Page 108 - Well Control for Completions and Interventions

100 Well Control for Completions and Interventions

3.2.1 Tubing size
Tubing size is defined by the nominal OD of the base pipe and excludes
connections. Integral connections and threaded couplings have a larger
diameter than the base pipe (except where flush joint connections are
used). Tubing is supplied in a range of industry standard sizes. The
1
American Petroleum Institute (API) defines pipe with a diameter of 4/2v
1
1
and smaller as tubing, whereas pipe having a diameter of 4/2v and larger
1
is defined as casing. Somewhat confusingly, 4/2v can be either tubing or
casing. The definition is further confused, since pipe with a diameter
1
larger than 4/2v is often used as production tubing. In fact, pipe as large
as 9/8v has been used in some fields. 2
5
3.2.2 Tubing weight
Tubing weight is recorded in pounds per linear foot of the base pipe (it
does not include the connections). Since the API defines tubing by OD,
increasing tubing weight per foot for a given OD must logically (and
obviously) come about through an increased wall thickness (reduced ID).
Tubing is specified by OD and weight of pipe per linear foot. If OD and
weight are known, the internal diameter (ID) can be found using tables,
such as the Halliburton Red Book, Baker Tach Facts or the Schlumberger
1
iHandbook. For example, 5/2v 17 lbs/ft base pipe has an ID of 4.892v.
3.2.3 Tubing grade and tubing yield
The grade of the tubing refers to the metallurgical properties. API desig-
nated grades are prefixed with a single letter, for example, L, N, P, and Q.
The properties associated with each letter are laid out in API 5CT .
For example, L grade material is suitable for sour service conditions,
while N grade is not. In addition to the API defined grades, most manu-
facturers have their own proprietary grade designations. For example,
Sumitomo prefix many of their grades with the letters SM. Information
about the properties of a proprietary grade must be obtained from the
manufacturer. Most manufacturers have comprehensive websites that list
the properties of their grades. Grade designations are often stenciled on
the pipe body. In addition, most manufacturers will color code the cou-
plings and pipe to aid grade identification (Fig. 3.11).
Generally, the letter denoting tubing grade is followed by a number;
for example, a tubing joint might be stenciled L-80. The number 80
denotes yield, and is given in thousands of psi, 80 equating to 80,000 psi,
110 equates to 110,000, and so on. The axial strength of a piece of tubing