Ni Interlayer to Improve Low-Pressure Diffusion Bonding of 316L SS Press Fit Tube-to-Tubesheet Joints for Coiled Tube Gas Heaters

Abstract

This study suggests a new approach to diffusion bonding (DB) 316L stainless steel: a low-pressure procedure that includes a nickel interlayer. In this approach, relatively lower pressure is applied to the sample before the DB process, in contrast to the usual approach in which higher pressure is applied during the DB process. This new procedure was tested on mock-up 316L stainless steel tube-to-tubesheet joints, which simulated similar joints in coiled-tube heat-exchanger applications. This study confirms that the new procedure meets the overall success criteria, namely, a pull-out force exceeding the force required for tube rupture. It also shows that the DB joint is improved by the use of a Ni interlayer; the joint strength increased by approximately 33% for a 0.25 μm Ni interlayer and by approximately 18% for a 5 μm Ni interlayer. The joint cross sections were qualitatively examined using optical microscopy (OM) and scanning electron microscopy (SEM); the observations suggest that only portions of the interface were diffusion bonded, as a result of the low-pressure procedure and the surface roughness (due to the sample fabrication). The portions that were diffusion bonded, though, were sound, as characterized by the fact that the steel grains grew through the interface line to create a continuous metallographic structure.

Impulse Pressure-Assisted Diffusion Bonding (IPADB): Review and Outlook

“…In a first step, pressure is used to deform the asperities and thus increase the area of contact between the two mating surfaces. The quality of the surface finish is an important factor in diffusion bonding as larger asperities need to be overcome if surfaces could not be properly polished in preparation of the diffusion bonding process [3,4]. The applied force will further break the protective oxide layer of the mating surfaces and create interfacial boundaries.…”

Diffusion Bonding and Transient Liquid Phase (TLP) Bonding of Type 304 and 316 Austenitic Stainless Steel—A Review of Similar and Dissimilar Material Joints

“…Taking advantage of different coefficients of thermal expansion to generate pressure for diffusion bonding is not unusual [60][61][62] and can be complemented by clamp-like apparatuses that apply compression using screws [63][64][65][66][67]. If the sample geometry allows it, parts can also be press-fitted and put under pressure into a vacuum furnace where they are then diffusion bonded when the temperature is increased [68][69][70]. If no relevant pressure was applied [67,[71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87], the experiments were not reported here since we considered them brazing rather than diffusion bonding using the definitions introduced earlier.…”

Diffusion Bonding of 9Cr Martensitic/Ferritic Heat-Resistant Steels with an Electrodeposited Ni Interlayer

“…Nevertheless, the bonding temperature, time, and pressure during the diffusion bonding process can be reduced by using the interlayer; meanwhile, it can also improve the joint qualities. In order to improve the joint qualities and reduce the bonding parameters, Reuven et al [16][17][18] did a lot of work to join 316L stainless steels by diffusion bonding using electroless nickel plating as interlayer. Tiwari et al [19] studied the effect of nickel nanoparticle (NiNP) interlayer application to diffusion bonding of stainless steel.…”