Sulfur Recovery Unit Reaction Furnaces Waste Heat Boilers Ferrule Failure Root Cause Analysis Presented By: Muhammad Bashir Khan – Manager, Technical Page 1 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
SRU and Ferrule Configuration • The Sulphur Recovery Units (SRU's) have 2 reaction furnaces in the thermal section of the Claus reaction Location of ceramic ferrule tubesheet lining Page 2 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
SRU and Ferrule Configuration • The tube-sheet of the waste heat boiler (WHB) is protected from the high temperature (approximately 1100°C) in the furnace by a lining made up of 2-piece ceramic ferrules (a hexagonal head and a cylindrical stem insertion). Ferrule Components Assembled Ferrule Gasket, Stem, Hexagonal Head Page 3 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
SRU and Ferrule Configuration • The 4,200 ferrules make up the tube-sheet lining as can be seen here. • The pattern is a result of the beige mortar and the white mastic grouting. – Both types of grout are white after dry-out Ferrule Tube-sheet Lining Page 4 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Inspection Findings • As part of the Warranty Shutdown (WSD) scope, one year after start-up, the two reaction furnaces of Unit 751 were scheduled to be opened and inspected in January 2016. – 99% of ferrules in both H-101 and H-102 found damaged • Circumferential crack of stem at tube to tubesheet interface • Corrosion deposit on stem at 6 o’ clock at crack point impregnating into ceramic stem body • Hot Sulphidation damage to tube end and tube to tubesheet strength weld Page 5 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Inspection Findings Cracked Ferrule Stem with Tube-end and Strength Weld 6 o’ clock Corrosion Deposit with Hot Sulphidation Damage Page 6 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Inspection Findings • The two reaction furnaces of three other units were inspected over the course of the next 12 months and the results were very similar only varying slightly by magnitude. Observation 751 754 752 753 Date of inspection Jan 2016 Feb 2016 Oct 2016 Jan 2017 Months in service at 12 12 21 23 time of inspection Between Between Between Between Corrosion deposit on ferrule stem 5 to 7 o’ clock 5 to 7 o’ clock 3 to 9 o’ clock 5 to 7 o’ clock % of ferrules cracked 99% 70% 100% 60% Hot Sulphidation at tube Significant Minor Very significant Minimal to tubesheet weld Page 7 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Investigation Details • After the initial inspection of the first 2 units (4 furnaces) in January and February 2016, representatives from all stakeholders worked together as a joint investigation team. This included: – Al Hosn Gas / Occidental Petroleum (Owners) – Saipem (as EPC) • Fluor (as Licensor) • Siirtec Nigi (Furnace OEM) • Industrial Ceramics (Ferrule OEM) – Other 3 rd Party Consultants • Nasato Consulting • The Welding Institute • Alberta Sulphur Research Limited • Porter McGuffie Page 8 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Investigation Details • After analysis of the findings, the failure mechanism was narrowed down to be one of the following four: – Hot Gas Bypass • Hot H 2 S passing between the ferrules, as a result of poor installation, resulting in hot sulphidation on the tube end. – Sagging Ferrules • Due to the weight of the ferrule hexagonal heads, the entire lining of ferrules would sag and result in compression of the ceramic fiber paper on the stem and creating a hot contact point which then induced hot sulphidation corrosion on the tube end. – Insufficient Thermal Protection by Ferrules • The ferrules were not providing sufficient thermal protection to the tube end leading to hot sulphidation on the tube end. – Two Phase Process • This is explained in more detail later in the presentation Page 9 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Investigation Actions • The first 2 units (4 waste heat boilers) inspected in January (751) and February (754) 2016 had all ferrules removed and the tube-sheet cleaned of residual Sulphur (by hand-tools) • The residual Sulphur was far greater than expected • The full set of ferrules were replaced with supervised installation by the OEM • New ferrules were ordered for the remaining two units (4 waste heat boilers) • These were scheduled for inspection and repair in October 2016 (752) and January 2017 (753) Page 10 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Investigation Actions • Further remedial actions were identified and implemented to address the various possible mechanisms. – Re-run of CFD analysis of tube-sheet lining design • Carried out by various parties – Review and revision of shutdown procedures • Increased fuel gas sweep flow rates (from 10% to 30%) • N 2 sweep of acid gas lines – A follow-up inspection of 751 was planned for February 2017 as there was inconclusive evidence to definitively support one mechanism over all others Page 11 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Further Investigation Findings • As mentioned earlier, Units 752 and 753 were inspected in October 2016 and January 2017 respectively. • These were shutdown using the revised procedure developed as part of the investigation. • When 752 and 753 were inspected, there was negligible residual Sulphur in the furnace compared to 751 and 754 (original procedure). • This confirmed that residual Sulphur found in 751 and 754 could have been prevented and that the original procedure was not fit for purpose. Page 12 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Further Investigation Findings • A year after reinstatement, the furnaces of Unit 751 were shutdown and inspected for a second time as per the follow-up actions. • The inspection process involved taking samples of ferrules out of the tube-sheet lining at pre-determined locations relevant to the previous inspection and documented: – Location of ferrules being removed (in clusters of 7 or 19 to maintain the ferrule wall) – Condition of the mastic and mortar (for poor quality in the installation or dislodgement through transient conditions) – Corrosion growth, cracking (circumferential or longitudinal) Page 13 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Further Investigation Findings • Representatives from key stakeholders were present for the duration of the investigation • The sequence of events was as follows: – 751-H-101 samples taken (3 clusters of 19 and 6 clusters of 7) – All ferrules were satisfactory – 751-H-102 samples taken (3 clusters of 19 and 6 clusters of 7) – 1 ferrule found with corrosion in lower left quadrant – Sample size was increased, further ferrules found with corrosion – Decision made with all stakeholders to remove all ferrules from 751-H-102 – A total of 118 found compromised in 751-H-102 – It was unknown if there were compromised ferrules in 751-H-101 that were not in the sampled zones – Decision made with all stakeholders to remove all ferrules from 751-H-102 – A total of 14 found compromised in 751-H-101 Page 14 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Further Investigation Findings • The main findings were: – No residual Sulphur – Only 14 and 118 ferrules (out of 4,200 in each furnace) were found affected with corrosion scale at 6 o’ clock position – No correlation between the affected ferrules and their installation condition (i.e. poor grouting) – No correlation between the affected ferrules and the thickness of ceramic fiber paper wrap on the stem – All affected ferrules located at the top and bottom extremities and on the left hand side of the tube-sheet. Page 15 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Further Investigation Findings • Locations of affected ferrules in each furnace Page 16 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
Failure Mechanism Analysis • For each possible failure mechanism, the findings from the follow-up inspection of 751 concluded the following: Failure Excluded or Expected Observations Actual Observations Mechanism Accepted Wide-spread ferrule failure 98.4% of ferrules were not Hot Gas Bypass with increased hot sulphidation affected. No further hot Excluded at tube end sulphidation on tube or tube-sheet Wide-spread ferrule failure Small clusters of ferrules with 6 o’ Sagging with similar corrosion growth at clock corrosion growth (only 14 & Excluded Ferrules 6 o’ clock position 118 out of 4,200 in each furnace) Insufficient Wide-spread ferrule failure 98.4% of ferrules were not Thermal with increased hot sulphidation affected. No further hot Excluded Protection at tube end sulphidation on tube or tube-sheet No failures as initiating 2-Phase Only 0.3% and 2.8% of ferrule mechanism (due to residual Accepted Mechanism failures at extremities Sulphur) was eliminated Page 17 Abu Dhabi Gas Development Company Ltd. CONFIDENTIAL
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