On July 20, 2020, according to contract No. 02/04/20 for technical inspection of the refractory lining of hot water boilers, specialists of Wellons.RU LLC carried out a visual inspection of the newly laid boiler lining No. 1-3 (after a major overhaul to replace refractory lining). The inspection results are shown in this report.
Before the start of work on the repair of solid fuel boiler furnaces, a work organization project (POR) was developed by ProektGeoStroy LLC (POR No. 1057747910923-10 / 2020-POR). Visual inspection of the boiler lining was carried out for compliance with the graphical part, as well as section 6 "Technical requirements when carrying out lining works" of this ERP.
Visual inspection of the boiler lining allows us to conclude that the work is in principle consistent with the graphical part of the specified POR.
Wall lining: the lining of the working layer of the boiler furnace walls is made of refractory aluminosilicate bricks (type SHA) using masonry mortar based on MSh-28 aluminosilicate mortar. The masonry of the walls has the correct geometry, there are no deviations in the vertical and horizontal planes. The masonry joints are completely filled with mortar, the thickness of the masonry joints is no more than 2 mm.
Wall expansion joints: expansion joints are provided in the corners of the masonry along the entire height of the panels. Expansion joints are filled with rolled heat-insulating material to compensate for the thermal expansion of the refractory and the metal structure of the boiler.
Anchors: made directly in the brickwork by installing T-shaped anchors and forming an open space around the anchor half brick in size, which is poured with refractory concrete. The total number of anchors is 9 pcs. (according to the project there should be 12 pcs.)
The fuel combustion air tuyere holes are formed from refractory concrete in the brickwork of the walls, according to the graphical section of the POR.
Monolithic refractory concrete lining: visual inspection of the working layer of the lining of such units as: the fuel loading chute, inspection and technological hatches, as well as the upper belt of the furnace head, did not reveal any visible defects in the lining of these units. Unfortunately, the absence of intermediate photographs of the stage of laying refractory concrete, as well as detailed drawings or a descriptive part in the technical requirements of section No. 6 (ERP) for the installation of anchors and support consoles (especially for the fuel chute and the upper chord of the furnace) does not allow make a conclusion about the reliability of the lining of these nodes.
A visual inspection of units made of refractory concrete did not reveal the device of temperature joints between concrete and metal: for example, refractory concrete of the upper zone of the furnace (furnace head) directly adjoins the lower boiler collectors along the entire perimeter (side and end screens). The situation is similar with regard to the lining of technological hatches: lower and upper. Section 6, clause 1.10 regulates the installation of rolled heat-insulating material on all metal structures of the boiler to form an expansion joint. Its absence can lead to cracking of the concrete.
Boiler furnace vault: one of the most critical boiler structures, requiring special skills and training, including the availability of the necessary range of wedge products, to form the correct circle (circular arc) of the vault, to ensure maximum structural strength.
The photographs show that the radius of the circle is close to the design one - a deviation of 15-20 mm and it is acceptable if the correct layout of the brick on the vault is observed. Unfortunately. we see that the brick layout does not form a regular arch arch. Even without instrumental measurements, it can be seen that part of the brick is "overwhelmed", there are steps up to 5 mm both along the inner and outer surfaces of the row. This indicates that the brick layout is incorrect and / or there is not enough range of wedge products to level the masonry.
A positive point is the use of bricks with a height of 230 mm, which allows minimizing errors when laying the vault.
Those in case of possible thermal deformation of the arch, for example, when the arch is opened, the brick will not fall out of the row, but will stand in the wedge due to the existing wedge and will not allow the arch row to collapse completely. Those during operation, it will be possible to carry out remedial measures (if necessary) to prevent further destruction of the vaulted structure of the boiler furnace.
During the inspection, a slight change in the structure of the vault was revealed, namely: the vault was formed by annular segments of three rows of bricks along the entire length of the vault. In the project, part of the vault (~ one third of the vault) is formed by circular segments of two rows of bricks. In fact, the vault, in the area of fuel combustion, is slightly underestimated in height. In our opinion, this does not carry negative factors for ensuring normal fuel combustion.
TOTAL: the performed visual inspection of the refractory lining of the boiler, after its replacement, makes it possible to make a conclusion on the compliance of the actual arrangement of the lining with the requirements of section 6, as well as the graphic part of the "Work organization design", with the exception of the identified remarks described above. Despite the revealed remarks, we believe that, in general, the boiler lining is made well and the boiler bodies can be allowed for further operation (in terms of the operation of the boiler lining).
