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9.2 Pressure Testing and Welding Procedures - Coggle Diagram
9.2 Pressure Testing and Welding Procedures
Here is a mind map outlining the key concepts from the provided sources:
Hydrostatic Testing
Definition and Purpose
Verifies integrity and safety of pressure equipment
Detects leaks
Confirms structural integrity
Applies internal pressure with liquid (typically water)
Identifies weaknesses, manufacturing defects, damage
Assures safe operation
Critical before commissioning and during maintenance
Applications Across Industries
Oil and Gas (pipelines, tanks, vessels)
Chemical Processing (corrosive substances)
Aerospace (fuel tanks, high-pressure components)
Transportation (gas cylinders, hazardous materials)
Utilities (boilers, water systems, heating equipment)
Hydrostatic Test Pressure Requirements
Multiple of Maximum Allowable Working Pressure (MAWP)
Historically 1.5 × MAWP
Recent revisions (ASME) 1.3 × MAWP
Calculation Formulas
Minimum Test Pressure = 1.3 × MAWP × LSR (Lowest Stress Ratio)
Minimum Test Pressure = (1.3 × MAP) – Hydrostatic head (MAP = Max Allowable Pressure at test temp)
Minimum specified, no upper limit in ASME Code
Inspector can reject if visible permanent distortion
Step-by-Step Hydrostatic Testing Process
Preparation Phase
Isolate the test section
Install test equipment (heads, gauges, relief valves, monitoring)
Valve positioning (ball valves 50% open, gate valves fully open)
Provide double block isolation (between pumps and equipment)
Execution Phase
Fill the vessel with liquid (typically water), remove air
Initial pressurization to MAOP, hold ~30 minutes (check for visible leaks)
Intermediate hold at 75% minimum test pressure, hold ~30 minutes (verify stability)
Final pressurization at controlled rate (≤ 10 psi/minute) to specified test pressure
Monitoring and inspection (hold for 10-30 minutes, check for leaks, pressure drops, deformation)
Post-Test Procedures
Controlled depressurization (partially open a small tap valve)
Visual inspection (after reducing pressure to ≥ test pressure / 1.3)
Drainage and drying (especially for stainless steel)
Documentation of test parameters, observations, results
Critical Water Quality Considerations
Impacts equipment integrity (corrosion, pitting, stress corrosion cracking)
Key Parameters
Chloride content
Max 50 ppm for most applications (austenitic stainless steel)
< 50 ppm for high-pressure service (> 100 barg)
≤ 1 ppm for operating temperatures > 50°C or crevices
pH level
: Typically between 6 and 9
Total dissolved solids (TDS)
: Controlled to prevent deposits and corrosion
Special Considerations for Stainless Steel
Use potable water or steam condensate with ≤ 50 ppm chloride
Complete drainage and drying within 48 hours
Consider hydrocarbon liquid or specially treated water if drainage/drying difficult
Temperature Requirements for Hydrostatic Testing
Prevent brittle fracture
Ensure accurate results
Relative to Minimum Design Metal Temperature (MDMT)
Guidelines
Minimum temperature: At least 30°F (17°C) above MDMT
Maximum temperature: Should not exceed 120°F (48°C)
Delay inspection if test temperature exceeds 120°F until it decreases
Test fluid and vessel should be at approximately the same temperature
Avoid pressurizing below MDMT or nil-ductility temperature
Safety Precautions and Hazard Mitigation
Personnel safety
: Stay away from discharge paths and line of fire
Pressure control measures
Install pressure relief devices set to 1⅓ times the test pressure
Never exceed pressure increase rate of 10 psi/minute during final pressurization
Never tighten connections under pressure; depressurize first
Emergency response preparation
Have spill response equipment ready
Establish clear emergency procedures
Preparation and planning
Include detailed procedures in site-specific safety plans
Verify all support points can sustain the hydrostatic load
Specialized Testing Considerations
Combination Units Testing (e.g., heat exchangers)
Test each chamber separately
Test common elements based on differential pressure
Perform simultaneous testing of adjacent chambers after individual testing
Isolation Testing
Identifies specific locations of leaks
Performed after detecting leaks
Helps determine specific drain line area or branch
Useful for complex piping systems
Welding Procedures
Recipe for a perfect weld
Must Include
Type of Metal
Type of Welding Process (Stick, MIG, TIG, etc.)
Heat Control
Inspection Requirements
Must be qualified following ASME Section IX (industry standard)