Metal tubes bonded together without heat application or brazing materials retain strength at elevated temperatures, and when subjected to constant or cyclic temperature gradients. Combination drawing and expansion process produces residual tangential tensile stress in the outer tube and tangential compressive stress in the inner tube

Hymes, L. C.

Stone, C. C.

English

NASA Technical Reports Server

March 1971	 Brief 71-10050 
•	
CO. 
	
(2	 AEC-NASA TECH BRIEF 
AEC Headquarters 
AEC-NASA Tech Briefs announce new technology derived from the research and development program of the U.S. 
AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial application. Tech Briefs are 
available on a subscription basis from the National Technical Information Service, Springfield, Virginia 22151. Requests 
for individual copies or questions relating to the Tech Brief program may be directed to the Technology Utilization 
Office, NASA, Code KT, Washington, D.C. 20546. 
Concentric Tubes Cold-Bonded by Drawing and Internal Expansion 
The problem: 
To form a strong mechanical bond between con-
centric metal tubes without the application of heat 
or brazing materials. The bond must retain strength 
at elevated temperatures and when subjected to con-
stant or cyclic temperature gradients. 
The solution: 
A combination drawing and expansion process 
that produces a residual tangential tensile stress in 
the outer tube and a tangential compressive stress in 
the inner tube. 
How it's done: 
The assembled tubes, with about 0.8 cm (0.03 in.) 
radial clearance, are first drawn through a die at room 
temperature to reduce their diameters. The assembly is 
then expanded at room temperature by drawing an 
oversized plug of commercial die steel through the 
inner tube of the assembly. This expansion strains 
both tubes beyond their elastic limits. No restraint 
is placed on the outer surface of the large tube during 
the expansion step. After the plug has moved through 
the entire assembly, the residual stresses produced 
cause the outer tube to clamp inward on the smaller 
tube and form a strong mechanical bond at the inter-
face between the tubes. 
Notes: 
1. A duplex (cold-bonded) steel tube, containing 
2.25% chromium, 1% molybdenum, 0.13% carbon, 
0.50% manganese, and 0.40% silicon, exhibited 
an interface shear of 12.4 MN/m 2
 (1800 psi) at 
room temperature and 6.9 MN/m 2
 (1000 psi) at
756°K (90017). The outer tube had an initial and 
final o.d. of 3.97 cm and 3.65 cm, respectively 
(1.563 in. and 1.438 in., respectively). A smaller 
duplex tube of the same material, with an initial and 
final o.d. of 1.74 cm and 1.51 cm, respectively (0.684 
in. and 0.594 in., respectively), exhibited an inter-
face shear strength of 31 MN/M 2
 (4500 psi) at room 
temperature. 
2. Tubes of different materials may be joined if the 
strain required to produce yielding of the outer 
tube is at least 75% of that required for yielding of 
the inner tube. 
3. Tubes of this type are used in condensers and heat 
exchangers. 
4. Requests for further information may be directed 
to:
Technology Utilization Officer 
Division of Technical Information 
AEC Headquarters 
Washington, D.C. 20545 
Reference: B71-10050 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Technology Utilization Officer 
Division of Technical Information 
AEC Heaquarters 
Washington, D.C. 20545 
Source: L. C. Hymes and C. C. Stone 
Metallurgy Division
(A RG-90033) 
Category 08 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000050 2020-03-17T02:18:21+00:00Z


Concentric tubes cold-bonded by drawing and internal expansion

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