Prakt. Met. Sonderband 38 (2006) 347 
CASE STUDY ON A DEFECTIVE PLATE HEAT EXCHANGER 
ar P17650- R. Haubner, S. Strobl 
Institute of 
e residual University of Technology Vienna, Institute of Chemical Technologies and Analytics, 
Vienna, Austria 
ABSTRACT 
‘superlong 
)0 A defective plate heat exchanger is investigated and the main aim is to find the reason for 
rbide and that damage and how this can be avoided. The plates are made of stainless steel 
eels”, Int J (Cr17Ni12Mo2, material No. 1.4401) and are brazed with pure copper. 
After cutting and examination of the heat exchanger no relevant corrosion of the copper 
ion fatigue braze is observed. Metallographic investigations by light optical microscopy (LOM) show 
1998, 661- that copper has diffused into the steel plates (liquid metal embrittlement). Using various 
etchings the areas of the steel plates, which are influenced by the copper diffusion, 
Work Tool become visible, and also an additional phase is observed. Electron beam micro analysis 
jue Crack (EBMA) and microhardness measurements show that this phase is a chromium-rich ferrite. 
35A, 2004, The observed phenomena can be explained by a too high brazing temperature. 
efects and 
act Engng 1. INTRODUCTION 
ith Internal Brazed plate heat exchangers are widely used for the heating or cooling of liquids. They 
ns A 152, are very effective compared to their low costs. Mostly stainless steel is used for the plates 
and copper for brazing. 
from gas- For the manufacturing of such heat exchangers the plates are contacted with braze films 
and put together in a furnace. For a better mechanical stability all contact points between 
iethods for the plates are brazed too. Vacuum brazing is one possibility for the final brazing process 
rials”, Conf [1]. 
As this type of heat exchangers is often used with drinking water, corrosion and failure are 
on fatigue possible. In literature different explanations for the failure can be found. 
Mat Struct = The copper braze can be attacked by the water and intergranular corrosion is 
reported [2]. 
sverhalten = Also the corrosion of the copper braze is explained by galvanic contact corrosion and 
i water chemistry. Additionally stress induced corrosion is observed in the stainless 
operties of steel plates [3]. 
s, Vienna, — In one case the corrosion is explained by carbide formation at the grain boundaries 
and intercrystalline corrosion [4]. 
rgestellten 
; In this work a heat exchanger, which got a leakage and had to be changed, is examined. 
he elastic The main question is the reason for this damage and how it can be avoided. The plates 
J Alloys consist of stainless steel (Cr17Ni12Mo2, material No. 1.4401) and the braze is copper. 
. Also in this case all the contact points between the plates are brazed. Therefore it is nearly 
> cracks in impossible to find the defective area. 
at Struct 7, Metallographic preparation as well as light optical microscopy (LOM), scanning electron 
microscopy (SEM) and electron beam micro analysis (EBMA) are used to investigate the 
heat exchanger