Tropari - Shock Damage

Shock damage is any physical injury to an instrument how-ever it occurred. During survey procedures, moderate protection parallel to the borehole is provided by shock absorbing elements in the instrument container and/or incorporated into the survey train. This protection is adequate for normal surveying, but a lack of attention during some procedures can lead to greater than normal impact conditions. Interestingly enough, about 50% of shock damage to instruments does not occur during survey procedures. Let us look at where these damaging events can occur.

Prevention of Damage During Shipping

Figure #1 Tropari Instrument Box Cat # 1.10.712		Packing the instrument in a 25x25x25 cm (10x10x10 inch) box with crumpled newspaper surrounding the instrument box on all sides will prevent damage and reduce cumulative wear during transit. The crumpled newspaper absorbs much of the force as it crushes to safely de-accelerate the instrument during impact and is one of the most effective packing materials that is readily available. Two sheets of bubble-wrap around the instrument box (mahogany type) also helps.
Note the packaging you received the instrument in - it is the best. It resulted from tests in which instruments, packed in various materials, were tossed against a wall to find a packing method that withstood all attempts to destroy the instruments. All too frequently we receive instruments in their mahogany boxes shipped in courier envelopes. There is no doubt that the instrument has sustained shock damage or excessive wear since it left the customer.

Figure #2 Tropari Transit Case Cat # 1.10.711	The aluminum Tropari Instrument Box (Fig #1) will totally protect the instrument against shock with free-fall distances of 2.5 m (8 feet). If the instrument box is inside a Transit Case (Fig #2), the combination can protect the Tropari through a formidable amount of physical abuse. The investment in these impact cushioned containers has an absolutely certain pay-back by preventing a significant percentage of shock damage.

Preventing Damage During Survey Procedures

IN THE HOLE - “BOTTOMING OUT” ACCIDENTS – here, we are concerned with the instrument survey train hitting the bottom of the borehole with force. “Bottoming Out” because of fast lowering into the bottom of the hole is a common problem. If this has happened in survey trains without an impact foot, the bottom of the container will show impact scars. If bottom impacts are common, sometimes a discussion with those responsible can help, but having specific lowering procedures during surveys is better.
		In our literature, written repair reports and in telephone conversations, we use the term “shock damage” to cover any physical injury to instruments incurred through impact. The shock absorbers in the container and other shock absorbing devices are designed for impact in the hole, but it takes far less shock to produce damage when the blow is received sideways onto the container in an unprotected direction. Decreasing the rate of lowering speed when the bottom of the hole is approaching, keeping the shock absorbers in the container in good condition, and using an “impact foot assembly” below the container will decrease incidents of shock damage and lessen the damage from severe bottom impacts.

		IN THE HOLE –“GOING THROUGH THE BIT”- during gravity lowering in wireline Tropari surveys, the lower end of the survey train is seldom, if ever, perfectly aligned with the inner diameter of the bit when it hits. While the instrument is protected by shock absorbers for end shock, it is vulnerable to “side-directed” shock during the initial deflection when the end of the container hits the side of the bit. Using an “Impact Foot assembly”, which places the container and instrument higher in the rod train, and slowing the rate of descent as the survey train approaches the bit are the normal remedies.
Since times and techniques have changed, one would think that Tropari wireline surveys should be safer from bottoming-out because the drill rods are raised above the bottom. But with the Inner Tube Method, a hard impact when the core barrel assembly seats on the landing ring can cause damage even if the survey train does not impact on the bottom. But what happens when the rods are not raised sufficiently and only a half-hearted attempt is made to slow the lowering rate as the bottom is approaching? Many drillers mark the wireline cable at the last depth drilled, but the raised rods are at least 7-8 meters (22-25 feet) higher in the hole. Having some kind of cable mark or other indication to initiate slowing well before the survey train comes to a stop is a big factor in reducing shock related wear. (see Tropari survey methods)

SURFACE ACCIDENTS - these can occur away from the job as well as on the job. An instrument placed on a desk rolls off; or a packsack containing the instrument, container and perhaps a few other hard objects is absent mindedly tossed into the back of a truck are examples of preventable damage. Here are a few reminders to help minimize Shock Damage.

DO NOT place instruments on their side on a flat surface - use the instrument box.
DO PROVIDE adequate protection during shipping and transportation.
DO keep your hands dry when handling the instrument.
DO WORK over a surface when handling the instrument. If that instrument slips out of your hands, it doesn’t have far to fall. In addition, if that surface happens to be soft, the instrument will definitely survive without damage.

Preventing Damage at the Collar

Loading the instrument into the waterproof container affords an excellent opportunity to make sure the shock absorbing foam washers (Shock Absorbers) are dry and clean. A grease packed and wet washer is not as resilient (shock absorbing) as a dry and clean one. When the survey train has to be assembled at the top of the drill rods or at the collar, the bottom part of the train already in the rods is usually held by hand while the additional sections are threaded in. One slip and down goes the unattached survey equipment.
Figure #3	Now there is a hands free secured method. The non-magnetic surveying rods used with this method have three 5/16" holes drilled through them, one at each end and one in the middle. Placing a 1/4" Spaenar hitch pin into the survey train will prevent the survey train from slipping into the rods (or collar) and it will rest securely unattended on top of the drill rod, while other survey rods or connectors are being attached.(Fig.3).
Let us look at the surveying situation where lack of "headroom" requires the non-magnetic rods to be added one by one. The container is attached to the first rod that has a hitch pin on the top end. Once the instrument is inserted into the container and the container firmly tightened with wrenches, the rod can be inserted into the hole and will securely rest on the hitch pin (Fig.4).
Figure #4	The second rod with a hitch pin at its upper end is threaded onto the first. Removing the hitch pin from the first rod will allow the assembly to be lowered to rest onto the second hitch pin. Additional rods follow the same procedure. No hands needed. The hitch pin holes are sufficiently below the coupling so they do not interfere with wrenches when the rods are tightened. We recommend this method and stock hitch pins and survey rods with holes already drilled.

OTHER SOLUTIONS- ‘In line’ shock absorbing hardware is available in a number of formats. If you need more protection or have a special shock related problem, contact tech service at Pajari Instruments Ltd. In over 60 years of surveying, designing and manufacturing experience, it is likely that something that might help has already been designed for someone with a similar problem.

----SO----

PREVENT INSTRUMENT LOWERING SHOCK DAMAGE BY STARTING TO SLOW THE DESCENT RATE ABOUT THIRTY METERS (100 FEET) BEFORE THE SURVEY TRAIN REACHES THE BIT AND USE “IMPACT ASSEMBLIES” BELOW THE CONTAINER WHERE POSSIBLE.

PC001 Rev. 3