OPERATING methods and practices, which had been developed when wooden sucker rods only were available, were, in general, applied to steel sucker rods when they came into use. Their introduction took place in what are now known as shallow fields, where the strength-load factor, under which the rods operated, was high, and, therefore, any ill effects on them from operating practices and methods passed almost unnoticed, since the service given was quite satisfactory and their handling at the well was more convenient for the operating crew, as compared to wooden rods. With the development of fields at constantly increasing depths of producing horizons, in some cases with sour or hydrogen sulphide content oils, and the flooding of the older fields with salt water, the loads carried by the rods increased correspondingly, thus lowering the strengthload factor. The service life of the rods became noticeably shorter, more and more unsatisfactory, and breakages became so frequent, in many cases, as.to as. to make producing at a profit possible only with high-priced oil. An examination of records for the year 1929, for instance, discloses amongst the worst cases of unsatisfactory service the following percentages of total lost operating time due to broken rods alone Udall, Kansas.........50-0% Oxford, Kansas.........35-5% Covington, Oklahoma......44-8 Tonkawa, Oklahoma......26-8% Records such as these were obtained with rods having a yield-point varying from approximately 60,000 lbs.to lbs. to 85,000 lbs. per square inch, and operating 'under a strength-load factor varying from 2-1 to 4-1 approximately. Some of the worst records were obtained when the strength-load factor was greatest, while in other instances unexpectedly better service, was obtained where the strength-load factor was quite low. A careful survey of operating conditions and practices and an examination of broken rods and pins lead to conclusions that were somewhat astonishing. Two main facts were clearly evident, viz.
Practically all breaks of rods or rod-pins were of the progressive fracture type. In fact the only failures the writer encountered, where loading beyond the strength of the rod was the cause of breakage, were where the pump plunger had become stuck and the rods were broken by pulling too hard in trying to free them.
The principal causes of failures were the common or usual operating practices and methods of handling the rods; it being estimated that as much as 75% of the failures were due to these causes alone.
At the time of the investigation, the following practices were quite common throughout the oilfields x Division Mechanical Engineer, Texas-Gulf Coast Division, Shell Petroleum Corporation, Houston, Texas, U.S.A. (1) Bundles of rods unloaded from railroad cars with short slings, allowing the rods to bend in an are when hoisting out of the car.