- Ratchet Marks
- Re-Entrant Angle
- Rivet Head
- Rivet Shank
- Root Cause Analysis
- Safety Factor
- Scanning Electron Microscope
- Semi-Quantitative Chemical Analysis
- Semi-Tubular Rivet
- Sequential Metallography
- Sharks Tooth
- Shear Dimples
- Shear Lip
- Shear Stress or Shear Force
- Sigma Phase
- Soap Bubble Pressure Testing
- Solution Anneal
- Split Locking Washer
- Steel Braided Hose
- Stray Current Corrosion
- Stress Analysis
- Stress Concentrationor Stress Concentrator
- Stress Corrosion Cracking
- Strut Structure
- Strut Stub
- Sulfur Reducing Bacteria
Ratchet Marks: Ratchet marks usually occur on a surface where high stress concentration is present, for example in thread roots, fillet corners, etc. Ratchet marks indicate that small cracks have initiated on multiple planes and are small tear steps or shear walls that often occur near the origin of multiple fatigue cracks. A small fatigue crack origin or initiation point will be located approximately midway between two ratchet marks. As the small individual fatigue cracks, which are initiated at slightly different levels, grow, a shear or tear wall is created joining the separate failure planes. As the small individual fatigue cracks grow larger, they merge forming a common and larger fatigue crack on a common plane and the ratchet marks disappear.
Example of ratchet marks on a metal surface.
Re-Entrant Angle: The angle formed by the weld, with the base metal or a previous weld pass.
Revolver: Hand held gun, which contains a rotatable cylinder that holds and rotates cartridges into firing position.
Rheology: The study of flow of materials, which are primarily highly viscous solids and/or liquids.
Rim: The item that supports the tire on a vehicle.
Rivet:: A permanent mechanical fastener that attaches two or more pieces together. A rivet has a head end that is formed in the factory and a bucked or tail end that is formed when the joint is fabricated. Rivets typically perform in shear stress situations but can also perform satisfactorily in tension/tensile and bending stress situations.
Rivet Head: The end of the rivet, which is produced by the rivet manufacturer. The usual shape of the rivet head is a dome as pictured below.
Rivet Shank: The smooth cylindrical portion of the rivet between the factory headed end and the field bucked end. The cylindrical portion of the rivet usually passes through holes in the items being riveted together. The rivet shank can be solid or tubular or a combination of both.
Root Cause Analysis (RCA): A problem solving method aimed at identifying the root or true, bottom line cause of a problem or event. The practice of RCA is predicated on the belief that problems are best solved by attempting to correct or eliminate root causes, as opposed to merely addressing the immediately obvious symptoms. Root cause analysis can and does often reveal that there are multiple necessary conditions, which must simultaneously and/or sequentially occur to the subject for failure to occur. That is, root cause does not necessarily signify only one cause.
Safety Factor: Safety factor is the design load or stress divided by the actual expected load or stress. In mathematical terms:
Scanning Electron Microscope (SEM): The scanning electron microscope (SEM) is little more than a large camera. Instead of using light to expose a film, the SEM uses a focused beam of electrons. The electrons interact or strike, bounce around, bounce back and undergo a variety of events with and within the surface being examined. The electrons resulting from this interaction are processed by the SEM electronics and a real time, black and white image is displayed. The resulting image has the appearance of the object in 3-D. The sample to be examined in the SEM must be examined and contained in a vacuum to facilitate passage of the beam of electrons from the electron source to the sample. Sample size is therefore limited to a size that can be accommodated in the SEM sample chamber. A photograph from an SEM is shown below.
Scanning electron micrograph of a fracture surface at a magnification of 14x.
Semi-Quantitative Chemical Analysis: A chemical analysis results in naming the chemical elements present, but not the precise amount of each element
Semi-Tubular Rivet: A rivet normally has a solid shank, however, in a semi-tubular rivet the field end appears drilled out and has been formed in the shape of a hollow tube.
Sensitization: Refers to a loss of alloy integrity. The precipitation of carbides at grain boundaries in a stainless steel or alloy, causing the steel or alloy to be susceptible to intergranular corrosion occurs in certain stainless steels when they are improperly heat treated or subjected to improper thermal treatment. When stainless steels containing more than approximately 0.03% carbon are heated into the temperature range 950°F to 1450°F and slowly cooled, excess carbon near the grain boundaries combines with chromium to form chromium carbides which deposit in the grain boundaries. This depletes the near grain boundary areas of chromium. The presence of chromium is why stainless steels resist corrosion. Since the near grain boundary regions are then depleted of chromium and then are chemically very similar to plain carbon steel and corrosion of the near grain boundary region can easily occur.
Sequential Metallography: A microscopic or metallographic examination where a known amount of metal is removed from the surface of the metallographic specimen by using a step-wise technique of examination; for example, sample thickness measurement, additional grinding/polishing etching, repeat sample thickness measurement, examination and metallographic of the newly revealed surface, etc. The depth and/or characteristic of a flaw/defect/crack can be sequentially evaluated.
Sharks Tooth: A raised circumferential rim on the surface of the brass fittings, which facilitate achieving a tight, waterproof joint between the PEX tubing and the brass fitting.
Shear: This fracture is usually on a slant or 45° angle with respect to the outside component surface. Shear fracture is usually created, at least in the case of metal fatigue, at the instant of final fracture.
Shear Dimples: Dimples, which are formed on the metal fracture, surface in the presence of large amounts of shear deformation. The tails of shear dimples point away from the source of the load causing the shear fracture.
Shear Lip: A narrow slanted fracture (≈45°) around the edge of a tensile specimen. A shear lip forms a typical cup and cone fracture during tensile overload of a rod, or circular test specimen or component. Shear lips may be found on predominantly brittle fractures and form a picture frame around the edge of a part.
