We present tensile test, stress amplitude fatigue life, and creeprupture data of six aa3xxx series tube. Cracks generally form at sharp corners, welds,and backside of the heat exchanger. The cause of cracked heat exchangers avoid this common scam. Structural stress based fatigue life evaluation for heat. Heat exchanger cracks can range in size from small, almost imperceptible fissures, to gaps wider than a half inch or more. Vibration excitation includes turbulence and lowlevel fluidelastic forces. The fatigue fracture of commercially pure cp titanium tubes at relatively low temperatures 120 c 250 f in a shelland tube heat exchanger was studied. Thermal expansion and contraction caused by alternate heating and cooling creates repetitive pulling and is a common cause for crack initiation. Failure analysis of tubetotubesheet welded joints in a shelltube.
Tensile, fatigue, and creep properties of aluminum heat. Heat exchanger tubes are vulnerable to tears and cracks due to accumulated stresses related to constant thermal cycling or high temperature differentials. The periodic load might come from the resonant vibration of the tube or the changes in temperature and pressure of the fluid inside the heat exchanger. Heat exchanger tube dents can result in stress corrosion cracks scc or fatigue cracking without any tube wall thinning. With the identification of the mode and root cause of the cracking, the failures were easily prevented by realigning the induction coil.
A combination of corrosive environments and repeated working of the metal may result in metal failure. Crack development in tube and tube sheet region of a stainless steel heat exchanger is a common problem. Have you heard this one recently, you have a cracked heat exchanger and your furnace has to be replaced, today. Vibrations and fatigue are the examples of most dangerous causes that can cause failure. The first step in boiler tube failure analysis by ais is to perform a visual inspection of the failed tube. The methodology incorporates monte carlo simulations to predict remaining service life of a vibrating heat exchanger tube with a small circumferential throughwall crack next to the tube sheet. The fatigue crack initiated from the defects at the tubetotubesheet welded joint. Sample piece of economizer inlet header showing crack. Repeated thermal cycling can lead to fatigue in shell and tube heat exchangers. Fatigue cracking of titanium tubes in an industrial heat. Excess environmental vibration from equipment including air compressors, refrigeration machines or other motors can cause tube failures that form as a result of fatigue stress cracks and or erosion where the tubes make contact with the baffles. Intergranular stress corrosion cracking, pitting, thinning, denting, tube fretting and wear, fatigue cracking and erosioncorrosion. Shell tube heat exchangers are widely used in chemical, petroleum, medicine and nuclear industries.
Excessive fluid velocity on either the shell or tube side of the heat exchanger can cause damaging erosion as metal wears from the tubing. Pitting, heat exchanger tube, stress corrosion cracking, corrosion fatigue cracking. Selecting reliable heat exchanger tube materials factors to consider presented at. This one is about a crack i found in a heat exchanger that caused no symptoms. What causes a heat exhanger in a furnace to crack and fail. Heat exchanger cracks can range in size from small, almost imperceptible fissures, to gaps wider. The nature of the aggressive conditions and the metal involved are not specific. Welding techniques used for materials also decrease fatigue resistance in them. Fatigue cracking of titanium tubes in an industrial heat exchanger.
Tube roll expansions in tubesheets resulting in fatigue failure due to stress raisers introduced by faulty mechanical roll expander, stress corrosion cracking at overroll locations at tubesheet intersections, crevice and wastage corrosion in open tubesheet crevices, stress corrosion cracking. The study of failure analysis of shell and tube heat exchangers will help to understand methods to analyze various types of failure in shell and tube heat exchangers. Tubes are the most critical part of the most heat exchangers made from aluminum brazing sheet. There are various causes by which heat exchanger may fail. Failure analysis of stress corrosion cracking in heat. Thermal fatigue in hvac heat exchangers hvac investigators. Ppt on failure analysis of shell and tube heat exchangers.
The fatigue crack initiated from the defects at the tube totubesheet welded joint. The fatigue fracture of commercially pure cp titanium tubes at relatively low temperatures 120 c 250 f in a shellandtube heat exchanger. Tube heat exchanger an overview sciencedirect topics. Let us check how the fatigue problems can be avoided with the help of great designs and changes in manufacturing practices. The fatigue is brought about by a routine cyclic application of stress. In this white paper, we show that fatigue problems can be. Failure analysis of tubetubesheet welds in cracked gas. A clogged air filter restricts airflow through the furnace, overheating the heat exchanger, and eventually resulting in stress cracks. Best practices for eddy current testing of heat exchanger. Stress corrosion cracking of heat exchanger tubes in district. The tube supplier quickly provided new defect free tubing, and the heat exchanger.
