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The Purpose of Quality Control Techniques
The Purpose of Quality Control Techniques
Nondestructive Examination – the purpose is to evaluate reliability and basic performance properties and parameters of the object being tested or its components or units in-situ and without taking the object out of service. Nondestructive control is also referred to as assessment of reliability by nondestructive methods or inspection without causing any damage to the equipment.
Visual and Measuring Inspection (VMI) – is a base inspection method, used prior to all other methods of defectoscopy. Visual method is used for quality control of basic metal materials, welds, joints and cladding surfaces both at the stage of preparation for welding and control of finished weld defects. Visual control is easily applicable, relatively cost-effective, as compared with many other visual control methods and provides accurate information on compliance of welded items to specification. VMI set consists of basic kits. Standard set includes: welder’s universal measuring gauge No.2 and universal measuring gauge No.3, universal gauge of Krasowski No.1, angle, caliper, torch, metal marker, thermostable chalk, measuring magnifier, set of clearance gauge №4, set of radius probes №1, №3, measuring tape, ruler, mirror with handle. VMI inspection is to be performed only by personnel, qualified for nondestructive control in accordance with qualification rules. Training of VMI specialists is to in line with GOST 23479, DSTU ISO 17637-2003.
Ultrasonic testing of welds (UT) is, along with other methods of inspection, (X-ray, liquid penetrant test, magnetic-particle testing) is a reliable and highly effective method to detect possible flaws; it enables to perform diagnostics of welded joints quality, inspection of metals, cast workpieces, cast steel products. UT method is based on an extensive range of inspection techniques, depending on specific conditions (material grade, its thickness, inspection surface geometry, minimum size of the detected flaws etc.) The five basic UT techniques are: shadow method, echo-shadow method, tandem inspection method, delta method and echo method. Ultrasonic waves used for UT metal inspection in the industry, as a rule, ranges from 0,5 MHz to 10 Mhz. In some cases ND testing of welds is performed by ultrasonic waves of 20 MHz frequency, which enables to detect small size flaws. Ultrasound of low frequencies is used for thick objects (ultrasound testing of casts, forgings, joints, welded by electro slag method), examination of attenuating coarse grained metals (cast iron, copper, austenitic steel) – “weak ultrasound conductivity”. UT inspection is to be performed only by personnel qualified for nondestructive control in accordance with qualification rules. The basic regulatory documents guiding UT operations are GOST 14782, ДDSTU 4001,4002-2000.
Radiographic testing (RT) — the method widely used for process pipelines quality control, steel structures, process equipment, composite materials in various industries and construction projects. Radiographic testing of welds enables to detect pores, lack of fusion, slag, tungsten, oxidic and other inclusions, shrinkage grooves, cracks. Also RT technique enables to assess weld root’s buckling and concavities in the areas inaccessible for visual inspection, from the opposite side of the welding joint, for example. Defectoscopy using metal X-ray is considered to be the most reliable inspection technique of welds and basic metal as it enables to identify the type and nature of the defected inconsistencies, their location, with sufficient accuracy, as well as archive inspection results. RT inspection is to be performed only by personnel qualified for nondestructive control in accordance with qualification rules. The basic regulatory documents guiding RT operations are: GOST 7512, GOST 23055-78, DSTU EN 12517-2002.
Magnetic particle method (MPM) is a complex of nondestructive methods used for detecting defects in ferromagnetic metals (iron, nickel, cobalt and a range of alloys based on these metals). Defects to be detected by MPM are: cracks, roaks, nonmetallic inclusions, lack of fusion, flakes. Flaws are detected only if open out for 2–3 мм, not more. Magnetic inspection technique is based on the examination of magnetic field dispersion around magnetized ferromagnetic item. Discontinuities are located by re-distribution of magnetic flux and formation of dispersion magnetic fields. Dispersion flux above surface discontinuities is located and fixed by various techniques. The most widely used method of magnetic defectoscopy is Magnetic Particle Method (MPM). In MPM defectoscopy technique magnetic powder or magnetic suspension (fine magnetic particles suspended in liquid) is applied over magnetized item. Ferromagnetic particles within magnetic field dispersion are attracted and settle on the surface near location of discontinuities. The area where magnetic particles settle may be wider than the real discontinuity area. Therefore, the outline of collected particles identify even minor cracks seen with unaided eye. Indication patterns are fixed visually or by pattern processing tools. Application of MPM inspection method is regulated by the following national standard codes: GOST 21105, DSTU EN 1290, 1291-2002.
