THE ECONOMICS OF HARDFACING  

Home Page

1.1 General

The importance of hardfacing is widely recognized.  There are many documented instances of savings that have been made in many industries by the use of hardfacing.

However, this does not imply that hardfacing is best in all instances and an analysis of the costs involved in hardfacing and other alternatives should be made.  The accurate calculation of costs involved may be quite complex, as many factors must be considered to determine whether hardfacing is cost effective.

This section explains in detail the factors involved in costing.  It is necessary that these factors be understood since their importance will differ from job to job and from workshop to workshop.  Labor and overhead will always be major costs and will vary depending on company, size, complexity, technology level and type of output.

  It is essential that each organization keeps accurate cost data concerning their own particular operation since reliable costing will be required for quotations, comparison between maintenance methods, evaluation of design and evaluation of welding procedures.

  While labor and overhead, and material costs are the easiest costs to identify in computing the cost of any hardfacing application, the following factors should be considered, since they also will impact the total cost of the job.

  (a)    Design

         The design or geometry of the original component will determine the amount of weld deposit required and ease of applying it.

  (b)    Position

         The highest deposition rates are achieved in the flat and horizontal positions.

  (c)    Process

         The welding process and process parameters (procedure) chosen will govern the time required as determined by deposition rate, deposition efficiency and operator factor.

  (d)    Costs

         Additional costs associated with the work such as transportation, machining, heat treatment and inspection.

  A comparison of deposition rates, expressed as pounds per hour, at different current setting is shown in Table 1.1.A.

Deposition efficiency is expressed as a percentage and is determined by dividing the weight of metal deposited by the weight of the consumable expressed as a percentage.  Efficiencies will vary with process as shown in Table 1.1.B.

Operator factor or efficiency is expressed as a percentage and is the effective deposition hours divided by total hours expressed as a percentage.  Time study methods or arc monitors are used to determine the operator factor and some typical factors are shown in Table 1.1.C.

Table 1.1.C. Operating Factors

*Semi automatic processes

Activities that affect the operator factor include:  preparation, setting up, idle time, instruction, crane time, preheating, deslagging, operator skill and degree of automation.

1.2. Hardfacing Cost Calculation

1.      Flux Cost (submerged arc welding only) per lb of weld metal deposited

               Unit Price ($/lb) x Consumption Rate (lb/hr) ÷ Deposition Rate of Wire (lb/hr)

                      (generally 1 lb of flux is used for each pound of wire deposited)

2.      Shielding Gas Cost (gas shielded processed only) per lb of weld metal deposited

               Unit Price ($/ft³) x Flow Rate (ft³/hr) ÷ Deposition Rate of Wire (lb/hr)

                                Example:   
                                   Argon/CO₂ @ $.15/ft³
                                   Flow Rate of 30 ft³ per hour                                    $0.15   x     30         =          $.64/lb
                                  Deposition Rate of Wire @ 7 lbs/hr                                    7

3.      Power Cost per lb of weld metal deposited

               [Unit price ($/kw hour) x kw per hour]÷ Deposition Rate (lb/hr)

                                  Example     Power Cost @ $0.126/kw hour
                                  Kilowatts = (welding volts x welding amps) ÷ 1000
                                  Voltage @ 21
                                  Current @ 200 amps                                       $0.126  x     4.2        =          $.08/lb
                                  Deposition Rate of Wire @ 7 lbs/lb                              7

4.      Welding Material Cost per lb of weld metal deposited

               Wire/Electrode Price ($/lb) ÷ Deposition efficiency (%)

                       Example     Welding Wire @ $5/lb                                                     $5                =          $5.26
                                           Deposit Efficiency @ 95%                                               .95

5.      Labor Cost per lb of weld metal deposited

               Labor Charge ($/hr) ÷ [Deposition Rate (lb/hr) x Operating factor (%)]

               Example     Labor Cost @ $25/lb                                                       $25               =          $5.95/lb
                                Deposition Rate @ 7 lbs/hr                                          7    x     .60
                                 Operating Factor @ 60%           

6.      Overhead Cost per lb of weld metal deposited

               Overhead price ($/hr) ÷ [(Deposition Rate (lb/hr) x Operating factor (%)]

               Example     Labor Cost @ $10/lb                                                       $10               =          $2.38/lb
                                 Deposition Rate @ 7 lbs/hr                                          7    x     .60
                                 Operating Factor @ 60%

7.      Total Cost per lb of weld metal deposited

Flux Cost + Gas Cost + Power Cost + Material Cost + Labor Cost + Overhead Cost

8.      TOTAL COST OF HARDFACED COMPONENT

  Note: Steel Density = 0.3 lbs/cu. in = .008kg/cu. cm

               Width of hardfacing (in) x Thickness of hardfacing (in) x Length of

               hardfacing (in) x Total cost/lb (7 above) x 0.3 = Total hardfacing cost

·   Metric Equivalent - Width of hardfacing (cm) x Thickness of hardfacing (cm) x Length of

                  hardfacing (cm) x Total cost/kg (7 above) x .008 = Total hardfacing cost

This calculation provides the means to determine the total cost of depositing a hardfacing layer of a given thickness based on a given width and length, with the deposited cost per pound previously determined.

1.3       Cost Advantage

The determination of the cost advantage of hardfacing over replacement enables management to reach an informed decision on whether to hardface a particular component.

  The cost advantage (CA) of hardfacing compared with a new component, in $ per unit output, is given by:

            Equation 1:      CA =    PC_N             PC_R
                                                  OP_N              OP_R

Where

PC_N       = Prime cost of new component = Cost of new component + downtime cost (new)

PC_R       = Prime cost of hardfacing ($) = Cost of hardfacing + downtime cost (hardfacing)

OP_N      = Work output during life of new component

OP_R     = Work output during life of hardfaced component

Where there is a positive cost advantage, hardfacing is likely to be the best solution, and an indication of the annual cost savings can be determined.

This simple equation for cost advantage does not take into account factors such as plant depreciation and replacement, cost of capitalization, taxation benefits, and other factors that may affect the decision.

Most of the data needed for the above calculation is relatively easy to obtain and will be available as predetermined costs in many shops.  The cost of hardfacing can be calculated using the method shown in Table 1.3.

Other factors may require consideration, such as the value of work output for the hardfaced component which may not be known and has to be estimated initially.

1.4.      Annual Cost Savings and Extra Expenditure

Where significant extra expenditure is required to implement a new hardfacing repair method which has a positive cost advantage from equation 1, a supporting case will normally be required by management.  Data required will include the annual cost savings and extra expenditure.

The annual cost savings (CS) expressed in $/year by using hardfacing instead of a new component is given by equation 2:

Equation 2:                  CS = CA x PR

CA       =    Cost advantage from equation 1 ($/unit output).

PR       =    Production rate (Averaged over the year including downtime, and here

                  assumed equal for both new and repaired components) (unit output/year).

Home Page