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manufacturing can significantly compromise the effective heat transfer by allowing higher bypass / leakage streams between the tube-to-baffle hole and baffle-to-shell ( refer to sketch below ). Poorly finished baffle holes can cause scratch marks on the tube OD , during tube insertion and when the tubes move through the baffle holes due to thermal expansion during operation . These scratch marks can lead to failure of the tubes in a few years of continual service , especially in high pressure / temperature operating conditions . Hence , utmost care is needed in their manufacturing and assembly . However , baffles being a non-pressure internal part , their design and manufacturing requirements are not controlled by the codes . And so , the performance of a shell-and-tube heat exchanger is not addressed by the codes .
Baffles are baffling The baffles in a heat exchanger are baffling simply because there is a limitless variety to choose from , and you can never be sure . Even when you are close to selecting the right one , the outcome will fluctuate according to circumstances such as manner , time and place . Nevertheless , having made a choice , what delivers results is workmanship . Refer to the following link for the lesson we learnt with helix baffles : https :// bit . ly / 3u0vGJW Despite being the most crucial item ( after the tubes ) in the entire Bill of Materials ( BOM ) of a shell-and-tube heat exchanger , not much thought is given to baffles in fabrication drawing . This happens primarily because , being a non-pressure part , most manufacturers outsource the work of baffle drilling and machining , and the quality-control inspection agencies do not give it the required importance . All pressure parts such as shells , tubes and tube-to-tubesheet joints are produced with stringent code requirements and are often the witness / hold points . All joints are subjected to NDT , and finally , helium / pneumatic / hydro-tested . As a result , failures in the tube bundle - the core of the exchanger - are common . The most expensive part of the exchanger which can cost over half of a complete unit has to be periodically replaced . Tema India has developed standards for baffle-hole drilling and OD machining to substantially enhance the life of the tube bundle .
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The selection of appropriate material for baffles is important . Incorrect material selection can lead to the following problems .
• In an electrolytic shell-side fluid , the baffle may form an electrolytic cell with the tubes and baffle holes may get corroded , leading to bypass of fluid through this clearance . This increases the possibility of autofrettage wear of tubes during vibration .
• The baffle hole may expand much more than the tube , leaving it unsupported and increasing the bypass of fluid through this clearance .
Interference of specifications in manufacturing To reduce the risks in the procurement of critical equipment from less experienced equipment manufacturers , customers and EPC companies specify additional details in their datasheet and specifications which should otherwise be engineered by the equipment manufacturer . Of late , process licensors / customers have been interfering in the manufacturing methods of the tube bundles by insisting on specific constructional details that compromise the bundle instead of improving it . The following are some examples . 1 . Insisting on a very small baffle-hole-to-tube OD clearance ( regardless of tube OD , tube qty ., baffle spacing ). This creates hindrances for the insertion of tubes in the baffle ; particularly , in cases where the baffle spacing is less and thereby inducing stresses in tubes .
2 . Insisting on all-around welding of sealing strips / sealing rods with baffles as well as transverse
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