STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drill String: Composition and Design 765
Drill pipe moment of inertia,
n
I = -[(4.54)4 -(3.826)4] = 9.61in.4
64
Maximum permissible hole curvature,
c=-
42,000 14,776 tanh (2.4061 lo-* )( 180) = 3. 47 o,l oo ft
z (30)( ( 4.5) (2.4061)( lo)-' ( 180)
The calculations, although based on reasonable theory, must be approached with
caution. For practical purposes, some safety factor is recommended.
Drill Pipe Inspection Procedure
To avoid costly fishing operations, loss of material and time, the drill pipe
must be carefully inspected according to the following procedure [30]:
1. Determine the pipe and joint cross-sectional area.
2. Determine tool joint outside diameter. Tool joint box should have sufficient
OD and tool joint pin sufficient ID to withstand the same torsional loading
as the pipe body. When tool joints are eccentrically worn, determine the
minimum shoulder width acceptable for tool joint class in Table 4-101.
3. Check the inside and outside surfaces for presence of cracks, notches and
severe pitting.
4. Check slip areas for longitudinal and transverse cracks and sharp notches.
5. Check tool joints for wear, galls, nicks, washes, fins, fatigue cracks at root
of threads, or other items that would affect the pressure holding capacity
or stability of the joint.
6. Ascertain if joint has proper bevel diameter.
7. Random check 10% of the joints for manufacturer markings and date of
tool joint installation to determine if tool joint has been reworked.
Optional:
1. Using data in Table 4-89, determine minimum shoulder width acceptable
for tool joint in class.
2. Check for box swell and/or pin stretch. These are indications of overtorquing,
and their presence greatly affects the future performance of the joint.
3. Use thread profile gauge for indications of overtorque, lapped, or galled
threads and stretching.
4. Magnetic particle inspection for cracks should be made if there is evidence
of stretching or swelling. Check box and pin threaded area, especially last
engaged thread.
Drill String Design
The drill string design is to determine an optimum combination of drill pipe
sizes and steel grades for the lowest cost of string or the lowest total load (in