Pipe Dope: Importance of Thread Compound in HDD Drill Rods
Equipment failure occurring in HDD takes place due to the insufficient or improper use of pipe dope. Pipe dope ensures smooth attachment and removal of pipe connections, preventing damage to the tools.
To get the most out of your drilling equipment, proper use and maintenance are very important. This is where pipe dope — also known as thread compound — and lubricants play a significant role and prevent unexpected failures resulting in an escalation of the project cost.
It has been found that many of the equipment failure occurring in horizontal directional drilling (HDD) takes place due to the insufficient or improper use of pipe dope. Pipe dope ensures smooth attachment and removal of pipe connections, preventing damage to the tools.
HDD is now extensively used for trenchless pipeline installation projects because of its cost-effective, quick and non-disruptive nature of the operation.
Contractors are expected to drill faster and pull longer runs and therefore are focused on getting the project completed efficiently and on time and moving to the next project.
However; this often results in overlooking the upkeep of HDD tooling such as the drill rod. HDD tooling especially the drill pipe is expensive and typically makes up about 3% of the total drilling cost.
Pipe Dope (Thread Compound)
Pipe dope is an anti-seizing compound that is applied to drill rods to prevent them from seizing. The compound used usually is a high-pressure, copper-petroleum based grease.
Thread compounds serve many functions such as reducing vibration, protecting metal surfaces of the thread, providing a good seal to prevent leaks, protection of the mating metal surfaces, and increased resistance to rust and corrosion.
The selection of the right drill thread compound has become very important now with stringent environmental regulations. Pipe dope is formulated with a combination of powdered solids, grease, lubricating fluid, and soluble additives.
Solids present in thread compound lubricants are lead, copper, zinc, graphite, muscovite, talc, calcium fluoride, calcium carbonate, and polytetrafluoroethylene (PTFE).
Problems Faced By Drill Rods
Drill rods are an integral part of the drilling equipment and their performance will impact the project. A healthy drill string can only be maintained with the proper and adequate use of proper thread compounds and lubricants.
Some of the problems faced by the drill rod are thread wear, box wear, mid-body wear, cracking and fatigue, bending and leakage.
Thread wear due to galling is considered to be the top reason for drill rod failure. It occurs due to the adhesion that takes place between metals of the same hardness such as when steel slides over steel. Once worn, the surface will continue to wear and when left unattended can lead to failure or seizure of the joint.
To protect the joint and to ensure it completes its service life, pipe dope should be of a good quality that will prevent the surfaces from interacting.
To prevent thread wear, choosing mating surfaces with dissimilar hardness helps.
Also, the joints should be cleaned and lubricated regularly, and worn out accessories should be immediately replaced.
Importance of Pipe Dope for Drill Rods
- Reduces in-hole vibration that can cause the drill rod to crack.
- Protects the metal surfaces of thread and provides an adequate seal to prevent leaks.
- Prevents galling by protecting the mating metal surfaces. A good quality thread compound will have some percentage of soft metal such as zinc, lead or copper.
- Prevents the belling of drill rods which occurs due to excess torque, excess tightening or excess vibration in a dry borehole.
- Increases the drill rods resistance to rust and corrosion as they are water repellant and therefore not washed out by water.
Selecting the Right Pipe Dope
While choosing a thread compound, it is necessary to consider factors such as torque, temperature variations, environmental regulations, and connection types.
Many HDD applications have a friction factor between 1.0 and 1.1 that ensures proper connection engagement and prevents leaks.
The correct makeup torque for the connection can be calculated by multiplying the friction factor by the required makeup torque for the connection.
The heat of summer makes the compound thinner while it becomes thicker in winter, either of which can adversely affect the rate of penetration.
To accommodate the variation in temperature some thread compounds are available in summer and winter grades, however; the all-season formula can be used for all seasonal variations.
Some projects require metal-free thread compounds that are environmentally friendly. Care should be taken not to select compounds that have poor performance such as poor water washout resistance.
Some good non-metallic solids are graphite, muscovite, Talc, PTFE, calcium carbonate, and calcium fluoride.
Using pipe dope and lubricants is essential to keep wear and tear at bay while increasing the usable life of the drill rod and its associated accessories.
It is recommended to use a thread compound with at least 50% zinc particle content for the entire life of the rod and casing.
Proper maintenance of the drill rod will lead to longer life, lower operational cost, better penetration rates, and improved overall drilling performance.