There are a myriad of causes and types of thread damage that can jeopardize the integrity of a threaded connection.
Some slight defects in non-crucial areas may be field repairable, but most damage will be grounds for rejection. Each manufacturer’s technical specs for a connection has it’s own tolerances and acceptance/rejection criteria that are adhered to by Cole Enterprises inspectors. Below is a sample of the most common types of damage.
Contact us with any questions and for your threaded connection inspection needs.
Typical Causes of Thread/Pipe Damage
- Mishandling of pipe during storage and shipping, or during running/pulling
- Improper doping procedure
- Misalignment during stabbing, make-up or breakout
- Rocking the pipe to correct cross threading
- Continued rotation of the pipe after breakout
- Setting backup tongs over box threads
- Dirty threads/dirty thread compound
- Excessive RPM while making up or breaking out connections
- Over-torquing the connection
- Any handling of the pipe without protectors over the connections
Types of Thread Damage
Mashed Threads
A result of heavy impact with a blunt object during handling (metal not broken/cracked).
Cut Threads
Cuts are a result of a blow during handling, typically from a sharp instrument or piece of equipment, causing a large discontinuity in the metal of the threads.
Pitted Threads
Pits are holes in the thread area caused by the threads being cut through air pockets or slag trapped in the surface of the metal. Pits may also be formed by corrosion of the thread surface.
Corroded Threads
Corrosion occurs when threads have been rusted or eaten away at their surface. In certain cases, very light corrosion is still acceptable. We defer to each manufacturer’s specs. The corrosion/rust must not exceed the thread height or cause discontinuity of the threads in any case.
Galled Threads
Galled threads are primarily found on used pipe. Galling can occur during the make-up/break-out process. They are characterized by a deformation of the original thread form typically caused by over-torque, repeated make-up, or improper thread form.
Tool Marks
These occur as a result of machinery, bolts, pipe wrenches, etc damaging the thread area during threading, handling, or hydro-static testing.
Grind Marks
These are areas of the threads which have been visibly ground down, causing imperfections and discontinuity of the thread surface. Grinds can also be visible in the pipe body.
Torn Threads
Torn threads are a result of the cutting inserts or chaser tearing the surface of one or more threads during the threading process.
Chatter (Skip or Sawtooth)
Skip or sawtooth chatter is an interruption of the continuity of the thread surface resulting from a dull cutting insert or improper setup of the cutting head during the threading process. The cutting insert jumps or vibrates causing irregularities in the crest, root or flanks, or a combination of them.
Shoulders on Threads
Shoulders on the connections themselves are the presence of positive or negative metal on the surface of the crest, root, or flanks, resulting in a “stair-step” or notched effect.
In many instances, a metal file may be used to field repair the thread if within manufacturer/API specifications.
Out of Round / Ovality
This can occur in the pin or coupling end and may prevent proper make-up to power-tight and may promote cross-threading.
Thread Eccentricity
Also called Black-Crested Threads. They can be caused by improper setup prior to threading or out of round pipe. Black crested threads appear as the original pipe surface remaining on the crest of the threads.
Check manufacturer specs. Buttress threads are permitted no more that 2 threads less than 25% of the circumferential distance around the pipe in the perfect thread area.
Laps and Seams
A lap is a discontinuity in the pipe metal which extends into the thread area. It appears as a hairline crack and must not extend into the perfect threads, past the root cone, or exceed 12.5% of the nominal wall thickness measured from the original pipe surface in the imperfect thread area.
A seam is a crevice in rolled metal which has been more or less closed by rolling or other work but has not been fused into sound metal. The seam must not extend into the perfect threads, past the root cone, or exceed 12.5% of the nominal wall thickness.
Connection Areas and Possible Issues found during threaded connection inspection
Pin or Box Threads:
Rust and/or scale
Galling
Pin nosing
Dents and/or mashed areas
Out-of-Roundness
Corrosion/pitting
Wiped-out threads
Excessive coating
Metal-to-Metal Seals:
Longitudinal cuts/scratches
Out-of-Roundness
Corrosion/pitting
Rust and/or scale
Galling or wear
Dents and mashed areas
Torque Shoulders:
Rust and/or scale
Dents and/or mashed areas
Rolling and flaring due to excess torque
Galling or Wear
Other Machined Surfaces Not Adjacent to Metal Seals:
Longitudinal cuts/scratches
Rust
Dents or mashed areas
Corrosion pitting
Non-Machined Surfaces over Box Threads:
Tong & wrench grooves
Slip grooves
Hammer marks
Out-of-Roundness that would preclude stabbing
Expanded box
Seal Rings
Proper placement in groove
Loping or protrusion into the ID
Cuts
Excessive plastic coating
Dents or mashed areas
Plastic or debris in groove
Corrosion pitting and/or scale