Tightness Testing of Environmentally Friendly Thread Compounds

Abstract In its most simple case the tapered round thread of casing or tubing is sealed by a thread compound i.e. a special kind of grease containing solids. To date, dopes that contain lead and other heavy metals, so called API-modified thread compounds, have found widespread use. This is surprising since metal free or even biodegradable thread compounds are available. OMV decided to initiate a project evaluating environmentally friendly thread compounds. To find out which of the non toxic products have a good sealing performance, laboratory tests were carried out. Due to the lack of a standardised sealing tightness test for thread compounds a new benchmark test method was developed. In the past, there have been two approaches for testing the "tightness" of the various thread compounds: the simplified grooved plate tests and the full scale tests on high pressurized and mechanically loaded pipes. Unfortunately, the plate tests do not provide reliable results, and the full scale tests are very expensive. For the test described in this paper threaded pipes in small standard dimensions were used; relatively low testing pressures and no mechanical load were applied. Two parameters were implemented in a new way: temperature load and test duration. Temperature load was applied for the whole duration of the tests. The usual test duration was approximately two weeks but during the development phase some tests were run for several months. This new combination of test equipment allowed inexpensive testing of many different thread compounds simultaneously. Not only performance differences between thread compounds could be examined, but also other relevant parameters such as varying temperature, pressure, torque etc. could be easily recorded. After this new method had been refined seven environmentally friendly thread compounds were selected for testing, two of them being universal compounds. For reference purposes API-modified thread compounds from two different manufacturers were tested. Enormous differences in the sealing abilities of the products were found. Life cycle costs can actually be reduced through the use of an inexpensive and effective thread sealing compound. Savings are possible due to a reduction in the number of workovers, of expensive down time and lost production. It was clearly shown that some of the environmentally friendly thread compounds perform better and are cheaper than the old fashioned toxic API-modified compounds.