In the world of oil drilling, there are some pretty big things. It's not just the rigs anchored out in the ocean that are huge: Everything that goes along with them seems to get supersized, including the need for gaging. Consider the drilling pipes and couplings that go thousands of feet down through the sea and into the bedrock. These connections have to be controlled to ensure the seal is good between the connections and there is no chance of leaking oil. Sub-surface pump barrels as well—some as long as 30 feet—must also be periodically removed from the well and checked for excessive wear from plunger motion.
While the diameters of these pipes and barrels are not that large—only a foot or so at most—the depths of the diameters in which these pipes have to be controlled can be many feet into the section. It is not unusual to have adjustable bore gages 6-, 12- or 18-feet long. Generally there are two types of gaging used for these checks: air and mechanical.
Mechanical bore gages can be used for lesser-tolerance checks, with two important considerations.
The first is the depth of the check. It is common in these applications to make checks every two feet or so along the barrel, and inserting a gage as far as 20 feet into a hole can cause serious wear of sensitive contacts. Using tungsten contacts can help reduce wear, but the real saver is to use bore gages with adjustable contacts.
Non-centralizing bore gages do not have fixed contacts. Instead, they have two or three sensitive contacts that retract with a trigger mechanism, thus reducing/eliminating wear during insertion and facilitating multiple checks. These gages require a bit more skill to use, and have relatively limited resolution (typically 0.0005 inches), but they also have a long measurement range (up to 1 3/8 inches). The heads of non-centralizing gages are automatically centered, which permits some rocking, even at great depths.
The other issue is documentation. Like many other measurement functions that are critical to safety or the environment, data collection is becoming increasingly important. Many industries from medical to aerospace to automotive now require data to document that parts have been produced and inspected correctly. The same is true in the oil and mining industries. Normally this is not a problem with gaging, as gages can have a digital display, and most digital indicators have some form of digital output. But this is not so simple when you have a gage that is 20 feet long, often held by two people and attached to a data-collection printer or computer by a delicate cable. Operation can become unmanageable and cables are frequently pulled loose or broken.
A recent solution for this is wireless data collection. By having a simple means of plugging in a data transmission module into the digital indicator and transferring data to the computer, the long cable is eliminated and measurement simplified. An additional benefit of wireless data collection is that the transmitter gets immediate feedback about data transmission. Lights on the transmitter signal the operator when the data is transmitted and when data has been confirmed at the receiver. There is no turning around to look at the PC receiver to ensure data was collected. Therefore, the operator can concentrate on his or her checks with almost no additional effort for making the data collection.
Very tight-tolerance checks typically require long-range air gaging. Air gaging is non-contact, so wear is not an issue. There are additional benefits as well. It is often difficult to thoroughly clean a deep hole. Air gaging is very forgiving of dirt, oil and other contaminants both in terms of accuracy, and in terms of maintenance and longevity of the gage. This is especially important when gaging IDs of oil well pump barrels, which are about as dirty as anything you would ever want to gage.