Prediction of Reheat Cracking Behavior in a Service Exposed 316H Steam Header

Reheat cracking in an ex-service Type 316H stainless steel steam header component has been investigated in this study. The examined steam header was in service for 87,790[Formula: see text]h and the cracks in this component were found in the vicinity of the weld toe. The root cause of this type of failure was due to the welding residual stresses. The welding-induced residual stresses had been present in the header at the early stage of the operation and were released during service. In this paper, a novel technique has been proposed to simulate the residual stress distribution normal to the crack direction by applying remote fixed displacement boundary conditions in an axisymmetric model. This approach can simulate the presence of residual stresses in actual components without the need to develop full weld simulation to quantify them. The predicted residual stress levels and distributions normal to the crack direction have been found in good agreement with the measured residual stresses available in the literature for a similar header. The creep crack growth (CCG) rates have been characterized using the fracture mechanics [Formula: see text] parameter and estimated using predictive models.

Calculation and Analysis of Steam Hammer in Main Steam Pipe in HPR1000

The steam hammer pressure is solved though the simplified calculation. PIPENET software is applied to model the nuclear island main steam system between the steam generator and the main steam header in HPR 1000. The transient module is used to simulate the occurrence and attenuation process of steam hammer. The maximum steam hammer pressure, the maximum steam hammer stress in the pipe system, when and where the load occurs are given. The influence of the straight pipe section length and valve closing time on the steam hammer effect is analyzed. With the other conditions unchanged, the steam hammer energy decreases as the straight pipe section shortens, or the valve closing time extends.

Heating of thick-walled steam header – an experimental study

The paper presented the description of the experimental installation for testing of the computer systems for on-line monitoring of the power boilers operation. The results of the experiment can be used for calculation of temperature and thermal stresses distribution in thick walled pressure elements based on the solution of the inverse heat conduction problem.

Determination of transient fluid temperature using the inverse method

This paper proposes an inverse method to obtain accurate measurements of the transient temperature of fluid. A method for unit step and linear rise of temperature is presented. For this purpose, the thermometer housing is modelled as a full cylindrical element (with no inner hole), divided into four control volumes. Using the control volume method, the heat balance equations can be written for each of the nodes for each of the control volumes. Thus, for a known temperature in the middle of the cylindrical element, the distribution of temperature in three nodes and heat flux at the outer surface were obtained. For a known value of the heat transfer coefficient the temperature of the fluid can be calculated using the boundary condition. Additionally, results of experimental research are presented. The research was carried out during the start-up of an experimental installation, which comprises: a steam generator unit, an installation for boiler feed water treatment, a tray-type deaerator, a blow down flashvessel for heat recovery, a steam pressure reduction station, a boiler control system and a steam header made of martensitic high alloy P91 steel. Based on temperature measurements made in the steam header using the inverse method, accurate measurements of the transient temperature of the steam were obtained. The results of the calculations are compared with the real temperature of the steam, which can be determined for a known pressure and enthalpy.

The Danger of Piping Failure Due to Acoustic-Induced Fatigue in Infrequent Operations: Two Case Studies

Failure in piping due to acoustic-induced fatigue can be considered catastrophic as it could happen only after a few minutes of operation. Acoustic-induced fatigue occurs mainly in gas piping systems with high velocity where high energy is dissipated through pressure reducing stations and pipe branch connections. It usually results in pipe through wall longitudinal cracks, pipe detachment from saddle supports, and complete shear off of branch connections. There are existing design criteria to avoid acoustic-induced fatigue based on comparison of generated power level to an acceptable power level. This criterion is normally used for the design of pressure relief and flare piping where high gas velocity exceeding 50% of the speed of sound (i.e., 0.5 Mach) is expected. However, acoustic-induced fatigue has been experienced in systems due to intermittent operations. Two case studies are presented in this paper. The first one is during a steam-out operation to clean a newly constructed steam header. During the cleaning operation, an orifice plate was used to control the flow in the steam header. Several pipe vents and drains failed due to fatigue in less than 1 h. The second case is for drainage of compressed natural gas during process upset condition. Because of the high level buildup in the liquefied gas separator vessel, the drain valve was opened to release the pressurized liquefied gas to the relief system to reduce the level buildup. Wall cracks and several pipe support detachments were found in the system after the upset condition. This paper presents the engineering analysis and material failure analysis conducted to find the root causes of the failures. Moreover, it highlights the recommendations and lessons learned from these two failures.

Analysis of the Auxiliary Steam Header’s Source Selection

Taking the actual production status of a 600MW unit as an example, under different steam flux, it has used the equivalent enthalpy drop theory in this paper to calculate the thermal economic indicators of the auxiliary steam header with different auxiliary steam sources. Moreover, it has conducted a quantitative analysis of the mechanism of the choosing of auxiliary steam source and auxiliary steam source switching’s influence on the thermal economy of unit in this paper.