Erick Ritter Archives

EFFECTIVE ASSESSMENT TECHNIQUES

By: Matt David, Michael Greveling, Daniels Peters and Erick Ritter

Recently, Structural Integrity Associates (SI) helped a client with a leaking deaerator tank (DA tank). DA tanks are traditionally used to remove dissolved gasses from liquids. The client’s DA tank in particular is used to remove dissolved oxygen in feedwater for steam-generating boilers; this is done because dissolved oxygen can create a corrosive environment within the boiler as it will attach to the metal components, creating oxides. The DA tank protects the boiler from these corrosive gasses, however, to the DA tank’s detriment, not much protects it from those same gasses. Repairs on DA tanks are common and additionally it is not uncommon for those repairs to continue to experience problems.

The DA tank being investigated for leaking in this investigation had an entire shell segment, various full thickness patch plates, and a head replaced in 2018 due to wall thinning caused by flow-accelerated corrosion (FAC). The current leak was caused by cracking of a girth and longitudinal seam weld in a mismatched repair patch. The failure prompted inspection, stress analysis, and repair consulting by SI. The following reveals the steps taken to repair the failed DA tank.

Initial visual inspection of the leaking DA tank indicated that the problematic repair patch had significant radial mismatch relative to the tank shell to which it was welded and grossly oversized weld layers resulting in high tensile shrinking stresses. The mismatch resulted in significant bending at the weld line and the excessive weaving of the weld layers led to tensile forces acting on the weld imperfections at the toe of the welds. Due to the visual finding, 3D scanning was performed to better understand the magnitude of the mismatch.

VESSEL LIFE CYCLE MANAGEMENT

By: Erick Ritter and Daniel Peters

Initial introduction of many of the hydrogen fueling stations to support this rapidly growing demand were installed around 2010. There were many designs of cylinders developed and installed at that time, many with known limitations on the life of the equipment due to the high pressures involved and cyclic fatigue crack growth issues due to hydrogen embrittlement. The designs were often kept relatively simple to lower their costs often with little or no considerations for in-service inspection or potential end of life considerations. Others involved innovative designs with reinforcing wrapping to try to enhance the life of the vessels, but by doing so, these designs limited the access to the main cylinder wall for in-service inspection.

Many of these vessels are now reaching or passing the design life established by ASME. This is resulting in problems for operators of this equipment as some jurisdictions will not allow the vessels to operate beyond the design life without inspection or re-rating of the vessels to extend the fatigue life. SI’s FatiguePRO is a commercial software solution which has been addressing this exact concern for over 25 years.

News & Views, Volume 51 | Deaerator Tank Failure

News & Views, Volume 50 | SI FatiguePRO for Hydrogen Fueling Station Assets