What does the “three inspections and four determinations” in the piping discipline entail? This checklist tells you

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On-site inspections can be divided into three aspects: checks for omissions in design and construction, unfinished works, and construction quality. (i) Omissions in design and construction: Omissions in design and construction can occur in various aspects. Based on the author’s experience and knowledge, the problems that arise most frequently include the following: a. Omissions regarding valves, cross-connections, high-point venting, and low-point drainage; b. The operation and measurement indicators being placed at too high a position, making it impossible to operate or observe them, especially when only on-site indicator elements are available ； c. There is a lack of ladders, or only a few ladders are provided; this makes routine inspections difficult ； There are insufficient D-type supports, resulting in pipe deflection exceeding the standard requirements or instability of the pipes ； e. Beams, columns, etc. of pipes or structures that affect the operation passage ； f. Equipment, pumps, special instrument components (such as thermocouples, instrument panels, flow meters, etc.), valves, etc., lack the necessary space for operation and maintenance, or the space is too limited, making such operations and maintenance inconvenient. II) Uncompleted projects: The inspection of uncompleted projects applies to intermediate inspections or inspections of installations that are put into operation in phases. For the works involved in this operation, it must be confirmed that they have been completed and do not affect the operation. For devices that are brought online in stages, those not included in this round of operation should be isolated to ensure that they do not affect each other. However, the following items do not fall under unfinished work: a. Insulation at flanges and valves. During the startup and heating process, leakage checks at detachable connections such as flanges and valves, as well as bolt tightening, must be carried out; therefore, local insulation should be applied after startup. b. Covers for trenches, covers for valve chambers, etc. The same principle applies; once driving is normal again, cover the panel properly. c. Temporary scaffolding or work platforms used for heat tightening flanges. The same principle applies; remove it only after driving is normal again. (III) Construction quality: Construction quality can be affected in various aspects, and a comprehensive inspection should be carried out. 1. Regarding pipes and their components, common problems in this area include: a. Valves with a directional requirement being installed in the wrong direction. Directional valves include check valves, globe valves, safety valves, corner valves, and most steam traps. If these valves are installed in the wrong direction, it can be very dangerous; therefore, they must be corrected before operation ； b. The position of the blind flanges (especially the 8-shaped ones) is incorrect, and adjustments should be made promptly in conjunction with the operations being carried out; c. The types of valves, flanges, bolts, etc., are not appropriate. Different types of valves have their own characteristics. If the valve actually installed does not match the design, it can have adverse effects on operation, and in severe cases, it may lead to accidents. Different flange types have their respective suitable application conditions. For instance, butt-weld flanges must not be replaced by slip-on flanges in harsh conditions; otherwise, the sealing performance cannot be guaranteed. Different bolts also have different applicable conditions; single-headed bolts cannot be used in place of double-headed bolts under harsh conditions, as this will likewise fail to ensure the sealing performance of the flange seal assembly. In addition, it is also necessary to check whether the number of bolts is sufficient, whether the bolt diameters and exposure lengths are uniform, and whether they meet the standard requirements; d. The material and pressure rating of the pipes and their components do not conform to the design specifications. This is a relatively serious construction error; once it occurs, there is a high likelihood of an accident. It is possible to determine whether the requirements of the design are met by checking the material markings on the pipes and fittings, the markings on the flanges and bolts, as well as the nameplates on valves and small piping equipment; e. The expansion joints made of bellows are not installed correctly, and the transportation safety rods have not been removed. Under normal circumstances, for restrained expansion joints, the position of their links or hinges corresponds to the direction of displacement compensation. Any error in this regard can lead to serious accidents; therefore, verification must be carried out prior to startup. The transportation safety rod is used solely for protecting the bellows expansion joint during transportation. If it is not removed prior to commissioning, it will impede the compensatory deformation of the expansion joint; therefore, it must be removed before the equipment is put into operation. 