Emerging Technology: Remote Controlled Hot Tap System for Subsea Pipelines

Subsea hot tapping of pipelines is performed for a variety of reasons, including tie-ins, pipeline repair, insertion of instrumentation, facilitating chemical injection or providing access for temporary isolation tools. The full hot tap process — that is, installing the hot tap assembly, performing the tap and recovering the hot tap machine — is normally conducted with diver assistance. After bolting the assembly of the machine, isolation valve and fitting to the pipeline (or machine and isolation valve to a pre-installed flanged membrane on the pipeline), the divers then operate the machine to perform the tap, under instructions from — and supervision — by hot tap technicians located on deck of the diving support vessel (DSV). Subsequent unbolting and removal of the hot tap machine is also carried out by the divers. The demands of deep water have necessitated development of a totally diver-less, remote-controlled system. Diver operations are limited to a maximum of 300 meters of water depth, whereas a significant portion of existing subsea field infrastructure, as well as projected future developments, are in deeper waters in depths up to 3,000 meters. In addition, diver safety concerns in shallow water, as well as impaired diver efficiency in difficult environmental conditions such as wave breaking zones, prompts the call for a reduction of diver exposure or complete elimination of diver assistance. The recent completion of a remote-controlled hot tap machine (Subsea 1200RC) is an important step toward developing a totally diver-less system. The installation of the hot tap assembly and subsequent removal of the machine still require diver assistance, but the performance of the tap itself is remotely controlled by a hot tap technician from the deck of the DSV. The concept is a topside-driven hot tap machine with “passive Remotely Operated Vehicle (ROV) interface”, which means a stationary ROV with its hydraulics and control system is attached to the hot tap machine and operated from an onboard laptop. This results in a light weight hot tap frame and total direct control of the cutting process. The machine has been designed, built, tested and successfully deployed on a recent subsea tap for a pipeline operator in Asia. This technology promotes the “separation of man and machine” proposition. It reduces risk by reducing diver exposure, enhances safety, provides direct control and visibility from a laptop and facilitates fast and accurate execution. Ultimately, the concept may be extended toward onshore hot tap applications in risky environments calling for remotely operated systems. Diverless tapping is now also qualified and offered by others.

An Update to the UKOPA Pipeline Damage Distributions

The United Kingdom Onshore Pipeline Operators Association (UKOPA) was formed by UK pipeline operators to provide a common forum for representing operators interests in the safe management of pipelines. This includes providing historical failure statistics for use in pipeline quantitative risk assessment and UKOPA maintain a database to record this data. The UKOPA database holds data on product loss failures of UK major accident hazard pipelines from 1962 onwards and currently has a total length of 22,370 km of pipelines reporting. Overall exposure from 1952 to 2010 is of over 785,000 km years of operating experience with a total of 184 product loss incidents during this period. The low number of failures means that the historical failure rate for pipelines of some specific diameters, wall thicknesses and material grades is zero or statistically insignificant. It is unreasonable to assume that the failure rate for these pipelines is actually zero. However, unlike the European Gas Incident data Group (EGIG) database, which also includes the UK gas transmission pipeline data, the UKOPA database contains extensive data on measured part wall damage that did not cause product loss. The data on damage to pipelines caused by external interference can be assessed to derive statistical distribution parameters describing the expected gouge length, gouge depth and dent depth resulting from an incident. Overall 3rd party interference incident rates for different class locations can also be determined. These distributions and incident rates can be used in structural reliability based techniques to predict the failure frequency due to 3rd party damage for a given set of pipeline parameters. The UKOPA recommended methodology for the assessment of pipeline failure frequency due to 3rd party damage is implemented in the FFREQ software. The distributions of 3rd party damage currently used in FFREQ date from the mid-1990s. This paper describes the work involved in updating the analysis of the damage database and presents the updated distribution parameters. A comparison of predictions using the old and new distributions is also presented.

Effect of Thermal Aging on Strain Capacity of X80 SAW Pipes

Application of API X80 grade line pipes has been promoted to increase the operating pressure. It is generally known that the deformability of submerged arc welding (SAW) pipes is decreased by increasing strength of the pipes. The assessment of the strain capacity of X80 SAW pipes is required for strain-based design (SBD). In the assessment of the strain capacity, one of the important issues is the effect of thermal aging during the anti-corrosion coating on the yielding phenomenon. In this study, full-scale pipe bending tests of X80 SAW pipes produced by UOE process were performed to evaluate the effect of thermal aging on the strain capacity.

