Crude Furnace Creep Assessment and High Temperature Degradation

Creep calculations indicate a crude furnace radiant section carbon steel tubes exceeding their life fraction due to flame impingement reaching up to 700°C for a year. The ambiguity of the temperature and material data means the life fraction of creep calculations were based on limited inspection data and infra-red scanning giving a conservative indication of end of life. Due to unavailable tubes in stock, a planned pit stop cannot be arranged due to economic and safety reasons as the furnace may not be started back up safely. To safeguard the integrity of the furnace until the planned outage, the temperature on the furnace tube was stabilized to a current limit of 540°C through improvements in burner operations. The crude diet was also maintained within the crude acceptance envelope. Visual checks at every shift were done to ensure no observation from tube bulging or uneven flame pattern. A decision tree was created to facilitate quick decision making using a go/no go criteria of which tubes to replace during the August 2015 planned turnaround. The criteria set for the decision tree required tube wall thickness, surface hardness test, tube outer diameter ring gauge to be examined. Failing any of the criteria will require the tube to be replaced. The replaced tubes (one worst and one representative) will also be lab tested through destructive examination to identify the degradation mechanism and high temperature properties of the worst tubes to quantitatively define the high temperature properties and life fraction of the tubes that are left in the furnace. The lab test will provide results after a year of creep testing and can give assurance of continued furnace operation for 4 more years until the next outage. The final decision after the examination based on the decision tree was made required 17 tubes to be replaced in this turnaround. The worst degraded tubes were found to be at the vicinity of the initial observed location around the flame impingement zone.

Swelling of VVER-1000 Core Baffle: Numerical Modeling and Direct Measurement of its Geometrical Dimensions

Traditionally, the brittle strength evaluation of reactor pressure vessel was the central issue in lifetime assessment of Ukrainian nuclear power plants (NPPs). The problem of swelling of the reactor core baffle only recently got due attention from the side of operator. Here the most efforts were given on numerical modeling of austenitic steel 08Kh18N10T swelling and its effect on induced stresses in core baffle and distortion of its geometry. The calculation shows that essential changing of core baffle dimensions is expected after 35–40 years of operation. Eventually this can lead to the contact with the core barrel. Yet, these predictions contain the big number of uncertainties related to the input data used in analysis: fluence distribution; temperature variation due to heat release induced by neutron and gamma radiation; thermal-hydraulic boundary condition between the baffle and coolant; and, especially, the adopted law of swelling in dependence with above factors as well as mechanical stresses. So, the second task was to measure the real geometry of baffle after 27 years of operation, to determine its change and compare these results with the numerically calculated data with accounting for the design tolerances. Thus, the spatial measurement system (SMS) equipped with ultrasonic gages was designed. It contains the central vertical beam which can move in vertical direction and rotate. To the lower end of the beam four horizontal levels are attached, which are equipped with device resistant to the hot water and radiation. The gages are used to measure the shortest distances to the edges of baffle. Two types of results were obtained. The first one are the measurements in the different horizontal planes obtained by rotation the SMS around the vertical axis with angular steps equal to 1 degree. These results were difficult to handle with and required a special mathematical treatment due to the possible shift of the centre of measurement. The second set of measurements was performed by moving the SMS in vertical direction. These data demonstrate the change of distance with the height. The results clearly show that problem of swelling do exists, and, in general, the measured patterns of the distortions along the vertical and angular coordinates correspond to numerically obtained results. Further work on baffle integrity is however needed.

