Two-Step Hydraulic Tube Expansion for Heat Exchanger Integrity
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Solution Overview
Problem
Conventional tube expansion methods can lead to the formation of recessed portions on the inner surface of heat exchanger tubes due to damage along the circumferential direction of the tube hole, resulting in local residual stress and stress concentration during thermal expansion.
Innovation Solution
A two-step hydraulic tube expansion method is employed, where the first step expands the tube at 15% to 70% pressure to fit the outer surface to the damaged area, and the second step expands the remaining areas at 100% pressure to ensure a uniform inner diameter and close contact with the tube hole, preventing recessed portion formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-step hydraulic tube expansion is performed at 100% pressure to ensure complete contact between the tube outer surface and tube hole inner surface, then the tube expansion completeness is improved, but recessed portions are formed on the inner surface of the heat exchanger tube due to damage on the tube hole inner surface
Solution Approach 1:
The tube expansion process is divided into two distinct steps: a first hydraulic tube expansion step at 15% to 70% pressure and a second hydraulic tube expansion step at 100% pressure. This segmentation allows the expansion to be performed in stages, first addressing damaged areas at lower pressure and then completing the expansion at full pressure, thereby preventing recessed portion formation while ensuring complete contact.
Solution Approach 2:
The first hydraulic tube expansion step is performed as a preliminary action before the second step. By initially expanding the tube at reduced pressure (15% to 70%), the tube outer surface is pre-positioned to avoid the damaged areas on the tube hole inner surface. This preliminary action prevents the formation of recessed portions before the final high-pressure expansion is applied.
2Manufacturing precision
If hydraulic tube expansion is performed at high pressure to ensure uniform inner diameter, then the tube dimensional uniformity is improved, but stress concentration occurs due to expansion along damaged areas
Solution Approach 1:
The expansion process is segmented into two pressure stages. The first stage at 15% to 70% pressure prepares the tube without forcing it against damaged areas, while the second stage at 100% pressure achieves uniform inner diameter. This segmentation prevents stress concentration by avoiding high-pressure expansion along damaged surfaces.
Solution Approach 2:
The first hydraulic expansion step serves as a preliminary action that positions the tube to bridge over damaged areas before the second high-pressure step. This preliminary positioning ensures that when 100% pressure is applied in the second step, the tube maintains uniform inner diameter without concentrating stress at damaged locations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively prevents recessed portion formation on the inner surface of heat exchanger tubes, reducing local residual stress and stress concentration during operation.
Implementation Method 1
a first hydraulic tube expansion step of performing a hydraulic tube expansion in a range including the damage at a pressure of 15% to 70%
Implementation Method 2
stress concentration may occur due to thermal expansion during operation of the heat exchanger
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(f)
Figure 3
AI summary
A tube expansion method of fixing a heat exchanger tube (105) inserted to a tube hole (104a) of a tubesheet (104) by tube expansion including: when there is damage (104b) along a circumferential direction with respect to an inner circumferential surface in the middle axis of an axis (S1) direction of the tube hole, a first hydraulic tube expansion step of performing hydraulic tube expansion at a pressure of 15% and 70% in a range including the damage, and thereafter, a second hydraulic tube expansion step of performing each liquid tube expansion at a pressure of 100% in each range divided except the damage.