RECOMMENDATIONS: when carrying out refurbishment or overhauls related to the replacement of the lining, we recommend that you take the following measures:
- Anchors - use heat-resistant steel for anchoring products and supports (support brackets). Provide a larger number of wall anchors (for example, three anchors for the entire area of the side wall is not enough) and also use a “floating” anchor design to provide compensation for thermal expansion. When using an existing structure (pouring concrete anchors), we recommend applying a layer of bitumen mastic at least 2 mm thick on the surface of the metal anchor. For structures made of monolithic refractory, the number of anchors should be calculated based on a distance of ~ 250 mm between the anchors (depending on the thickness of the lining).
- Expansion joints - we recommend making an additional expansion joint on the side wall, dividing it into two panels. It is recommended to cover metal products with rolled heat-insulating material at the lining / metal interface.
- Vault masonry - we recommend checking the recommended layout of wedge-shaped products on the site, to check it and make, if necessary, changes through the use of various wedge-shaped products. The goal is to obtain a vault of the most correct shape, without steps and blocking bricks. For a vault of this standard size, it is sufficient to use a brick with a thickness of 200 mm.
Due to the fact that boilers No. 1 and No. 2 are of the same type, the lining is also made according to the same technical documentation, according to the same drawings. In this regard, all comments, as well as recommendations related to boiler no. 1 (shown in section 1) are also valid for boiler no. 2. Additionally, we are forced to draw your attention to the roof lining, as one of the critical unit of the entire lining as a whole.
Boiler furnace vault: when lining the boiler, it is necessary to have theoretical knowledge that will allow, in the presence of any actual deviations from the drawing, to prevent deviations of the geometric dimensions of the vault masonry, namely to ensure the correct geometry of the vault without overlap and the formation of steps when laying bricks, ensuring the maximum structural strength.
The photographs show that a sawn fragment of a brick with a toe thickness of 10 to 20 mm, the so-called glazed, is used as a key brick. It is impossible to use sawn bricks of this size in the vaulted structure. In the event of temperature loads, the thin flask will collapse first of all, weakening the structure of the arch. The thickness of the castle brick must be at least half of the ordinary brick (minimum). Thus, in order to avoid using glazing beads as key bricks, it is necessary to have an assortment of wedge products that allows the masonry to be fitted in the vaulted segment using full-size bricks.
In the absence of the necessary assortment, adjust the brick by sawing on a machine for at least 2/3 of the thickness of the main brick. If necessary, use two or three sawn bricks, distributing them in the vaulted segment.
Photos of the general view of the boiler lining No. 2 and its units are shown below:
TOTAL: the performed visual inspection of the refractory lining of the boiler, after its replacement, makes it possible to conclude that the actual arrangement of the lining meets the requirements of Section 6, as well as the graphic part of the "Work Management Design", with the exception of the identified comments described above, including in the section # 1. Despite the revealed remarks, we believe that boiler No. 2 can be allowed for further operation (in terms of the operation of the boiler lining).
The masonry of the walls has the correct geometry, there are no deviations in the vertical and horizontal planes. The masonry joints are completely filled with mortar, the thickness of the masonry joints is no more than 2 mm. In the corners of the masonry, expansion joints are provided along the entire height of the panels. The fuel combustion air tuyere holes are formed from refractory concrete in the brickwork of the walls, according to the graphical section of the POR. The monolithic refractory concrete lining of the fuel loading chute and inspection hatches does not have any visible defects in these units.
Boiler vault – we are forced to pay attention once again to the vault design, namely to the thickness of the refractory used. All other geometrical dimensions being equal (radius of the arch, inner width of walls, height of formwork, etc.), different bricks are used: in boilers No. 1,2 - 230 mm thick (ША-21, ША-22), in boiler No. 3 - 160 mm (SHA-17, SHA-18). The meaning of the various designs of practically identical vaults is not clear. But the use of thicker masonry at a given radius carries more masonry errors in comparison with the vault of boiler No. 3 and for their timely correction it is necessary to perform the measures described in section 1. The vault of boiler No. 3 has a more correct design and corresponds to the design documentation of the plant as much as possible - manufacturer.
Photos of the general view of the boiler lining No. 2 and its units are shown below:
TOTAL: the conducted visual inspection of the refractory lining of the boiler No. 3, after its replacement, allows us to make a conclusion on the compliance of the actual lining device with the requirements of Section 6, as well as the graphic part of the "Work Management Design". We believe that the boiler No. 3 can be allowed for further operation ( regarding the operation of the boiler lining).