Investigation of Burst Pressure in T-Joints With Wall-Thinning by Using FEA

Boilers and pressure vessels are heavily used in numerous industrial plants, and damaged equipment in the plants is often detected by visual inspection or non-destructive inspection techniques. The most common type of damage is wall thinning due to corrosion under insulation (CUI) or flow-accelerated corrosion (FAC), or both. Any damaged equipment must be repaired or replaced as necessary as soon as possible after damage has been detected. Moreover, optimization of the time required to replace damaged equipment by evaluating the load carrying capacity of boilers and pressure vessels with wall thinning is expected by engineers in the chemical industrial field. In the present study, finite element analysis (FEA) is used to evaluate the load carrying capacity in T-joints with wall thinning. Burst pressure is a measure of the load carrying capacity in T-joints with wall thinning. The T-joints subjected to burst testing are carbon steel tubes for pressure service STPG370 (JIS G3454). The burst pressure is investigated by comparing the results of burst testing with the results of FEA. Moreover, the maximum allowable working pressure (MAWP) of T-joints with wall thinning is calculated, and the safety margin for the burst pressure is investigated. The burst pressure in T-joints with wall thinning can be estimated the safety side using FEA regardless of whether the model is a shell model or a solid model. The MAWP is 2.6 MPa and has a safety margin 7.5 for burst pressure. Moreover, the MAWP is assessed the as a safety side, although the evaluation is too conservative for the burst pressure.

Optimization of the Receipt and Delivery Schedules for a Transfer Tank Farm of Products Pipeline Network

Transfer tank farms play an important role in an oil products pipeline network, which receive oil products from upstream pipelines and deliver them to downstream pipelines. The scheduling problem for oil products supply chain is very complicated because of numerous constraints to be considered. The published literatures on schedule optimization of oil products pipeline network usually focus on the batch plans of each pipeline, without consideration on the receipt and delivery schedule of transfer tank farm. In this paper, a mixed-integer linear programming (MILP) model is developed for the schedule optimization of transfer tank farm. The objective of the model is to minimize switching times of the tank operations of a tank farm during a planning horizon, while fulfilling the products transmission requirements of the upstream and downstream pipelines of the tank farm. The constraints of the model include material balance, the operational rules of tanks, the topological structure constraints of the tank farm, the settling period of the oil products stored in dedicated tank and so on. To satisfy the constraint of fulfilling the specific transmission requirements of pipelines, concepts of static and dynamic time slot are proposed. A continuous time representation is used to obtain accurate optimal schedules and decrease scale of the model by reducing the number of variables. The model is solved by CPLEX solver for a transfer tank farm of an oil products pipeline network in China. Some examples are tested under different scenarios and the results show that global optimal solution can be obtain at acceptable computational costs.

Research Progress of High Temperature Naphthenic Acid Corrosion Rules and Prevention Methods in Petrochemical Plants

Naphthenic acid corrosion is a kind of corrosion state that occurs frequently in the high temperature locations of the petroleum distillation and secondary processing units. It is the main factor influencing the long-cycle safe operation of petrochemical plants, and also one of the hottest issues to be solved urgently in the petroleum refining industry. This paper overviewed the research progress related to high temperature naphthenic acid corrosion including the mechanisms, influencing factors, test and controlling methods; analyzed the engineering problems in the processing of high acid crude oil, pointed out the shortcomings of current research methods, and proposed the future research suggestions on the corrosion rules and prevention methods.

Thermal Aspects of Safety Analysis for Shipment of West Valley Melter

The thermal aspects of a safety analysis for shipment of the West Valley melter are presented. The West Valley melter was used from 1996 to 2002 to vitrify regionally sourced high level radioactive waste. The U.S. Department of Energy (DOE) set up the West Valley Demonstration Project to encase this melter and grout it in low density cellular concrete, for disposal. DOE-West Valley requested the Savannah River National Laboratory to prepare a Safety Analysis Report. The thermal portion of the safety analysis covers Normal Conditions of Transport (NCT) and Hypothetical Accidents Conditions (HAC), as defined in the Code of Federal Regulations. For NCT, it is assumed that the encased melter is stored in either shade or direct sunlight at an ambient temperature of 311 K (100 °F). The defining HAC is exposure to a 1075 K (1475 °F) fire for 30 minutes. Finite element computer models were used to compute temperature profiles for NCT and HAC, given the thermal properties of the melter and its contents and tabulated radiolytic heating source concentrations. The resulting temperature conditions were used to estimate the pressurization due to evaporation of water from the concrete. The maximum calculated gauge pressures were determined to be 81 kPa (12 psig) for NCT and 580 kPa (84 psig) for HAC.

