THREAD GAUGING TECHNIQUES
API Tubing and Casing Threads
Connection Thread Styles API Tubing and Casing Tapered Threads
Pin (External)
Coupling (Internal)
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
API Connection Names
EUE – External Upset Tubing
STC – Short Thread Casing
NUE – Non-Upset Tubing
LTC – Long Thread Casing
BTC – Buttress Casing Datum
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
What are Tubing & Casing Threads
Purpose: Join two pieces of pipe together to produce a gas tight seal
API Specification 5B covers all Tubing and Casing dimensions
There are two types of pipe sizes ◦ Tubing sizes: 1” – 4½” ◦ Casing sizes: 4½” – 20”
There are two cone angles or tapers ◦ All 8-round threads are ¾” Taper Per Foot (TPF) ◦ Buttress sizes 4½”- 13⅜” are ¾” TPF ◦ Buttress sizes 16”- 20” are 1” TPF
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
How Threads Lock Up and Seal
There are no lock washers or jam nuts on tapered threads to lock them together
The pin and box tapered threads interfere and allow them to form a seal when torqued together as the flanks of the threads compress against each other.
However, a clearance remains between the crests and roots of the threads, resulting in a helical leak path
Thread compounds or “pipe dope” plug up this helical path to produce a seal under high pressures
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
8R Thread Form
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Pin Threads Datum
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
What is a “Datum Plane”?
Unlike straight threads where the pitch diameter is the same along the axis, a tapered thread changes in diameter along its axis. The Datum Plane is a starting point or reference location on a part. All diameters are dimensioned at a distance from this location. Example L1, L2 & L4. Locate these on your TDWIN TAPER drawing. Also, it is referred to as the face or end of pipe.
Please see the following pages for illustrations.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Datum Plane on a Pin Datum
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Datum A
Datum Planes on a Coupling
Datum B
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
What is the first step?
Request a product drawing on the threads.
Verify which thread form is required.
Request the threading insert called out on the drawing.
Request a gage Set-Up Sheet.
List all the gage serial # used to inspect the part.
Verify the ball contacts are the right size.
Set your gages to a zero value on a standard.
Now thread the part and start the inspection.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
External Inspection API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
TDWIN TAPER Drawing- 7” LTC Pin
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Thread Lead Inspection with an LG-5002
Set the LG-5002 on Setting Standard* and zero the dial. After locking the bezel clamp, always double check your zero setting. Now, measure the part and compare the standard to the machined lead. *Every different TPF requires a different lead setting standard.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Thread Lead Inspection with an LG-5002
The LG-5002 is used the same way on the part as on the standard. Place the fixed ball contact in the first full depth thread. Move the fixed ball back one thread and check again. Record your measurement. API Tubing and Casing Tapered Threads
Thread Height Inspection with a TH-3002 Set the TH-3002 on Setting Standard and tilt the base back and forth to obtain the lowest reading. After locking the bezel clamp, always doublecheck you zero setting. Now, measure the part and compare the standard to the machined thread groove. Thread Heights: 8 Round = .072125” 10 Round = .05560” Buttress ¾”TPF = .0620” Buttress 1”TPF = .0620”
API Tubing and Casing Tapered Threads
Thread Height Inspection with a TH-3002 The TH-3002 is used the same way on the part as on the standard. Measure only within the perfect thread length. (On your thread drawing, this length dimension is called “L2”) Align the base parallel to the thread axis and tilt the base back and forth to obtain the lowest reading. Record your measurement.
API Tubing and Casing Tapered Threads
Pin Taper Inspection with an ET-7000 Zero the dial on the first thread.
Do not lock the bezel clamp!
Note the radial location of the gage to the part or chuck. Move the gage up the taper 1” (8 R = 8 threads, Buttress = 5 threads). Place your index finger on top of the indicator stem to hold the ball contact into the thread groove.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Pin Taper Inspection with an ET-7000 After moving back 1” up the taper double check your radial position of the gage to the part or chuck. Failure to stay in the same radial position will induce errors caused by the thread helical path. If the gage rotated, the ball contacts will move up or down the taper. You are checking the change in diameter about a radial location or plane. On a 8R ¾ TPF connection, every 45° rotation of the gage = .00097” change in diameter.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Pin PD Inspection with the MRP-2001 (Crest Cone Diameter Inspection) MRP-2001 is set to a connection size by the use of “A” & “B” Rod Standards. The rod standards position the gage to measure the “Crest Cone” diameter at a known location from the datum plane or face.
“B” Standard
“B” standard sets the distance off the face. Hold light pressure between the shoe and wear pad and tighten both black knobs. “A” standard sets the crest cone diameter. Sweep the standard until the lowest indicator reading is obtained and zero the dial. Double- check the zero after locking the bezel clamp.
