Steam Pipelines Research Articles

On-line corrosion monitoring in geothermal steam pipelines

A Fluid Flow Test Rig has been designed and commissioned to simulate corrosion occurring in geothermal steam pipelines. The test rig was used to evaluate the effectiveness of a variety of corrosion monitoring techniques for application to full-scale pipelines. Although unsuccessful, the thin layer activation method, which is based on the conversion of Fe to 56Co upon irradiation with high-energy protons, showed potential for application to geothermal systems. Corrosion rates measured in the test facility were similar to those estimated for the Ohaaki (New Zealand) steam pipelines after three years of service.

Remaining creep life study of CrMoV main steam pipe lines

Identification and quantification of accumulated creep damage to estimate the remaining life of high temperature pipe lines has attracted world wide attention for the past several years. This paper briefly presents NML's experience in this field acquired in the course of the execution of an on-going national project “Component Integrity Evaluation Programme”. This paper mainly deals with the remaining life assessment of a main steam pipe line of a 100 MW coal fired power plant. The steel for the pipe line was 1 Cr-0·3 Mo-0·25 V (Russian grade 12 Kh 1 MΦ) steel which had widely been used in the older plants. The microstructural evolution occurred in this steel after 10-year and 15-year service exposure has been extensively analysed and discussed. These samples were provided for investigation by the same plant. Contrary to general expectation, damage in the form of creep cavitation was not observed even after 15 years service, indeed, some structural/morphological changes in the carbides had occurred. Also, any conclusive evidence of Mo-depletion as earlier suggested by some workers in similar steels, was not found. Interestingly, the 15-year sample showed only 0·3% diametrical expansion and a marginal drop in hardness of about 12 HV. The ‘threshold stress model’ earlier proposed by one of the authors based on the creep data on the 10-year sample is also now validated with reference to the 15-year service exposed samples. An important feature of this model is that below the threshold stress the creep rate is practically independent of microstructure. And, a unique relationship exists between the minimum creep rate and the applied stress, regardless of the initial microstructure; the relationship can be used for the remaining life prediction.

Evaluation of the structural degradation and damage of steel of steam pipelines subjected to the long-term action of thermomechanical factors

We demonstrate the efficiency of the method ofJ-integral for the analysis of the kinetics of structural degradation and accumulation of microdamages in the metal of steam pipelines after different periods of operation. The results of the tests carried out at room temperature show that, as the operating time of the metal increases, its short-term static crack-initiation resistanceJIc increases. The operating time of steam pipelines produces, in fact, no influence on the value ofJIc measured at a working testing temperature of 540°C. By applying the parameterj=dJ/da under the conditions of high-temperature tests, one can show that the difference between the characteristics of crack resistance of the intact metal and the same metal after a long period of operation is significant. As the operating time increases, the values ofj decrease. The observed drop of crack resistance means that the structural degradation of steel caused by its in-service embrittlement decreases its resistance to subcritical crack growth. This fact is explained both by the formation of grain-boundary precipitations of complex carbides and by the accumulation of damages in steel in the process of long-term operation.

A simple method to compute hydrogen chloride abatement in geothermal power plants

One of the most important problems affecting geothermal fields is the abatement of hydrogen chloride contained in the vapor phase. If the chloride concentration exceeds a few ppmw, steam scrubbing must be provided in order to prevent corrosion of the gathering system and turbine failure. In some fields at Larderello, one of the most important geothermal areas in Italy, steam scrubbing is performed by injecting a caustic solution directly into the steam pipeline. In particular, the abatement system depends on absorption with chemical reaction of hydrogen chloride by a sodium hydroxide solution. This paper describes some of the Larderello power plant abatement systems and presents analyses of the different solutions adopted for this purpose. Finally, some simplified models for computing abatement efficiency in sprays, pipelines, static mixers, cyclones and vane type demisters—the equipment generally used in these plants—are proposed. The proposed models are able to predict the data measured in these power plants with good accuracy, and so they can be regarded as useful tools for designing new abatement systems or optimizing the existing ones.

Creep damage to a steam pipe of an intermediate superheater operating for 90,000 hours

A longitudinal crack appeared in a straight segment of a steam pipeline of an intermediate superheater after operating for 90,000h. The pipeline of 14MoV63 steel with dimensions 609 × 25 mm operated at a temperature of 540°C under a pressure of 18 MPa. We found that its failure is mainly explained by creep. To establish the causes of creep in the straight segment of the steam pipeline, whose predicted service life was 100,000h, we determined the mechanical characteristics of the material and studied its microstructure and fracture surfaces.

