Heat Transfer tubesheet thickness-this is more rigid compared to tack welding impingement rods on the back face of the tubesheet. The authors have encountered heat exchangers in which impingement rods were fillet- or tack-welded; due to a lack of accessibility, the welder may have been unable to deposit a continuous fillet weld. This quality deficiency caused the impingement rods to get dislodged/ separated from their attachment welds during service. The separation of impingement rods resulted in oscillating deflection of the rods, which kept striking the tubes underneath, ultimately causing failure of the tubes. Tapped hole Tack weld The operating company using this type of exchanger in the plant detected tube leakage that led to the contamination of the shell-side fluid due to leakage of tubeside fluid into the shell-side stream. The exchangers required an urgent offline repair that forced an unscheduled shutdown. The API standard provides narrative guidance on how the impingement rods should be installed. The arrangements shown in FIG. 6 may be interpreted as meeting API narrative guidelines. Bundle retainer not provided for kettle-type heat exchangers. TEMA2 Paragraph RCB-4.9 provides non-mandaImp rod end inserted in blind hole Tack weld Tack weld tory requirements for a bundle retaining arrangement and permits other arrangements that serve a similar purpose. The authors observed that the bundle retaining or equivalent device was not shown in the detailed fabrication drawings of some kettle-type heat exchangers. It was also determined that the requirements of the bundle retainer were not specified in the fabricator's scope by the purchase order. Excluding the bundle retainer on such types of exchangers may cause shifting (dislocation) of the bundle from its correct position during transportation or unexpected plant operation conditions. The bundle retainer is an essential device for alignment and hold-down purposes of the bundle for kettle-type exchangers. According to TEMA2 , it is A FIG. 6. Fixing arrangement for an impingement rod. Hub Hub thickness Shell thickness thickness 1:3 taper by weld buildup Shell thickness Tubesheet R A FIG. 7. Hub radius detail. Tubesheet R B B recommended that a bundle retainer or equivalent device be provided at the last baffle over the u-bend. The retainer helps the alignment of the bundle along the shell and acts as a hold-down device for the bundle because there is significant room for bundle misalignment or movement in the kettle-type shell. Using a Class 2 forged tubesheet with hub for low-alloy steel exchangers. This unique design lesson could have significant cost and schedule impacts if it is uncovered during fabrication. In a few exchangers from low-alloy steel materials, the authors noticed the hub of the low-alloy steel (LAS) forged tubesheet was given the same thickness as the adjoining low-alloy steel cylindrical shell to which it was butt-welded. This issue is particularly found in LAS heat exchangers where the shell material TABLE 3. Section III, Classes 2 and 3;* Section VIII, Div. 1 and 2;** and Section XII maximum allowable stress values (S) for bolting materials Line number Nominal composition Product form Ferrous materials Carbon steel Carbon steel Carbon steel Carbon steel Carbon steel Carbon steel Carbon steel 1 2 3 4 5 6 7 Bolting Bolting Bolting Bolting Bolting Bolting Bolting *See maximum temperature limits for restrictions on class 86 JUNE 2022 | HydrocarbonProcessing.com Spec. number SA-307 - SA-449 SA-325 SA-325 SA-449 SA-354 Type/grade A B 1 - 1 1 BC **Use with Part 4.16 of Section VIII, Div. 2 Alloy designation/ UNS number - - K04200 - K02706 K04200 K04100 Class/condition/ temperature - - - - - - - Size/thickness, mm 6 ≤ t ≤ 100 - 38 < t ≤ 75 - 32 < t ≤ 38 25 < t ≤ 38 64 < t ≤ 100http://www.HydrocarbonProcessing.com