Drill Pipe

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D RILL PIPE

27. DRILL 27. DRILL PIPE 27.1 PHYSICAL DATA FOR STEEL DRILL PIPE DRILL PIPE A joint of drill pipe is composed of 2 parts: the body and the tool joint. Body: central part Tool Joint: connections welded to each end of the pipe body and threaded - one box threadand one pin thread. API 5D specifies the dimensions and characteristics of the body. API 7 specifies the dimensions and characteristics of the tool joint. The ISO reference is the draft 11961. ENI requirements are defined by internal specification. Drill Pipe - Scheme

- Transition between the pipe body and tool joint The transition between the pipe body and tool joint can be: INTERNAL UPSET EXTERNAL UPSET INTERNAL-EXTERNAL-UPSET DP usually has: has: INTERNAL EX TERNAL UPSET API - Upset Drill Pipe

DRILL PIPE BODY API 5D covers Group 1 and Group 3 DP. Group 1 - Grade E drill pipe. Group 3 - All high strength grades of drill pipe. (Grades X-95, G-105, and S-135) - Upset Drill Pipe Body (Group 1)

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- Upset Drill Pipe Body (Group 3)

TOOL JOINT

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- Dimensions DP / Tool Joint Dimensions NC26 - NC40 DP / Tool Joint Dimensions NC46 - NC50 DP / Tool Joint Dimensions 5 1/2 FH - 6 5/8 FH - Mechanical Pro perties

- DP Tool Joint Threads The number connections and their equivalent connections are as follows Equivale nt Connections Number Connection Equivlent Connection NC26

2 3/8 IF


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NC31

2 7/8 IF

NC38

3 ½ IF

NC40

4 FH

NC46

4 IF

NC50

4 ½ IF

- Rotary Shouldered Connections

- API Threads type

Tool Joint Hardfacing To reduce the wear on the tool joint, some contractors weld a hard-facing material on the weararea of the tool joint. In some deviated wells the hardfacing has been dangerous because it was damaging the casing with rotation. Recently technology has developed hardfacing materials producing a minimum wear on the tool joint and on the casing. ENI policy stipulates the using of "Casing friendly Hardfacing". - DEA comparation table As shown in DEA comparation table (see following table) sometimes the hardfacing has better performances than the DP without it. ENI accepts a maximum csg wear of 7%.


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DRILL PIPE

- NKK High-Torque Tool Joint

- OMSCO TuffTorq Tool Joint


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- VAM EIS Tool Joint

- HYDRIL High-Torque Tool Joint

High torque connections table comparison

27.2 DRILL STEM DESIGN CALCULATIONS Areas to analyze for working stress on a DP are the: BODY TOOL JOINT BODY STRESS Stresses on the DP body DP operational limits( API RP) Maximum Tension Load and Torque


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DRILL PIPE Biaxial Loading Fatigue Stress

- Stresses on the DP body Stresses on the DP body include: TENSION LOADING TORSIONAL STRENG TH INTERNAL PRESSURE COLLAPSE - TENSION LOADING A.7 Tension P = Ym A where P = minimum tensilestrength, lbs, Ym = material minimum yielstrength, psi. A = cross-section area sq.in.(Table 1, Colon 6, for drillpipe)

- TORSIONAL STRENGTH A.9 Drill Pipe Torsional Yield Strength A.9.1 PURE T ORSIONAL ONLY 0.096167 J Ym Q=

