By Khaled Al Khouja, Senior Static Equipment Engineer, ADNOC Sour Gas
Process piping systems are generally designed based on static analysis with little or no attention paid to the vibration induce fatigue phenomenon. This is since most piping codes do not address the piping vibration issue in a meaningful way resulting in piping induced fatigue failures (IFF) which are handled on reactive basis.
The system empowered ADNOC Sour Gas to cover multiple challenge in operations like the dynamic change of operating parameters during summer high temperatures and winter conditions due to the change of kinetic energy (and multi-phase void fraction) in the piping.
The system allows to develop a preliminary understanding of vibrations, mechanisms, causes, effects, and to provide guidelines to perform vibration screening of process piping prior to performing any vibrations measurements, henceforth, focus efforts and manpower on piping with high likelihood of failure (LOF), Such practices will allow engineers to identify the piping system subjected to concern level of vibration that will require the intervention of a vibration specialist.
This document will only cover flow induced vibrations and will not discuss acoustic induced vibrations and is in alignment with Energy Institute Guidelines for Avoidance of Vibration Induced Fatigue Failure in Process Pipework1.
It can be use but not limited to the following cases:New Process System is designed
Modifications (Expansion, debottlenecking, etc.) to an existing plant.
Assessment of the health of a piping system for an operating plant
It is important to understand the vibration and its causes in order to carry technical studies and the risk imposed on oil and gas plants. The methodology followed by ADNOC Sour Gas is based on the guidance given in the EI Guidelines for New Design, Existing Plant and Change to Existing Plant1.
Measurements Assessment
Vibration non-specialists who will be using the system will only be required to identify lines to be taken for further assessment by vibration specialist, and thus, building the confidence on other safe to operate lines. A simple schematic below summarizes the process to be followed, and it will be described in detail in the following sections.
The overall governing methodology flow charts:
Populate:
The first step is to populate all lines that either already vibrating, has the potential to vibrate and/or special cases to be considered if any modification is proposed. This includes all information required to properly assess the lines, the following data is required as a minimum:
P&IDs
PFDs and HMB for Stream Properties
Isometric drawings to find span length and stiffness
Piping specifications
The list of lines to be screened should also incorporate all plant integrity issues and failures as follows:
Identify the locations of failures and any similar susceptible locations
Review failure investigation or metallurgical reports
Correlate operating conditions with high vibrations or failure history and identify under what conditions the vibrations occur.
Review design studies.
Review any available previous measurement data, considering the frequency and the amplitude
Screen:
Screening includes developing general understanding of the piping systems to be screened and evaluate the LOF (likelihood of failure) of each line as per the expected potential vibration causes described earlier in the document. Screening can be done manually or using a web-based application described in the paper and developed by Wood (Veridian).
Veridian is a web-based screening tool available online for everyone to use. It is used to identify and assess vibration risk in process piping systems as per the EI guidelines1.
Veridian must be loaded with all required information in order to make the qualitative assessment as highlighted earlier and to determine the LOF before completing further studies and implementing mitigation measures.
Data required for Veridian screening:
P&IDs are referred to identify the possible causes of piping vibration
PFDs and HMB to extract the Stream Properties
Piping specifications documents
Upon completion of the entry of line details, users will be provided with a preliminary assessment of Likelihood of failures and the source and mechanism of vibration based on the information provided by user, below figures highlights multiple lines plotted into the interface and the resultant LOFs.
Following calculation of the mainline LOF scoring, there are various actions that are initiated depending on the LOF level, these are detailed as follows:
Measure:
Post Screening Visual Assessment
The primary objectives of the post screening visual assessment are to:
Carry out a visual, experience-based inspection of the identified piping identified piping, with respect to reviewing the as-built condition, identifying as-built anomalies, determining measurement requirements, e.g. access constraints, piping insulation for removal, etc.
Where possible, carry out spot vibration severity and dynamic stress “basic” measurements on the lines identified as being of concern.
Where appropriate, collect small bore connection geometry data for mainlines for input into a quantitative small-bore connection assessment.
Generation of site work packs showing locations of high vibration and dynamic stresses to guide subsequent, more detailed ‘complex’ measurements (where required).
