Tube-to-Tubesheet Weld Inspection Secondary Transfer Line Exchangers (STLEs) – Innovative Paut Inspection Technique

Chevron Phillips Chemical Company, LP (CPC) operates numerous cracking furnaces at its various ethylene plants in the Gulf Coast and the Middle East which utilizes proprietary design Secondary Transfer Line Exchangers (STLE) provided both by BORSIG Process Heat Exchanger GmbH and SCHMIDTSCHE SCHACK. The purpose of the STLEs (and Tertiary Transfer Line Exchangers, if present) is to further cool the heater effluent from the Primary Transfer Line Exchangers to the desired quench system inlet temperature and to recover this heat in the generation of very high-pressure steam, boiler feed water preheat, or increase feed preheat to the furnace convection section.

Due to the uniqueness of the tube-to-tubesheet weld design, standard inspection techniques, such as visual inspection (VT) of the root of the tube-to-tubesheet weld may only be performed up to 80% of the welds and a 100% liquid penetrant (PT) on the completed welds does not assess the critical root zone, only the external weld surface and tubesheet area. As a result, a Phased Array Ultrasonic Testing (PAUT) technique was developed to provide a near full volumetric inspection of the weld, with emphasis on high resolution coverage of the critical root zone.

This paper discusses development, testing, proof-of-concept, and implementation of this PAUT technique to ensure the integrity of the welds during fabrication of the STLE’s and the field repairs, when required, so that the equipment could be returned back to service with assurance of safe, reliable operations.