Capillary method (CM) / Liquid Penetrant Inspection (LPI) – the method based on capillary penetration of indicating liquids (penetrants) into the surface defects and open discontinuities. Detected indications are fixed visually or recorded by pattern processing tool. CM techniques enable detection of discontinuities, length and surface orientation. LPI is used for detection of minor flaws that cannot be located visually. Depending on the ways the initial information is obtained, capillary methods are referred to as colored (chromatic) method, brightness method (achromatic), luminescent method and luminescent and colored method. Discontinuities are filled with penetrant capillary, vacuum, compression and other methods. Mostly used method is a capillary one, with which discontinuities are filled with sprayed penetrant or by brush. Basic conditions of Capillary inspection method are regulated by GOST 18442, DSTU EN 1289-2002.
Electrical ND inspection (EI) is based on generation of electrical field in the item being inspected or by direct exposure, electrical perturbation, or indirectly by thermal. mechanical exposure. Electrical inspection enables to measure the parameters of electrical field, interacting with the item being inspected (electrical method, as such) or field, generated in the item as a result of external (thermoelectrical method) and is used for inspection of dielectric and conducting materials. Methods of electrical inspection (electrostatical, powder, thermoelectrical, electro sparking, electrical potential, capacitive) are used to locate materials flaws, measure thickness of coatings and coating layers, sort metals by grade, inspect dielectrical and semiconducting materials. The disadvantage of the listed electrical ND techniques is the requirement of contact with the item being tested, stringent requirements to the item surface cleanness, measurements process control difficulties and dependence on measurement results of ambient conditions. Basic provisions of Electrical ND inspection method are regulated by the national code GOST 25315.
Thermal Inspection (TI) – method based on the object of interest temperature measurement, monitoring and analysis. Basic condition for the application of TI method is the presence of heat flows in the object of interest. The process of transfer of heat energy, release or ingress of heat in the object changes the object’s temperature against the background. Distribution of temperature over the object’s surface is the basic parameter in TI method, as it carries the information on the heat transfer specific features, object’s operation mode, its internal structure and presence of hidden flaws. In theory TI method is divided into two types: active and passive. In passive TI technique no external source of energy is required. Active TI technique, in opposite, requires the object’s exposure to heat induced by external sources. Passive TI technique implies the presence of heat field in the object at its manufacturing and service phase. The basic advantage of this method is that it enables inspection without taking the object out of service with no need in additional heating of the object being inspected. Typically, passive thermal inspection is used for the inspection of structural elements, electrical operating devices, live contacts and other industrial objects. Thermal nondestructive inspection devices mostly used in passive technique are thermovisors, pyrometers, infrared thermometers, heat flowmeters, data loggers etc. Active thermal inspection technique is used in those cases when the object while in service does not generate heat enough for thermal testing. The object being tested by the active thermal inspection technique can be heated by different external sources. Typical objects inspected with this technique are laminated composite materials and other objects that require external heat input. Depending on the temperature measuring mode thermal inspection devices are divided into contact and contact free types. Basic provisions regulating the application of thermal inspection method are laid down in the national code GOST23483.
Leak detection (LD) is a method used to detect leaks in vacuum technique, failure of air tightness in vacuum systems. Leak detection is tested by devices called leak detectors. The simplest technique of leakage detection is with spark leak detector, which locates leaks in glass envelopes by the spark occurring at the contact of leak detector’s antenna with defective area. More “sensitive” leaks in any type envelopes (glass, nonmetal etc.) are tested by mass-spectrometric leak detectors. Faulty sealing is localized by penetration into the system of the testing substance blown externally. Mass spectrometer is connected to the vacuum system and by the register’s readings the presence of leak and its size is established. Operation of halogen leak detector is based on the property of some metals emitting ions of alkaline metals impurities at heating, to increase emission in the presence of halogens (halogen effect responsible for surface ionization). Most often used testing reagents are freons. Change of ionic current shows the presence of leak and its size. Among other less popular leak detection methods is luminescent technique, etc. Basic provisions regulating the application of leak detection method are laid down in the national code GOST 23483.
Vibration diagnostics (VD) is a diagnostic method applicable to engineering systems and equipment which is based on the data analysis of vibration, caused either by the operating equipment or as a secondary vibration resulting from the structure of the object being tested. Like other methods of technical diagnostics, vibration diagnostics is used to solve the tasks of localization of failures and evaluation of technical condition of the object of interest. The subject of investigation in vibration diagnostics, normally, is time signal and vibration spectrum of certain equipment. Vibration test parameters are chosen depending on the type of mechanisms being inspected, amplitude and frequency range of oscillations being measured. Vibration displacement parameters are often measured at low frequencies, vibration velocities - at medium frequencies, vibration acceleration is measured at high frequencies. Vibration displacement presents interest in those cases, when one needs to know the relative displacement or deformation of the object. Vibration velocity is measured to analyze efficiency of vibration machinery, as it determines force impulse and kinetic energy. For assessment of object’s reliability, the basic parameter to be measured is vibration acceleration Non-contacting gauges are based on kinematic method of measuring relative vibration parameters which uses optical radio waves, etc. electromagnetic fields. Most frequently used methods in non-contacting vibration diagnostics are the optical vibration parameters measuring techniques and tools which are divided into amplitude and frequency types depending on the information extraction mode.