(A.15) D

where Q = minimum torsional yield strength, ft-lb Ym = material minimum yiel strength, psi. J = polar moment of inertia = π(D4 – d 4)/32 for tubes = 0.098175 (D4 – d 4) D = outside diameter, in d = inside diameter, in - INTERNAL PRESSURE A.5 Internal Pressure A.5.1 DRILL PIPE Pi= 2 Ym tPi/D (A.8) where Pi = internal pressure psi Ym = material minimum yiel strength, psi. t = remaining wall thickness of tube, in. D = nominal outside diameter of tube, in. Notes: 1. Internal pressure for new drill pipe in table 3 were determinedby using the nominal wall thickness for t in the aboveequation and multiplying by the factor 0.875 due topermissible wall thickness tolerance of minus 12 ½ percent. 2. Internal pressure for used drill pipe were determined byadjusting the nominal wall thickness according to footnotesbelow Table 5 and 7 and using the nominal outside diameter,in the above Equation A.8 - COLLAPSE A.3 Collapse Pressure for Drill Pipe Note: See API Bulletins 5C3 for derivation of equations in A.3


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The minimum collapse pressures given in Tables 3, 5 and 7 arecalculated values determined from equations in API Bulletin 5C3.Equations A.2 through A.5 are simplified equations that yield similarresults. The D/t ratio determines the applicable formula, since eachformula is based on a specific D/t ratio range.For minimum collapse failure in the plastic range with minimum yieldstress limitations: the external pressure that generates minimumyield stress on the inside wall of a tube. Pc = 2 Ym [ (D/t) – 1 ]/(D/t)2 (A.2) Applicable D/t for aplication of Equation A.2 are as follows: Grade D/T Ratio E 75 1 3. 60 and le ss X95 12.85 and less G105 12.57 and less S135 11.92 and less - DP operational limits( API RP) API RP 7G classifies DP operational limits based on wear: NEW PREMIUM CLASS (wall thickness 80% of new joint) CLASS II (wall thickness 70% of new joint) Biaxial Loading - Example Calculation of Biaxial Loading An example of the calculation of drill pipe collapse resistance, corrected for the effect of tensile load is as follows: Given: string of 5-inch OD, 19. 50 lb per ft,Grade E P remium Class drill pipe. Required: Determine the collapse resistancecorrected for tension loading during drill stemtest, with drill pipe empty and 15 lb per gal. mudbehind the drill pipe. Tension of 50,000 lb onthe joint above the packer.

Solution: Find reduced cross section area ofPremium Class drill pipe as follows: Fatigue stress Drill pipe is subjected to cyclic stresses in tension, compression, torsion and bending.Drill pipe will suffer fatigue when it is rotated in a section of hole in which there is a change of holeangle and/or direction, commonly called a dogleg. - LUBINSKI method's LUBINSKI has developed a method for estimating the cumulative fatigue damage to pipe whichhas been rotated through severe doglegs.


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Dogleg Severity Limits for Fatigue


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TOOL JOINT STRESS Tension Torque Combined Stresses Tension - Ca lculations Calculations are the sameas DP body. 120,000 is the minimumYield. The critical area is 5/8 fromtool joint shoulder.

Torque - Calculation

- Combined Stresses


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27.3 DRILL PIPE CODE IDENTIFICATION


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27.4 DRILL PIPE INSPECTIONS - Periodical inspections Drill pipes shall be inspected according to API RP 7G and API RP 5A5. The relevant ISO standard is the 10407 Spec.ENI requirements are defined by internal specification. DS1 and NS2 are new standardization issued by independent body.


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- Classifications of used Drill pipe (API RP 7G) Exterior Conditions Interior Conditions 27.5 DR ILL PIPE BRITTLE FOR H2S - Sulphide Stress Cracking SSC In the presence of hydrogen sulfide (H2S) tensile-loaded drill stem components may suddendly failin a brittle manner at a fraction of their nominal load-carrying capability after performing satisfactorily for extended periods of time. Failure may occur even in the apparent absence of corrosion, but is more likely if active corrosionexists (Sulphide Stress Cracking SSC ). With H2S, Strength of steel between 22 and 26 HRC is suggested. - Minimize H2S attack H2S attack can be minimized by keeping the following properties: Temperature > 57C Oil base mud Mud with pH > 10 Reduce contact time Steel grade example comparison in H2S environment

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