Multi-Tier Tensile Strain Models for Strain-Based Design: Part 2 — Development and Formulation of Tensile Strain Capacity Models

This is the second paper in a three-paper series related to the development of tensile strain models. The fundamental basis of the models [1] and evaluation of the models against experiment data [2] are presented in two companion papers. This paper presents the structure and formulation of the models. The philosophy and development of the multi-tier tensile strain models are described. The tensile strain models are applicable for linepipe grades from X65 to X100 and two welding processes, i.e., mechanized GMAW and FCAW/SMAW. The tensile strain capacity (TSC) is given as a function of key material properties and weld and flaw geometric parameters, including pipe wall thickness, girth weld high-low misalignment, pipe strain hardening (Y/T ratio), weld strength mismatch, girth weld flaw size, toughness, and internal pressure. Two essential parts of the tensile strain models are the crack driving force and material’s toughness. This paper covers principally the crack driving force. The significance and determination of material’s toughness are covered in the companion papers [1,2].

Simulation of the Response of Buried Pipelines to Slope Movement Using 3D Continuum Modeling

Pipeline integrity is affected by the action of external soil loads in addition to internal fluid pressure. External soil loads can be generated by landslides or at sites subject to ground subsidence, heave or seismic effects. Under these varied conditions of ground movement potential pipeline safety involves constraints on design and operations. The design processes includes developing an understanding of strains that could be imposed on the pipe (strain demand) and strain limits that the pipe can withstand without failure. The ability to predict the pipeline load, stress or strains state in the presence of soil restraint and/or soil displacement induced loading is not well described in design standards or codes of practice. This paper describes the ongoing work involved in a study investigating the mechanical behavior of buried pipelines interacting with active landslides. Detailed pipe-soil interaction analyses were completed with a 3D continuum SPH method. This paper describes the LS-DYNA numerical modeling process, previously developed by the authors, which was refined and applied to site-specific conditions. To illustrate the performance of the modeling process to consider a translational slide, additional numerical model validation was completed and is described in this paper. These comparisons illustrate that good agreement was observed between the modeling results and experimental full scale trial results. Sample results of the application of the validated 3D continuum modeling process are presented. These results are being used to develop generalized trends in pipeline response to slope movements. The paper describes both the progress achieved to date and the future potential for simplified engineering design tools to assess the load or deformation capacity requirements of buried pipelines exposed to different types of slope movement.

Applying the Quantitative Risk Assessment (QRA) to Improve Safety Management of Oil and Gas Pipeline Stations in China

The oil and gas pipeline companies in China are facing unprecedented opportunities and challenges because of China’s increasing demand for oil and gas energy that is attributed to rapid economic and social development. Limitation of land resource and the fast urbanization lead to a determinate result that many pipelines have to go through or be adjacent to highly populated areas such as cities or towns. The increasing Chinese government regulation, and public concerns about industrial safety and environmental protection push the pipeline companies to enhance the safety, health and environmental protection management. In recent years, PetroChina Pipeline Company (PPC) pays a lot of attention and effort to improve employees and public safety around the pipeline facilities. A comprehensive, integrated HSE management system is continuously improved and effectively implemented in PPC. PPC conducts hazard identification, risk assessment, risk control and mitigation, risk monitoring. For the oil and gas stations in highly populated area or with numerous employees, PPC carries out quantitative risk assessment (QRA) to evaluate and manage the population risk. To make the assessment, “Guidelines for quantitative risk assessments” (purple book) published by Committee for the Prevention of Disasters of Netherlands is used along with a software package. The basic principles, process, and methods of QRA technology are introduced in this article. The process is to identify the station hazards, determinate the failure scenarios of the facilities, estimate the possibilities of leakage failures, calculate the consequences of failures and damages to population, demonstrate the individual risk and social risk, and evaluate whether the risk is acceptable. The process may involve the mathematical modeling of fluid and gas spill, dispersion, fire and explosion. One QRA case in an oil pipeline station is described in this article to illustrate the application process and discuss several key issues in the assessment. Using QRA technique, about 20 stations have been evaluated in PPC. On the basis of the results, managers have taken prevention and mitigation plans to control the risk. QRAs in the pipeline station can provide a quantitative basis and valuable reference for the company’s decision-making and land use planning. Also, QRA can play a role to make a better relationship between the pipeline companies and the local regulator and public. Finally, this article delivers limitations of QRA in Chinese pipeline stations and discusses issues of the solutions.

