API 660 vs TEMA: Major differences скачать в хорошем качестве

API 660 vs TEMA: Major differences

Explain why most refineries and petrochemical complexes now require API 660 (ISO 16812) in addition to the standard TEMA (Tubular Exchanger Manufacturers Association) guidelines. • The Big Picture: API 660 is built on practical considerations and past experience, often imposing stricter requirements that impact both fabrication cost and effort. • Disclaimer: Note that this comparison focuses on design and drawing requirements and does not include API 660 Supplementary Requirements. II. Core Design and Material Requirements • Tubesheet Cladding: API 660 mandates thicker minimum cladding. For expanded joints, API 660 requires 10 mm, whereas TEMA Class R & B only require 7.8 mm. • Tube Dimensions: ◦ Minimum OD: API 660 sets a floor of 19.05 mm (3/4”), while TEMA allows tubes as small as 6.4 mm. ◦ Thickness: API 660 defines minimum thicknesses based on the material of construction, a specific guideline TEMA lacks. • Exchanger Types: API 660 is more restrictive, prohibiting TEMA types “P” (outside packed floating head) and “W” (externally sealed floating tubesheet), whereas TEMA allows them for specific services like water or air. III. Internal Components & Hardware • Baffles and Support Plates: ◦ Corrosion Allowance: API 660 requires carbon steel/low-alloy baffles to be at least twice the shell side corrosion allowance. TEMA generally does not require corrosion allowance for baffles. ◦ Impingement Plates: API 660 requires a minimum thickness of 6 mm and prohibits perforated plates, which TEMA allows as a recommended practice. • Bypass Sealing: API 660 provides specific requirements for seal strips, tie rods, and dummy tubes to prevent bypassing, while TEMA offers no specific guidelines. • Hardware: API 660 requires hardened washers (at least 6 mm thick) for bolts with diameters of 38 mm or larger. IV. Fabrication and Quality Control • Shell Ovality: API 660 requires checking ovality using a metal template made from two disks, while TEMA relies on circumferential measurement. • Welding and PWHT (Post-Weld Heat Treatment): ◦ API 660 requires full penetration welds for the first 50 mm of pass partition plates. ◦ It also specifies PWHT for channels with six or more passes or high nozzle-to-channel ID ratios, whereas TEMA is silent on these specifics. • Tube-to-Tubesheet Joints: ◦ API 660 provides specific maximum tube wall reduction percentages and requires an additional pneumatic test for welded-and-expanded joints to ensure integrity before final expansion. V. Expansion Joints and Gaskets • Thin-Walled Expansion Joints: API 660 covers life cycle and liner requirements; TEMA does not cover thin-walled joints. • Gaskets: API 660 specifies construction (welded vs. non-welded) based on size and type (e.g., serrated, spiral wound), which TEMA does not detail. VI. Conclusion • Summary: API 660 acts as a "rugged" overlay to TEMA, prioritizing durability and reliability in harsh refinery environments. • Final Thought: While API 660 increases fabrication complexity, its focus on stringent tolerances and practical experience helps prevent premature failure in critical systems