Surface blistering

CC. Base metal Assuring and surface blistering in heat exchanger shell. 

Description Conventional wet fluorescent AC yoke magnetic particle inspection used for detection of cracks at a surface. Blending the welds and sanding smooth increases sensitivity. Polish and etch as in a creep evaluation looking for microscopic damage. Replicas can be taken for laboratory analysis. Conventional radiography used to inspect welds for cracks. Internal visual inspection of pressure vessels for surface blistering. Monitors the sound that cracks emit when they are stressed. 

Detection Capability Can detect HTHA only after cracks have formed. Cannot detect microscopic damage. Can detect and distinguish microfissuring and micro voids due to HTHA from other indications very reliably. Can detect HTHA only after macro size cracks have formed. Cannot detect microscopic damage. Blisters are readily apparent when present. However, HTHA may frequently occur without the formation of surface blisters. Reported to be capable of detecting cracks. Currently not known whether microscopic damage can be detected. 

Figure 52-6 Note rough surface. Blisters indicate either wet surface or water in the substrate, drawn up by the heat of the hot asphalt. The interior of the kettle may have been wet, or rain water may have fallen into the kettle before or while the kettle was being heated.

Skin blisters a soft surface blister which can be broken... 

Blisters Usually indicates delamination/trapped air or solvent over large area can also indicate undercured resin [and may take six months after molding to show). Can also form when subjected to excessive radiant heat during cure. Often caused by using liquid rather than paste catalyst. Below-surface blister probably due to imperfect wetting of fiber from allowing insufficient time for mat to absorb resin (can usually be detected by inspection on demolding). 

Exfoliation is a related type of anodic path corrosion in which attack of rolled or extruded aluminum alloy results in surface blisters followed by separation of elongated slivers or laminae of metal. It occurs in various types of aluminum alloys in addition to the copper-bearing series. Proper heat treatment may alleviate such attack. 

Pimple pim-p3l [ME pinple] (14c) n. Small, conical protrusion on the surface. It also may refer to small surface blister. 

Production of sheeting of such thickness presents great problems on more conventional equipment. Normal two- or three-bowl rubber calenders can produce satisfactory sheet at thicknesses of 1-2 mm maximum. At greater thicknesses blisters become a problem. If very thick sheets (7 mm and above) are attempted there is an additional problem with air inclusions in the body of the sheet, as well as surface blisters. The traditional method for obtaining very thick sheets has been to ply together many thin ones, a troublesome and expensive procedure. An Alternative process is to extrude a tube which is slit to form a sheet this process is used for comparatively low outputs and widths (maximum 500 kg hr , 1000 mm). 

Hydrogen will dissolve in aluminum alloys in the molten state and during thermtd treatments at temperatures close to the melting point in atmospheres containing water vapor or hydrocarbons. Upion solidification, this causes porosity and surface blistering. 

Figure 7-14 Typical forms of delamination (a) vertical splitting, (b) stepped interlayer delamination, (c) circnlar delamination, (d) internal interlayer delamination, and (e) surface blistering.

Figure 3-15a. Hydrogen surface blisters in steel pipe caused by H2S service. API, 19901...

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