Where vibration measurements are required, there are two broad definitions of field measurement activity, these are as follows:
Basic – Simple spot vibration severity or dynamic stress assessments utilizing portable, handheld vibration measurement equipment – this type of measurement is typically sufficient to give an efficient assessment of a systems fatigue integrity as per the EI Guidelines1.
Complex – Detailed vibration assessment (operating deflection shape, modal test, pulsation assessment, motion amplification, and multi-channel transient data capture) utilizing portable handheld measurement equipment or a fixed multi-channel data acquisition set-up – this type of assessment is utilized to quantify the fatigue integrity of piping systems that undergo a more complex excitation profile (such as transient behavior).
Small Bore Connection Assessment
Where appropriate a small-bore connection (SBC) quantitative assessment should be carried out. This predicts the LOF for SBCs on the main lines of concern. The table below describes the required actions based on the SBC LOF values.
Typical recommendations include changing the welded connection type to a lower risk design, reducing the number and size of the valves, and minimizing the length of the SBC. As with the main lines, corrective actions will only be confirmed following the detailed site survey.
Site Measurement Survey
Based on the post screening visual survey and the screening assessment results, a detailed site measurement survey should be undertaken for the lines identified as requiring ‘complex’ assessment. This consists of mobilizing a team of specialist piping vibration (field) engineers to undertake the following:
Detailed site survey and data collection to identify all applicable process parameters, routing adopted, line sizes, and locations of previous failures or areas of reported high vibration
Perform ‘complex’ vibration assessments of main lines and small-bore connections of concern, to quantify the integrity threat
Perform a piping vibration and integrity assessment (as per the EI Guidelines [1])
Issue a site summary report summarizing preliminary findings and identifying any immediate integrity threats that require short term remediation.
Anomaly Management
On completion of the site measurement surveys, the recorded site data is analyzed in detail using the EI assessment criteria1, so that the risk of the piping vibration can be quantified.
The screening assessment results are updated in the Veridian software and an Anomaly database produced as a formal record of the outstanding piping vibration concerns. This consists of a fully auditable list of the piping vibration anomalies – see below as an example – with clearly defined follow up actions and responsibilities. Anomalies are prioritized based on the severity of the piping vibration, and where appropriate, identified suitable modifications, or more detailed studies to mitigate the identified problems.
The management system links to the vibration assessment results captured and provides an easy-access, online database that enables maintenance and operations teams to capture all information pertinent to the vibration threat of a particular asset, including screening, line walk-down or vibration measurements. It acts as a single source from which operators can assess the need for and priorities remedial actions, allocate tasks and responsibilities, maintain an up-to-date record of all actions taken for a given anomaly, and monitor all such anomalies on an asset-by-asset basis worldwide.
Benefits of the anomaly manager can be summarized as:
Visibility: gain complete, real-time visibility into your asset’s anomalies
Cost reduction: Eliminate repeat work, improve efficiency, and ensure inspection activities lead to improvements
Accountability: Full transparency on team tasks and completion progress
One database: All projects or assets contained in one secure database and accessible online
Control: Assurance that your integrity program is delivering the intended results
Collaboration and coordination: All stakeholders are more effective in managing the risk
Web-based: No special software required, easy to access and share.
Results
The methodology described in this paper has been utilized by ADNOC Sour Gas over the last three years and has been employed to support various production expansions, troubleshooting of vibration concerns and ongoing vibration Anomaly management.
The online database has become the single point of reference for vibration Anomalies and has been rolled out as a shared reference point between site Technical and Integrity teams and well as third-party vibration specialists. This has greatly increased the understanding of vibration concerns at the site and focused the remedial works.
The Anomaly manager for the site is currently tracking about 260 vibration anomalies, which are being managed and mitigated by various methods. This action is allowing the site to move toward the low as reasonably practical (ALARP) stage with regard to vibration risk.
Conclusion
This paper has presented an outline method for vibration management via an online database developed in line with the guidance presented in the EI Guidelines [1].
Incorporation of this methodology at ADNOC Sour Gas has resulted in greatly increased the understanding of vibration concerns at the site and focused the remedial works.
This implementation of this method action is allowing the site to move towards and As Low as Reasonably Practical (ALARP) stage regarding vibration risk. P&GJ
References
Energy Institute, “Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework,” 2008.