Codified fitness for service methods such as API 579 or BS 7910 require consideration of residual stresses in fracture assessments, and guidance is given for upper bound residual stress distributions in common weld geometries. However, these distributions are not appropriate for some welding processes currently or historically used in the manufacture of linepipe, such as high frequency induction welding or flash butt welding. In addition, some linepipe manufacturing routes generate large plastic strains which result in high residual forming stresses, or mechanically relax residual stresses generated in earlier stages of production. This paper first reviews the code recommendations for the effects of plastic strains and stresses from high level pressure testing on residuals stresses. The paper then briefly describes the major methods of producing carbon steel linepipe and provides recommended residual stress levels for the seam weld and parent material of linepipe using the code recommendations. These are based on assumed uniform residual stresses combined with mechanical stress relaxation due to manufacturing steps such as cold expansion and hydrostatic testing. The recommendations are compared with measured residual stress levels from the open literature. Proposals are given for reduced residual stress levels when assessing axial cracks in carbon steel linepipe.

Pressure testing of pressurised equipment is crucial in establishing confidence that it is capable of performing the duty for which it has been designed and fabricated. A pressure test is usually mandated by pressurised equipment design codes for newly fabricated equipment. Also many regulations or industry codes for the design and fabrication of pressurised equipment require that a pressure test is performed on any modified in-service pressurized equipment to verify that the integrity of the equipment has not been compromised after such modifications. Although the usual and normally the preferred method of pressure testing is conducting a full hydrostatic test on the entire equipment (i.e. using a liquid medium, typically water), there may be occasions that a hydrostatic test is simply not practical. As an alternative to a full hydrostatic test, the designer may consider performing a localized pressure test or sometimes a full pneumatic test on modified equipment. It must be emphasized that a full pneumatic test can create extreme hazards to a facility and nearby personnel and therefore needs a careful and methodological assessment prior to being attempted on any equipment. This article is structured primarily as an attempt to assist the organizations in charge of design and inspection of newly fabricated or in-service equipment to identify general hazards associated with pneumatic test of pressurised equipment in a structured manner. An analysis of a simple cylindrical pressure vessel is presented to provide a better understanding of hazards associated with pneumatic test. Two tables in the paper provide the recommended exclusion zones from the equipment being pneumatically tested in order to reduce hazards associated with shock waves and/or projectile fragments. The paper also briefly explains alternative methods of testing in lieu of a full hydrostatic or pneumatic test. [1, 2]

The current upper limit of hydrostatic test pressure in KT-3 of ASME Sec. VIII Division 3 is determined by general yielding through the thickness obtained by Nadai’s equation with a design factor of 0.866 (= 1.732/2). On the other hand, the upper limit of hydrostatic test pressure in 4.1.6 of the ASME Sec. VIII Division 2 is determined by general yielding through the thickness with a design factor of 0.95. In cases where a ratio of hydrostatic test pressure to design pressure of 1.43 similar to PED (Pressure Equipment Directive) is requested, the upper limit of hydrostatic test pressure may be critical for vessel design when material with a ratio of yield strength to tensile strength less than 0.7 is used. In order to satisfy the requirements in KT-3, it is necessary to decrease design pressure or increase wall thickness. Therefore, it is proposed to change the design factor of intermediate strength materials to obtain the upper limit of hydrostatic test pressure. In this paper, a new design factor to obtain the upper limit of hydrostatic test pressure is proposed and the validity of this proposal was investigated by burst test results and elastic-plastic analysis.

Pneumatic pressure testing is used extensively during construction of LNG plants to avoid the problems that can be caused by water that may be left in a piping system (particularly in valves) if hydrotesting was performed. Due to the much greater compressibility of gas, there is significantly more energy (and thus risk) associated with a pneumatic test than with a hydrostatic test. A major gas project safely conducted numerous pneumatic tests with stored energies of up to 6,675 MJ. Observing a commonly used limit of 270 MJ would have resulted in hundreds of additional closure welds. This paper discusses practical aspects of performing pneumatic testing, the risk mitigations put in place and present two calculation methods that can be used to check whether exclusion zones for blast wave pressure are adequate for fragment throw.

