An Inspection Demonstration Program/A Quality System
Authors: Cox L.D. 
Published: October 2008

Mobil relies on tubular manufacturers to consistently supply OCTG which complies with all material requirements of API SPECIFICATION 5CT. This paper details the Mobil Inspection Demonstration Program; Mobil?s method for qualifying ultrasonic inspection systems for use during Mobil receiving inspections. Additionally, the basic fundamentals of the Mobil quality system and acceptance sampling are presented with an emphasis on tracking short-term and long term supplier performance.

BACKGROUND

Mobil's implementation of Load and Resistance Factor Design (LRFD) to oil & gas wells has put renewed emphasis on the need for oil field tubulars which meet the material requirements specified by API SPECIFICATION 5CT l "Specification" for Casing and Tubing" (API 5CT). MWD well design is based upon defining well conditions or "load factors" (e.g., pressure, temperature, H2S content) and then tailoring tubular material attributes or "resistance factors" (e.g., fracture toughness, mechanical strength, maximum flaw size, wall thickness) to meet the performance requirements desired for a specific well application, API 5CT provides a convenient industry standard for the well designer to use in selecting the appropriate tubular materials to satisfy the material requirements of a well design.

WHY DOES MOBIL HAVE TO INSPECT OILFIELD TUBULARS?

Ideally... Mobil should not have to inspect oilfield tubulars and could confidently purchase and use tubular products certified to meet API 5CT material requirements with the understanding that specified defect and wall thickness requirements are satisfied. Unfortunately, based upon experience, Mobil expects to occasionally be offered material which is certified and monogrammed to meet API 5CT...but actually contains defects which violate API 5CT material requirements. This problem is illustrated by examining 4 months of ful14ength ultrasonic testing (FLUT) inspection results2 obtained from Tubular Inspectors, Inc. (TII) in Houston, Texas (See Figure 1).

There are various reasons why defective material is being certified, monogrammed, and presented to Mobil as meeting API 5CT requirements. Due to the complex nature of manufacturing oilfield tubulars, a certain percentage of non-conforming material may be produced. The quantity of non-conforming material is related to the manufacturer?s process and capability. Manufacturers rely upon inspection and testing to identify and segregate non-conforming material in order to provide assurance that API 5CT material requirements are satisfied. Although manufacturers may perform the required API 5CT inspections... there is typically no evidence that the inspections performed are capable of reliably detecting all defects which violate API 5CT material requirements. Additionally, the manufacturer?s consequence for occasionally missing defective material is not severe...defective joints detected by the user are typically culled out and replaced with "good footage". Hence, in order to assure oilfield tubulars are fit for intended service, a considerable burden of quality is placed on the user to confirm that API 5CT material requirements are met.

HOW CAN MOBIL ASSURE EFFECTIVE AND RELIABLE INSPECTIONS?

To reduce the risk of purchasing and using defective oiltield tubulars, Mobil requires nondestructive inspection systems which demonstrate consistent detection of flaws on the OD surface, midwall, and ID surface of API tubulars.

Mobil relies upon third party nondestmctive inspection services such as FLUT or electromagnetic inspection (EMI) to provide ameans for detecting defec