“A” Standard
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Pin PD Inspection with the MRP-2001 (Crest Cone Diameter Inspection) The MRP Shoe makes contact with the crest cone within the L2 perfect length. Gagemaker calculated the crest cone diameter from the Spec 5B’s pitch diameter. The shoe swivels so the taper tolerance will not effect the diameter reading. Using a shave gage the distance from the crest cone to the pitch diameter can be measured. As the threading insert wears the pitch diameter plane moves closer to the crest cone. The connection makes up on the thread flanks and not the crest cone. *Can preset with MIC TRAC API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Pin PD Inspection with the MRP-2001 (Crest Cone Diameter Inspection) While holding the gage against the part face, sweep left & right to find the largest indicator value. Then, rotate the gage 90° and repeat. If the indicator value changes, this indicates “Ovality” or out of roundness. Take multiple readings around the part to find the largest and smallest values. Write these High and Low values down on your inspection report.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
What do you do with the high and low indicator values? Largest and smallest indicator readings provide the data for calculating Average Cone Diameter and Thread Ovality. They both use the same data but calculate the readings in different ways.
Average Cone Diameter is the size, it would be, if it were round. Determining the “round” diameter of a connector requires locating the largest and the smallest diameter readings on the part and taking the average of the two readings, as shown in the following formula:
Ovality is how egg or out of round it is. Ovality is the amount of out-of-roundness in a piece of pipe or a coupling. Determining ovality requires locating the largest and the smallest diameter readings on the part and subtracting the smallest reading from the largest reading. Ovality readings are always positive (no sign attached).
Average Cone Diameter (Largest Diameter + Smallest Diameter) = Diameter 2 Largest Diameter
Smallest Diameter
Averaged Diameter
+.005
-.010
-.0025
Largest Diameter
Smallest Diameter
-.005
Ovality Largest Diameter - Smallest Diameter = Ovality LARGE READING
Largest Diameter
Smallest Diameter
Ovality
+.005
-.010
.015
Averaged Diameter
Largest Diameter
Smallest Diameter
Ovality
-.010
-.0075
-.005
-.010
.005
Largest Diameter
Smallest Diameter
Averaged Diameter
Largest Diameter
Smallest Diameter
Ovality
-.015
+.001
-.007
-.015
+.001
.016
SMALL READING
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Average Cone Diameter Average Cone Diameter is the distance across the face of the pipe or coupling. Determining the “round” diameter of a connector requires locating the largest and the smallest diameter readings on the part and taking the average of these two readings. Largest Diameter
Smallest Diameter
Averaged Diameter
Largest Diameter
Smallest Diameter
Averaged Diameter
+.005
-.010
-.0025
+.005
-.005
.000
LARGE READING
SMALL READING
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Ovality Ovality is the amount of out-of-roundness in a piece of pipe or a coupling. Determining ovality requires locating the largest and the smallest diameter readings on the part and adding the smallest reading to the largest reading, as shown in the following formula. Ovality readings are always positive (no sign attached). Largest Diameter
Smallest Diameter
Total Ovality
Largest Diameter
Smallest Diameter
Total Ovality
+.005
-.010
.015
+.005
-.005
.010
LARGE READING
SMALL READING
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Pin Thread Form Inspection
TP-8R Profile inspecting a pin thread. Always check the first starting thread.
© 2014 Gagemaker, LP
When deburring the thread with a flapper wheel, burrs can be rolled into the thread groove. This will cause gauling when the connections are made up on the rig.
Pin Length Inspection
Always keep the scale parallel to the pipe axis. A digital depth gage can be used in place of a scale.
L4
L2
L2=Perfect thread length. Crest of thread must have a full radius top. L4=Last scratch length.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Inspection © 2014 Gagemaker, LP
Datum A
Coupling Threads
Datum B
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
What is the first step?
Request a product drawing on the threads.
Verify which thread form is required.
Request the threading insert called out on the drawing.
Request a gage Set-Up Sheet.
List all the gage serial #’s used to inspect the part.
Verify the ball contacts are the right size.
Set your gages to a zero value on a standard.
Now, thread the part and start the inspection.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
TDWIN TAPER Drawing 7” LTC Coupling
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Thread Lead Inspection with an LG-5002
Set the LG-5002 on Setting Standard* and zero the dial. After locking the bezel clamp, always double-check your zero setting. Now, measure the part and compare the standard to the machined lead. *Every TPF connection requires a different lead setting standard. We will discuss setting standard design in the next class.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Thread Lead Inspection with an LG-5002
LG-5002 Inspecting Coupling The LG-5002 is used the same way on the part as on the standard. Place the fixed ball contact in the first full depth thread. Move the fixed ball back one thread and check again. Record your measurement.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Thread Height Inspection with a TH-3006
Set the TH-3006 on Setting Standard and tilt the standard back and forth to obtain the lowest reading. After locking the bezel clamp, always double-check your zero setting. Now, measure the part and compare the standard to the machined thread groove. Thread Heights: 8 Round = .072125”, Buttress = .0620” API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Thread Height Inspection with a TH-3006
The TH-3006 is used the same way on the part as on the standard. Align the gage parallel to the thread axis and lift up and down to obtain the lowest reading. Record your measurement.