Shear Stress or Shear Force: A shear stress or shear force can be thought as the stress, which occurs when the face of a playing card slides over another card, for example, as one card is moved relative to the other. A shear stress is defined as a stress, which is applied parallel to the surface of interest.
Sheath: The exterior of a designed product inteded to house, protect or insulate the interior. Usually comprised of steel, copper, stainless steel, or Incoloy, they can be frequently found containing heating insulation and a heating filament.
Sigma Phase: An iron (Fe), 30 chromium (Cr), nickel (Ni), and 4-7 molybdenum (Mo) phase that is formed and observed in duplex stainless steels. The presence of sigma phase is detrimental to mechanical properties, ductility and toughness. Sigma phase is also detrimental to corrosion resistance of stainless steel alloys.
Slag: Slag is a non-metallic residue left on or around a weld from the flux. Flux is a non-metallic material, which melts during the welding process and protects the molten metal from oxidation while in liquid state.
SMYC: The various grades of API line pipe have minimum yield strength specifications. That is, the yield strength of the steel must meet or exceed these minimums to receive that level or category of specification. For example, the X70 grade must have minimum yield strength of 70,000 psi (or 70 ksi). Since yield strength is defined as a strength at which a certain amount of permanent deformation occurs, exceeding the SMYC will result in permanent deformation to the pipe.
Soap Bubble Pressure Testing: Soap bubble pressure testing is a non-destructive testing technique in which the item in question is pressurized to an internal pressure greater than atmospheric pressure (14.7 psi). When the item to be tested is pressurized, the outside surface is sprayed/soaked with a soap bubble solution. If the internal pressured gas, usually air, escapes into the atmosphere through a hole or crack, which is coated/covered with the soap bubble solution, then a coherent volume of soap bubbles will be generated, thereby identifying the leak area.
Solution Anneal: A heat-treating process in which primarily the type 300 class of stainless steels are heated to or above 1950ºF. The heating and holding time at that temperature is conducted to allow carbon to go into solution, for example, it's much like dropping a lump of sugar into a cup of coffee and stirring to uniformly disperse the sugar. The homogenized material is quickly cooled to prevent re-precipitation of the carbon or carbide phases into the grain boundary, etc.
Spall or Spalling: A mechanical process whereby the surface of the metal or something that is adhered to a metal surface flakes off or de-adheres from the metal object.
Split Locking Washer: A washer is a circular sheet of metal with a central hole through which a bolt is placed. A split locking washer is cut or sheared radially on one side and hardened to help prevent a torqued or tightened joint from loosening.
Spoliation: Refers to the intentional or possibly unintentional, reckless, or negligent destruction, loss, material alteration or obstruction of evidence that is relevant to litigation. Spoliation results in the unavailability of evidence, causes the inability for parties to present their case fully, and places parties in a less apt position to accurately assess the strengths and weaknesses of their case.
Stabbing: An oilfield term describing the act of adding and inserting the male pin end of a joint of drill pipe into the collar box end of the top joint in the drill string. Each individual joint of drill pipe must be stabbed, and then threaded into the collar and tightened to makeup or construct the drill string.
Steel Braided Hose: Steel braided hose is rubber hose that has alternating layers from the inside surface to the outside of rubber, steel wire braided reinforcement, another thin layer of rubber, an additional layer of braiding, etc. The final outer layer is rubber. The steel wire braiding is placed into the hose structure in order to allow the hose to be used in high internal pressure applications usually with hydraulic fluids.
Stepladder: A portable ladder, which is hinged at the top and typically is set up in an A-frame configuration.
Stereomicroscope: A general all purpose lab microscope equipped with two eyepieces, which allows object to be viewed in three dimensions or stereo at higher than naked eye magnifications.
Strain: The elongation caused by a load or force on an object referenced to the original length without the applied load. Strain is dimensionless for example, inches of elongation/inch of original length or feet of elongation/foot of original length. After removal of the load that causes a strain, that strain was recoverable and is called elastic strain. The strain is plastic or has a plastic component if the object remains stretched and longer than its original length or dimension, after the load is removed.
Stray Current Corrosion: When a metal object becomes anodic with respect to another structure. When the object is anodic to another structure, the surface acts as if it is a sacrificial anode, in other words, the surface is dissolved while electrically protecting the other cathodic structure. The photograph below shows stray current corrosion on a copper water pipe.
Stress: The stress in a component is the force applied to the component divided by the area over which that stress is applied.
Stress Analysis: The analysis of the expected or normal stress in a joint.
Stress Concentrationor Stress Concentrator: A change in the diameter or a corner in a flat structure, of an object. Stresses tend to accumulate and concentrate at such physical discontinuities. The root or bottom of a thread in a threaded hole or bolt is an example of a stress concentrator.
Stress Corrosion Cracking: Stress corrosion cracking (SCC) occurs when a material, which is susceptible to corrosion, is placed in a particular and specific environment that allows mechanical stress and produces a failure by cracking. All three components; a) specific environment, b) susceptible material and c) presence of tensile stress is necessary to support SCC.
Strut: A strut is a structural member usually used as a brace or can be used to resist longitudinal compressive stresses.
Strut Structure: A structural member consisting of two strut legs and X-style cross bracing between the two strut legs.
Strut Stub: The strut stub is a rectangular piece of tubing that fits inside the strut legs. The strut stub is welded to the axle and the strut structure legs slip over and onto the strut stubs.
Sublimation: The changing of a substance from the solid state or phase into the gas phase without passing through a liquid state.
Sulfur Reducing Bacteria (SRB): Bacteria that grow and expands by ingesting sulfur/sulfate and converting the ingested material to hydrogen sulfide.