Application Procedures - Storage
BESTOLIFE® recommends the following procedures for the application and use of our thread compounds on tubulars prior to long-term storage:
CONTROL OF PROCESS CONDITIONS
A variety of process conditions can accelerate the corrosion and pitting of threaded surfaces:
• Composition and type of cutting fluids
and hydrostatic test fluids
• Contaminants such as chlorides and sulfides
in process fluids
• pH of process fluids
• Bacterial growth in process fluids
Addressing, monitoring, and controlling these factors is essential to ensure that post-process treatment for long-term storage will be effective.
THREAD SURFACE PREPARATION AND CONTAMINATION
All connection contact surfaces should be clean and free of moisture and contaminants (including storage compounds) prior to the application of the thread compound, whether intended for storage only or as a “running” compound. Corrosion effects are the result of an electrolytic process in which both water and dissolved ions (chlorides, sulfides, sulfates, and other dissolved ions) serve together as an electrolyte.
Most corrosion inhibitors are “surface active,” meaning that the active molecules attach themselves to metal surfaces to prevent access by corrosion-causing contaminants. If, however, the contaminants are present on the threaded surface prior to application of the thread/storage compound, they will be trapped against the surface and cause corrosion. Simply drying the surface with compressed air is insufficient, because dissolved contaminants remain on the surface when moisture evaporates.
To remove moisture and contaminants, apply a dewatering fluid/corrosion inhibitor to threaded surfaces. Remove all dewatering fluid/corrosion inhibitor material from the thread surface before thread/storage compound application.
The primary difference in the functional properties of storage-only compounds and compounds with storage capabilities (hybrid compounds) is one physical property: viscosity. Since storage compounds are more fluid than running compounds, the method of application is not a critical factor.
Once applied, storage compounds flow readily around the thread surface and flow easily between the clearances of an installed thread protector. Running compounds, however, are fairly stiff and contain a high volume of solid materials. Take care to apply a uniform coating over the threaded surface. After application of the compound to the pin and installation of the thread protector, the protector will push the compound away from the pin nose and, in most cases, leave voids that allow moisture to enter between the protector and the threaded surface.
To assure an even distribution of running compound under the protector and eliminate voids near the pin, apply a small amount of compound to the inside of the pin protector prior to installation. This will force the compound to spread in both directions inside the protector as it is installed. Ideally, a small amount of excess compound will extrude from both ends of the protector, the pin nose, and the base of the threads. The excess material will seal off the protector from ambient moisture and prevent water from entering and being trapped between the protector and the threaded surface.
If using thread compound and screw-on test caps for hydrostatic testing, remove the compound that is contaminated with the hydrostatic test fluid and clean the thread surfaces as described above prior to the final application of any storage or hybrid compound.
Thread protector material and design can have a significant influence on the incidence of pitting and corrosion in long-term storage. A major drawback of the metal protectors widely used 10-15 years ago was that they promoted corrosion if moisture got under the protector, since the composition of the metal in the protector was different than the metal in the pipe body. When metals with different compositions come into contact, the difference in electrolytic potential accelerates corrosion.
Most protectors currently in use are either all plastic or plastic/metal composites. These types of protectors prevent dissimilar metals from coming in contact and eliminate electrolytic potential problems. However, such protectors cannot control expansion or contraction due to changes in ambient temperatures.
The difference in the thermal coefficient of expansion between plastic and steel is significant. Plastics commonly used in protectors, such as polyethylene, polypropylene, and polyurethane, can have a thermal coefficient of as much as 10 times that of steel. Even in composite protectors, the difference can be substantial. During a normal daily temperature cycle, a pipe in storage can be exposed to a temperature fluctuation of more than 75ºF (45ºC).
The result is a “pumping” action when the protector expands and contracts at a much greater rate than the steel pipe body. If moisture due to rainfall or condensation comes into contact with the protector/pipe interface without a positive seal (either by mechanical means or excess compound), the moisture will work its way under the protector and eventually cause corrosion, regardless of what compound has been applied.
Another factor in thread protector design is the clearance between the protector and the pipe threads. The clearance must be large enough to allow the compound to distribute evenly over the contact surface without wiping off as the protector is installed.
At the same time, the compound or the protector must provide a positive seal to prevent moisture between the protector and the pipe surface, which can cause “crevice” corrosion. If materials that promote corrosion (water, contaminants, and other ions) become trapped between two surfaces in tight contact (crevice), the reaction products generated will not be able to dissipate, increasing the ion concentration (contaminants) in the electrolyte (water) and greatly accelerating the corrosion process.