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Oil and Gas Industry Equipment Reliability

Introduction

Each year billions of dollars are spent around the globe to construct/manufacture, operate, and maintain various types of equipment/systems used in oil and gas industry. Nowadays, reliability of equipment used in the oil and gas industry has become an important issue due to various types of equipment reliability-related problems. For example, in 1996, corrosion-related failures including maintenance, annual direct cost in the US petroleum industry alone was $3.7 billion [1,2].

Today, the global economy is forcing all the companies involved with oil and gas to modernize their operations through increased automation and mechanization. Thus, as equipment used in the oil and gas industrial sector is becoming more complex and sophisticated, its cost is increasing quite rapidly. In order to meet production targets effectively, oil and gas companies are increasingly demanding better equipment reliability.

This chapter presents various important aspects of oil and gas industry equipment reliability.

Optical Connector Failures

Optical fiber connectors are used for joining optical fibers in situations where a connect/disconnect capability is needed. In oil and gas applications, fiber-optic equipment including wet-mate optical connectors is an important part of the current subsea infrastructure. A study of reliability-related data (excluding cables or jumpers) collected over the period of 10-years reported four factors/issues (including their percentage breakdowns), as shown in Figure 11.1, that cause optical connector failures [3]. The data include field failures and the failures that took place during integration into equipment and testing process prior to field deployment.

It is to be noted from Figure 11.1 that 86% of the optical connector-related failures were due to material, external, and mechanical factors, and only 14% of failures were related to optical-related issues. Furthermore, when just field failures were studied, the optical connector-related failures occurred due to two types of issues only. These two types were mechanical issues and material issues. The mechanical issues accounted for 61% of the failures and the material issues accounted for 39% of the failures [3].

Factors along with their percentages in parentheses that caused optical connector failures

FIGURE 11.1 Factors along with their percentages in parentheses that caused optical connector failures.

Additional information on optical connector-related failures is available in Dhillon [3].

Mechanical Seals’ Failures

Mechanical seals have been increasingly used for many decades to seal rotating shafts. Nowadays, they are the most common types of seals found on items such as centrifugal pumps and compressors used in the oil and gas industrial sector. Over the years, mechanical seals’ failure has become a very important issue. For example, a study carried out in a petroleum company reported that around 60% of plant breakdowns, directly or indirectly, were due to mechanical seal-related failures [4].

A study of mechanical seal failures conducted in a company reported the following ten causes for the failure of mechanical seals [4]: [1]

Mechanical Seals’ Typical Failure Modes and Their Causes

Past experiences over the years indicate that mechanical seals can fail in many different failure modes due to various causes. Typical failure modes and their corresponding causes for mechanical seals are presented below [5].

  • Failure mode: Accelerated seal face wear. Its causes are excessive torque, shaft-out-of-roundness, surface finish deterioration, misalignment, excessive shaft and play, inadequate lubrication, and contaminants.
  • Failure mode: Compression set and low-pressure leakage. Its cause is extreme temperature operation.
  • Failure mode: Fractured spring. Its causes are corrosion, stress concentration due to tooling marks, misalignment, and material flaws.
  • Failure mode: Seal embrittlement. Its causes are idle periods between use, thermal degradation, fluid/seal incompatibility, and contaminants.
  • Failure mode: Torsional shear. Its causes are excessive torque due to improper lubrication and excessive fluid pressure surges.
  • Failure mode: Excessive friction resulting in slow mechanical response. Its causes are excessive seal swell, seal extrusion, excessive squeeze, metal-to- metal contact (i.e., out of alignment).
  • Failure mode: О-ring failure. Its causes are installation error, excessive temperature (i.e., greater than 55°C), and excessive fluid pressure.
  • Failure mode: Open seal face-axial. Its causes are impeller adjustment error, thrust movement, temperature growth, spiral failure (caused by conditions that allow some parts of the ring to slide and others to roll that cause twisting), etc.
  • Failure mode: Fluid seepage. Its causes are insufficient seal squeeze (loss of spring tension) and foreign material on rubbing surface.
  • Failure mode: Seal fracture. Its causes are excessive pressure velocity (PV) value, excessive fluid pressure on seal, and stress-corrosion cracking.
  • Failure mode: Seal face distortion. Its causes are excessive PV value of seal operation, foreign material trapped between faces, insufficient seal lubrication, and excessive pressure on seal.
  • Failure mode: Clogged bellows. Its causes are particles stuck at the inside of the bellows and hardening of fluid during downtime.
  • Failure mode: Axial shear. Its cause is excessive pressure loading.
  • Failure mode: seal face edge chipping. Its causes are excessive shaft deflection, seal faces out-of-square, and excessive shaft whip.
  • Failure mode: Open seal face-radial. Its causes are shaft detection, shaft whip, and bent shaft.
  • Failure mode: Clogged spring. Its cause is fluid contaminants.
  • Failure mode: Small leakage. Its causes are insufficient squeeze and installation damage.

Additional information on mechanical seal failure modes is available in Skewis [5].

  • [1] Cause I: External system or component failure (e.g., bearings) • Cause II: Shaft and seal face plane misaligned • Cause III: Auxiliary seal system failure (e.g., flush, cooling, recirculating,quench) • Cause IV: Dry-running • Cause V: Wrong seal spring compression • Cause VI: Seal component failure (i.e., other than the faces or secondary seals) • Cause VII: Highly worn carbon (i.e., greater than 4 mm of wear) • Cause VIII: Hang-up (i.e., crystallization) • Cause IX: Metal particles embedded in the carbon • Cause X: Hang-up (i.e., coking)
 
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