Brittle fractures in parent material carbon steel pipe, fittings, and flanges are surfacing in recent ASME B31.3 refinery and gas plant construction and facility start-ups with unexpected low toughness of 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at −10°C (14°F) to −29°C (−20°F). The issue is becoming wide-spread globally, affecting up to 30 percent of materials tested, although many manufacturers are not experiencing this issue. The issue creates a new brittle fracture risk that needs to be addressed as the uncertainty of not knowing suitability for service at temperatures down to −29°C (−20°F) is concerning for reliability and safety. These components are considered by ASME VIII Div I and ASME B31.3 Code as being inherently ductile, and brittle fracture resistant without any Charpy impact testing requirements. Testing showed brittle transgranular cleavage cracks. The components were deemed to be unsuitable and not safe for use at low temperatures even though they complied with the applicable ASME Codes [1, 2] and ASTM material standards. Low toughness can result in brittle fracture of the material during hydrostatic tests, cold start-ups, or upset conditions that result in low temperature operations. Additionally, some ASTM A350 LF2 CL1 [3] forged flanges certified to −46°C (−50°F) exhibited the same 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at −46°C (−50°F). This paper discusses historical literature, metallurgical investigations, findings, and factors that contribute to susceptibility to brittle fracture including chemistry, grain size, heat treatment and forming techniques and also issues of ductile to brittle temperature transition shift, and fracture mechanical assumptions. This paper provides guidance to ensure the components are suitable for service and proposes options in addition to the current minimum Codes requirements to mitigate risks of in-service brittle fracture.

In response to the National Transportation Safety Board (NTSB) Recommendation P-09-1, the Department of Transportation (DOT) Pipeline and Hazardous Material Safety Administration (PHMSA) initiated a comprehensive study to identify actions that could be implemented by pipeline operators to significantly reduce longitudinal seam failures in electric resistance weld (ERW) pipe. As part of the project, Task 4 in Phase II was designed to validate existing failure prediction models and, where gaps exist, refine or develop these models needed to assess and quantify defect severity for cold welds, hook cracks, and selective seam weld corrosion (SSWC) (the primary ERW/Flash Weld seam threats) for failure subject to loadings that develop both during hydrotests and in service. These models would then be used to develop software to support integrity management of seam welds with enough flexibility to benefit from the experience gained during this project. The purpose of this paper is to review the models used for fatigue crack growth rate (FCGR) calculations. Both the Willenborg Model, which is used to incorporate the retardation of crack growth after an overload occurs (such as a hydrostatic test in a pipeline), and the Walker Model, which is used to account for variation in stress ratio during the operation of a structure (i.e. pressure cycles in a liquid pipeline), will be discussed. Laboratory fatigue crack growth rate test results on several grades of pipe will be used to generate the constants employed in these models. The reports generated during the course of the project are publicly available and are located on the following PHMSA website: http://primis.phmsa.dot.gov/matrix/PriHome.rdm?pri=390.

Large, pressure-containing equipment used in subsea production, including Christmas trees (XTs), gate valves, flowloops, jumpers, and connectors, are constructed of low-carbon steel and cladded with corrosion resistant alloys such as Alloy 625. Cladding is a welding process that generates high tensile residual stresses on the cladded layer and on the heat affected zone (HAZ). High pressure high temperature (HPHT) equipment for subsea applications, designed to operate above 15 ksi internal pressure and 350°F, is also cladded. This equipment experiences severe working conditions in the field, plus cyclic loading during operations, such as riser loads, installation, intervention and, most importantly, startup and shutdown sequences. Per API 17TR8 guidelines, all HPHT equipment be hydrostatically tested to 1.5 times the equipment rated working pressure (RWP). For 20 ksi equipment, the hydrostatic test pressure is 30 ksi, which can significantly deform any highly localized stressed regions. These regions deform plastically when test pressure is applied. When the pressure is bled, these regions experience high compressive stresses due to surrounding materials that are still elastic. This paper analyzes a simplified HPHT cladded gate valve (GV) body for fatigue loading (pressure cycles only) using the ASME Sec VIII, Div-3 method. The fatigue stress amplitude is calculated using an elastic-plastic material (E-P method) finite element analysis. In this method, first, the residual stress from the cladding process is simulated, and then the hydrotest is simulated on the component. During the hydrostatic test, fatigue sensitive regions (FSRs) or highly localized stressed regions such as the valve cavity and seat pockets, deform plastically, and the initial weld tensile residual stress turns to compressive (similar to autofrettage). Later, when these components are subjected to working pressure cycles (startup and shutdown), the shear stress range remains the same but the mean stress on the FSR reduces significantly. By considering all types of residual stresses, the high cycle fatigue life can be predicted with a high degree of accuracy.