Acoustic Emission Method (AE) is an effective nondestructive method of inspection and material evaluation, based on detection of acoustic waves, generated at abrupt stressed material deformation. These waves are propagated directly from the source to the gauges where they are transformed into electrical signals. AE instruments measure the signals and display data, which are used to evaluate the condition and behavior of the entire structure of the object being inspected. Current systems measure both individual parameters of AE signal: amplitude, duration, energy, oscillation, arrival time, response time and other parameters related to its frequency values characteristics and digitized signal format. Population analysis of AE signals sequence enables to localize the source, its type and hazard level. Detailed analysis of the digitized signal format/spectrum provides more accurate information on the source type and signal propagation data. As the source of acoustic emission energy is the elastic stress field in materials, AE inspection is normally conducted by loading the object being inspected. This can be inspection before the object is put into operation, cyclic in-process control or monitoring. Possibility of using the method remotely makes it more advantageous over other inspection methods which require removal of isolation jackets, for example, removal of the contents from the object being tested or large areas scanning.
Eddy current Method (ECM) is based on the analysis of interaction between the external electromagnetic field and electromagnetic field generated by eddy current, induced by this field in the object being tested. Distribution and density of eddy currents depend on the electromagnetic field source, geometry and electromagnetic parameters of the object being inspected as well relative disposition of the source and object being tested. The source of the current induced by electromagnetic field is most often a sine- wave current induction coil, referred to as eddy current transducer (ECT). Basic advantage of the method is that it provides multiple parameters and non-contact inspection of the object Eddy current control in this technique can be conducted by moving the object relative to ECT with the speed that can be substantial, which ensures high efficiency of the inspection. Additional advantage of the method that ECT signals are not affected by humidity, pressure and contamination of the gas media, radiation, presence of nonconductive substances on the object’s surface and simple design of eddy current transducer. As eddy currents are generated only in electro conductive materials, the objects for inspection can be items, made of metal, alloys, graphite, semiconductors and other electro conductive materials. Eddy current method is used for defectoscopy, structurescopy, determination of coating thickness, size, conductivity and thermal treatment quality. Objects of Eddy current inspection may be electro conductive rods, wire, tubes, sheets, plates, coatings, including laminated, bearings, fittings and many other industrial products.
The acronym “EPCM” stands for Engineering, Procurement Construction Management. The Russian equivalent is Management of Capital Construction Projects. EPCM structurer implies that risks are distributed between Client and Contractor. Risks on EPCM scheme are established with regard to the chosen pricing structure.
EPCM is one of the most convenient forms of relations between Client and Contractor, as it enables to develop individual terms and conditions for implementation of each specific project. ЕРСМ Contractor is referred to as General (Main) Contractor, responsible for the investment project implementation from engineering over to commissioning and hand-over to the Client, including guarantees/warrantees after the project has been completed. EPCM services provider works with Client starting from the project idea to the early stage of the development of Business plan. Following are the key advantages of EPCM contract arrangement:
- Project cost and Budget control;
- Early identification of difficulties and possibility of working out solutions promptly;
- Contractor’s motivation to meet the Client’s interests;
- Client is free to have control over the project at all its stages.
EPCM scheme implies project management services and not the project operations management. Project Engineering & Design scope is assigned by the General Contractor to subcontractors and vendors with the duty imposed on the General Contractor to evaluate their capabilities and distribute, with good knowledge, the scope and the areas of responsibility between them. EPCM Contractor coordinates the project activities, evaluates efficiency of the work in progress, is capable to promptly react on the project changes and minimize consequences for the entire project. Depending on the Client’s preferences EPCM Contract price is established based on one of the following structures:
- Lump sum - implies enhanced risks for General Contractor. This affects Contract price.
- Unit price – extends project completion schedule with the change of the cost of works caused as a result.
- Mixed pricing – constitutes additional risks for Client in terms of the Contract price change in the course of the project.
- Cost plus – most frequently used EPCM scheme which makes Contractor much motivated to do a quality work on schedule. Indicative price may vary based on meeting the deadlines, quality requirements, subcontractors’ costs.
EPCM covers the following functions assigned to the General Contractor:
- Basic Engineering design;
- Detailed design;
- Selection and purchase of materials;
- Selection and purchase of structural elements;
- Selection and purchase of equipment;
- Selection and purchase of components.