On the analysis of pressure transients in pipelines carrying compressible fluids

Pressure transients in pipelines are triggered by various events, some of which are accidental and others form a part of operational and safety procedures. Nevertheless it is important to determine beforehand the pressure increases, the velocity changes and the forces that these transients cause, so that the consequent vibrations and stresses can be calculated in order to ascertain the integrity of a pipeline. This paper is concerned with the analysis of transients in pipelines carrying compressible fluids. The procedure adopted is based on the method of characteristics (MOC). A tandem technique has been developed here, first to operate on the main nodes of any complex piping network and subsequently to analyse each individual pipeline to determine the state of the fluid at different sections in the circuit at the end of a preselected time step. A general purpose computer code based on this technique has been developed. The time-history of pressures, velocities and densities can be calculated with the help of this code for any complex piping network. The program is very versatile and can handle any number of pipes, nodes, branches, valves, etc. Sudden operations like opening or closing of valves, slamming of check valves or rupture of pipelines, etc., in a circuit have been simulated. A case study to predict pressure transients in the main steam pipeline of a 500 MW thermal power station, in the event that the load on the turbine is suddenly removed and the main stream stop valves are rapidly closed, has been undertaken and is illustrated in this paper.

Effects of high temperature creep on magnetic properties of steels (pipeline inspection)

An investigation was performed into detection of creep damage in the welded area of high-pressure, high-temperature steam pipelines. The measurements involved the use of a portable magnetic inspection device called the Magnescope. Results indicated a decline in the coercivity and remanence in creep-damaged pipes, probably due to segregation of impurities occurring during creep. The orientation of the inspection head with respect to the weld line affects the ability to detect creep damage. Measurements taken parallel to the weld line showed greater differences in the coercivity and remanence between the damaged and undamaged specimens. Measurements taken perpendicular to the weld line did not show large differences. >

Method of estimating the remaining life of steam pipelines operating at high temperatures on the basis of the deformation criterion

A method of estimating the remaining life of high-temperature pipelines based on the deformation criterion was developed on the basis of the Kachanov-Rabot-nov model of creep and long-term failure, including the damage rate parameter. The concept of generalized creep curves is used. The condition of long-term strength under varying loading conditions is derived, which has advantages over traditional conditions based on the principle of linear summation of damages.

Heat Losses From Underground Steam Pipelines

A new transient solution describing the heat transfer around a single buried steam pipe was developed. The solution technique uses Green’s functions and is particularly appropriate at distances greater than two or three pipe radii from the pipe. The solution models the pipe as a line heat source and considers a convective boundary condition at the soil surface. It was shown that for long time periods, the solution reduces to a steady-state expression that is believed to describe heat loss rates better than some current, commonly used steady-state relations. The solution was used with parameter estimation techniques to design an experimental procedure for determining buried steam pipe heat loss rates and depths from near-surface soil temperature measurements. Sensitivity coefficients derived from the solution were used to identify the linearly independent parameters and the optimum locations for the temperature measurements. An example of the use of this procedure is presented.

Losses in Very Long Insulated Steam Pipelines

A numerical method has been developed for calculating the losses and property variations in very long insulated steam pipelines. This method is based on the fundamental equations of compressible fluid flow and heat transfer, and utilizes computer software for evaluation of steam properties. Examples illustrate the effects of different inlet conditions, mass flows, and insulation thicknesses. Choking occurs under some conditions.

Developments in geothermal energy in Mexico—part thirteen: the operation of surface equipment for geothermal fluid conduction at Cerro Prieto I

At Cerro Prieto I 34.5 PJ e have been generated and 334 million tonnes of geothermal fluid have been produced. The length of the present system of 300 mm (12 in) to 350 mm (14 in) dia. steam pipelines is 24 km. That of the water pipeline system of 200 mm (8 in) to 400 mm (16 in) dia. pipe is 46.5 km. A total of 32 wells, 41 separators, 51 silencers, 7 steam driers, and 290 200 mm (8 in) to 400 mm (16 in) dia. valves are in operation. Corrosion in the pipelines and other surface equipment has not been a serious problem. The principle maintenance problem has been the cleaning of silica scaling and sediments in pipelines, equipment and channels. Frequent maintenance is necessary in order to maintain the capacity of water pipelines, separators and channels. The well liners and in some cases the deposits themselves have been affected by scaling. Even the small amounts of silica that are carried by the separated steam cause scaling of turbine blades, reducing their capacity.

