Sour service corrosion testing helps prevent the corrosion problems commonly encountered in the Oil & Gas industry.

 

A variety of corrosion problems can be encountered in industries such as oil and gas production, oil and gas transmission, and energy conversion systems. Such problems include weight loss corrosion, pitting corrosion, corrosion fatigue, stress corrosion cracking, sulfide stress cracking, and hydrogen-induced cracking.

Through our network of global laboratories, state-of-the-art equipment and expert capability we offer testing solutions for corrosion problems with Full Ring Corrosion Testing.

Stress Corrosion Cracking (SCC)

Stress Corrosion Cracking (SCC), is the formation of brittle cracking in a material, produced by the combined action of a corrosive environment and tensile stress, causing unexpected sudden failure. This Stress Corrosion Cracking (SCC) can either be applied (external load), or can be residual stress in the metal (e.g. due to the production process or heat treatment). Stress Corrosion Cracking (SCC) is usually unpredictable in nature, and the metal part can suddenly crack without any warning or previous deformation. The essential conditions that must be present to be able to get Stress Corrosion Cracking (SCC), are particular metal environment combination and surface tensile stresses.

Our metallurgy group is able to provide screening techniques for metals, which we can subject to a specific severe environment for an accelerated time. These tests will identify potent environments for a given material. Certain tests are used to evaluate the tendency of cleaning materials or insulations to promote Stress Corrosion Cracking (SCC).

Typical test methods that may be requested, are listed above. A list of some of the environments that promote Stress Corrosion Cracking (SCC) in various materials is outlined below.

Stress Corrosion Cracking (SCC) Test

The objective of this test is to predict the service behavior or to screen alloys for service in a specific severe environment for an accelerated time. Stress corrosion specimens can be smooth, or precracked or notched. Smooth SSC specimens allow for the evaluation of the total SCC life, which includes crack nucleation and propagation. The use of precracked or notched specimens is based upon the engineering concept that all structures contain cracklike flaws. Precracking can contribute to the susceptibility of SCC of alloys such as titanium which may not be evident from smooth specimens.

C-Ring specimens (ASTM G38 C-Rings) - these are commonly used to determine the susceptibility to SSC of alloys in different product forms such as tubing, rods, and bars in the short transverse direction.

Tensile specimens, per ASTM G49 - This is one of the most versatile methods of SCC testing because of the flexibility permitted in the type and size of the test specimen, the stressing procedures, and the range of stress level. It allows the simultaneous exposure of unstressed specimens with stressed specimens and subsequent tension testing to distinguish between the effects of true SCC and mechanical overload.

Bend Specimens - Bent Beam specimens are used to test sheets, plate and flat extruded material or wires and extrusions with circular cross sections. Three-point bend specimens are used because of the ease of load application and the ability to use the same loading rigs for different stresses. Four-point bends provide a uniform tensile stress over a relatively large area of the specimen. (ASTM G30 U-Bends) U-Bend specimens are prepared by bending a strip 180° around a mandrel with a predetermined radius. This method is used to qualitatively evaluate the susceptibility of alloy and heat treatment to SCC.

Typical tests preformed include:

• ASTM G36 - (Boiling Magnesium Chloride)
• ASTM G123 - (Boiling Acidified Sodium Chloride)
• ASTM G44 - (Alternate Immersion)
• ASTM C692 - (Influence of Thermal Insulations on external SCC tendency of Austenitic Stainless Steel)