In this article we have analyzed a water hammer event that occurred during the hydrostatic test of an oil pipeline. As a result of a significant dynamic loading event the piping was thrown off of its supports. We have performed dynamic calculations in the frequency domain with two models. The first model is a 2-DOF mass-spring model, used to perform an engineering assessment of the pipeline. The second model is a complex piping model of the aboveground section, which matches the real pipeline geometry and physical properties as well as possible. The Duhamel integral was used to calculate the transient response of the pipeline to the local water hammer impulse loading. The analysis results were used to estimate the pipeline displacement, and to develop certain practical recommendations to prevent such damage in the future.

Pressure vessels designed for the internal pressure are required to be subjected to hydrostatic test after completion of their fabrication. Two methods are provided in the ASME Sec. VIII Div.2 to calculate the minimum test pressure. One method is based on the Maximum Allowable Working Pressure of the vessel or the MAWP and the other is based on the highest permissible pressure of the vessel at the test condition. This latter pressure is also known as the ‘calculated’ test pressure or the pressure based on the Maximum Allowable Pressure in new and cold condition or the MAP. In either case, the induced primary membrane stress, Pm, shall satisfy the below condition Pm ≤ 0.95 * Sy where, Sy is the yield strength of the material at the test temperature. It is common to notice in many User’s Design Specifications (UDS), the requirement to test the vessels at the ‘calculated’ test pressure. In the year 2007, major changes were made to ASME Sec.VIII Div.2. Some changes that had relevance to the hydrostatic testing were the change in the basis of the allowable stress at room temperature to the yield strength for most materials, increase in the factor on the test pressure basis to 1.43 and the corresponding increase in permissible limits on the induced primary membrane stress to 0.95*Sy. It is noted in pressure vessels, built with cylindrical shells and(/or) with hemispherical dished heads with materials whose maximum allowable stresses at room temperature were dependent on the yield strength, that the membrane stress induced when subjected to ‘calculated’ test pressure exceeded the Code limit of 0.95*Sy. Increasing the thickness of the shell and(/or) head did not result in containing the stresses below 0.95*Sy as such an increase in thickness resulted in proportional increase in the MAP values and therefore, further increase of the test pressure. The objective of this paper is to first derive the actual membrane stress induced in the vessel subjected to the ‘calculated’ test pressure and provide an engineering solution to the problem of induced stress exceeding the Code limit in order to achieve Code as well as the UDS compliance.

After the replacement due to the well known problem of weld seam #111 the steam generators (SG) of the Ukrainian WWER-1000 type nuclear power plants (NPP) have been in operation for almost 25 years. So now, the main practical problem related to the SG is the leakage/breaking of heat exchanger tubes (HET). If the leakage criterion is not satisfied the NPP Unit has to be stopped until the corresponding HET is plugged, which leads to unexpected huge financial losses. Every year at least 12.5% of the SG HETs are controlled by eddy current inspection, after which some of the HETs are plugged according to the appropriate plugging criteria (in most cases – 65% loss of tube wall thickness). Thus, every SG has its own statistics of plugging. From the practical point of view the Utility is interested in the following questions: whether the failure of the HET happens during the normal operation mode (NOM) up to the next NPP stop or not; what is the probability of this event; what is the defect growth rate? Answers on these questions could give us the opportunity to increase the effectiveness of the HET in-service inspection and to improve the plugging criterion. A simple statistically-based method for HET integrity assessment is proposed. The method based on an exponent distribution law and HET plugging statistics of specific SG, taking into account defect growth. Based on the history of the tubes plugging (year of operation versus quantity of pluggings) the three statistical parameters inherent to this specific SG have to be found: initial number of defects, parameter of the exponential distribution (initial defect size) and the defect growth rate. The developed method was used for the prediction of HET leak/break number for all Ukrainian WWER-1000 SG. It is shown that for those SG which has less than 2% HET pluggings the accumulated pluggings as of the end of the next year of NOM will not exceed this value. Based on the Ukrainian history of WWER-1000 SG operation the database of HET plugging is presented. This method is also used for justification of pressure reduction of periodic hydrostatic test (HT) for primary circuit of WWER-1000 and WWER-440 NPPs from 24.5 MPa to 20.3 MPa and from 19.1 MPa to 15.7 MPa, correspondingly. To justify a reduction of the HT pressure, a quantitative, risk-informed assessment of HT effectiveness has been performed with taking into account the HT pressures change. The HET failure probability is calculated as the proportion of defects which exceed critical sizes for NOM and HT. Limit load models are used for the determination of the critical defects size. The variation of reliability is calculated as the difference between fracture probability during NOM after HT at routine and reduced pressures. It is shown that HT pressure reduction does not practically increase the fracture probability during operation, and satisfies the criteria of risk change.