The path to crack initiation during low cycle thermal shock fatigue

Low cycle thermal shock fatigue crack initiation, and the microstructural changes in materials during this process, have been studied for three types of steam pipeline steels. The roles of thermal strain ageing, subgrain formation, dislocation density, high temperature void formation and grain boundary segregations have been studied and the number of cycles needed for the formation of microcracks has been established.

New evidence on magnetite oxygen isotope geothermometers at 175° and 112°C in Wairakei steam pipelines (New Zealand)

Millimeter deep surface layers of magnetite occur in the steam pipelines of the Wairakei geothermal power station as part of serious corrosion discovered after 15 years of service. These quasi-experimental growths provide the following oxygen isotope calibration points of magnetite and H 2O below the previously available experimental range: Δ(175°C) = −7.9 ± 0.5 and Δ(112°C) =−3.7 ± 0.5 The data support the earliest proposed magnetite−H 2O fractionation curve, by J.R. O’Neil and R.N. Clayton, with an isotopic “cross-over” near 50°C, and could indicate a relatively low-temperature origin for some Precambrian iron formations.

Remote Control of a Geothermal Steam Pipeline

Summary Aminoil U.S.A. Inc. (AUSA) operates a pipeline delivering geothermal steam to a Geysers. Lake County, CA, power plant by means of a distributed control system. Microprocessors located in the field squire data and transmit it digitally to a control building adjacent to the power plant. From this building the shift operator monitors and controls every well in the system, regulates the delivery pressure to the geothermal power plant, and controls the condensate reinjection system. This paper discusses design, operation, and future objectives of this control system. The design covers selection of the control system, data acquisition and control requirements for individual wells, pipeline over pressure relief system control, and condensate reinjection system. The operation of the steam pipeline since power plant start-up has been very favorable. Steam delivery pressure fluctuations are controlled to less than +0.5 psi (+/-4 kPa) under normal conditions. Shift operators are capable of responding to power plant upsets (turbine trips and load reductions) in minutes, minimizing steam venting to the atmosphere. Currently the geothermal steam pipeline is manually remote operated by a shift operator. This operation has provided valuable information for conversion to an unmanned computer control operation. This proposed unmanned computer control is discussed along with our methods of approach. Introduction Our project is in the Castle Rock Springs area of The Geysers field in California, approximately 100 miles (160 km) northeast of San Francisco. The operator supplies geothermal steam to a public utility's geothermal power plant rated at 138 MW gross, 133 MW net delivered to the transmission line. Twenty-three geothermal steam wells deliver a total of approximately 2,700,000 lbm/hr (340 kg/s) of steam at rated capacity. Individual well deliverabilities range from 40,000 to 325,000 lbm/hr (5 to 41 kg/s). Approximately 5 miles (8 km) of insulated pipe is required to deliver the necessary steam flow to the power plant. Individual wellhead pipelines vary in diameter from 10 to 18 in. (25 to 46 cm), depending on steam flow capability. The wellhead pipelines feed into 24- to 30-in. (61- to 76-cm) branch lines that connect into two 36-in. (91 -cm) main steam lines with separators for condensate and particle removal. These two 36-in. (91-cm) pipelines join to form a 48-in. (122-cm) header that delivers steam to the power plant. Along the pipeline, drip legs are positioned at low points to collect condensate. These drip legs are vented to the atmosphere to remove condensate during start-up or shutdown of the pipeline. To provide electrical power for the control system. a three-point 480-V electrical distribution system parallels the pipeline. Transformers step down the line voltage to 120 Vac at the wellheads. The remote control system used to monitor and control the geothermal steam pipeline was selected primarily as a mechanical H2S-abatement method for compliance with the Lake County Air Pollution Control Dist. (LCAPCD) regulations. During power plant outages and start-up conditions, all steam is vented to the atmosphere. The LCAPCD H S-abatement requirement for an unscheduled power plant outage is given in Fig. 1, Under these conditions the vented steam rate must be limited to 35 % of full flow within 1 hour after an outage. Further reduction to 10% of full flow is required if the power plant outage is expected to be greater than 7 hours. AUSA determined that only a remote control system capable of controlling all wells in the system could accomplish this flow reduction in the short time frame required. This paper presents our control system structure, design. operation, and proposed computer control. Control System Structure A Honeywell TDC-2000 control system combined with a Honeywell 4500 computer (super station) was selected and installed. JPT P. 989^