2. Regarding supports and hangers, common problems in this area include a. Incorrect type of supports and hangers. For example, converting guide brackets into ordinary load-bearing brackets (i.e., omitting the guide clips), welding sliding pipe supports to the support beams to turn them into fixed pipe supports, installing fixed brackets as ordinary load-bearing brackets (i.e., not using fixing bolts), and so on. An incorrect installation of the support type is a serious error; in mild cases, it can lead to excessive stress on the piping system itself, excessive forces on the equipment connections, and excessive thrust on the pipe racks and supports. In severe cases, it can directly cause damage to the pipes, the supports, and the anchoring facilities, as well as damage to the connected equipment. b. The installation condition of the supports and hangers is incorrect. For example, the height of the load-bearing supports is insufficient, causing the pipes to become unsupported in their installed state; the suspension rods of the hangers are loose, resulting in the pipes not being able to bear weight once installed; the installation load or position of the spring-mounted hangers does not meet the design requirements, and so on. All these issues can render the bracket ineffective or prevent it from performing its intended function; in severe cases, they can also cause damage to the pipe or the connected equipment. c. The material and specifications of the support brackets are incorrect. In terms of materials, problems often arise with those components that are in direct contact with pipes or equipment (i.e., pipe attachments and components fixed to the equipment); these materials are of poor quality, thereby affecting the stability of the corresponding equipment or pipe materials. Generally, the parts of supports and hangers directly connected to pipes and equipment should be made of the same material as the respective equipment or pipes, or of a similar type of material. The specifications of the components of supports and hangers shall not be lower than those specified in the design drawings; otherwise, the supports may lack sufficient strength and fail, thereby jeopardizing the safety of the pipelines. d. Arbitrary welding of temporary supports and hangers. In fact, there are many pipelines on which field welding is not permitted, such as pipelines prone to stress corrosion cracking, high-pressure thick-walled pipelines, and other pipelines that require post-weld heat treatment. If temporary support and hanger joints are welded, the weld points may cause a deterioration in the properties of the pipe material. Once such issues are identified during inspection, relevant personnel should be organized to conduct an assessment, or appropriate measures should be taken to eliminate their impact. 3. Welding: Common problems in this area include a. The visual quality of the welds on pipes and their components exceeding acceptable standards. It is mainly manifested as excessive weld metal, incomplete filling, undercutting, and weld beads. These defects in the welds affect the performance of the welded joint, thereby compromising the safety of the pipeline. b. The welds of the pipeline supports and hangers are not up to standard. It is mainly manifested in: insufficient weld length (in some cases it is even spot welding), insufficient height of the fillet welds, and the welding through of thinner support and hanger components, etc. These welding defects can affect the strength of the supports and hangers themselves, thereby compromising the safety of the pressure pipelines. C. The welds of the steel structures for platform ladders and structures are unqualified. It mainly manifests as insufficient weld length, thin components being welded through, and platforms between hot and cold equipment, or between equipment and frames, or between equipment operating at different temperatures being welded together, etc. Although these do not pose a direct threat to the safety of pressure pipelines, they do pose a direct risk to human safety; therefore, they should be addressed once detected. 4. In terms of heat insulation and corrosion protection, common construction problems related to pipeline heat insulation and corrosion protection are failure to follow the design requirements or the construction procedures, which in turn affects subsequent inspections. It is mainly manifested in the following aspects: a. The thermal insulation thickness does not meet the design requirements. b. The insulation layer is not sealed properly, resulting in it absorbing moisture and becoming damp. c. Valves on insulated pipes, as well as hot oil pumps, etc., are not insulated (unless otherwise specified in the design). d. Insulation work is carried out before the pipeline hydrostatic test, or insulation is applied to detachable joints such as flanges and threads prior to the hydrostatic test, airtightness test, or commissioning. e. Rust removal was not carried out in accordance with design or standard requirements, and the paint thickness did not meet the standard or design specifications, resulting in the paint layer starting to peel off even before the equipment was put into use. f: The weld was coated with paint prior to surface non-destructive testing, preventing inspection of the weld surface.