This paper mainly introduced the Chinese codes and standards of glass-lined pressure vessels. The manufacture and major maintenance of pressure vessels shall be subject to supervision and inspection by the authorized inspection institutions in accordance with the safety technical codes. Design, materials, weld, nondestructive testing, glass-lined process, hydrostatic test and leak test were investigated. In addition, test specimens for calculating wall thickness, Welding Procedure Qualification and Glass-lined Procedure Qualification were analyzed. TSG R7004-2013 Regulation on Supervision Inspection for Pressure Vessel specifies Glass-lined Procedure Qualification shall be carried out before glass-lined. Glass-lined procedure qualification is used to control temperature range, heating rate, holding time, and cycle times. The glass-lined process is absolutely critical to the longevity of the glass-lined vessel.

A quick opening closure using a new rubber sealing ring was proposed in this paper, which can be used in natural gas transmission filters. An innovative saddle-shaped sealing ring with the feature of floatability was designed for substituting of traditional rubber C-ring. A lager gap could be allowed between the door and the top flange which made the assembling and disassembling easier than before. The theory of strength calculation and check for the whole steel structure were also presented. For an actual engineering case, a device with internal diameter of DN1550 (62inches) and design pressure of 12.6MPa (1827.5psi) was designed by rule according to Chinese national standard GB150 and analyzed by FEA (ANASYS). In addition, the sealing performance was simulated by FEM analysis (ABAQUS). Finally, the prototype was produced and the experiments for its sealing and load-bearing performance using hydrostatic test and stress test were carried out successfully.

An analysis is formulated to determine how reductions in test pressures change the effectiveness of hydraulic strength tests (HT). The analysis is applied to Series 1000 Water-Water Energetic Reactor (WWER-1000) nuclear power plants (NPP) operating in countries of the former Soviet Union. During periodic HT for these reactors, the applied pressure exceeds the pressure for the normal operation mode (NOM) by a factor of more than 1.5. These HT pressures are among the highest in the nuclear industry. It is desirable to reduce the HT pressure in order to minimize potential damage to equipment due to pressurization during the tests. To justify a reduction in the HT pressure, a quantitative, risk-informed assessment of HT effectiveness for changes in HT pressures has been performed. This assessment follows the guidelines of INSAG-25 [1]. A deterministic analysis is used to calculate the HT minimum temperature, based on the estimation of the damage caused by HT and the evaluation of the warm prestressing effect. A probabilistic analysis is used to estimate the change in the probability of equipment fracture caused by a reduction in the HT pressure. The probabilistic analysis assumes that HT is performed as a destructive control method for replaceable components, so that HT combined with replacement or repair of defective components increases their reliability. A simple probabilistic analysis method, based on an exponent distribution law for defect depth and a lognormal law for the defect aspect ratio, taking into account laws for defect growth, has been proposed. The fracture probability is calculated as the proportion of defects that exceed critical sizes for NOM and HT. Limit load models are used for the determination of the critical size of defects. The variation in reliability is calculated as the difference between fracture probability during NOM after HT at routine and reduced pressures. The calculation results make it possible to analyze the effect of HT pressure reduction for WWER-1000 NPPs.

