How to prepare a plan for the supervision and verification of construction processes in combined cycle power plants or plants
To produce the electrical energy that feeds the services and infrastructure of a population, region or country; Generation “plants” or “centrals” are required, which are commonly located on the outskirts of urban centers and are made up of a large number of interconnected facilities and equipment. As the main element of a power plant, the turbogenerator is the equipment that, through a rotating mechanism, transforms mechanical energy into electrical energy. To activate the rotary mechanism requires a fluid under special conditions of pressure and temperature.
Depending on this fluid, the plants are divided into Thermoelectric, Wind, and Hydroelectric. Combined Cycle power plants are a sophisticated type of thermoelectric power plant, because they have two kinds of turbo generators, one is made to run (mechanical energy) by the gases produced by the ignition of an air-fuel mixture and the second is made to run with steam. which is produced by raising the temperature of the water in liquid state (supplied from an external source) with the exhaust gases from the first turbogenerator. For the construction of a combined cycle “plant” or “central”, engineering projects are designed that include the elaboration of calculations, specifications, plans, diagrams, models, plans and programs;These are materialized through a project management group that selects equipment suppliers and contractors that finally carry out the construction and assembly of the facilities and equipment acquired.
For the Plant to start the production of electrical energy with the quality and quantity characteristics for which it was designed, an adequate review and verification of the processes is required during the construction stage. This work is carried out by a supervision group that is located at the selected site from the beginning of construction. The steps to define a supervision plan for the construction of a combined cycle thermoelectric plant are described below.
1) Break down the plant into systems
a) The plant can be considered as a closed system, however, to correctly visualize the construction process, the systems, subsystems, structures and components that comprise it must be identified.
i) In relation to the operation of the plant, each system has a purpose or function; Under this criterion, there are three types of systems:
(1) The Main Systems.- are those that intervene directly in the process of transformation of mechanical energy into electrical energy, considering the input, development and output elements of said process. The main systems of a combined cycle power plant are the following:
(a) fuel supply
(b) steam generator
(c) gas turbine
(d) steam turbine
(e) electric generator
(f) main transformer
These systems are generally found on the force island of most power plants and are treated as critical
(2) For the main systems to function closely related, there are interfaces between them, these interfaces are physically constituted by means of Interface Systems, more commonly called Main Subsystems, such as:
(a) steam conduction
(b) isolated phase bus
(c) distributed control system
(d) excitation system
(3) Finally, for the efficient, safe and reliable operation of the main and interface systems (or main subsystems), there are the Auxiliary Systems, such as:
(a) steam condensate
(b) fire water system
(c) feed water system
(d) circulating water system
(e) lubrication systems
(f) compressed air system
(g) chemical injection system
(h) land network system
(i) cathodic protection system
(j) water treatment system
(k) buildings
Generally, most of the interface and auxiliary systems are found on the periphery of the force island and commonly all of them are called Plant Balance.
ii) The components are all the pieces of different materials, the equipment and instruments, that once installed and intimately coupled together, form a system. There are equipment such as the Main Transformers that, due to their size, capacity, complexity or importance, are considered as systems, but if this is the case, all the components that such equipment requires to reach the borders of the adjacent systems with those that it connects, also including auxiliary equipment or components that it requires for its operation. Otherwise it is represented by the large number of pumps that are required throughout the plant, which cannot be considered as systems no matter how large they are,since in general they all have the same function (increase the internal energy of a fluid) and therefore the place where they are located does not change this function; then then each pump must be considered as a component of a system.
iii) In the case of civil works necessary for the establishment of the plant, these can also be considered as systems if we attend to the criteria of the design and operation analysis with which they are projected and / or conceptualized, since they also fulfill a function in the operation of the plant; however, the most appropriate term to name them should be Structures. In some cases the structures can also be considered as part of a system. By way of example, the heat recovery foundation can be classified as part of the heat recovery system, since said foundation works closely in conjunction with the metal structure to transmit the static and dynamic forces produced by the equipment in operation. Otherwise it is the foundation of the powerhouse,which cannot be considered as a component of the generation system, since the steam turbine works independently of said foundation. In this case, the foundation of the powerhouse should be considered part of the structure called the powerhouse (building), which has an auxiliary function (protect the equipment and support its maintenance).
Generally, design and construction companies define the list of systems, subsystems, structures and components without explicitly addressing the previous classification, that is why, when they identify the main systems, they subdivide them into subsystems. This is a very common practice considering that some systems, such as steam generation, are very complex. However, what they are actually doing by subdividing into subsystems is identifying auxiliary systems and some interface systems. Finally, the classification does not have a significant impact on the way of planning supervision, but it is relevant that all systems are identified regardless of their category or classification assigned to them.
In summary, every main, interface or auxiliary system must fulfill a unique function, (different from that of any other system) and additionally with the following criteria:
• Keep its components closely related
• Be able to be controlled independently from other systems
• Have clearly identifiable physical boundaries.
2) Define for each system, subsystem, structure or component; all the processes required for its construction, installation and assembly
A constructive process is the set of activities that transform input elements, resulting in a tangible product, either a component or a structure of any plant system. If an input or one of the transformation activities is required, the process cannot be started or the product would not be complete. Transformation activities are inherent to the process and unique to each other.
To define the processes, the following considerations are taken into account:
a) Each construction process must contain:
i) Inputs,
ii) Transformation activities (development), and
iii) A resulting product (outputs)
In order to adequately illustrate the concepts (i) inputs and (ii) transformation activities, in Fig. 1 “SCHEME OF A CONSTRUCTION PROCESS” the construction process called “Pipe Welding” is shown, modeled based on the methodology Idef 0.
In the central box the transformation activities are shown. Around the central box and highlighted in yellow are all the input elements classified by their type (title highlighted in green):
• Controls.- In the upper part of the box. These are the guidelines that guide the transformation activities.