Plateandshell heat exchangers have become very popular over the last decades thanks to their high thermal efficiency, compact size and ability to withstand high pressures. The detection of circumferentially oriented cracks in heat exchanger tubing is difficult to detect with the usual bobbin probes for two reasons. Eventually, fatigue cracks can span the diameter of the tube and completely sever it. Fatigue can cause cracking in the tubes beginning with small, hardtosee striations that can quickly grow larger. The periodic load might come from the resonant vibration of the tube or the changes in temperature and. Heres why your furnace heat exchanger cracked heating. Tube vibrations have resulted in failure due to mechanical wear, fretting and fatigue cracking. Heat exchangers should be isolated from this type of vibration. A look at a heat exchanger crack that cant be found youtube. The combined stresses resulted in numerous intergranular cracks in circumferential direction. Boiler tube failure analysis is about corrosion, stress.
Heat exchangers failure analysis metallurgical technologies, inc. No individual nondestructive testing ndt technique is. In hvac heat exchangers, thermal fatigue is accelerated by the corrosive combustion gasses that pass through the heat exchanger tubes on their way to the exhaust flue and by condensation that may collect in the heat exchanger during heat transfer. Structural stress based fatigue life evaluation for heat exchanger motor operated valve. Services are provided by customers who buy our equipment and have.
A probabilistic assessment technique applied to a cracked. An oversized furnace can also cause overheating and heat exchanger cracks. However, many companies have discovered that this type of heat exchanger is sensitive to metal fatigue. Bad welding and unsuitable expansion position of the tubes at the tube. Analysis of t11 boiler superheater tube rupture summary. Selecting reliable heat exchanger tube materials factors. Fatigue cracking heat exchangers that have straight or ubend tubes can be inspected with our rigid or flexible probe. Such crack is propagated by stress corrosion cracking or thermal fatigue, or localized corrosion. Collection and analysis of commoncause failures of heat.
Pdf an experimental study of thermal fatigue on astm a 2. Then make preliminary observations and make suggestions on how to proceed in the boiler tube failure analysis or heat exchanger tube. Sometimes it is a design issue, sometimes it can be attributed to poor maintenance. A heat exchanger tube that suffers cracking can cause operational failures in power generators and steam generators, including chemical plants and oil refineries. The causes of cracking in the closing circumferential tubetubesheet welds of five cracked gassteam heat exchangers in a petrochemical plant were studied, in order to identify the. Thermal fatigue occurs when extreme temperature differences between the shell and tubes result in tube flexing. What caused my heat exchanger to fail check out these. Collapsed and ruptured copper tube resulting from steam hammer. Failure analysis of tubetotubesheet welded joints in a.
Ppt on failure analysis of shell and tube heat exchangers slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. The cp titanium tubes were subjected to flowinduced vibration and compression axial loading in service. Six causes of heat exchanger tube failure fluiddynamics. The most common cause of an overheated heat exchanger is as simple as a dirty air filter. The cause can be improperly adjusted burners or a cracked heat exchanger. As they are used at wide range of temperatures hence there is possibility that crack may induce in it and can cause. Stress corrosion cracking of steel in liquefied ammonia service a recapitulation. Bad welding and unsuitable expansion gave rise to the formation of initial cracks. How to minimize fatigue problems in plateandshell heat. The bobbin coil creates eddy currents in the tube wall which flow in the circumferential direction.
This video is part of the heating and cooling series of training videos made to accompany my. Leakage calculations are made on the throughwall crack. Utilizing highquality instrumentation and probing is the best way to detect anomalies and flaws during the early stages and prevent critical failures down the line. Any corrosion already present is accelerated as erosion removes the tubes. Fatigue failure of welded joints in a shelltube heat exchanger was analyzed. Examining the entire heat exchanger process and optimizing it based on fatigue related issues is the most efficient way to reduce fatigue. And when heat exchangers do crack, the failure not only results in. Since automotive heat exchangers are operated at varying temperatures and under varying pressures, both static and dynamic mechanical properties should be known at different temperatures. Fatigue crack initiated from the defects at the tubetotubesheet welded joint. The nature of the aggressive conditions and the metal involved are.