1 Steam Cars : Phorum
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Flanged Fittings
Posted by: Peter Heid (IP Logged)
Date: March 18, 2002 07:31PM
<HTML>In my post on corrosion mentioned the use of non metallic gaskets to prevent galvanatic corrosion between dissimilar metal junctions. The use of flanged fittings seems to be the only way to accomplish this but flanged fittings seem to be limited to temperatures of about 700 to 750 degrees F.. Above this point, the bolts will relax and only certain alloy bolts or studs are recommended for temperatures in the 400 to 750 degree range. Relaxation is when some of the elastic strain changes to plastic strain, in essence, tension becomes stretch or creep. Cold torque of the bolts should be enough to provide 30,000 pounds per square inch minimum. Harder gasket materials may require as much as 60,000 psi for initial cold seating. Studs with a 125,000 psi proof strength are available in only three alloys and these are dependant on the size. Studs from 1/4 to 3/4 are available in 4037 alloy, 3/4 to 1 1/4 inch are in 4140 alloy and 1 1/4 to 2 inch are the 4145 alloy. These alloys were selected for a minium tempering temperature of 850 degrees F.. The nut used is of less importance because the shear area of the threads is usually about twice the tensile stress area of the bolt. Grade 8 nuts are suitable preferably of the stronger, fine thread version.
A 1/2 inch 600 pound flange requires 4, 1/2 inch bolts while 3/4 to 1 1/4 inch must use 4, 5/8 inch bolts. A 900 pound flange and higher requires 4, 3/4 inch bolts for 1/2 and 3/4 inch pipe sizes.
To torque bolts to 30,000 psi requires 30 foot pounds for 1/2 inch bolts, 60 for 5/8 and 100 foot pounds for 1/2 inch bolts. To achieve 60,000 psi the torque values must be doubled. A high temperature lube must be used on the threads and bearing faces to reach the correct torque. Dry threads require 75 to 100% more torque effort to reach the desired tension. A 30,000 psi tension results in aproximately .001 inch elongation per inch of effective stud length or the distance from the inside of one nut to the outside of the other. The length is often measured on a few, in service test bolts to determine the amount of creep that has occurred.
This information is dated about 1970 and should be verified before construction is begun.
Peter Heid</HTML>
A 1/2 inch 600 pound flange requires 4, 1/2 inch bolts while 3/4 to 1 1/4 inch must use 4, 5/8 inch bolts. A 900 pound flange and higher requires 4, 3/4 inch bolts for 1/2 and 3/4 inch pipe sizes.
To torque bolts to 30,000 psi requires 30 foot pounds for 1/2 inch bolts, 60 for 5/8 and 100 foot pounds for 1/2 inch bolts. To achieve 60,000 psi the torque values must be doubled. A high temperature lube must be used on the threads and bearing faces to reach the correct torque. Dry threads require 75 to 100% more torque effort to reach the desired tension. A 30,000 psi tension results in aproximately .001 inch elongation per inch of effective stud length or the distance from the inside of one nut to the outside of the other. The length is often measured on a few, in service test bolts to determine the amount of creep that has occurred.
This information is dated about 1970 and should be verified before construction is begun.
Peter Heid</HTML>
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