1、 STP-PT-023 GUIDELINES FOR IN-SERVICE INSPECTION OF COMPOSITE PRESSURE VESSELS Prepared by: John H. Smith Date of Issuance: February 23, 2009 This report was prepared as an account of work sponsored by ASME Pressure Technology Codes this is indicated on the tank marking. This marking should first be
2、 checked to ensure that such tanks are within their designated service lifetime. 7.2 Identification of External Damage The external surface should be inspected for damage to the composite. Any damage is classified into two levels of damage as shown in Section 9 of these guidelines. The acceptance/re
3、jection criteria shown in Section 10 of these guidelines should be followed, as a minimum. The external surface of the tank is subject to mechanical, thermal and environmental damage. The external surface of the tank may show damage from impact, gouging, abrasion, scratching, temperature excursions,
4、 etc. Areas of the surface that are exposed to sunlight may be degraded by ultraviolet light which results in change in the color of the surface and may make the fibers more visible. This discoloration does not indicate a loss in physical properties of the fibers. Overheating may also cause a change
5、 in color. The size (area or length and depth) and location of all external damage should be noted. Tank support structures and attachments should be examined for damage such as cracks, deformation or structural failure. 7.3 Types of External Damage 7.3.1 General Several types of damage to the exter
6、ior of composite tanks have been identified. Examples of specific type of damage are described below. The acceptance/rejection criteria for each type of damage are described in Section 10 of these guidelines. 7.3.2 Abrasion Damage Abrasion damage is caused by grinding or rubbing away of the exterior
7、 of the tank. Minor abrasion damage to the protective outer coating or paint will not reduce the structural integrity of the tank. Abrasion that results in flat spots on the surface of the tank may indicate loss of composite fiber overwrap thickness. 7.3.3 Damage from Cuts Cuts or gouges are caused
8、by contact with sharp objects in such a way as to cut into the composite overwrap, reducing its thickness at that point. 7.3.4 Impact Damage Impact damage may appear as hairline cracks in the resin, delamination or cuts of the composite fiber overwrap. 9 STP-PT-023 In-Service Inspection of Composite
9、 Pressure Vessels 7.3.5 Delamination Delamination is a separation of layers of fibers of the composite overwrap. It may also appear as a discoloration or a blister beneath the surface of the fiber. 7.3.6 Heat or Fire Damage Heat or fire damage will be evident by discoloration, charring or burning of
10、 the composite fiber overwrap, labels or paint. If the composite fiber overwrap is merely soiled by soot or other debris on the surface that can be easily removed, and the underlying fibers are intact with no evidence of charring or burning, the tank may be cleaned and returned to service. 7.3.7 Str
11、uctural Damage Structural damage will be evidenced by bulging, distortion or depressions on the surface of the tank. 7.3.8 Chemical Attack Some chemicals are known to cause damage to composite materials. Environmental exposure or direct contact with solvents, acids, bases, alcohols and general corro
12、sives can cause damage to composite tanks. Long-term contact with water can also contribute to corrosive damage. Chemicals can dissolve, corrode, remove or destroy tank materials. Chemical attack can result in a significant loss of strength in the composite material. Chemical attack can appear as di
13、scoloration and, in more extreme cases, the composite overwrap can feel soft to the touch. 10 In-Service Inspection of Composite Pressure Vessels STP-PT-023 8 PROCEDURES FOR THE INTERNAL VISUAL INSPECTION (IF NECESSARY) 8.1 Requirements for Internal Visual Inspection Internal visual inspection is no
14、rmally not required. The purpose of an internal visual inspection is to determine if corrosion has occurred on the metal liner (for tanks having a metal liner) or on the plastic liner/metal boss assembly (for fully wrapped tanks with non-metallic liners). When the tanks have been filled only with pu
15、re, dry hydrogen, corrosion of the interior of the liner should not occur. Internal visual inspection of the tanks should only be carried out when: (1) There is evidence that any commodity except pure dry hydrogen has been introduced into the tank. In particular, any evidence that water, moisture, c
16、ompressor cleaning solvents, or other corrosive agents have been introduced into the tank will require an internal visual inspection. (2) There is evidence of structural damage to the tank, such as denting or bulging. (3) The tank valve is removed for maintenance or other reason. When an internal vi
17、sual inspection is conducted, the following procedures should be followed. 8.2 Identification of Internal Damage 8.2.1 Tanks with Metallic Liners For tanks with metallic liners, the objective of the internal visual inspection is primarily to detect the presence of any corrosion or corrosion cracks.
