News & Views, Volume 45 | Metallurgical Lab: Case Study – Thermowell Failure Analysis
By: Wendy Weiss
Structural Integrity (SI) was recently asked to examine a fractured thermowell and determine the damage mechanism. The thermowell had been removed from bypass line piping in a heat-recovery steam generator (HRSG) that ran from the High Pressure (HP) bypass valve to the cold reheat section, and sent to the SI Materials Science Center. As reported by plant personnel, the fracture was located within the pipe wall. The pipe material was specified as ASME SA-335, Grade P22, and the thermowell was specified to be ASME SA-182, Grade F22.
Examination Procedure and Results
The fractured thermowell sections were visually examined and photographed in the as-received condition, as shown in Figure 1. The thermowell was comprised of two pieces: the thermowell housing itself which protruded into the steam stream, and a fitting connection to the pipe into which the thermowell housing was inserted.
Acid dewpoint corrosion can occur in conventional and HRSG units in locations where temperatures fall below the sulfuric acid dewpoint temperature. This can occur when either the tube metal temperatures are below the acid dewpoint so that condensate forms on the metal surface, or when flue gas temperatures are below the acid dewpoint, so that the condensate will form on fly ash particles.
Whether it’s fair-trade coffee, sustain-ably harvested lumber, energy efficient appliances, or other certified products, consumers and companies look for products that have high standards of origin, production, and performance.
Structural Integrity is mentoring students from the University of California, San Diego during their senior design Capstone project. The goal of the mentorship is to give the students real-life working experience through participation in a design project with industry mentors. The students are learning how to develop forces on equipment during earthquakes and how to design anchorage so that the equipment remains in place and functional during and following an earthquake. At the end of the project, the students will write a report and make a presentation to their Professor, their classmates and other industry mentors.
Grade 91 steel is widely used in tubes, headers and piping of superheaters and reheaters because of its higher strength at elevated temperature compared to low alloy steels such as Grade 22.
suction pipe-to-elbow stainless steel weld was identified in both units of a nuclear power plant as depicted in Figure 1.
Structural Integrity (SI) has significant depth and expertise in current pipeline safety regulations and dedicates substantial resources to ensure a comprehensive understanding of proposed pipeline safety regulations.
Determining a course of action once in-service damage is discovered often requires applying a multi-disciplinary approach that utilizes Nondestructive Examination (NDE), analytical techniques such as stress analysis, and metallurgical lab examination.