Hydrogen Embrittlement

Hydrogen incuded damage describes any of a number of forms of degradation of metals caused by exposure to environments (liquid or gas) which cause absorption of hydrogen into the material to cause degradation in mechanical performance. Examples of hydrogen induced damage are:

1. formation of internal cracks, blisters or voids in steels.
2. embrittlement (i.e. loss of ductility).
3. high temperature hydrogen attack (i.e. surface decarburation and chemical reaction with hydrogen).

Prevention or Remedial Action

1. internal cracking or blistering
   • use of steel with low levels of impurities (i.e. sulfur and phosphorus).
   • modifying environment to reduce hydrogen charging.
   • use of surface coatings and effective inhibitors.
2. hydrogen embrittlement
   • use of lower strength (hardness) or high resistance alloys.
   • careful selection of materials of construction and plating systems.
   • heat treatment to remove absorbed hydrogen.
3. high temperature hydrogen attack
   • selection of material (for steels, use of low and high alloy Cr-Mo steels; selected Cu alloys; non-ferrous alloys).
   • limit temperature and partial pressure H₂.

Standard Test Methods

• NACE TM0177 - laboratory testing of metals for resistance to sulfide stress cracking in H₂S environments.
• NACE TM0284 - evaluation of pipeline and plate steels for resistance to stepwise cracking.
• ASTM G129 - slow strain rate test for determination of environmentally assisted cracking.
• ASTM G142 - tension tests in hydrogen environments.
• ASTM G146 - hydrogen induced disbonding of stainless clad steel plate in refinery hydrogen service.
• ASTM F-326 - method for electronic hydrogen embrittlement test for cadmium electroplating processes.
• ASTM F-519 - method for mechanical hydrogen embrittlement testing of plating processess and aircraft maintenance chemicals.
• ASTM A-143 - practice of safeguarding against embrittlement of hot dip galvanized structural steel products and detecting embrittlement.
• ASTM B-577 - hydrogen embrittlement of deoxidized and oxygen free copper.

Evaluation for Hydrogen Induced Damage

Since hydrogen can induce many types of damage in engineering materials, itis impossible to look to only one test method for all problems.

• Slow strain rate test methods are good to obtain general information on the inherent susceptibility to hydrogen embrittlement is a short period of time. However, the results will generally be very conservative.
• For higher strength materials, the use of constant load tests for determination of an apparent threshold stress for cracking is a generally accepted technique.
• Hydrogen induced cracking and blistering of low strength steels can be tested using non-stressed coupons exposed to the test environment. However, in some cases, the addition of an externally applied or residual tensile stress can cause materials to crack that do not show cracking in the non-stressed condition. Also, constant load specimens may not fail under tensile stress even though they may have extensive internal cracking or blistering.

High temperature hydrogen damage and disbonding must be evaluated for the specific conditions of time and temperature for the intended use. However, it can in many cases, be accelerated with the combination of higher temperature and/or hydrogen pressure.