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# How to consider the heat preservation time of thin-walled pipe fittings

Dec. 15, 2020

For forged pipes, the effective size of a long pipe and the state with both ends closed is 4×the wall thickness of the pipe; the effective size of a short pipe with open ends is 2×the wall thickness of the pipe. Holding time = effective size × overall heating coefficient.

There are many methods for estimating the quenching heating time of long pipe fittings. In practice, the heating time obtained by the empirical formula is quite different from the actual heating time. When the ratio of tube length L to tube outer diameter 2R L/R>2.5, the shape has a greater influence on the quenching heating time. If the long pipe is converted into a bar of equal length, and the heating time is estimated with the diameter of the bar 2V, more accurate results can be obtained.
The conversion method is to treat the pipe fittings as equal-length bars of equal volume, and find the radius R′, that is, π(R2-r2)L=πR′2L

In the formula, r and R are the inner diameter and outer diameter of the pipe respectively, mm, δ are the wall thickness of the pipe, mm, δ=R-r. The factors that affect the heating time of long pipe fittings are related to the outer diameter and wall thickness of the pipe.
For structural steel pipe fittings, they are heated in an ordinary electric furnace, the effective size is D=2R′, and the heating coefficient α=0.8~lmin/mm according to the zero heat preservation heating process. Furnace loading factor K=1, single-layer close-packed arrangement. Heating and holding time T=α×D×K(min).