This paper proposes an analysis method for Section III, Division 1, Class 3 buried High Density polyethylene (HDPE) piping system in the nuclear power plants (NPP). Although HDPE pipe would yield at high temperature (limited to 140°F), it may be suitable for the areas prone to earthquakes; owing to its comparable ductility and flexibility. Thus, the buried HDPE piping may be applicable for the safety related Essential Service Water (ESW) system in the NPPs. Despite some limitations to buried HDPE piping, the piping could be designed based on ASME Code Case [1]. Generally, codes and standards including ASME Code Case [1] do not provide load combinations for the design of both buried steel piping and HDPE piping. Meanwhile, EPRI Report [4] provides load combinations including thermal expansion effects and seismic loads with detailed seismic criteria for polyethylene pipe. In this paper, load cases and load combinations for buried HDPE piping are suggested for implementation of reference documents and a buried HDPE piping system is analyzed referring to EPRI Report [4] to evaluate stress, force, and moment using a piping stress analysis program. Additionally, this paper will recommend the design procedure in accordance with ASME Code Case [1] using an example of buried HDPE piping analysis. An investigation of soil spring coefficients and the design considerations for hydrostatic tests are suggested for the enhanced analysis of buried HDPE piping.

Title 10 of the Code of Federal Regulations, Part 50 Appendix G (10CFR50 App. G) prescribes the pressure-temperature (P-T) limits for light water power reactors by incorporating American Society of Mechanical Engineers (ASME) Boiler & Pressure Vessel Code, Section XI, Appendix G (ASME App. G) by reference. The P-T limits in ASME App. G are based on the fracture toughness of the vessel limiting material accounting for irradiation effects. The fracture toughness of the limiting material is determined based on the plane strain fracture toughness, K Ic , indexed to the material reference temperature, RT NDT . Prior to the 2000 Addenda of ASME App. G, fracture toughness was based on the arrest fracture toughness, K Ia , but the approval of Code Case N-640 [1] in 1998 changed the fracture toughness basis to K Ic . In addition to the P-T limits determined by ASME App. G, 10CFR50 App. G sets additional minimum temperature requirements that limit the operating pressure based on other factors such as the minimum unirradiated reference temperature, RT NDT(u) , of the material in the closure head flange region. This paper presents an analysis of the closure head flange region minimum temperature requirements based on both K Ia and K Ic . Recommendations for potential alternative minimum temperature requirements are made for normal operation and hydrostatic test conditions.

Fitness-for-service assessment of pressure vessels and piping often involves the evaluation of existing or potential crack-like flaws to guard against fracture or leaks that could be caused by the presence of such flaws. This paper presents an inelastic fracture mechanics model that has been developed to evaluate longitudinal surface cracks in pipelines, piping and pressure vessels subjected to internal pressure loading. The model uses the J-integral parameter to predict toughness-dependent failure and an effective flaw concept to predict flow-strength dependent failure. The concepts of the model are reviewed. Then, the model is used to evaluate the results of in-service failures and full-scale burst testing of steel pipe and pressure vessel samples. Application of the model to remaining life assessment based on inspection data and hydrostatic testing results is illustrated. Stress-corrosion cracking (SCC) and fatigue are considered as possible crack-growth mechanisms. Examples of typical remaining crack-growth life calculations are presented using both deterministic and probabilistic methods. The benefits of each method are discussed. Finally, planned future additions to the model are presented.

The emergence of fitness-for-service standards has created an opportunity to advance pipeline integrity assessment technology and methodologies. This paper describes modern approaches for assessing cracks and other planar flaws in pipelines. Many traditional approaches rely on simplistic characterizations and equations that have not evolved to take into account advancing technologies. For example, the NG-18 method dates from the early 1970s and is still widely used today. However, so-called conservative methods such as NG-18 can actually be unconservative in some instances, such as when used to determine hydrostatic testing intervals. This paper highlights today’s advanced approaches to pipeline integrity assessment. Case studies are presented illustrating the assessment of pipeline anomalies, such as crack assessment following hydrotesting and simulation of burst tests using a ductile fracture model.

