Ramming Hammers to Aid HDD Productivity in Difficult Circumstances

HDD has been around as a technique for several decades now and has become established as a significant and widely used technique in the area of new installations of pipeline, particularly for crossing works under roads, rail tracks and other significant obstacles/buildings where open trench operations would be difficult if not impossible.

Drill Rod Pipe ExtractionHowever, on occasion, even with the most extensive pre-project ground investigations, planning and the highest skill level in the drilling crew, circumstances can arise that cause a bore to grind to a halt. These circumstances are generally related to significant and often unexpected changes in ground conditions that cause the drill string, cutting head or product pipe to lodge in the ground making it impossible to continue the bore using just the power of the drill rig.

One method that has been developed to help overcome this set of circumstances is the use of the Hammerhead pipe ramming hammers to effect a rescue in some of the more dramatic circumstances by enabling the operator to add impetus and increased energy into the drill string over and above that available through the rig alone.

Drill Assist Options

There are three accepted methods by which the use of ramming hammers can assist in freeing stuck drilling operations including:

• The Drill Rod Extraction Method
• The Pullback Assist Method
• The Pipe Extraction Method

Taking these the order that they might occur during a drilling operation the first potential problem area is when the pilot bore drilling head/drill string gets stuck.

The Drill Rod Extraction Method is used to helpHDD Pipe Extraction recover the expensive drill stems. To achieve this type of rescue a rammer is attached to the drill stem with a fabricated adapter (see pipe extraction section later for details). On starting the hammer, the impact force of the rammer combined with the static pullback of the drilling rig usually creates enough added power to extract the stuck drill stems.

Where during the product pipe insertion the drilling rig has difficulty HDD Pullback Assistcompleting the pull-in operation due to either usually a hydro-locked or immovable pipe the Pullback Assist Method is used. Here a ramming hammer is attached to the product pipe to add the extra power needed to get the pipe moving again.

Three methods are available to attach the hammer to the pipe depending on the type of pipe being installed:

1. Where a steel casing/product pipe is being installed, the rammer is locked into the steel casing using collets. The steel casing is installed using the pullback force of the HDD rig and the percussive force of the hammer, with the hammer action ‘pushing’ the pipe in the direction of travel.
2. Where the product pipe is HDPE (plastic) pipe, the rammer is locked into a steel casing using collets. This steel casing, which is not originally part of the product pipe assembly, is connected to the end HDPE product pipe using a steel-to-HDPE flange compression kit. The combination of the HDD rig pull force and the hammer action in the direction of the pull on the rear of the pipe is used to complete the installation.
3. Finally, another option for assisting the installation of an HDPE product pipe has the rammer locked into a steel casing via collets. The steel casing is then welded to a steel ring that is flush with the HDPE pipe face and welded onto a steel sleeve. The steel sleeve is run over the HDPE pipe and bolted to it to create the connection. The pull force of the HDD rig is again used in conjunction with the rammer to install the pipe.

Should a circumstance occur where none of the Pullback Assist methods HDD Pipe Extractionwork but where there is already a length of the product pipe part way into the bore it may be necessary to try to retrieve the product pipe and restart the operation. To do this the Pipe Extraction Method is used to recover the product pipe. The impact hammer is attached to the product pipe but this time the impact force is directed to pull the pipe out of the bore rather than push it into it. The impact force of the rammer is combined with static force of the HDD rig to extract the product pipe. This can be a very cost-effective way of saving on expensive pipe.

Two techniques can be used for the Pipe Extraction method depending on the product pipe being used:

1. Where a steel product pipe is used a steel casing is welded onto the product pipe and a rammer is locked into the steel casing via collets.
2. Where an HDPE product pipe is being installed the rammer is locked into a steel casing that is welded onto a steel sleeve. The steel sleeve is run over the HDPE pipe and bolted to it.

In both cases the static force of the drill rig combined with the rammer force is used to extract the product pipe from the bore.

Frank Gowdy, Sale Director for U Mole said of the technique:

“We have provided some of our HammerHead ramming hammers to clients for just this type of operation because the units are easy to handle, powerful and cost-effective in what is often a limited access area on many HDD projects. The advantages that ramming hammers can bring when recovering stuck bores be this for the drill string/product pipe rescue or pullback assist is that potentially huge cost savings can be made using these rescue techniques when compared with having to restart the bore at another location or retrieving the equipment using open cut or abandoning it altogether.”

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