Non-Automotive Issue

[MikeSimon]

I would like to pick the collective brainpower of the members for something that stumps me:

I am working on the revision of an assembly method for an industrial heating unit (used to heat a car storage facility)
It is basically a heavy-duty radiator filled with hot water/steam and a fan that blows air through it through a set of ribbed heat exchangers.
All the components are cast iron and rather heavy.
The radiator consist of an upper and lower manifold and said heat exchangers.
The manifolds are bolted to the heat exchangers by means of hollow "nipples" through the holes that also conduct the medium.
The threads are 1" straight.
Between the flat machined surfaces of the manifold and heat exchangers sit flat 1/32" thick copper washers that function as seals.
The assembly instructions say to use 450 lbs-ft to tighten the nipples. That's my issue.
That seems like an awfully high amount of torque and I believe has been specified because the copper seals are solid flat washers and not crush gaskets.
The units are tested with a water pressure of 500 PSI, which I assume is the max pressure in operation.
I would like to replace the flat washers with crush gaskets and lower the torque.

Any thoughts?

[wayne R]

Mike sounds  like would be better idea, what size are the nipples that require that high tension,
When i see my torque wrench that only goes to 150ft pd, makes you wonder.regards.