HEAVY WALL DRILLPIPE (HWDP)
Heavy wall drillpipe (or heavy weight drillpipe) has a greater wall thickness than ordinary drillpipe and is often used at the base of the drillpipe where stress concentration is greatest. The stress concentration is due to:
• The difference in cross section and therefore stiffness between the drillpipe and drillcollars.
• The rotation and cutting action of the bit can frequently result in a vertical bouncing effect.
HWDP is used to absorb the stresses being transferred from the stiff drill collars to the relatively flexible drillpipe. The major benefits of HWDP are:
• Increased wall thickness
• Longer tool joints
• Uses more hard facing
• May have a long central upset section (Figure 5)
HWDP should always be operated in compression. More lengths of HWDP are required to maintain compression in highly deviated holes.
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CLASSIFICATION OF USED DRILL PIPE AND USED TUBING WORK STRINGS (All Sizes, Weights and Grades. Nominal dimeneion is basis for all calculations)
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1 |
2 |
3 |
4 |
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PIPE CONDITION |
PREMIUM CLASS’ Two White Bands |
CLASS 2 Yellow Band |
CLASS 3 Orange Band |
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I. EXTERIOR CONDITIONS A. OD Wear Wall |
Remaining wall not less than 80% |
Remaining wall not less than 70% |
Any imperfections or damages exceeding CLASS 2 |
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B. Dents & Mashes |
Not over 3% ot OD |
Not over 4% of OD |
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С Slip Area Diameter Variations 1 Crushing3 2 Necking |
Not over 3% o( OD Not over 3% of OD _ |
Not over 4% of OD Not over 4% of OD |
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D Stress Induced Diameter Variations 1 Stretched 2 String Shot |
Not over 3% of OD reduction Not over 3% of OD increase |
Not over 4% of OD’ reduction Not over 4% of OD increase |
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E Cuts, Gouges & Corrosion 1 Round Bottom 2 Sharp Bottom Longitudinal Transverse1 |
Remaining wall not less than 80% Remaining wall not less than 80% Remaining wall not less than 80% and length not over 10% of circumference |
Remaining wall not less than 70% Remaining wall not less than 70% Remaining wall not less than 80% and length not over 10% of circumference |
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F Fatigue Cracks4 |
None |
None |
None |
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II INTERIOR CONDITIONS A Corrosive Pi^ng Wall В Erosion & Wear Wall |
Remaining wall not less than 80% measured from base of deepest pil Remaining wall not )ess than 80% |
Remaining wan not less than 70% measured from base of deepest p+t Remaining wall not less than 70% |
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С Fatigue Cracks’ |
None |
None |
None |
Table 6 Classification of used drillpipe and used tubing work strings