Safety Levels Associated With the Ultimate Limit State Reliability Targets in Annex O of CSA Z662

In 2005, guidelines for the application of reliability-based design and assessment (RBDA) to natural gas pipelines were developed under PRCI sponsorship. The methodology underlying these guidelines has since been adopted as a non-mandatory Annex in the CSA Z662 standard (Annex O). Because the methodology is based on the concept of consistent risk, it is more restrictive than current design standards for some pipelines and less restrictive for other pipelines. Specifically, the RBDA reliability targets for ultimate limit states (ULS) are lower than the reliability levels achieved by current design standards for large diameter, high pressure pipelines in Classes 2 to 4 (referred to in this paper as high consequence pipelines) and for all pipelines in Class 1. This has naturally led to questions among users and reviewers of RBDA regarding the adequacy of the ULS reliability targets for these pipelines. For high consequence pipelines, the safety levels associated with the ULS reliability targets are compared to risk tolerance criteria from three published European standards. The comparison demonstrates that the targets are generally more conservative than all three standards. For Class 1 pipelines, the average failure probability for pipelines designed to the RBDA methodology is compared to the average failure probabilities for pipelines designed to ASME B31.8 and Clause 4 of CSA Z662. This shows that there is no significant difference in overall failure probability because the wall thickness for most Class 1 pipelines with low ULS targets are governed by other criteria, such as minimum permitted wall thickness and maximum diameter-to-thickness ratio for standard line pipe. Recognizing the potential difficulties with reliability targets that do not govern any designs, a possible modification to align the targets with the actual reliability levels is proposed.

Hierarchical Bayesian Corrosion Growth Model Based on In-Line Inspection Data

A hierarchical Bayesian growth model is presented in this paper to characterize and predict the growth of individual metal-loss corrosion defects on pipelines. The depth of the corrosion defects is assumed to be a power-law function of time characterized by two power-law coefficients and the corrosion initiation time, and the probabilistic characteristics of the parameters involved in the growth model are evaluated using Markov Chain Monte Carlo (MCMC) simulation technique based on ILI data collected at different times for a given pipeline. The model accounts for the constant and non-constant biases and random scattering errors of the ILI data, as well as the potential correlation between the random scattering errors associated with different ILI tools. The model is validated by comparing the predicted depths with the field-measured depths of two sets of external corrosion defects identified on two real natural gas pipelines. The results suggest that the growth model is able to predict the growth of active corrosion defects with a reasonable degree of accuracy. The developed model can facilitate the pipeline corrosion management program.

Meeting the New Regulatory Requirements for Pipeline Control Room Management

The U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) has amended the U.S. pipeline safety regulations to prescribe safety requirements for controllers, control rooms, and Supervisory Control and Data Acquisition (SCADA) systems used to remotely monitor and control pipeline operations. The objective of Control Room Management (CRM) is to help assure the controllers will continue to be successful in maintaining pipeline integrity and safety, and help reduce the number and consequences of shortfalls in control room management practices and operator errors when remotely monitoring and controlling pipelines and responding to abnormal and emergency conditions. CRM helps to address this by prescribing safety requirements intended to verify that procedures, systems, and equipment are well thought out and function as intended. CRM also intends to help assure that pipeline operators are addressing human fatigue risks and other human factors inside the control room that could inhibit a controller’s ability to carry out the roles and responsibilities the operator has defined for the safe operation of the pipeline. This paper will go over the background and elements of the rule, additional guidance and resources that have been provided publically, and lessons learned through the development and roll out of the new requirements.

Pressure Correction Factor for Strain Capacity Predictions Based on Curved Wide Plate Testing

Strain-based girth weld defect assessment procedures are essentially based on large scale testing. Ever since the 1980’s curved wide plate testing has been widely applied to determine the tensile strain capacity of flawed girth welds. However, the effect of internal pressure is not captured in curved wide plate testing. Accordingly, unconservative predictions of strain capacity occur when straightforwardly transferred to pressurized pipes. To address this anomaly, this paper presents results of finite element simulations incorporating ductile crack growth. Simulations on homogeneous and girth welded specimens indicate that a correction factor of 0.5 allows to conservatively predict the strain capacity of a pressurized pipe through wide plate testing under the considered conditions.