Full Structural Weld Overlays (FSWOL) have been used successfully in the nuclear power industry for a number of years to mitigate and repair small (4 ″ ) to medium (10 ″ ) bore welded piping components susceptible to primary water stress corrosion cracking (PWSCC). Mitigation is provided by the creation of compressive residual stress on the inside surface of the pipe as layers of weld overlay are deposited over the outside surface of the pipe. ASME Code Case N-740-2 requires that these overlay designs provide adequate structural integrity considering the growth of postulated 75% through-wall inside surface flaws by PWSCC and cyclic fatigue. Application of this repair procedure to larger diameters components such as 30 inch reactor vessel nozzles is not practical due to the large amount of weld metal (overlay thickness) which would be required to satisfy the design requirements of a FSWOL and the associated demands on implementation schedule and exposure to radiation. An alternate procedure is currently being considered for these larger components which utilizes an Optimized Weld Overlay (OWOL) design based on a reduced thickness and smaller postulated flaw. In particular, ASME Code Case 754 specifies, in part, that 50% through-wall inside surface flaws be shown to be acceptable. Furthermore, an OWOL would continue to provide mitigation of materials susceptible to PWSCC by requiring that the thickness of the overlay be sufficient to induce compressive residual stress on the inside surface. This paper presents results of finite element analysis for an optimized weld overlay on a large bore (30 ″ ) reactor vessel coolant nozzle dissimilar metal weld, with particular attention to the incremental development of residual stress with each layer of weld metal. Through numerical simulation of the complete fabrication history, including repair of the original dissimilar metal weld, hydrostatic testing, and completion of the nozzle safe end-to-pipe joint prior to implementation of the overlay, the pre-overlay state of stress is defined for use as the basis for evaluating the stress improvement provisions of the weld overlay process. Results are obtained for both kinematic and isotropic hardening rules to study the effect of these two extreme measures of material characterization on the development of residual stress. Additional results are presented to study the sensitivity of the welding simulations to material yield strength and mesh refinement. Predicted stresses are also compared to measured data from a full scale mockup of a large bore reactor vessel nozzle with an optimized weld overlay.

The objective of this study is to analyze the effectiveness of the Cold Hydrostatic Test (CHT) process and determine the optimum method of completing a CHT through case studies in the Korea nuclear power plants. In this study, all the 9 CHT cases, performed for the past sixteen years (1993 to 2009) in Korea nuclear power plants, will be examined and evaluated. There are twenty (20) operating Units and eight (8) Units under construction at 3 nuclear facility sites in Korea. Among the 20 Units, only 4 Units at the Wolsong site are pressurized heavy water reactors (PHWR), the others are pressurized light water reactors (PWR). CHT is based on the requirements of ASME NB-6200 & NC-6220. CHT is a mandatory test to verify integrity of weld points and interfaces associated with the equipment and pipes of the Reactor Coolant System (RCS) pressure boundary. The design pressure of the RCS is 2,500psia (175.8 kg/cm 2 a). The major steps of test sequence of a CHT is RCS filling, venting, heat up, pressurization and inspection. Reactor Coolant Pump (RCP) operation is utilized as thermal input to raise RCS temperature over 120 °C. The Chemical and Volume Control System (CVCS) Charging Pump, or temporary hydro pump is used to pressurize the RCS. CHT requires pressure to be raised and maintained more than 10 minutes at 1.25 times of design pressure, and then be depressurized and inspected at the design pressure of 2,500psia (175.8 kg/cm 2 a). According to the analyzed results of the CHT cases, all CHTs were successfully conducted but there are several items which need to revised and modified for increased effectiveness of the CHT. These items include pressurizer manway gasket leakage, improper process of the procedure and others. In conclusion, the results of this study will be used to prevent similar errors and improve the effectiveness of the CHT for future nuclear power plants projects in Korea.

This paper will examine some of the considerations for using finite element analysis when evaluating pressure vessels constructed using the layered-shell construction. Since the layers of the shell interact through contact and at the circumferential welds, these particular aspects are discussed. Special attention is paid to the proper selection of the initial gap between the layers. The use of an elastic-plastic stress-strain curve is also discussed. Since the material model is non-linear, the path-dependency of the loading sequence is demonstrated, including the inclusion of the initial hydrostatic test. The techniques presented will be demonstrated using an example of a typical layered shell pressure vessel. Since the evaluation of this type of vessel is usually undertaken in a fitness-for-service sense, and fatigue is often the primary damage mechanism, the remaining fatigue life of this typical pressure vessel is calculated.