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NACE Corrosion 2019


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March 24 – 28, 2019      


Music City Center | Nashville, TN

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NACE Corrosion 2019
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Presentations and Papers

Effect of Low Frequency on the Fatigue Response of Wellhead Extension Joint Welds Exposed to Simulated Seawater with Cathodic Protection

by Adam Rowe

TUESDAY, MARCH 27  |  9:35 AM

This work considers wellhead extension joint welds for high-pressure, deepwater Gulf of Mexico prospects with a design shut-in tubing pressure (SITP) above 15,000 psi.  The structural welds joining 75K 8630M low pressure wellhead housing (LPWH) forgings to API 5L Grade X80M PSL 2 conductor casing are expected to be fatigue-sensitive due to water depths approaching 6,000 ft. and substantial estimated weight of a 20K BOP stack.  Cyclic loading is expected to be from wave‑induced motions (WIM) and vortex‑induced vibration (VIV).   The wellhead extension joints extend 10 to 15 ft. above the mudline and will be exposed to seawater as well as cathodic protection when the wellhead is connected to either the BOP stack or the tubing head spool and subsea tree.

The present work considered both S-N and fracture mechanics based designs.  Fatigue curves such as those in BS (British Standard) 7608 are not yet proven for structural steels with yield strengths in excess of 400 N/mm2 (58 ksi) in the presence of cathodic protection, and fatigue crack growth laws such as those in BS 7910 for steels in a marine environment are only applicable to materials with yield strengths less than 600 N/mm2 (87 ksi).  Materials in the subject assemblies may have yield strengths in excess of 690 N/mm2 (100 ksi), so both S-N and fatigue crack growth rate (FCGR) testing in a simulated seawater with cathodic protection environment were determined to be appropriate.

This paper describes the environmental fatigue testing of welds and the relationship between the test data, established fatigue curves, and published literature.  Tests were performed in a 3.5% NaCl solution at 40 °F with pH adjusted to 8.2 and an applied potential of -1100 mV Ag/AgCl.  Frequency scans were conducted in several weld microstructures to assess growth rate sensitivity of each microstructure to cyclic frequency, and the fatigue response at the low end of the frequency range was explored in greater detail.

High Temperature Hydrogen Attack Life Assessment Modeling and Inspection

by James Johnson


Key elements of a technology initiative aimed at developing high temperature hydrogen attack (HTHA) assessment methodologies for equipment and piping operating in hot hydrogen service are presented.  Two assessment methodologies have been developed: (1) a Screening Assessment and (2) an Advanced Assessment, both of which predict the development of HTHA damage with time.  The HTHA assessment methodologies utilize fitness-for-service (FFS) frameworks and are in good agreement with reported HTHA incidents in API 941RP and API 941TR for carbon steel and C-0.5Mo materials. The Screening Assessment provides an improved decision basis by classifying and ranking equipment operating in hot hydrogen service, which are tied to recommended action and levels of concern.  The Advanced Assessment models through-wall damage progression.  Additionally, the use of inspection findings as a means of risk mitigation and guidance on inspection interval decisions are also discussed.  Select case studies are used to illustrate the advantages of the proposed methods.  The developed methodologies provide an improved link between HTHA damage assessment and progression, inspection and detection limits, damage tolerance, and operation severity.

Under Deposit Corrosion of API X-65 Carbon Steel in the Presence of Acid Gases

by Suresh Divi


Deposits can play an important role in the corrosion rate and morphology of carbon steel in a production environment as well as affect the efficacy of an inhibitor. A test method has been developed to investigate the corrosion characteristics of carbon steel in a stratified flow regime where deposits of solids accumulate in the bottom of a pipeline.

Previous testing showed higher under deposit corrosion rates of API X-65 carbon steel when the deposit consists of iron sulfide (FeS)  versus sand in a 100%H2S environment. There is a need to investigate the effect of CO2 on these findings, as the lower pH should affect the corrosion rate, morphology, and galvanic action, particularly with respect to the FeS deposits.

This paper presents the effect of mixed gases (50%H 2 S + 50%CO2 ) on corrosion behavior of API X-65 carbon steel coupons in the FeS and sand deposits. The average corrosion rate, thickness loss of the coupons and pitting at the solid/liquid interface will be presented.


Keywords: Under deposit corrosion, Iron sulfide (FeS), sand, mill scale, acid gases

Corrosion Resistant Alloy Failures in Refining Operations

by Sudhakar Mahajanam

MONDAY, MARCH 25  |  2:35 PM

Corrosion Resistant Alloys (CRAs) are routinely utilized to mitigate against the complex damage mechanisms encountered in refining operations that carbon and low alloy steels are highly susceptible to. However, CRA materials can suffer similar corrosion damage when improperly manufactured or exposed to aggressive environments. In this paper, three modes of CRA failure observed at a client’s site were analyzed in a lab and mitigation strategies proposed.

Tower trays near the top of a crude tower made of 410S martensitic stainless steel failed as a result of localized undersalt corrosion due to formation of amine hydrochloride salts. Appropriate crude pre-treatment was implemented to mitigate this corrosion mechanism.

Inconel 625 flexible hoses located at the inlet of a reformer in a hydrogen plant failed upon start-up during a turnaround. It was found that these materials were heavily sensitized with embrittling phases present at the austenite grain boundaries. Improper annealing processes at the manufacturing plant likely caused the sensitization of the microstructure.
Downstream of the reformers, 304L SS tube ends of the boiler feed water (BFW) heat exchanger underwent a failure. The tube to fixed tube sheet seal weld failed as a result of fatigue cracking originating at a lack of weld deposit location. Ensuring a proper weld profile in compliance with the weld procedure would reduce such stress riser concentrations.