Before casing joints are installed in a well, they are exposed to a variety of harsh conditions during transport, handling and storage. The threaded pipe ends frequently have to withstand accidental impact loading during shipment from the mill to the wellsite and once at the wellsite, during handling, cleaning and running into the hole.
In addition, these threaded ends are often exposed to corrosive environments during storage. Therefore, it is of vital importance to protect the threads and seals against impact loading and water penetration all the way from the mill up to the drill floor, with a thread protector. These thread protectors can be divided into two types:
Threaded protector or transit protector This type of protector for both pin and box, can be used from the mill onwards up to the moment the joint is laid down on the casing rack at the location, where it is taken off to allow removal of the storage compound. Most of these heavy-duty-type of protectors are composed of a moulded polymer body reinforced with a cylindrical steel insert. However they can also consist of a 100% polymer.
Non-threaded protector or handling protector This type of protector is installed on the pin prior to lifting the casing joint up to the drill floor. It is usually either a clamp-on type or an inflatable type.
Performance criteria
Until recently there have been no generally accepted performance criteria for protectors and selection of a suitable product has been left to the manufacturer or the customer. From research on protectors for 31/2 in (0.0889 m) tubing and 7 in (0.1778 m) tubing, a suggestion for acceptance criteria came forward. These criteria were proposed for thread protectors, installed on Premium connections, and were generated on the basis of conditions expected to occur in the field. Find below a summary of these criteria:
Impact resistance
A protector must be able to absorb impact energy in the axial and radial direction and also in the angular direction, without damage being inflicted on the threads or sealing area of the pipe. Also the protectors should be able to meet these requirements under extreme temperature conditions, as stated in API Spec 5CT.
Protection against water penetration
The protector should be able to prevent water penetration along the threaded area in order to prevent a potential corrosive attack on thread and seals. This criterion must be met with or without the presence of suitable storage grease.
Resistance to thread stripping
A protector should be able to sustain an axial load, uniformly applied around the inner perimeter.
Resistance to vibrational loading
The protector must be able to sustain vibrational loads such as can occur during transport.
Chemical resistance
If subjected to oil field chemicals, like degreasers and solvents, the volume of the protector should not increase by more than 10%, and the hardness should not change significantly.
Weathering resistance
The protector should not show sensitivity to ageing as caused by climate.
Thread profile
The thread profile of the protector should provide a number of basic functions: it is the primary barrier to moisture, therefore a good match between protector and threads is essential. Storage grease is considered to be an additional secondary barrier; the profie should provide a locking fit between the protector and the pipe; a protector should have a threaded profile all along the threads of the pipe; the general fit of a protector should be satisfactory, which means that the threads of the protector should have a pitch, a taper and diameter that corresponds within reasonable limits to those of the pipe end.
Additional criteria
The protector should bottom out near the sealing area of the pipe to protect the seal from the inside.