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If your oven is big enough, you will need only one machine.

The specific heat of steel is about 0.12, if memory serves; but please check.

Miscellaneous losses (heat leakage through insulation, heat going to air but not to the piping, etc.) might amount to say 20%-40% of the total heat supplied. This will vary according to your setup.

One watt = 3.41 Btu/h.

The power consumption of each machine is stated on the manufacturer's rating plate attached to it and the manufacturer's instructions supplied with it.

The number of machines required is determined by the time that each machine is in service on each joint and the maximum duration of the test interval. For example, for 2000 joints at 8h per joint, 16000 machine-hours are needed. If there is only 1 week working 24h per day on this task, then 96 machines are needed. However, if the machine can be taken off the pipe after the soaking time then only 10000 machine hours are needed, and in a week at 24h per day then only 60 machines are needed. Whatever number of machines multiplied by the individual machine's power rating gives the total power required. Get the idea?

There is likely to be a balancing act going on between the aggregate power requirements and the duration of the tests. Without knowing the details, the hunch here is that the power limit of the supply will influence the duration of the test period and also limit the number of machines that could be used.

Most PWHT machines have multiable outlets. Depending on the size of the pipe you may use one or as many as six outlets. Most heat treat machines have six or twelve outlets. They usaly need a single one hundred amp supply for a six outlet machine and either two one-hundred amp supplies or a single two-hundred amp supply. Most of the time the machines will not be fully loaded and not draw full amperage. But since the machines have 3- phase primarys and single phase outlets it is easy to load one phase to full amps.

Two questions: Are you doing these welds in situ or in a fab shop? What is the time frame you are working to. There are several companies that do this and would be glad to give you a quote that would include the information you need. If you are doing the PWHT in a fab shop you should consider a combustion fired furnace. Useing popane or natural gas is much cheaper than gas. The furnace can be either permant or temporary. If you are doing these welds in situ or are doing them as indivual welds I would use the D10.10 guide lines regarding soak bands, gradient control bands. Since you are having two hour soak including the smaller sizes, I would be heating P5 alloy piping. If you are P91 pipe it inperative that you use the D10.10 guidelines. All welds will need hardness testing (weld, HAZ, pipe), on smaller pipe top and bottom, larger pipe need hardness checked top, bottom, and sides.