Severe service
Failure of verification methods for hydrofluoric acid alkylation plug valves
After shrinkage was identified in a highnickel-alloy body after a change in gating pattern , it was clear that the well-established , industry standard
RT angles were unable to adequately show all casting defects .
By Marshall Norris , Dennis Baker and Keith Walker ,
Flowserve Corporation
Flowserve provides equipment for use in severe services in the petrochemical industry , including to several organizations involved in oil refineries . During the refinery process , hydrofluoric ( HF ) acid alkylation ( alky ) is used to convert isobutane and alkenes into alkylate , which is used to make gasoline . HF acid is a highly hazardous substance , and even limited human contact with it can result in severe osteonecrosis or death if not treated immediately . Because of the risk involved , valves that are used for this service are subject to a high degree of verification , including pressure testing , material verification , and radiographic inspection ( RT ) to verify that cast components do not contain porosity , voids , inclusions , cracks , hot tears , or shrinkage . ASTM E446 governs the methodology for identification and disposition of the results of RT in cast components with a wall thickness of up to two inches , a category many of Flowserve ’ s valves fall into . Flowserve takes additional measures for in situ detection of leakages using a reactive yellow paint that responds in red discoloration in the presence of HF acid .
Leaking valves at HF alky unit
In May 2021 , the Flowserve Cookeville ( CVO ) facility was contacted by an HF alky processing unit and informed that a three-inch class 300 Monel valve had been identified as leaking after being in service only a couple of weeks . The facility shut down the line and followed procedures to contain any process media before human or environmental exposure occurred . The leakage occurred through the valve body wall at the top of the valve where the flange meets the neck ( as shown in Figure 1 ), and Flowserve launched an investigation to identify the root cause for the leakage . Within the month , the alky unit identified two additional valves with body material from the same heat that also began to leak in the same location . The investigation identified the root cause of the leakage as shrinkage ( Figure 2 ) that was not identified during RT examination .
Figure 1 . Leakage identified by red coloring on a threeinch G4 plug valve .
Figure 2 . Shrinkage observed in the cross section .
Upon the investigation ’ s completion , it was determined that the RT views used to verify casting integrity were insufficient to capture the problematic area . At that time , Flowserve revised its requirements for areas of the valve requiring RT inspection . Concurrently , the customer also hired a third party that launched its own investigation and identified shrinkage in the area where leakage was identified by lining the inner diameter of the valve ends with film as shown in Figure 3 . Flowserve ’ s RT supplier was able to orient the valve body at an alternate angle that revealed the previously
Figure 3 . Root cause analysis included alternate angles of the area of interest .
Figure 4 . Flowserve ’ s third party RT supplier identified that the area of interest could be examined using an off normal angle .
32 Valve World August 2023 www . valve-world . net