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Introduction
As technologies develop, the oil companies make the stricter and stricter requirements towards quality of the purchased products. Special attention is paid to the equipment intended to operate under conditions of aggressive marine climate. One of the requirements is highly strong flange fastener treated with a coating based on PTFE (polytetrafluorethylene).This PTFE-coating is designed to stabilize torsion coefficient at connection tightening, and, the main thing, to protect the fastener in a reliable way against environment factors impact, and corrosion spreading.
Troubles at operating fastener treated with PTFE-coating
Classical coatings based on PTFE don’t have effect of running-in, and peel off the thread turns after several times of unscrewing already. The issue gets worse by low-quality mounting during which the coating splits and stops protecting the fastener. Facets of the nuts are particularly affected.
Under conditions of marine climate, corrosion penetrates through the cracks fast, and spreads under the coating. As a result, we get non-unscrewable pair, or complete destruction of the connection.
Figure 1. Damages coating on the fastener
Such events development is unacceptable since the flange fastener is used at assembly of the very important equipment such as locking-and-adjusting fitting, safety valves, pumping units. In process of scheduled maintaining or when emergency situation occurs the maintenance personnel must have an opportunity to do dismantle of the threaded connections without any difficulty, and afterwards easily re-assemble everything backwards.
System approach towards anticorrosive protection for fastener
To improve reliability and durability of the threaded fastener under conditions of marine climate, MODENGY 1014 anti-friction solid-film coating based on polytetrafluorethylene and molybdenum disulfide is widely used.
Figure 2. MODENGY 1014 coating
This composition has running-in effect unlike the conventional PTFE agents what enables to provide wholeness of the coating at multiple disassemble of the fastener. MODENGY 1014 has high anticorrosive properties. Accelerated tests in the salt mist chamber according to the ISO 9227 international standard have proved retain of the protective features of the coating up to 700 hours.
We applied MODENGY 1014 onto the fastening items of the oil-and-gas industry equipment many times including marine ice-resistant fixed platforms. This chemically resistant product is also successfully used on the downhole equipment for hydrofracturing, pressure sensor valves, face seals of the main pumps, internal surface of the pneumatic cylinder liners.
Due to feedback from the technical specialists of the enterprises we have got to know that mechanical damages at mounting are a rather common issue. And since MODENGY 1014 requires curing at heating in a kiln, the customer cannot restore wholeness of the protective layer by his own means.
We keep working on widening the service conditions range of our products, and extend their durability. To solve the issue of coating damaging at mounting, we have improved the coating application technology by adding applying of a primer layer into the technological process.
This intermediate layer holds strong on the fastener surface, improves adhesion of the basic layer. The main thing is that it is able to protect against corrosion even in case of mechanical damage in process of operating or mounting. This coatings system is able to resist corrosion forming for more than 1,000 hours in salt mist according to ISO 9227 standard.
Figure 3. Fastener treated with MODENGY coatings system: primer layer and MODENGY 1014
The coatings system consisting of the primer layer and MODENGY 1014 has already proved itself perfectly on the flange fastener intended for operating offshore.
We hold the researches of corrosion resistance of the coatings at our Engineering Center in Bryansk town. Testing chamber enable to artificially create aggressive media such as salt mist, acid mist, alkali mist which are selected according to the operational peculiarities of the items.
Figure 4. Salt mist chamber
To testing fasteners treated with the coatings that will be used for mounting marine platform structures, we hold tests in salt mist. This method enables to compare the coatings detecting the impact degree of the surface preparation ways for resistance towards corrosion, select the optimal coatings systems to meet the customer’s tasks.
At our Engineering Center there is the required equipment that enables to apply the coatings onto large volumes of the fasteners within short terms including automated and semi-automated centrifuges, spraying equipment.
Conclusion
MODENGY anti-friction solid-film coatings have low friction coefficient, high load-carrying capacity, anticorrosive and antiscuffing properties, chemical resistance, that’s why they are widely used to protect the parts and units operating under aggressive conditions of marine climate.
The MODENGY coatings system including applying primer layer enables to extend service lifetime of the flange fastener for oil-and-gas facilities by improving its corrosive resistance even in case of the coating damage at mounting or after longterm operating.