Risk Analysis and Reduction in the Development of High-Sulfur Natural Gas

Transcription

1 Risk Analysis and Reduction in the Development of High-Sulfur Natural Gas M. Andrew Crews CB&I 7 th Oil and Gas Industry Forum 1

2 Objectives: Consider the problems associated with high sulfur content natural gas Discuss the identification and analysis of risk of high sulfur natural gas Consider mitigation through design, construction and operating procedures and practices Consider mitigation by removal and the advantages which it may provide 2

3 Agenda Risk Identification Risk Analysis Risk Reduction/Mitigation Materials Welding Inspection and Safety Storage Operating Removal Conclusions 3

4 Risk Identification Reserves Wellhead Pipeline Processing Storage H 2 S is: Colorless Flammable Corrosive Invasive There is a risk of: Operation and accidental discharge Corrosion, failure and discharge Potential damage to Equipment and material Environment Humans plant operating personnel, contractors and the public at large 4

5 Risk Identification Health Effects of H 2 S Exposure Airborne Concentration 0.02 ppm 10 ppm 100 ppm ppm ppm ppm Health Effect Odor threshold Eye irritation Coughing, headache, dizziness, loss of sense of smell Marked eye inflammation and respiratory tract irritation after one hour Loss of consciousness and possibly death in 30 minutes to one hour Rapid loss of consciousness, cessation of breathing, and death Solutions > 1000 ppm Unconsciousness in seconds with early cessation of breathing and death in a few minutes unless victim is removed from exposure and breathing is restored. Death may result regardless. Preparation: Quantifying the risk the sulfur poses in development and operation plans Engineering: Selecting materials and welding procedures to fit the environment Safety and Inspection: Mitigating risk to prevent sulfur from posing a hazard Removal: Using technologies that remove up to 99.99% of sulfur from the natural gas/acid gas streams as a liquid sulfur by-product 5

6 Risk Analysis Determine potential pipeline and wellhead accidents that could create life threatening hazards to persons located near pipeline or well sites Derive frequency of occurrence (probability) Determine the consequences Combine the consequences and probability of occurrence to arrive at a measure of risk created by the pipeline and well network Review procedures of construction and the ability of contractor to execute these procedures to achieve required specification and metallurgical requirements Probability density plot of a pipeline system 6

7 Risk Reduction/Mitigation Engineer to reduce/mitigate Material selection Welding procedures Quality Control of Welding Material Procurement Material Production Operate to reduce/mitigate Inspection and safety procedures Plant monitoring Remove risk at source 7

8 Risk Reduction - Materials It is the responsibility of the user to determine the operating conditions and to specify when special material needs are applicable It is the user s responsibility to ensure that a material will be satisfactory in the intended environment The manufacturer is responsible for meeting metallurgical requirements User Responsible for operating equipment that is installed and operated in the field Manufacturer Responsible for meeting metallurgical requirements International standards have been clarified with increased responsibility for the user NACE MR /NACE MR0175/ISO

9 Risk Reduction - Materials Sulfide Stress Cracking (SSC) is defined as cracking of a metal under the combined action of tensile stress and corrosion in the presence of H 2 S and water SSC is a form of hydrogen stress cracking resulting from absorption of atomic hydrogen that is produced by the sulfide corrosion reaction on the metal surface SSC is affected by: Types of Service Induced Hydrogen Cracking Due to H 2 S Material composition, strength (hardness), heat treatment and microstructure Total tensile stress (applied plus residual) Hydrogen flux generated in the material as a function of the environment that it is in Temperature and time NACE MR /NACE MR0175/ISO

10 Risk Reduction - Materials International Standards for Pre-qualified Materials Material susceptibility to SSC is primarily related to material strength Materials with high hardness generally have an increased susceptibility to SSC Improper design, processing, installation, or handling can cause resistant materials to become susceptible to SSC Control of weldment hardness with or without reduction of residual stresses is a recognized method of reducing SSC Techniques are known that lower residual stresses from welding around the weld metals NACE MR / NACE MR0175/ISO

11 Risk Reduction - Welding Maximum allowable hardness is specified as a primary requirement for materials and final manufactured products Method that can readily be measured and tested on procedure qualification and in production Fairly simple measurement compared to taking mechanical tests (tensile tests to measure ultimate and yield strength) Welding Quality Control is a critical component of risk reduction for materials in H 2 S service. Welding Procedure Specifications and their qualification (Procedure Qualification Records) must be properly developed and qualified by the manufacturer/contractor to meet requirements Developed in accordance with AWS, API, ASME and other international industry codes as required for specific applications User Approved Welding Procedure Specifications and supporting Procedure Qualification Records NACE MR / NACE MR0175/ISO

12 Risk Reduction - Welding Hardness tests are typically completed on Welding Procedure Qualifications per MR0175/ ISO requirements - Vickers 10 kgf (HV10) or 5 kgf (HV5) methods ISO Rockwell 15N Method ISO Maximum hardness for carbon / low alloys steels per MR0175/ISO15156 Weld Root, & base metal, HAZ at weld root 250 HV or 70.6 HR15N (maximum) Weld Cap: Base metal, HAZ and weld metal of unexposed (to H2S) weld cap 275 HV or 73.0 HR15N (maximum) - Contactor/Manufacture must control and properly apply the Qualified Welding Procedure Specifications in the field to provide assurance that production weldments will have the required hardness - Production hardness checks can be completed on the surface of weldments using portable Vickers, Rockwell or Equiptip (trade name) hardness testing NACE MR / NACE MR0175/ISO

13 Risk Reduction - Storage Important to ensure that specification of materials and installation does not compromise the material properties Ensure that post-weld heat treatment does not change the material strength Ensure that hardness is met to avoid corrosion Train welders in a laboratory and in production environments welding supervision is a key to success with high sulfur gas Build quality in instead of inspecting it out 13

14 Risk Reduction - Inspection and Safety Pipeline Inspection Tool Leak Detection Pipeline Markers Gas Sampling Preventive Maintenance Emergency Response System Data Monitored by the US DOT Alarm Systems NDE (Ultrasonic Inspection including thickness measurement) Pig - Pipeline Inspection Tool Source: Duke Energy Gas Transmission Canada 14

15 Risk Reduction - Operating Contractor and Owner Safety Procedures Should Contain: Definition of management, supervisor and employee responsibilities for exposure control Definition of requirements for description of potential exposure to H 2 S Description of potential exposure to H 2 S Atmospheric monitoring for H 2 S, LFL, and Oxygen Engineering and work practice controls Confined space entry procedures (if applicable) Respiratory protection Emergency procedures (including the site s emergency action plan) Training 15

16 Risk Reduction Removal Dehydration Gas Sweetening Unit Claus Process Sulfur Recovery Unit Tail Gas Treating Unit Thermal Incineration Unit Oxygen Enhancement Unit (Optional) Liquid Sulfur Degassing Unit Sulfur Solidification Unit 16

17 Risk Reduction - Removal Benefits of Removal Decreased risk of H 2 S exposure to the environment Decreased corrosion Decreased metallurgy considerations Decreased pipeline cost 17

18 Conclusions The user is responsible for ensuring the materials used are satisfactory for the environment they will be used in Adequate risk analysis is crucial to identifying areas of risk to the public around well head and pipelines Use of internationally pre-qualified materials helps reduce risk Welding procedure and welding quality control can significantly reduce risk Active safety inspections of pipelines and wellheads reduce the risk of exposure Sulfur reduction technologies can be a safe method of reducing the transportation risk of high sulfur natural gas There is no right answer.. Safety, social concerns and economics must all be evaluated to achieve the most advantageous result. 18