Performance Evaluation of Commercially Available Thread Protectors
Authors: Spruijt E.J.C. 
Published: December 2007

Spruijt, E.J.C., Koninklijke/Shell E and P Laboratorium

A range of heavy-duty-type protectors for 3.5-inch VAM and 3.5-inch Hydril-CS premium threads has been evaluated in a series of performance tests based on conditions to be expected in the field. Acceptance criteria for these types of protectors have also been proposed. The results of the evaluation indicate that currently no product is available that can meet all the criteria set. Some products are acceptable, but selection between them should be based on the intended purpose. A need for commonly accepted performance requirements to rationalise the diversity of design philosophies currently being followed by the various, manufacturers is highlighted.

Introduction

Before oil-field tubular joints are installed in a well, they are exposed to a variety of harsh conditions during transport, handling and storage. The threaded pipe ends, which are usually equipped with premium threads, frequently have to withstand accidental impact loading during shipment from the mill to the well site and, once at the well site, during inspection and cleaning. In addition, these threaded ends are often exposed to corrosive environments during storage.

More than regular threaded connections, premium-type connections rely on precision-engineered threads and seals accurately machined within narrow tolerances. The actual sealing mechanism is provided through interference of smooth metal surfaces located at the front section of the threaded area.

Besides being expensive, premium threads are also vulnerable in the sense that any distortion of the critical area might lead to malfunctioning of the seal, and eventually even to string failure, with high production losses as a consequence. Therefore, it is of vital importance to protect the tubing all the way to the rig floor; thread protectors are the primary means of achieving this objective.

However, until now there have been no generally accepted performance criteria for protectors, and selection of a suitable product has been left to the tubing manufacturer or the customer. The API provides some guidelines and Exxon Research Company has evaluated a variety of protector designs, but both publications are of limited use in selecting a suitable product and in assessing proper acceptance criteria. Moreover, performance and prices of thread protectors vary over a wide range and so does the commercial and technical support that manufacturers provide with their products.

Consequently, an investigation was started into the performance of thread protectors with the following objectives:To evaluate the performance of current commercially available products.To generate requirements that these protectors should meet.

This document describes a series of performance tests to which protectors from nine major manufacturers have been subjected. Furthermore, a number of acceptance criteria are proposed that have been generated on the basis of the test experience and conditions expected in the field.

PRODUCTS

The protectors selected for the evaluation are "heavy-duty" types for 3.5-inch VAM and 3.5-inch Hydril-CS premium thread tubing. Moreover, on a limited scale, 7-inch protectors with a VAM profile were also included. A photograph of all products is shown in Figure 1.Most heavy-duty-type protectors are composed of a moulded elastomer body reinforced with a cylindrical steel insert.

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