A rod string is only as strong as its weakest connection
Di-Corp drilling and manufacturing technology expert Chris van Schaayk explains why consistency is key when choosing coring rods.
Far too often in mineral exploration drilling, coring rods were considered interchangeable. As long you were buying your drill steel from a reputable dealer and drilling in standard ground conditions, there wasn’t a large difference between one rod and another. Thus, for a lot of drillers, the biggest consideration when choosing rods was price. You need a lot of rods to get to core and contracts are competitive, so focusing on the cost per rod is understandable.
Choosing a drill rod
Choosing a quality, consistently manufactured drill rod is essential to a successful drilling program, and interchanging between manufacturers’ products (although it often does work) can add a significant layer of risk. Unlike API joints used in the oil industry, there is no standard for dimensions on exploration drill rod threads. Exploration rod designs have a tapered interference fit and a very thin wall to work with, so tolerances are inherently tight during manufacturing. Due to these facts, variations in fit between manufacturers can exist.
What to consider
Modern drilling involves deeper, harder-to-access deposits, frequent deviations, automated rod handling, and a competitive, volatile global mineral exploration market. In these conditions, a failed rod or mismatched rod connections could cost you a shift tripping out bent tubes or fishing out broken ones. Or worse, losing a hole altogether.The risks aren’t just incurred by drilling companies. Mine owners must also consider what failed rods mean to them. Delays in the completion of drilling programs have the potential to push back decisions on development, wasting precious time and of course money.
Reducing the risks
Choosing more durable, consistently manufactured rods can reduce these risks. That means looking for thread forms designed to eliminate areas of high stress concentration and deliver high tensile and tortional strength. To find this, it is helpful to look for providers with a reputation for using high quality steel and applying the highest quality control measures to machining and surface treatment processes. And mostly, it means not mixing rods and rod string components (including adaptor subs and locking couplings) from multiple manufacturers.
A rod string is only as strong as its weakest connection, from the water swivel to the core barrel. Mismatching threads with a rod string component can cause rods to fail. Saving small amounts of money on adapters isn’t worth putting a rod string in danger.
The fact is, in 2025 rod failure should be the exception, not the rule. Drillers that only choose equipment on cost or mix products from multiple manufacturers expose themselves to greater risk than necessary. In today’s challenging and competitive environment, it is time to stop evaluating drill rods and components primarily on price and start evaluating the cost associated with the risks of rod failure. Choosing a more durable, better engineered rod string may cost more up front, but will save money in the long run.
To learn more, visit: www.di-corp.com