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Taper Inspection with an IT-6000
Zero the dial on the first thread.
Do not lock the bezel clamp!
Note the radial location of the gage to the part or chuck. (6 or 12 o’clock is best.)
Zeroed on Coupling
Move the gage down the taper 1” (8 threads for 8R or 5 threads for Buttress).
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Taper Inspection with an IT-6000 After moving 1” down the taper, double-check your radial position of the gage to the part or chuck. Failure to stay in the same radial position will induce errors caused by the thread helical path. If the gage rotated, the ball contacts will move up or down the taper. You are checking the change in diameter about a radial location or plane.
Inspecting Coupling
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling PD Inspection with an MRP-2002 (Crest Cone Diameter Inspection) MRP-2002 is set to a connection size by the use of “A” & “B” Rod Standards. The rod standards position the gage to measure the “Crest Cone” diameter at a known location from the datum plane or face.
“B” Standard
“B” standard sets the distance off the face. Hold light pressure between the shoe and wear pad and tighten both black knobs. “A” standard sets the crest cone diameter. Sweep the standard until the lowest indicator reading is obtained and zero the dial. Double- check the zero after locking the bezel clamp.
“A” Standard
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling PD Inspection with a MRP-2002 (Crest Cone Diameter Inspection) While holding the gage against the part face, sweep left & right to find the largest indicator value. Then, rotate the gage 90° and repeat. If the indicator value changes, this indicates “Ovality” or out of roundness. Take multiple readings around the part to find the largest and smallest values. Write these values down on your inspection report. Inspecting Coupling API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
What do you do with the high and low indicator values? Largest and smallest indicator readings provide the data for calculating Average Cone Diameter and Thread Ovality. They both use the same data but calculate the readings in different ways.
Average Cone Diameter is the size, it would be, if it were round. Determining the “round” diameter of a connector requires locating the largest and the smallest diameter readings on the part and taking the average of the two readings, as shown in the following formula:
Ovality is how egg-shaped or out of round it is. Ovality is the amount of out-of-roundness in a piece of pipe or a coupling. Determining ovality requires locating the largest and the smallest diameter readings on the part and subtracting the smallest reading from the largest reading, as shown in the following formula. Ovality readings are always positive (no sign attached).
Average Cone Diameter (Largest Diameter+Smallest Diameter) = Diameter 2 Largest Diameter
Smallest Diameter
Averaged Diameter
+.005
-.010
-.0025
Largest Diameter
Smallest Diameter
-.005
Ovality LARGE READING
Largest Diameter - Smallest Diameter = Ovality
Largest Diameter
Smallest Diameter
Ovality
+.005
-.010
.015
Averaged Diameter
Largest Diameter
Smallest Diameter
Ovality
-.010
-.0075
-.005
-.010
.005
Largest Diameter
Smallest Diameter
Averaged Diameter
Largest Diameter
Smallest Diameter
Ovality
-.015
+.001
-.007
-.015
+.001
.016
SMALL READING
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Average Cone Diameter Average Cone Diameter is the distance across the face of the pipe or coupling. Determining the “round” diameter of a connector requires locating the largest and the smallest diameter readings on the part and taking the average of these two readings. Largest Diameter
Smallest Diameter
Averaged Diameter
Largest Diameter
Smallest Diameter
Averaged Diameter
+.005
-.010
-.0025
+.005
-.005
.000
LARGE READING
SMALL READING
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Ovality Ovality is the amount of out-of-roundness in a piece of pipe or a coupling. Determining ovality requires locating the largest and the smallest diameter readings on the part and adding the smallest reading to the largest reading. Ovality readings are always positive (no sign attached). Largest Diameter
Smallest Diameter
Total Ovality
Largest Diameter
Smallest Diameter
Total Ovality
+.005
-.010
.015
+.005
-.005
.010
LARGE READING
SMALL READING
API Tubing and Casing Tapered Threads © 2014 Gagemaker, LP
Coupling Thread Form Inspection
TP-8R Profile inspecting a pin thread. Always check the first starting thread.
© 2014 Gagemaker, LP
When deburring the thread with a flapper wheel, burrs can be rolled into the thread groove. This will cause gauling when the connections are made up on the rig.
Coupling Length Inspection Q
“Q” is measured from the coupling face to the start of the 35° chamfer.
Always keep the scale parallel to the coupling axis.
Coupling Length (NL)
NL/2
NL/2 = ½ the coupling length. NL = Length of coupling. API Tubing and Casing Tapered Threads
© 2014 Gagemaker, LP