18、The internal surface of the tank should be inspected with adequate illumination to identify any degradation or defects present. Any foreign matter or corrosion products should be removed from the interior of the tank to facilitate the inspection. If any chemical solutions are used in the interior of
19、 the tank they should be selected to ensure that they do not adversely affect the liner or composite overwrap materials. After cleaning the tank should be thoroughly dried before it is inspected. All interior surface of the tank should be inspected for any color differences, stains, wetness, roughne
20、ss, or cracks. The location of any degradation should be noted. Any tank showing significant internal corrosion, dents or cracks should be removed from service. 8.2.2 Tanks with Non-metallic Liners or No Liners Tanks with non-metallic liners may show corrosion on the plastic liner or metal boss ends
21、. Tanks with non-metallic liners or no liners may also show internal degradation in the form of cracks, pitting, exposed laminate or porosity. The internal surface of the tank should be inspected with adequate illumination to identify any degradation or defects present. Any foreign matter or corrosi
22、on products should be removed from the interior of the tank to facilitate the inspection. If any chemical solutions are used in the interior of the tank they should be selected to ensure that they do not adversely affect the liner or composite overwrap materials. After cleaning the tank should be th
23、oroughly dried before it is inspected. The inspector should look for cracks, porosity, indentations, exposed fibers, blisters and any other indication of degradation of the liner and/or laminate. Deterioration of the liner may include softening of the matrix or exposed fibers. 11 STP-PT-023 In-Servi
24、ce Inspection of Composite Pressure Vessels 9 LEVELS OF DAMAGE OR DEGRADATION Damage or degradation that is found in composite tanks can be classified according to the severity of the damage or degradation. Two general levels are used describe the severity of damage or degradation. 9.1 Acceptable Da
25、mage Acceptable damage or degradation is minor and is normally found in service and is considered to be cosmetic. This level of damage or degradation does not reduce the structural integrity of the tank. This level of damage or degradation should not have any adverse effect on the continued safe use
26、 of the tank. This level of damage or degradation does not require any repair to be performed at the time of in-service inspection. When there is an external, nonload-bearing, sacrificial layer of filaments on the tank, any damage or degradation should be limited to this layer. There should be no ev
27、idence of any cut filaments. 9.2 Rejectable Damage (CondemnedNot Repairable) Rejectable damage or degradation is so severe that the structural integrity of the tank is reduced enough to consider the tank unfit for continued service. The tank must be condemned and removed from service. No repair is a
28、uthorized for tanks with rejectable damage or degradation. 12 In-Service Inspection of Composite Pressure Vessels STP-PT-023 10 ACCEPTANCE CRITERIA Certain specific types of indications can be identified by the external in-service visual inspection. Indications of certain types and sizes may not sig
29、nificantly reduce the structural integrity of the tanks and may be acceptable enough that the tanks can be left in service. Other types of indications and larger indications may reduce the structural integrity of the tanks and the tanks must be condemned and removed from service. Table 1 is a summar
30、y of the acceptance criteria for the indications that are found by external visual inspection of the tanks. Table 1 - Visual Acceptance Criteria for Composite Pressure Vessels Type of Degradation or Damage Description of Degradation or Damage Acceptable Level of Degradation or Damage Rejectable Leve
31、l of Degradation or Damage Abrasion Damage to the filaments caused by wearing or rubbing of the surface by friction. Less than 0.050 in. depth in the pressure bearing thickness. More than 0.050 in. depth in the pressure bearing thickness. Cuts Linear indications or flaws caused by an impact with a s
32、harp object. Less than 0.050 in. depth in the pressure bearing thickness. More than 0.050 in. depth in the pressure bearing thickness. Impact Damage Damage to the tank caused by striking the tank with an object or by being dropped. This may be indicated by discoloration of the composite or broken fi
33、laments. Slight damage that causes a frosted appearance or hairline cracking of the resin in the impact area. Any permanent deformation of the tank or damaged filaments. Delamination Lifting or separation of the filaments due to impact or a cut. Minor delamination of the exterior coating. Any loose
