Expert interview HDD: Developments, challenges and desirable prospects
Over recent years, the HDD method has become increasingly important and will continue to come to the fore even further in the future. Dr. Thorsten Späth, Head of egeplast Product Management, had an exchange with Marc Schnau, Vice President of the DCA, about this environmentally-friendly installation method.
Mr. Schnau, in addition to your activities in your own engineering office, you are involved in the Drilling Contractors Association (DCA) and are currently its Vice President. What is the DCA association actively involved in?
The goal of the association is to maintain, promote and develop the technical standard of horizonal drilling on the European level. Moreover, the focus is on improving the framework conditions for applying this procedure.
In addition, the association provides an international forum which allows for a permanent exchange of experiences executing HDD companies, companies from the suppliers industry, planners, clients and authorities.
What challenges is the industry currently impacted by?
For several years, the requirements related to high and extra-high voltage cable projects have dominated the demand in the field of HDD. Both clients and HDD companies had to and have to develop a mutual understanding of the requirements and possibilities as well as of the limitations of their application. This process has not yet been completed and will continue for a while. That is because both on the client’s as well as on the side of the contractor personnel resources are being expanded, often in the form of lateral entrants into HDD technology who in addition to everything else need to be integrated into this process.
What are the requirements that have impacted the HDD method and driven its development in recent years?
The first thing to mention here are the higher requirements related to the drilling accuracy for the cable projects. A vast number of drillings required for these projects are related to the so-called “small-diameter drilling rigs “. This context requires horizontal drillings with lengths of up to approx. 400 m using drilling rigs of up to 400 kN traction force. In the past, applying walkover locating procedures not meeting any particular precision requirements were commonly used in this segment to install cable protection or product pipes made of HDPE. However, since high- and extra-high voltage cable projects usually involve carrying out multiple parallel HDD drillings (in some cases up to 14) and since the cable spacings and depths represent decisive criteria which ensure the calculated heat dissipation in the course of cable operations later on, they are subject to particular accuracy specifications. This is why in the field of small-diameter drilling techniques wired pipe surveying systems have come to be used much more frequently compared to the past. The knowledge and skills which all parties involved generated as a result, now certainly have to also benefit other projects beyond the installation of high- and extra-high voltage cables. Accordingly, the DCA devoted its annual members‘ forum in May 2023 to the subject of drilling accuracy.
Of course the high demand mentioned above results in a constantly growing number of lines which have been installed using the HDD method. Accordingly, professional inventory documentation plays a very important role with a view to providing a reliable basis for identifying available installation space also for future construction projects. In addition to inventory documentation, however, documentations related to execution of the construction works in the form of daily reports, drilling- and flushing logs are important. Modern drilling equipment has come to offer systems for automated drilling data capture. To channel the wide variety of the information which can be captured this way, the DCA has also founded a work group the role of which is to compile a collection of related specifications as a recommendation.
In which way does the option to install lines using the HDD method contribute to a sustainable protection of the environment?
The HDD method is an environmentally-friendly alternative installation option, since it helps to avoid or minimize any interference with sensitive natural environments. This is being proven in the context of shore approaches for cables connecting offshore wind parks-in the North Sea. But even in onshore environments, this approach helps to preserve natural areas along various planned energy routes by passing under them based on trenchless installation using the HDD method.
Domestic capacities do not seem to suffice for the projects which have already been scheduled on the market. Do you view foreign companies whose qualifications might be insufficient as a risk?
This, indeed, is a major issue on the market. The capacities currently available in Germany will not be enough to satisfy the demand. As a result, a number of HDD companies from abroad can be witnessed on projects in Germany even now. We from DCA are well aware of the risk that the quality standard which has been established in Germany over years, e.g. by certifying HDD companies according to the DVGW work sheet GW 302, might be undermined. In view of an increasing Europeanisation, however, national regulations and the related certifications will continue to drop in significance. Both the DCA as well as other associations are currently working on measures to internationalise both domestic regulations as well as international ones. The same holds true for making qualification measures such as trainings for skilled staff accessible in English for foreign firms. Generally speaking, training skilled personnel is becoming even more relevant since, as I mentioned before, additional resources need to be built up and numerous lateral entrants will need to familiarize themselves with the HDD industry.
Which are some of the additional or improved properties that might be desirable for future pipe systems?
Plastic pipes made of HDPE provide a high degree of flexibility, their tensile strength for long horizontal drilling operations, however, has its limits. Currently, drilling length for cable projects are still limited by the cable lengths which are deliverable at present. Should longer cables become an option here over time, it would of course be desirable to have the corresponding HDPE pipes which provide sufficient tensile strength.
Moreover, it is not always feasible to prefabricate the full length of a pipe string prior to its insertion into a HDD drill hole if the length of the working area behind the horizontal drill is not enough. Although prefabrication of partial strings and welding of the partial strings during the insertion of the pipe is an option, its downside is that it causes the pulling in of the pipe to stall temporarily and means that the inner bead of the weld seam at the junction cannot be removed. The latter constitutes a potential obstacle or risk for the subsequent insertion of the cable. In this setting, it would be desirable to have a pipe connection system which allows for fast connection and does not require any increase of the inner and outer wall thickness. For shore approaches in particular, this kind of technology might also allow for welding single pipes, double or triple lengths etc. on a pontoon during insertion into the drill hole, thus making the time-consuming floating in and positioning of the entire pipe string redundant. The egeplast Smart Connect system already goes into exactly this direction. The pipe connection must demonstrate the same strength properties as the base pipe.
About the author
Marc Schnau is the owner of the engineering office x-plan schnau engineering GmbH & Co. KG, which provides planning and consulting services in the field of trenchless pipe installation and horizontal flush drilling (HDD) in particular. Both national and international network operators, route planners and executing companies count among their customers. As a publically appointed and sworn in expert in the horizontal flush drilling technology (HDD) and related approaches, he also works for courts and insurance companies. He performs company audits in the context of certifications according to the DVGW worksheet GW302 by order of DVGW Cert GmbH. He has been a long-standing member of the management board and currently serves as the DCA Vice President.