Maintenance Strategy for High Pressure Piping Systems by Ewert Snyman
Introduction Basic Design Principles Piping Inspections Maintenance Strategy Maintenance Methods Conclusion and Questions Content
Steinmüller Engineering Services specialise in High Energy Piping Systems High Temperatures normally between 500 C and 560 C but systems as high as 800 C has been analysed High Pressures normally between 5MPa and 30MPa Introduction
Introduction A specialized maintenance strategy is required on these piping systems due to the following: Limited system life Severe impact in case of failure Specialised testing requirements and methods Extraordinary long lead times on replacement material Specialised replacement or refurbishment methods
Basic Design Principles To understand the maintenance strategy the basic design principles must be understood: Material selection Piping layout Support system The implementation of these principles must first of all meet the design code requirements, but also have a direct impact on the long term health of the plant.
Basic Design Principles Before any maintenance activity can start, detailed information on the piping system must be available: The relevant piping design code The design conditions, i.e. design pressure and design temperature The operating conditions, i.e. originally anticipated operating pressure and operating temperature The piping material and the code to which it was ordered The piping dimensions, i.e. the outer diameter or inner diameter and wall thickness the piping was ordered to The piping layout, i.e. an isometric drawing showing the basic layout of the piping The cold pull dimensions A schedule indicating the support types, loads and travels, as well as clear indications on the isometric drawings where the supports are The isometric drawing must also indicate the locations of the piping welds The insulation specification, i.e. the thickness, density and conductive properties of the insulation
Piping Condition Evaluation To determine the maintenance strategy and maintenance activities the following information must be available: Material Condition Life Usage Factor As-built Flexibility Model Results Support System Condition Sloping and Drainage Thermal Insulation Condition
Piping Inspections and Testing The purpose of the inspection and testing of a piping system is two fold: Firstly to verify the integrity of the piping system, which is aimed at its short term operation and mostly consists of non destructive testing NDT to determine integrity of welds Pressure testing Replica taking to determine creep degradation Secondly to determine the condition of the system, which is aimed at its long term health Record operational data Perform dimensional tests Perform elevation surveys Survey support system Test and calibrate supports Perform infrared scanning Replica taking to determine creep degradation
Maintenance Strategy The maintenance strategy of the piping is thus forced into pure condition based maintenance.
Maintenance Activities Due to the inherent complexity in the configuration of the piping system, specialised methods are required for the replacement of components. With the replacement of piping components the originally installed cold pull must be retained: Re-instate the original cold pull as per the original installation method Restrain the piping movement local to the section to be replaced
Maintenance Activities Restraining the piping only maintains the cold pull for the sections not influenced by the refurbishment work - the installed cold pull influence the shape of the entire piping system, and thus the larger the portion being replaced the more cold pull will be lost. The restraining of the piping is achieved by the installation of the blocking frames. The loading on the blocking frames and the amount of cold pull that will be lost must be calculated.
Maintenance Activities Without restraining the piping or due to partial loss of cold pull, the piping must be balanced (balanced erection) during installation such that the piping is in it s neutral position when the piping is aligned for welding. The alignment for the final weld must be such that the piping ends are the required cold pull distances apart. This requires detailed planning upfront to take place since the last and second last weld locations must be specifically selected to achieve the required cold pull successfully.
Conclusion and Questions Thus to ensure the short and long term health of a high pressure and high temperature piping system, a specialized maintenance strategy is required. Questions?