Applicability Assessment of Long-Term Stored Seamless Steel Pipes

Literature Overview

This study by Yang Hongli and colleagues from Xi'an Sanwei Stress Engineering Technology Co., Ltd. and Sinopec Northwest Oilfield reports on the evaluation of seamless steel pipes that have undergone extended periods of storage. Published in 2021 in the journal Steel Pipe, the paper addresses a practical and frequently encountered issue in oil and gas field operations where pipes may be stockpiled for extended durations before installation. The assessment was conducted against GB/T 9711—2011, the Chinese national standard for petroleum and natural gas industry steel pipe specifications.

Test Methodology and Results

The evaluation program encompassed a comprehensive set of tests to determine whether the stored pipes remained fit for service. The following table summarizes the test categories and their outcomes:

The geometric dimensional checks confirmed that the pipes maintained their original tolerances for outside diameter, wall thickness, and straightness over the storage period. Mechanical property tests, including tensile strength, yield strength, elongation, and impact toughness, all met the minimum requirements specified in GB/T 9711—2011 for the applicable grade.

Corrosion Analysis

The internal wall of the stored pipes exhibited brown-colored corrosion products identified as predominantly Fe2O3 (iron oxide). The presence of a layer of loose rust on the inner surface indicated that moisture ingress during storage had initiated a mild uniform corrosion process. While the corrosion was characterized as slight, the study correctly highlights that even minor internal corrosion can have significant implications for the long-term integrity of pipelines, particularly in high-pressure oil and gas service where internal pressure combined with corrosion can lead to wall thinning and potential failure.

Engineering Recommendations and Practice Integration

The authors recommend two key actions for the downstream processing and operation phases. First, enhanced anti-corrosion measures should be implemented during the pipeline construction phase, such as internal coating application or the use of corrosion-resistant pipe grades. Second, periodic internal corrosion monitoring should be established during pipeline operation to track the progression of any residual corrosion.

From a welding and fabrication standpoint, the presence of surface rust and corrosion products on the pipe interior poses challenges for any in-situ repair welding or internal inspection procedures. Pre-welding cleaning and surface preparation would be essential if any weld repair work is required on these pipes. Additionally, the loose rust layer must be removed before any internal coating is applied to ensure proper adhesion and long-term coating performance.

Study Insights and Implications

This study underscores an important practical reality in the oil and gas industry: pipe storage logistics can introduce corrosion risks that compromise the integrity of otherwise compliant materials. The systematic evaluation approach adopted here, covering geometric, mechanical, pressure, and corrosion assessment, serves as a model for similar acceptance evaluations. For engineers involved in pipeline procurement and construction planning, the key takeaway is that storage duration and environmental conditions must be factored into the risk assessment and quality assurance plan. The finding that even compliant pipes can develop internal corrosion during storage reinforces the need for robust storage management protocols, including proper ventilation, moisture control, and periodic inspection during the storage period. This work provides a practical framework for making go/no-go decisions on stored pipe inventory.