EPCM Contractor is responsible for the Project Construction on a turn-key basis and the project guarantee liabilities following after the project completion. Client selects EPCM Contractor based on the best offer with regard to technological, technical and commercial parts of the project. EPCM Contractor is required to be ready for the Engineering & Design part and entire project completion in full scope based on the technology approved by the parties.
EPC – an English abbreviation for “engineering, procurement, construction”, ЕРС Contract is a contract between Contractor and Client, on which Contractor is responsible for the execution of the entire scope of work and bears all the risks in relation to the project construction. EPC arrangement is one of the basic types of arrangements to be considered for the purpose of construction project planning and control. Along with other types of arrangements for construction management EPC contract covers major construction process phases, namely: Engineering & Design, Procurement and Construction.
Following are the distinctive features of EPC structure:
- Construction on a turn-key basis;
- Fixed price – being Lump sum in most cases;
- Level of Contractor’s responsibility to Client is often limited by the cost of work, fixed in the Contract;
- Contractor is free to act quite independently in construction planning, with minimum authorities for the Client in relation to EPC Contractor;
- All agreed risks, including contingencies, are carried by Contractors.
Turn-key construction planning on EPC contract envisages involvement of the following categories of participants:
- Client;
- ЕРС Contractor (General Contractor);
- Engineering subcontractors for Basic Engineering design and detailed design;
- Vendors / suppliers of building materials, technologies, structural elements and equipment;
- Construction subcontractors.
Three final categories of participants of construction process work under the EPC Contractor who is responsible to the Client for their work. Client awards the project to the General Contractor and accepts the completed asset at the end of the project thus being both the first and the final link in the construction process chain. This type of arrangement is preferable to customers due to minimum level of risks, whereas contractors would not give same preference to EPC for a number of disadvantages:
- lack of typical projects;
- complexity, uncertainty and unpredictable conditions over the project construction period;
- scope and costs cannot be established with accuracy at the contract signing stage;
- multiple subcontractors involved due to the immature market of construction and installation companies in the local market which creates additional risks for EPC General Contractor in the course of the project.
EPC contractor is selected by the customer on a bid basis based on the most feasible offer of all those received, in terms of price and quality. EPC contract scheme is often used for those projects where general contractor can establish at an early stage all the costs and draw up the project budget with sufficient accuracy and foresee all possible risks which may occur in the course of construction. It is selection of the right contractor that determines construction final result.
EPCS is one of the contract arrangements between Client and Contractor for the actual construction and procurement management and construction supervision. EPCS scheme is an abridged version of EPC and EPCM models whereby the scope of work which is the responsibility of Contractor is substantially reduced, along with associated risks, as Client on EPCS contract takes up certain construction functions. Such model is more cost effective for Client as the scope is divided between a number of different subcontractors. Each contractor, involved in the project, is responsible only for part of all risks which brings down their cost of work. The limit of their responsibility and extent of potential risks in this scheme is also lower. EPCS construction management model has a number of specific features:
- Client undertakes one of the functions, which in other arrangements is assigned to the General Contractor;
- Limit of Contractor’s responsibility and potential risks become lower;
- Distribution of the construction scope between a number of subcontractors is more cost effective for the Client than execution of the entire work by the General Contractor.
Along with EPCS contract types, widespread use has been gained by some other abridged contract types, like EC (engineering and construction) and EP (engineering and procurement). In these contracts one contractor may be in charge of procurement, whereas engineering would go to the other contractor. Following are the responsibilities of Contractor under EPCS contract standards:
- Front-end Engineering;
- Feasibility study;
- Initial Design documentation (budgets, estimation of costs etc);
- Procurement management (required equipment and materials);
- Quality Control in the course of construction;
- Construction Supervision;
- HSE at the construction site;
- Participation in the transfer of the turn-key built facility.
PCM (acronym for Project Construction Management) – generally accepted international rules and standards regulating different projects management in construction industry. PCM main goals consist in formulating the notion itself and area of project management, as well identification of all typical activities in the course of the project execution and results of these activities – without being bound to specific industry peculiarities of this business. This document also includes description of all key areas of responsibility and distribution of authorities. By definition, PCM is only part of the globally tackled notion of Project Management with regard to the construction business and its projects. Basic value of the Project Management (PM) technology, in general, and Project Construction Management (PCM), in particular, consists in the following definitions:
- Client is in a position to have clear understanding of the amount of money spent, when and for what purpose;
- The Client knows exactly how much time will be required for certain process in the course of the project;
- In case of force-majeure or in case the Client makes changes, Contractor would know the cost of same – both in terms time and finance.
Following are the processes that are covered by PCM contracts:
- project content management;
- project schedule management;
- project cost management;
- project risk management;
- quality management;
- human resources management;
- procurement management.
«TechnoExpertService» developed, implemented, obtained certification and effectively operates the Integrated Management System per ISO 9001:2015 and OHSAS 18001:2007.
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