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Fabrication
Channel flat head
Channel head barrel( thickness = 99 mm)
Tubesheet
Shell – Low Alloy( thickness = 95 mm)
Shell – Carbon Steel( thickness = 95 mm) Rear head( thickness = 67 mm)
Figure 2. Components and circumferential weldments in E-02A / B / C.
made of carbon steel, which is a relatively lower complexity compared to dissimilar metal and low alloy material joints.
These exchangers are designed in accordance with ASME BPVC Section VIII Division 2( 1995 Addendum) and follow TEMA Class R standards with a DEU-type configuration— characterised by a high-pressure closure and a one-pass U-tube bundle arrangement.
Problem statement E-02A, at the top of configuration as shown in Figure 3, was the first unit to exhibit signs of degradation in 2010, after more than a decade in service. A leak was observed at CS02 circumferential weldment, indicating that a crack had propagated through the wall thickness. Based on the operational margin of the system and confirmation from Operations and Process teams, the unit was taken out of service while maintaining plant performance with the remaining two units, E-02B( middle) and E-02C( bottom). Following the installation of the replacement unit for E-02A in 2012( tagged as E-02A-01), all three heat exchangers continued operating without any incidents until the scheduled plant shutdown in 2018, during which, a proactive internal inspection was carried out on all CS01, CS02 and CS03 circumferential welds of the three units. During the inspection of E-02B, a transverse crack approximately 5 mm in length was identified near the 1 o’ clock position at CS02. Additional cracks were also observed in the weldments connecting the pass-partition plate support to both the tubesheet and the channel head. Similar to the E-02A, unit E-02B was removed from service, and operations continued with the remaining two units until the next scheduled shutdown. Based on the recurrent findings, proactive inspection by means of PAUT was planned during shutdown in
2021. Again, similar findings were observed on the new E-02A-01 and E-02C. The findings revealed a total of two cracks on the weldments of CS01 and CS03 inE-02A-01 and four cracks on the weldments of E-02C – two at CS01 and one each at CS02 and CS03. Similar failures have been reported in other ammonia plants internationally, where comparable Boiler Feed Water( BFW) Preheaters experienced early-life cracking. In several documented cases, equipment failures occurred within one to four years of service. A published article in the Ammonia Technical Manual( 2005) highlighted instances of similar failures of similar heat exchangers characterised by significant transverse cracks after four years of operation. In many
Figure 3. Configuration of E-02A / B / C at site. www. heat-exchanger-world. com Heat Exchanger World October 2025
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