34、filament ends showing on the surface. Any bulging due to interior delaminations. Heat or Fire Damage Discoloration or melting of the composite due to temperatures beyond the curing temperature of the composite. Merely soiled by soot or other debris, such that the cylinder can be washed with no resid
35、ue. Any evidence of thermal degradation or discoloration or distortion. Structural Damage bulging, distortion, depressions Change in shape of the tank due to severe impact or dropping. None Any visible distortion, bulging, or depression. Chemical attack Environmental exposure that causes a change in
36、 the composite or failure of the filaments. Any attack that can be cleaned off and that leaves no residue. Any permanent discoloration or loss or softening of surface material. Cracks Sharp, linear indications. None None Scratches/gouges Sharp, linear indications caused by mechanical damage. Less th
37、an 0.050 in. depth in the pressure bearing thickness No structural fibers cut or broken. More than 0.050 in. depth in the pressure bearing thickness or structural fibers cut or broken. Soot A deposit on the composite caused by thermal or environmental exposure. Soot that washes off and leaves no res
38、idue. Any permanent marking that will not wash off. Over-pressurization Excessive pressure due to operational malfunction. None reported. Any report of pressurization beyond the MAWP or any indication of distortion. 13 STP-PT-023 In-Service Inspection of Composite Pressure Vessels Type of Degradatio
39、n or Damage Description of Degradation or Damage Acceptable Level of Degradation or Damage Rejectable Level of Degradation or Damage Corrosion Degradation of the composite due to exposure to specific corrosive environments. None visible. Any surface damage identified as corrosion. Dents A depression
40、 in the exterior of the tank caused by impact or dropping. None visible. Any dents with a depth greater than 1/16 in. or with a diameter greater than 2 inches. Reported collision, accident or fire Damage to the tank caused by unanticipated excursion from normally expected operating conditions. None
41、reported. Any indication or report of impact or heat damage. Environmental damage or weathering Ultraviolet or other environmental attack. None Any discoloration that cannot be washed off.* Crazing Hairline surface cracks only in the composite resin. Light hairline cracks only in the resin. Any dama
42、ge to the filaments. Damage to a protective or sacrificial layer Abrasion, cuts, chemical attack, scratches/gouges, corrosion, environmental damage or crazing that are limited only to the protective or sacrificial layer The depth of any damage to the protective or sacrificial layer that does not exc
43、eed the thickness of the protective or sacrificial layer plus 0.050 inch. The depth of any damage to the protective or sacrificial layer that exceeds the thickness of the protective or sacrificial layer plus 0.050 inch. Note: Only damage beyond the sacrificial or coated layer should be considered, a
44、nd any damage to sacrificial or coated layers should be repaired by suitable techniques (i.e., epoxy filler). Refer to ASME data report for sacrificial layer thickness. *Washing off UV scale will accelerate attack into lower composite layers. For this reason, if there is superficial UV damage we rec
45、ommend cleaning and painting the affected area with a UV tolerant paint. If broken, frayed or separated fibers in the non-sacrificial layer are discovered during the cleaning process then the cylinder must be condemned. 14 In-Service Inspection of Composite Pressure Vessels STP-PT-023 11 RECORD KEEP
46、ING A detailed record of external and internal inspections shall be retained by the owner of the tank for the life of the tank. After satisfactory completion of the periodic in-service inspection, the tanks should be permanently marked or labeled with the date of the inspection, the mark of the insp
47、ector and the date of the next periodic in-service inspection. ASME data report shall be kept on file for the life of the vessel. 15 STP-PT-023 In-Service Inspection of Composite Pressure Vessels 12 REMOVAL OF TANKS FROM SERVICE 12.1 At End of the Designated Service Life Tanks that have reached thei
48、r designated service life must be removed from service. These tanks must be condemned and made unserviceable. If residual gas is likely to be present, expired tanks should be flushed with an inert fluid such as water. The tanks can then be rendered unserviceable by cutting, crushing or drilling so t
49、hey can no longer hold pressure. 12.2 Tanks Found to have Rejectable Damage or Degradation Tanks that are found to have rejectable damage or degradation cannot be repaired and must be condemned and removed from service. If residual gas is likely to be present, the tanks should be flushed with an inert fluid such as water. The tanks can then be rendered unserviceable by cutting, crushing or drilling so that they can no longer hold pressure. 16 In-Service Inspection of Composite Pressure Vessels STP-PT-023 REFERENC
