Transferline Exchanger Internal Diameter Tube Inspection

Transfer Line Exchangers (TLE’s) are a critical part of an ethylene producing unit. Similar to a high temperature, high pressure boiler, TLE’s convert heat from the effluent gas coming from the radiant coils of the ethylene cracking heater to steam by exchanging the hot temperature of the gas to a feedwater source that produces steam. The effluent gas flows through the inside of the tube while the feedwater is on the outside of the tube. As with any high-pressure steam system, a leak in the tube causes a breach between the gas and feedwater side ultimately resulting in a shutdown of the unit. Improving reliability through inspection is always the goal especially when the industry can benefit from sharing experiences.

Routine maintenance cycles are common and set on typical frequencies most often for cleaning of the tube ID’s. Build-up of coke products from the process effluent on the tube ID’s is a common occurrence at the inlet tubesheet. Unbolting and removing the heads allows for tube ID access to clean or in our case to inspect. In general, Non-Destructive Examination (NDE) inspection performance is improved when cleaning is conducted prior to the inspection and is especially the case with electromagnetic and ultrasonic techniques.

This paper presents various inspection techniques for some of the most common tube degradation mechanisms found in TLE’s. Two of the most common degradation mechanisms are ID erosion and OD corrosion. To detect these mechanisms, we focus the presentation on two techniques. The first is an Ultrasonic technique known as IRIS and the second Remote Field Testing known as RFT is an electromagnetic technique. Both techniques are volumetric inspections with defect sensitivity originating either from the ID or OD. However, capabilities and limitations exist for both techniques which will be presented as well as sharing results of over 7 years of testing in-situ TLE components.