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Published byKendal Merriam Modified about 1 year ago

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11.2 Nominal masses Nominal mass is used in connection with pipe having end finish such as threads and couplings, upset and threaded ends, upset ends, etc., primarily for the purpose of identification in ordering. It is also used generally in the design of casing and tubing strings as the basis for determining joint safety factors in tension. Nominal mass is approximately equal to the calculated theoretical mass per foot of a 6,10 m (20 ft) length of threaded and coupled pipe, based on the dimensions of the joint in use for the class of product when the particular diameter and wall thickness were introduced. Some nominal masses are based on sharp thread joints that were in use before this specification was adopted. The same nominal masses are used for short thread joints, long thread joints, buttress thread joints, extreme-line joints, and the various proprietary joints offered to the oil industry. For calculation of new nominal masses the length of a piece of pipe is taken as 9.14 m (30 ft) for casing and 6.10 m (20 ft) for tubing. Nominal masses for upset drill pipe for weld-on tool joints are based on the calculated mass-per-foot values of the original threaded and coupled drill pipe. In determining the nominal mass from calculated masses, it would appear that historical rounding was implemented with no definite procedure. Rounding increments of 0,01, 0,05, 0,1 and 0,5 should be used for adding isolated new nominal masses, selecting the increment most compatible with adjacent nominal masses. WG 2350 Mass Density Values Proposed Letter Ballot Changes and Justification Part A – Proposed Change: add sentence to TR 5C3 11.2 defining the joint length to be used in nominal mass calculations for “new” casing weights for 5CT Part A – Justification: proposed joint length provides a better match to recent “new” weights than the 20’ default length currently in the standard.

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Part B - Justification: L j is not known for historical weights of casing. Thus, using equation 74 and assuming 20 ft often results in an incorrect value of e m. Direct calculation of e m is the proper and accurate method and is covered in clauses 11.5.2, 11.6.2, and 11.7.2 Part B – Proposed Change: Delete equation (74) and its description.

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Part C – Proposed Change: Replace “-” with “for” in the clause titles for threaded and coupled pipe. for upset and threaded pipe for upset pipe. Part C – Justification: Prevents potential confusion of the hyphen with a minus sign.

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Part D – Proposed Change: add a sentence to the 1 st paragraph of 11.5.1 and reword L j definition to cover casing and tubing is taken as 9.14 m (30 ft) for casing and 6.10 m (20 ft) for tubing. For calculation of new nominal casing masses only the buttress connection is used. Part D - Justification : All threads use the same nominal mass / ft but no guidance was provided as to which thread type is used to set the nominal mass / ft.

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