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Becht Engineering Blog

In this section of the site contributing authors submit interesting articles relating to the various services, industries and research & development efforts of Becht Engineering.

Five Keys to a Cost-Effective Repair/Modification Package for Tanks-Vessels-Piping

: Process : Does the repair change the process chemistries, physics (fluid phase), and thermo-hydraulics (flow rates, pressures, temperatures)? Does the modification change the control room indications and the operating envelopes? Material : Are the selected metallic materials (base metal and welds) and non-metallic materials (gaskets, packings, etc.) compatible with the existing materials, with the environment, and with the service, for the design life of the repair? Is the material compliant with (a) the material specification (ASTM or ASME II), (b) the supplementary Code requirements, and (c) the supplementary plant-specific requirements? Will the material be procured from an approved supplier; does it require supplementary Quality Controls? ASME Code design : Does the modification alter the system layout? If yes, has the layout been checked for good practice and consistency with the process design (item 1 above)? Are the loads and load combinations well defined and categorized as Service Levels A,...
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12 Checks When Qualifying Piping Systems in Nuclear Applications

The analysis and qualification of piping systems in nuclear power plants involves more than meeting Code stress limits. Generally, a piping system is qualified if the following criteria have been met. These various qualification criteria are typically specified in the plant FSAR, the plant design procedures, or the ASME Code. Pressure design in accordance with the design Code. This check will govern the schedule of pipes, the thickness of tubing, the schedule and pressure class of fittings, the reinforcement of openings and branch connections, the pressure rating of valves, the pressure class of flanges, and the pressure design of specialty fittings. ASME Code stress limits . This check will verify that the Code stress equations for the load combinations corresponding to Test, Design, and Service Levels A, B, C, and D loadings have been met. NRC Standard Review Plan (SRP) Section 3.6 stress limits for the postulation of high energy...
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Purpose of the Flange Bolt Rules in ASME VIII and ASME III

The partial objective of the ASME Appendices ASME VIII Div.1 Appendix 2, and ASME III Div.1 Appendix XI provide “Rules for Bolted Flange Connections” with ring-type gaskets. One of the rules provided applies to the calculation of the minimum required bolt area. In other words, what should be the minimum combined cross-section area of the flange bolts to (a) seal the gasket, while (b) not exceeding the bolt allowable stress? The two force components W m1 and W m2 The rules are intended to provide bolts with sufficient pre-tension to achieve two objectives: (1) Counter a pressure-induced force W m1 which tends to pry open the flange in operation, and (2) provide a compressive force W m2 which is needed to seat the gasket during initial assembly of the flange joint. The at-pressure force W m1 The W m1 force is in turn comprised of two contributions, illustrated in the...
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Differential Thermal Expansion: A Challenge to Flange Joints

by George Antaki and Jeremy Lundquist It is not uncommon to use B7 low alloy high-strength bolts on stainless steel flanges. If that is the case, and if the flange operates at high temperature, then the thermal expansion-induced stress in the bolt should be checked. Consider, for example, a stainless steel flange SA-182 Grade F304, with SA-193 Grade B7 bolts, in a line that operates at 600 o F. The line is insulated, so both the flange and its bolts will be at 600 o F during steady-state operation. In hot operation, the stainless steel flange wants to expand more than the low alloy steel bolt. This will induce a tensile stress in the bolt equal to: σ bolt  = E b  × (α flange  - α bolt ) × ∆T Where E b = modulus of elasticity the bolt at 600 o F = 26.9E6 psi; a flange = coefficient...
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George Antaki

Avoiding Leakage

If the flange is in a service where delta-T is sufficiently large so that stress-preload (depends on the initial torque) + stress-... Read More
Saturday, 13 January 2018 09:37
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