For further information, please refer to "Estimator's Piping Man-hours Tool."

Important Considerations for Pipe Welding Man-Hour Calculations

The welding time calculations include only the following:

• Piping welding

They do not account for:

• Complicated pipe handling
• Painting
• Insulation
• Supports and clamps
• Scaffolding for piping

Conclusion: Optimizing Welding Man-Hours

A quick estimation of welding man-hours is essential for making informed decisions in project management.
By utilizing historical performance data and taking into account factors like material, thickness, pipe diameter, and carbon steel pipe grade, project managers can swiftly quantify the piping job. Although this quantification is an estimate, it serves as an invaluable tool for effective project management

Piping Works

Estimator's Piping Man-hours Tool

In the book "Estimator's Piping Man-hours Tool" you will find complete information on how to calculate the total man-hours required to fabricate and assemble this section of piping.

The book includes the man-hours required for fabricating and assembling supports, painting, and welding pipes of all diameters. It includes examples, illustrations, and tables.

Example

Only the hours required to weld the piping shown in the figure below will be analyzed in this example.

We emphasize that the total welding hours for the pipe section in the figure are based on historical welding times that the author has confirmed in numerous works.

Task Summary

Estimate the number of welding man-hours required for the section of pipe between joints 1 and 10 (see Figure 1).

The welding man-hour estimate between joints 1 through 10 is made by applying the verified performance tables contained in this author's book. (This will give you the HRTW, which is Hours Required per Table for Welding). 

These man-hours will have to be corrected in order to fit this particular project.

Materials List

Diameter of the pipe 4" A 53 SCH 40

Elbow 90 ° RL NPS 4", butt weld end A234 Gr B

Standard Flanges NPS 4" S 150#.

Gate valve NPS 4" S 150#

Steps to execute the Estimation

1 Man Hours for Assembly and Welding

To obtain the man-hours required for this task, use the labor rates shown in the tables in this book.

As shown in the table, the total number of man-hours is 22.80 man-hours.

Comparison

To compare, let us now see what the man-hours would be if we were working with prefabricated pipes.

Man-hours for assembly and welding if you are working with pre-fabricated parts

With prefabricated parts, the only welds that are carried out on site are the first and the last (marked in red), so the table of total hours of assembly and welding with prefabricated joints is:

Note:

To execute each weld bead in precast, 1.25 hours are used.

The total number of man-hours for this case is 16.55.

Corrections to be made

For each specific project, the estimated hours per table need to be corrected.

We refer to this as "Correcting to Fit":

A correction for the variables.

Correction for project location.

Correction for the type of piping material to be used.

Correction for prefabrication or spooling.

A- CORRECTION FOR VARIABLES

CORRECTION FOR VARIABLES; or correction for the influence of variables that affect the historical times of our tables.

The variables listed below are not the only ones, and it is the estimator's responsibility to define them for each budget.

• Contractor's experience in the execution and supervision of similar projects.
• Degree of precision of the information for quoting.
• Degree of labor and union demands.
• Rating for the type of soil at the construction site and ease of access to the site.
• Rating for the climatic conditions where the work will be carried out.
• Rating for the height level of the work plane, where the work is carried out.

We proceed to weigh the correction for variables, to be applied in this project:

1- Contractor's experience in the execution and supervision of similar projects.

Has your company implemented projects of this type? How often? What is the experience of monitoring these projects? Is there qualified and experienced personnel?

English:Answer: If the Contractor has experience in carrying out this type of work, this variable is weighted at 100/100.

2- Degree of precision of the information for quoting.

Is the quality of the preliminary engineering sufficient to quote accurately? Was a site visit carried out prior to the estimate with experienced personnel, who reviewed all the aspects that will influence the performance of the resources?

Answer: For this project, which is a simple task, the variable is weighted at 100/100.

3- Degree of labor and union demands

What are the work schedules? Will work also be carried out at night?

Working at night not only affects the hourly rate, but also the worker's performance.

The characteristics of the union of the trade where the worker works must also be evaluated.

For example, if the union requires the Contractor to take a percentage of the workers who are going to carry out the work from its union job pool, this could affect performance.

English: Answer: In our project, the task is of little importance and correction for the degree of labor and union demand does not take place.

We are certain that the Union of the area does not intervene in these sizes of facilities.

The variable is weighted at 100/100.

4 - Rating for the type of soil at the construction site and ease of access to the site.

What is the condition of the site? Is it low and muddy, and difficult to drain, or is it high and dry? Does the staff have to travel long distances to get to work? Are the access roads passable?

Answer: In our case, it is a covered place with a stable concrete floor and easy access to the work area.

The variable is weighted at 100/100.

5 - Rating for the weather conditions of the area where the work will be carried out

What are the historical weather conditions in the project area? What are the future weather forecasts? Will there be a lot of rain, wind or snow? What differences are expected in the climate compared to where our workers usually work?

Answer: The workplace is ideal because it is an enclosed space, so there is no decrease in performance due to climatic factors.

In this work, the weighting of this variable is 100/100.

6 - Rating by height level of the work plane, where the work is carried out

The hours recorded in tables correspond to tasks carried out on work planes that do not exceed heights of 2.00 m. If the work heights are greater, corrections must be made.

At what height will the work be carried out? Are work times increased due to the handling of materials, equipment and personnel to get to the job site? Should times be considered for setting up scaffolding?

Answer: There is no loss of performance because the work plane is at floor level.

The variable weight is 100/100.

Final result of correction for variables in this example.

Next, we calculate the EFV (Efficiency Factor by Variables) this factor is the sum of the variables considered from point 1 to 6 divided by the number of variables and gives us 1.

In short, we have no impact on returns due to the effect of the Variables.

B - CORRECTION BY LOCATION

CORRECTION BY LOCATION or correction in the case that the work is carried out within an operating plant or is a new construction in an isolated site.

When the work is going to be executed within the facilities of an operating plant, the importance of the correction is linked to the characteristics of said plant.

For this particular project and our own experience, 5% more hours are added due to the fact of working within an operating chemical process plant.

In other words, the total hours will be:

22.80 x1.05 = 23.96 hrs

C - CORRECTION BY MATERIALS 

The times we saw apply to ASTM A53 Gr A/B, EWR A-53 / API 5L PSL2 Gr B steel pipes

When the materials of our work are different, a conversion factor must be applied for the change in material, which we call k (Specific topic that we will develop in Manuals No. 2 to 8)

In this case, the elements of the section are of similar quality to that used to calculate the yields recorded in our tables, so the conversion factor k is 1 and the total hours are not modified.

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Diameter inch calculation

Inch Diameter Calculation 

How are inches of weld in piping counted?

The number of diametrical inches welded depends on the design and specifications of the piping system.

For example, a piping project typically involves the installation of pipe runs and fittings of different diameters, with each welded joint contributing to the count. It is necessary to consult the piping drawings, specifications or project documentation to determine the exact number.

Here is a typical case of how to count inches of weld using the picture in the book: "Estimator's Piping Man-hours Tool"

 Number of Inches of Weld

Diameter Inch Calculation. The illustration above shows a discharge line starting at the discharge flange (2 1/2" diameter) of a centrifugal pump, then connecting through a 2 1/2" x 4" concentric reducer to a 4" diameter line terminating in an NPS 6" manifold.

To count the number of inches, count the welds according to the following table.

We notice that for the number of welds, we only consider the diameters of the components of the section we are considering. In the next entry we will analyze how the thickness (SCH), the tube materials and the external conditions affect the welding times for the same pipe diameter.