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Maintenance causing them to bind . This issue is further compounded by thermal cycling , where repeated expansion and contraction of components during operation create uneven stress across the bolts . Such stress intensifies when bolts are improperly torqued during assembly , either through overtightening or uneven load distribution , which can distort the threads and make future disassembly even more difficult . The cumulative effect of these challenges , stemming from insufficient tooling , corrosion , and improperly maintained fastenings , creates a domino effect that significantly prolongs disassembly procedures , increasing operational costs but also results in unnecessary delays , impacting overall plant productivity and operational efficiency .
Seized pushed bolts .
Mock up push bolts removal .
This aggravates the bolt load issue as when thermal cycling occurs , gaskets will undergo relaxation — a reduction in their ability to sustain compression over time . Combined with the non-uniform thermal expansion of stacked components , this relaxation amplifies the likelihood of bolt load loss . The diminished clamping force heightens the risk of leaks at critical points or even complete joint failure , particularly during thermal upsets where rapid temperature fluctuations intensify stresses on the joint .
Difficulties in disassembling high-pressure heat exchangers Disassembling high-pressure heat exchangers for maintenance or inspection presents significant operational challenges , often resulting in time-consuming delays . Based on previous experiences at plants , a recurring issue is the inadequate tooling available for the removal and reassembly of key components , particularly the push bolts . The absence of properly calibrated tools to manage these bolts leads to frequent tool breakage when attempting to loosen them , further complicating the disassembly process . In many instances , push bolts often become seized due to the harsh operating conditions inherent to high-pressure heat exchangers as shown in Figure 3 . Over time , exposure to high temperatures and process fluids accelerates corrosion , weakening the bolt threads and
Operational insights and lessons learned The experience with high-pressure heat exchangers has provided valuable insights into key aspects of future system development . Lessons from real-world challenges have deepened understanding of the complexities in designing , implementing , and maintaining these systems . This knowledge forms the foundation for improving future designs and performance in demanding conditions . We will now explore two significant lessons learned , their implications , and how they have shaped our problemsolving approach .
Inadequate push bolt design One of the refineries experienced an issue with push bolt load loss . Based on a comprehensive root cause analysis , it was revealed that an inadequate design methodology had been applied . Originally , there are three standards that we used as reference which are ASME VIII-1 , EN1591-1 , and EN13555 . These standards are used to ensure all internal components , including the partition assembly , internal flange , and internal ring , could withstand the forces exerted by push bolts without experiencing buckling or distortion — even when tightened to their yield strength . The detailed design philosophy prioritized robust engineering practices , ensuring resilience under extreme operating conditions and accommodating potential variances during maintenance and assembly . However , a critical gap was identified in the ASME VIII-1 code , as highlighted in ASME STP-PT-036 : Bolted Flanged Connections in Elevated Temperature Service . The study revealed that component relaxation was not fully considered in the ASME VIII-1 calculations , indicating the limitations of this standard in hightemperature applications . This gap underscores the importance of integrating supplemental design codes , such as EN1591-1 and EN13555 , which address material creep and joint behaviour under elevated temperatures more comprehensively . By aligning the design with the provisions and strengths of these international standards — ASME VIII-1 , EN1591-1 , and EN13555 — user can significantly enhance the reliability and resilience of its high-pressure heat exchanger systems . These standards provided a robust framework to address critical design requirements , ensuring the components could withstand operational stresses and prevent failures , thereby establishing a solid foundation for longterm operational excellence .
18 Heat Exchanger World February 2025 www . heat-exchanger-world . com