Corrosion resistance of bronzes in fresh water: recent results

Tin bronzes and other related tin‐containing, copper‐base alloys are used in a large number of industrial applications since they possess a combination of desirable properties. These include high mechanical strength, ability to be worked and very good resistance to corrosion and wear. Binary copper‐tin alloys containing between 3 and 8% tin are widely used for such purposes as springs, chemical hardware, pump and valve parts, and nuts and bolts. Increasing the tin content to around 10–12% generally improves the alloy's resistance to wear and corrosion. Gunmetals, which are copper‐tin alloys with additions of small proportions of zinc to make casting easier, are also used for applications such as valves and fittings for water and steam pipelines and in other casting applications needing a non‐ferrous alloy having good resistance to corrosion.

Numerical simulation of a steam pipeline network

The present paper describes a computer program that can simulate the behaviour of a network of steam pipelines, such as those used in Larderello geothermal field, fed by superheated steam. Also given are some applications of this program to a network in operation.

Methods for Improving Accuracy of Paper-Sheet Moisture Control

A mathematical model of the drying part, as a controlled member for paper sheet moisture control is being constructed. In constructing it the distribution of temperature along the thickness of the cylinder as well as the distribution of the moisture along the length of the drying part is taken into account. The optimization of the dynamic responses of the controlled member is achieved with using of model through the choice of the proper structure of the steam pipeline, of the proper design of the drying cylinder and of the proper value of some technological parameters. In construction the combined system of control the vacuum in the chamber of the couch-roll is used as an indirect indicator of the basic disturbance. A further improvement of the efficiency of the moisture control is achieved by the statistical prediction of the indirect indicator of disturbance.

Design and construction of steam pipelines

The output characteristics, delivery, pressure, and temperature, their theoretical and statistical research, with the analysts of similarities and anomalies, enable the selection of optimum values for the output of geothermal sources during their long life. From these optimum values, by adding economic considerations, the most rational evaluation of the size of the diameters of steam pipelines can be attained, as well as the thickness of the thermal insulation. Having recalled the most important phenomena from the practical viewpoint, occurring during conveyance of the endogenous fluid (chemical corrosion and mechanical wear of the pipes, etc....) the planning of steam pipelines is discussed, together with an examination of the methods used for taking up the thermal expansions, the static-calculations, and also the devices used in the actual construction of self-compensating pipelines. Some particularly interesting achievements are then discussed, also in connection with standardization requirements.

Measurement and transmission of steam in Matsukawa geothermal power plant

Matsukawa geothermal power plant has been under smooth operation since its establishment in October 1966 as the first power plant using geothermal steam in Japan. The most important problems in setting up the geothermal power installation were the pressure in the well and the selection of the materials to be used. Both were decided by the characteristics of the well. In Matsukawa the characteristic of the steam was tested in wells Nos. 1, 2, 3. The items of the investigation discussed in the paper are the following: • — amount of the steam output, pressure and temperature in wells; • — chemical contents of the discharge; • — hot water and corrosion tests; • — problems in the specifications of the geothermal steam pipeline and its design.

Paper 16: Effect of Thermal Cycling on Pre-Stressed Steam Pipelines

Investigations into the effect of temperature and pressure cycling on a pre-loaded model main steam line of 0·5% Cr-0·5% Mo-0·25% V steel have shown that a relatively large increase in length occurred over a few cycles at 100 per cent cold pull, and a decrease in length occurred at 50 per cent cold pull. Using high temperature platinum-tungsten strain gauges, it has been found that large changes in strain occur round an expansion loop in the model pipeline. It is suggested that large changes in the design stress distribution in a main steam line occur during the commissioning stages of a generating unit, making creep behaviour of the line during base loading difficult to predict. It is further suggested that failure in pipelines when a unit is working under a twoshift system is due to low cycle fatigue, as the strain changes occurring do not appear to approach an equilibrium minimum under cycling conditions. It would appear that strain changes, and hence the effect of low cycle fatigue, can be minimized by choosing a level of cold pull between 50 and 100 per cent, the actual level depending upon the physical characteristics of the pipe material, the more important ones being thermal expansion and the change of yield stress with temperature. Using the plastic strain range measured in the test a prediction can be made regarding the time to failure.