Valves are a core mechanical component of piping and production systems, designed to direct, start, block, control, mix and regulate a process fluid’s flow, pressure, or temperature.
This makes valves essential for oil and gas production, particularly deepwater exploration and processing on floating production storage and offloading (FPSO) units, and highlights the importance of implementing effective and preventative valve management.
The ability to safely service valves that are inline and under pressure – without shutting down production – is essential for safe, efficient, and profitable operations.
Operators typically consider three main approaches to managing valves at oil and gas facilities: new valve procurement, which involves high-quality but long lead times; maintaining valve stock, which eliminates delays but can be costly and requires storage; and valve repair and maintenance, which offers a balance of speed and cost-effectiveness.
An effective valve maintenance regime should include regular greasing, open-close operational checks, continuous improvement of maintenance checklists, condition monitoring, training and competence, and a valve condition inspection database.
FPSO platforms receive hydrocarbons from subsea oil wells for processing and separation into produced water and natural gas.
During this process, valves and other equipment are exposed to corrosive chemical compounds, necessitating appropriate management as well as specifications around valve repair and remanufacture.
The four main types of valve damage are external corrosion, internal corrosion, valve sealing failure, and erosion of internal valve parts due to particulates or solids in the fluid, as well as high velocity flow.
Parts commonly affected by external corrosion include the flanges, while internally, components such as the seat ring can become corroded.
Valve sealing failure can arise from various factors, including incompatible operating conditions, rapid decompression, erosion, improper material selection, improper installation, and inadequate maintenance.
When replacing parts, there are three important aspects to ensure the quality and reliability of the replacement: design engineering, material requirements, and inspection and testing. Along with replacement, valves can also be remanufactured, which involves the reassembly of newly refurbished components with the existing valve structure, a process that demands precision and attention to detail.
Compliance standards around valve repair require a comprehensive testing protocol that includes conventional leak and pressure tests, as well as additional performance, functional, and safety tests.
Valves are usually constructed with a carbon steel body and stainless-steel internal components.
In this application, carbon steel contains pressure, and in some cases, metallic or polymeric coatings are applied to internal interfaces that come into contact with the fluid.
These coatings are typically applied through an overlay cladding welding process, utilising anti-corrosive superalloys.
Stainless steel is categorised into four groups: martensitic, austenitic, duplex, and super duplex, each with distinct applications in oil and gas production.
Martensitic stainless steel contains about 13 per cent chromium and is used internally in valves, like carbon steel, it serves the function of controlling pressure or flow.
Austenitic steel is also used in parts that contain pressure and has good corrosion resistance, a result of nickel, chromium, and molybdenum alloys.
Duplex stainless steel can be used for both external and internal valve components, and uses a two-phase microstructure with balanced proportions of austenite and ferrite.
Duplex components are often used offshore as they have high corrosion resistance and exceptional mechanical strength.
Adding alloying elements like copper and tungsten to certain duplex steel grades produces super duplex steel, which offers enhanced resistance to chloride corrosion.
However, this steel has low machinability due to the high presence of alloying elements, low thermal conductivity, high temperatures in the cutting zone, high degree of work hardening, and a higher production cost.