• Inputs.- On the left side of the box. They are the components that will be transformed to obtain or join the parts that make up the system. Inputs are generally a permanent part of the finished system. Also in this classification are the plans and diagrams, which through a cognitive process of interpretation, are transformed by the personnel who direct the process, into instructions for the operating personnel.
• Mechanisms.- At the bottom of the box. They are resources that allow the carrying out of transformation activities and that are not part of the finished product.
b) To ensure whether the resulting product will meet the specified characteristics, inspection and measurement activities are carried out on the inputs, before and during the different transformation stages, to reject defective inputs and / or correct the activities in case of deviations, avoiding or minimizing the rejection of wrongly transformed inputs, rather than having to reject the finished product. However, there are so-called "special" processes, which contain activities that are carried out in such a way that they prevent the product from being fully inspected or measured during the development of such activities. In these cases, to avoid costly rejections of finished products, other types of processes are implemented, those of "validation" of the inputs of the mechanism type and the input type,and they are not part of the construction process. In Fig. 1 “SCHEME OF A CONSTRUCTION PROCESS” the special process “Pipe Welding” is shown, which contains the transformation activities: root step, filling and view; whose measurement and / or visual inspection are not sufficient to determine if the resulting component will meet the specified characteristics. In the same figure these “validation” processes are shown, represented by the boxes with interior highlighting in blue and that are found around the central box.they are not sufficient to determine whether the resulting component will meet the specified characteristics. In the same figure these “validation” processes are shown, represented by the boxes with interior highlighting in blue and that are found around the central box.they are not sufficient to determine whether the resulting component will meet the specified characteristics. In the same figure these “validation” processes are shown, represented by the boxes with interior highlighting in blue and that are found around the central box.
c) Design and Manufacturing are processes that produce tangible products that will form part of the plant's systems, but they cannot be considered as activities of the construction process.
d) The activities of handling and control of materials and components are not part of the construction process, since they do not transform the tangible product that was part of a system. Rather, these activities constitute a control-type process, which results in the preparation of the inputs for their entry into the construction process.
e) One process is different from another when they differ in at least one of their inputs and / or in one of their activities; both representative. Example: Fire pipe network installation (buried HDPE) vs. Installation of fire piping in transformers (carbon steel aerial). In this example both processes are different because the most representative input, which is the tube material, in both processes is different and therefore the installation activities will be different.
3) Define the specific activities of the process that will be supervised
a) Break down each process into the specific transformation activities that are inherent to said process and that are executed by the contractor.
b) Specific activities are reached when there is no resulting product.
c) They are also considered as specific activities of the process, those of inspection and testing during the development of the process and the product in its different stages of transformation
d) The most representative activities of a process must be chosen for their supervision, in accordance with the impact that these activities have on the entire process.
4) Define the inputs of each specific activity that will be supervised during the development of the process
The inputs of the process give the quality characteristics to the finished product. By ensuring that the necessary inputs are present, the characteristics specified for the product are ensured.
To maintain a preventive approach, the inputs of the process must be monitored before the transformation activities are carried out, this premise is the basis of a "Preventive Supervision".
The inputs are identified using the classification of inputs, mechanisms and controls, to avoid omissions and preserve order.
Here are some guidelines that will be helpful in selecting inputs:
a) Inputs are obtained through design and manufacturing processes.
i) Regarding the design, the inputs to be verified should be limited to the minimum documents that establish the characteristics of the process, the components and the system (Drawings, Diagrams and Specifications), and where appropriate the verification of the data contained in said documents could only be made by supervising the design process, such a decision should be considered in accordance with the impact that the design products have on the construction process and the operation of the systems.
ii) In relation to the manufacture of materials and components, a first-level supervision would only verify the physical state of the supplies upon arrival, and the validity and consistency of the documents (which support some of their characteristics) that accompany them; However, the scope of the retrospective verification towards the manufacturing processes will depend on the impact that these inputs cause on the operation of the plant's systems.
b) Mechanisms
i) Construction machinery and equipment give the process the characteristic of opportunity
ii) Human resources give the process the characteristic of opportunity
iii) In special construction processes, the input mechanisms must be validated, so their verification is essential to ensure the quality of the construction process and therefore of the product itself. In this case, the scope of the verification retrospectively towards the validation processes will depend on the impact that the mechanisms have on the operation of the systems.
iv) Inspection and testing activities are considered as part of the construction process, but are carried out with human resources and equipment that are input mechanisms. Considering that inspection and testing activities allow observing the characteristics of the product before the completion of the construction process and avoiding rejection in the final stage, its impact is significant on the opportunity, cost and quality characteristics required of the product, which is why these mechanisms must also be verified.
c) Controls
i) The presence of all controls that establish acceptance criteria for the way in which the transformation activities will be carried out must be verified, for example, the technical process standards, management standards and construction specifications; establish guidelines that, if followed, provide reliability to the process.
5) Define the opportunity for supervision with respect to the type of entry, activity or exit
a) Continuous supervision must be carried out on the characteristics of the input that can be inspected at the time it enters the process, and even when the changes suffered by the characteristics of said inputs can be monitored during the execution of specific activities.
b) A scheduled surveillance must be carried out when the entry corresponds to products of manufacture, validation and in some cases of inspection and testing, or control whose characteristics cannot be visually, practically and / or unilaterally appreciated before entering the process. or during specific transformation activities. Surveillance can also be applied in the verification of the characteristics of the finished product, when for any reason, these were not determined or verified during the execution of the process.
Bibliography:
Integration Definition For Function MODELING (IDEF0)
Federal Information Processing Standards Publications
Processing Standards Publication 183, December 21, 1993
Fig. 1 Scheme of a construction process