Influence of Impact Angle and Real Target Properties on Drop Test Results of Cubic Containers

Drop test scenarios with cubic containers without impact limiters at interim storage sites or in a final repository have been investigated by numerical simulations. An ideally flat drop is impossible to conduct as a free fall of a container even under laboratory conditions. Dynamic stresses and strains inside the container structure are sensitive to the impact angle. Even very small impact angles cause remarkable changes in the experimental or numerical results when a flat bottom or wall of a container hits a flat target. For drop tests with transport packages the International Atomic Energy Agency (IAEA) regulations define an essentially unyielding target. In contrast, potential accident scenarios for storage containers are derived from site-specific safety analyses or acceptance criteria in Germany. Each interim storage site or repository has a yielding or so-called real target with individual structural and material properties. The real target acts as a kind of impact limiter. A more conservative container design is required if the impact limiting effect of the target is not considered.

Remaining Life Assessment of an External Pressure Vessel in Creep Range and Inspection Findings

As widely recognized in the industry, it is important to evaluate the creep damage of an elevated temperature vessel so that the mechanical integrity of the vessel can be achieved through the adequate repair and replacement planning. This is quite straight forward procedure for internal pressure vessels. For an external pressure vessel, it is not easy to assess the creep damage due to the complexity of the creep buckling analysis. Eventually, creep cavity evaluation technique without identifying the correct stress distribution has been used so often. However, due to the uncertainty of the technique itself plus conservative mindset of the inspectors, it tends to leads to an excessive maintenance most of the cases. In order to conduct a reasonable remaining life assessment, it is desirable to use the creep cavity inspection in conjunction with another assessment technique such as FEM creep analysis as stated in API 579-1/ASME FFS-1 10.5.7. In this paper, comprehensive approach with FEM and field inspection such as creep cavity evaluation to reinforce the uncertainty of each method will be demonstrated.

Recapturing Net Positive Suction Head Margins in Boiling Water Reactor Emergency Core Cooling Systems

Boiling Water Reactor pressure suppression pools have stringent housekeeping requirements, as well as restrictions on amounts and types of insulation and debris that can be present in the containment, to guarantee that suction strainers that allow cooling water to be supplied to the reactor during a Loss of Coolant Accident remain operational. By introducing “good debris” into the cooling water, many of these requirements/restrictions can be relaxed without sacrificing operational readiness of the cooling system.

Ultrasonic Testing and Photographic Imaging System for Tube to Tubesheet Weld of Heat Exchanger

This paper describes non-destructive testing systems that were constructed to inspect tube-to-tubesheet welds of a heat exchanger operating in a chemical plant such as urea products. A phased array ultrasonic testing system inserts a testing device into the tube, rotates it and scans the tube-to-tubesheet welds, thereby detecting any weld defects that are not only parallel to a tube axis but also in any direction, and displaying the size and location of the defects on a computer screen using system software. These welds have conventionally been inspected by liquid penetrant testing and visual testing as surface inspections during fabrication at shop and periodic inspection at plant site. This new method, however, provides a practical way to the inspection of weld inside. In addition, in a photographic imaging system, an imaging device is placed on the tube end to take photos of the inner surface of tube and the outer surface of tube including the tube-to-tubesheet weld. These photos are analyzed any suspected damage area, then displaying the location of the area on a computer screen using system software. In the periodic inspections at site, the presence or absence of a local corrosion dent or other damage are determined by visual testing and finger touch, but it is concerned that hundreds of welds will not be covered by these methods sufficiently. Consequently, this new method enables us to eliminate lacks of inspection and the secular change of each weld will be easily grasped with the suitable records. The above testing systems perform in a short amount of time and are highly reliable methods with inspection records. For this reason, in particular, the application of the new method to a periodic inspection at site is expected to reduce the period until the plant resumes operations, and also to remove any concerns about emergency shutdown of an operating plant due to damages in the tube-to-tubesheet welds.