The horizontal directional drilling (HDD) industry has investigated and found out that many equipment failures are due to improper or insufficient thread compound use. This downtime can be extremely high and can cut into the budget. Protecting pipe threads from damage ensures the longevity of a drillers investment.
Thread compounds, also known as pipe dopes, are vital in ensuring makeup and safer break out of pipe connection. In addition, specialty thread compounds are specially formulated with a combination of powdered solids, grease, lubricating fluid, and soluble additive boosters to:
a. Reduce the coefficient of friction at makeup
b. Create a barrier to prevent metal to metal contact of the thread forms (prevent seizing and galling)
c. Compact to form a leak-proof seal
Importance of Specialty Blends in Thread Compound
Traditional solid particles in thread compound lubricants are lead, copper, zinc, graphite, muscovite, talc, calcium fluoride, calcium carbonate and polytetrafluoroethylene (PTFE). Lead powder, zinc dust and copper flake are malleable and ductile, allowing them to compact and deform without fracturing, thereby, forming a seal either in the thread form of casing or tubing or between the shoulders of rotary connections. Depending on the operation and connection used, the thread compound composition and the solids utility varies.
Thread compound performance is optimized when the appropriate product fit for the drilling conditions is selected, and the material is properly applied to the threads. Some factors to consider when choosing a thread compound are torque, temperature requirements, environmental regulations, connection type, etc. It is important to note that selecting the correct compound is worthless if the product is not adequately prepared before use and not applied correctly.
Choosing the Correct Compound
Following are some important criteria to consider
1. Friction Factor – Proper friction factor ensures proper connection engagement, prevents leaks and protects connections from damage. Many HDD applications have a friction factor between 1.0 and 1.1. To determine the correct amount of makeup torque necessary for a connection, multiply the friction factor by the required makeup torque for the connection or refer to your pipe manufactures recommendation.
2. Seasonal Temperature – In summer, the compound is thinner and vice versa in winter. This affects the penetration rate. Thick or heavy thread compounds are difficult to stir and stick to the dope brush or pump in an automatic lubrication system. Summer and winter grades are available for certain thread compounds to accommodate for the variation in temperature. The best solution is to use an all-season formula that can be used all year round, reducing the risk of application and adhesion issues if using the wrong grade. If it is too cold to spread, the thread compound can be warmed in a room or have a heat band or heat tape wrapped around the container. Solvents or diesel or light oil should never be added to thin the material as these contaminants will affect adhesion, the friction factor, and galling resistance.
3. Environmental Regulations – It is important to choose a quality thread compound that is environmentally friendly without sacrificing performance (poor water washout resistance). Metallic or non-metallic, that is the question. Some contracts require metal free thread compounds which are better for the environment. Graphite, muscovite, talc, calcium fluoride, calcium carbonate and PTFE are great non-metallic solids that will aid in protecting the threads and sealing.
Once the correct thread compound is selected for the job, it is imperative dope is applied to the threads correctly by following few basic steps.
1. Check Shelf Life – Before opening the pail, check the label to ensure the material is not expired. Two potential risks of using expired thread compounds are:
- Settling of the solid components. If the material is not thoroughly mixed before use, the composition of the solids could be compromised leading to galling and/or seal leaks
- Oxidation of compound components which could cause corrosion and accelerated wear
2. Compound Preparation – Upon opening the container, stir the product with either a dope brush or other suitable tools to blend the oil and the component solids that may have settled during shipment and storage. Stirring is particularly critical for high-density materials such as lead and zinc and for high-temperature (greater than 90 F) storage conditions.
3. Connection Surface Preparation – The surfaces should also be clean so that surface-active additives can attach to the thread’s metal. If dirt and debris are left on the threads, the additives are blocked from attaching to the metal surface for protection from extreme pressure or corrosion.
4. Brush Application – Drilling connections rely on the compacted solids in the thread compound to prevent drilling fluid leaks. Apply the thread compound liberally and uniformly to the entire contact surface of both the pin and box.
5. Automatic Lubricator – Ensure the thread compound selected is pumpable so that the material can be dispensed through an automatic lubrication device. There are a few lab methods to determine the mobility of grease, such as US Steel method (LT-37), Kesternich technique and Lincoln Ventmeter procedure. However, the best way to determine pumpability is in the field. Ensure that proper amount of compound is dispensed to coat the threads. Thread compounds contain grease and lubricating fluids which aids in reducing the coefficient of friction for makeup so the connection will engage properly. Furthermore, a lack of grease on the threads could result in improper makeup causing leaks, damage, and possibly losing the connection downhole. Applying too much compound has disadvantages as well. The excess compound will sling off the threads during make-up and contaminate the site.
Thread compounds’ sophisticated formula is designed to protect threads, create a seal to prevent leaks, and lubricate to provide smooth makeups and breakouts. Selecting the compound that is fit for use will give your customers and operators confidence in performance. Applying the compound correctly will optimize your connections life and increase efficiencies for the dig.
HDD drilling is a complex job. The best practices shared will make one aspect of the drilling plan easier.