Qualification of Seamless X60QOS and X65QOS Line Pipe Grades for Extreme Sour Service Conditions with Partial Pressure of H2S beyond 1 Bar

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Seamless X60QOS and X65QOS line pipes are widely used for offshore and onshore Sour Service applications. Sour Service refers to the risk of hydrogen related cracking as Sulfide Stress Cracking (SSC). The International standard (NACE MR0175 / ISO 15156) provides requirements for assessing the resistance to SSC, specifically on how to qualify for use in region 3 of the environmental severity diagram (Figure 1 in paragraph 7.2.1.2 of part 2). It is requested to expose materials in an acid solution saturated by 1 bar of H2S (NACE TM0177 Solution A) and to apply a tensile stress above 80% AYS by means of different methods: uniaxial tensile, C-ring or Four-Points Bend. However, for very sour fields presenting H2S partial pressures much higher than 1 bar, the preservation of the SSC resistance might be questioned and is presently a major concern for the O&G industry.
The present paper is dedicated to the evaluation of the SSC resistance of seamless quenched and tempered X65 grades, including the girth weld in the standard NACE TM0177 Solution A up to 15 bar of H2S partial pressure. Corrosion tests consisted of four-point bend tests performed in autoclave vessels. Different test configurations were investigated as specimen sampling locations through the wall thickness and surface state preparation.

Product Number: MPWT19-15127

Author: Florian THEBAULT, Laurent LADEUILLE, Harold EVIN, Laurent LAMPS

Publication Date: 2019

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Chelating Agents for Iron Sulfide Scale Removal at 300°F (149°C)

Product Number: 51320-14859-SG

Author: Raja Ramanathan , Hisham A. Nasr-El-Din

Publication Date: 2020

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Iron sulfide scales create well deliverability and integrity problems such as reduced production rates and damage to well tubulars. Chelating agents have scarcely been studied for iron-sulfide dissolution. This paper evaluates EDTA, DTPA, and HEDTA for its iron sulfide (FeS) dissolution capacity and kinetics at 300°F (149°C).

A comparative study of the chelating agents with a low pH (3-5), moderate pH (5-9), and high pH (9-14) determined the optimum pH for the scale treatment. These tests were conducted in glass bottles and a high-temperature autoclave apparatus under anoxic conditions. Results show that the iron-sulfide dissolution increases tremendously at 300°F (149°C) when using chelating agents with a pH>5. At 300°F (149°C), the bond strength is reduced, allowing the chelating agents to remove the metal ion from the solid surface. The ranking of the chelating agents in terms of iron-sulfide scale dissolution capacity and effectiveness was DTPA>EDTA>HEDTA at all pH conditions. The role of chelating agents in iron sulfide dissolution at 300°F (149°C) has not been thoroughly investigated. There is no study that reports the optimum treatment time at that temperature. This paper investigates chelating agents and provides the optimum dissolver composition and treatment time for field operations at high temperature conditions.