Welding - cost of preheating

[WeldUK]

Dear All,

I am a welding engineer working on a spreadsheet to estimate fabrication cost. Whilst the cost of welding alone is 'relatively easy' to estimate (considering duty cycles, labour costs, equipment depreciation etc), I am struggling with the cost of preheating.

I have found formulas in literature to calculate the power required, hence the energy costs. However, the majority of costs associated with preheating is due to labour and equipment (especially for resistance heating).

Does anyone have any suggestions? The estimate needs to be sensible, but not extremely accurate. I would be happy with something better than the current "let's just use the same cost as we assumed for the previous projects"

 

[metengr]

Normally, for preheating costs we either request a quotation or proposal from a preheat/PWHT subcontractor or a mechanical contractor who subcontracts this service, if preheating is going to involve electric resistance heating blankets. Preheating using rosebud torches would be through a mechanical contractor and that is based on labor cost and gas use.

What I am trying to tell you is your cost will depend on type and application of preheat – gas or blanket heating.

 

[WeldUK]

Thanks metengr, I am trying to work out costs for those shops that carry out preheat and PWHT directly, without subcontracting. I have split between flame and resistance and I have calculated the cost of gas/electricity, but labour depends on too many factors (especially for blanket heating.)

However, the more I consult people and read publications, the more I realise it is not possible to provide a 'one size fits all' method for preheat cost calculations, there are too many variables which cannot be quantified.

Besides, as you say, so many welding shops contract preheat and PWHT out hence receive a specific quote.

 

[metengr]

WeldUK;
You are spot-on by recognizing the fact that “one size fits all” is not a correct approach for estimating costs. Estimating preheating costs as well as PWHT cost is like trying to estimate the cost of welding consumables for each specific job. I do believe if you were to solicit requests for proposal from organizations that provide field pre and post weld heating, you should be able to obtain a per job ball park estimate.

 

[Guest102023]

I expect there is a lot of variation between shops. Which I guess repeats the "one size fits all" comment above.

Some shops who leave it to the whims and folk knowledge of their workers might not do it efficiently, or even satisfactorily. (There are still welders who believe preheating is what the first weld pass is meant for.)

Others have done the math, and preheat using the most efficient methods that suit their operation and products.