Fatigue Testing of Drillpipe

Twenty-nine tests in air and 27 tests in a 3.5% NaCl solution were conducted to test the fatigue strength of Grade E 4.5-in.-OD, 16.6-lbm/ft [114-mm-OD, 24.7-kg/m] drillpipe. The effects of stress range, mean stress, corrosion, and upset geometry were tested on the drillpipe body alone and on specimens that included the tool joint, upset, and drillpipe body. Stress range and mean stress effects were significant in noncorrosive and corrosive environments. The effect of upset geometry was minimal on an external upset compared with that on an internal/external upset. Among the specimens that failed, grinding marks on the drillpipe surface, which occurred during inspection at the mill, caused failure of about 60% of the specimens. Grinding created a notch effect and induced a detrimental residual-stress pattern on the pipe surface, which decreased drillpipe fatigue life. API guidelines for cumulative fatigue of Range 2 drillpipe were evaluated in light of these experimental test results and were found to be unsafe for drilling in noncorrosive conditions and possibly too conservative for corrosive conditions.Vingt-neuf (29) essais dans l?air et 27 essais dans une solution de chlorure de sodium (NaC1) \ue0 3,5 % ont \ue9t\ue9 r\ue9alis\ue9s pour \ue9valuer la r\ue9sistance \ue0 la fatigue de la tige de forage de grade E, de 4,5 po diam. ext., et d?un poids de16,6 lb/pi (114 mm diam. ext., 24,7 kg/m). Les incidences de l?\ue9tendue de variation de la contrainte, de la contrainte moyenne, de la corrosion, ainsi que de la g\ue9om\ue9trie de l?extr\ue9mit\ue9 refoul\ue9e ont \ue9t\ue9 \ue9valu\ue9es, sur le corps de la tige de forage s\ue9par\ue9ment et sur des \ue9prouvettes qui comprenaient le joint de tige, l?extr\ue9mit\ue9 refoul\ue9e et le corps de la tige. Les incidences de l?\ue9tendue de variation de la contrainte et de la contrainte moyenne se sont r\ue9v\ue9l\ue9es significatives dans les environnements non corrosifs et corrosifs. L?incidence de la g\ue9om\ue9trie de l?extr\ue9mit\ue9 refoul\ue9e s?est r\ue9v\ue9l\ue9e minime sur une extr\ue9mit\ue9 refoul\ue9e externe par rapport \ue0 celle sur une extr\ue9mit\ue9 refoul\ue9e interne/externe. Parmi les \ue9prouvettes qui ont \ue9chou\ue9 \ue0 l?essai, des marques de meulage sur la surface de la tige, lesquelles se sont produites au cours de l?inspection \ue0 l?usine, ont occasionn\ue9 la d\ue9faillance de pr\ue8s de 60 % des \ue9prouvettes. Le meulage a cr\ue9\ue9 un effet d?entaille et induit une tendance de contrainte r\ue9siduelle pr\ue9judiciable sur la surface de la tige, r\ue9duisant ainsi sa dur\ue9e de vie en fatigue. Les lignes directrices de l?API relativement \ue0 la fatigue cumulative des tiges de forage de gamme 2 ont \ue9t\ue9 \ue9valu\ue9es \ue0 la lumi\ue8re de ces r\ue9sultats d?essais exp\ue9rimentaux, et se sont r\ue9v\ue9l\ue9es peu s\ufbres aux fins du per\ue7age en conditions non corrosives et, \ue0 l?oppos\ue9, peut-\ueatre trop prudentes en conditions corrosives.Peer reviewed: YesNRC publication: Ye