上周有个做服务器液冷管路的客户，拿着一段改性尼龙样管来问我们。
管子是半透明的，外壁还贴着一张手写标签，写着"爆破 4.0 MPa"。他坐下来第一句是："爆破压力够高了吧，为什么装上三个月还是渗？"
这句话里藏着一个典型误判：把"打不爆"当成了"用不漏"。
液冷管路的失效，绝大多数不是被打爆的，是长期受压之后慢慢渗出来的。这篇就讲这一件——服务器液冷管路——把管径壁厚、长期静液压外推、冷却液相容、蠕变与接头应力这四件事拆开说清。
一、管路这一件，难在"一直压着"而不是"压一下"
先说清服务器液冷管路在系统里的位置。
它连在冷量分配单元（CDU）和机柜歧管之间，里面走的是去离子水或者低浓度水-乙二醇，温度通常在 40–55℃，压力不高，常见也就 1–3 bar。看起来比汽车液冷温和得多。
温和，不等于好做。
汽车液冷管路怕的是高温水解，服务器管路怕的是另一件事：长期、连续、低幅值的静压，加上接触介质带来的尺寸漂移。 前者考验瞬间强度，后者考验十年不掉链子。
这就是为什么管路选料不能只看"强度够不够"。真正决定它能不能用的，是下面四个量：
管径与壁厚，决定这件管子能扛多大环向应力；长期静液压强度，决定它扛十年会不会蠕变渗漏；冷却液相容与离子析出，决定它泡在去离子水里会不会把系统电导率抬上去；接头应力，决定它和金属冷板、密封圈配合的位置会不会先开裂。
这四个量里，后面三个在老文章的"电池液冷"里被讲过一半，但服务器这件有自己的账——温度低、压力低、对洁净度却更挑剔。下面一段把工况摊开。
一句话：服务器液冷管路选料，第一问不是"结不结实"，是"加压十年、泡在去离子水里，它还能不能守住密封。"
二、工况六维：这件管路被什么约束
按六个维度把工况拆开，缺一个，后面选料都是猜。
温度。 冷板式液冷回路一般 40–55℃，比汽车液冷低一截。但别因此放松——这条回路里最大的隐患不是热，是"一直泡着"。温度低只意味着水解慢，不意味着尺寸问题和蠕变消失。
载荷（压力）。 常见 1–3 bar 的环向压力。换算一下：一根 DN10（内径约 10 mm）、壁厚 1.5 mm 的管子，承受 0.3 MPa 内压时，环向应力大约是 1.0 MPa（公式 σ = p·D / 2e）。这个数看着小，但它一直都在，一天二十四小时、一年三千一百多万秒，从不卸载。
介质。 去离子水是主角，也有用水-乙二醇的。去离子水干净，却有个麻烦：它自己电导率极低（常要求低于 0.1 μS/cm），会反过来从材料里"抽"离子和助剂。 一旦管路析出杂质，整条回路的电导率就往上走，系统报警。
寿命。 数据中心服役十年起步。判据不是"哪天爆"，是"第十年密封还守不守得住、强度保持率还剩多少"。
外观与洁净。 机房有人工作环境，要求低烟、低毒、低析出。透明或半透明管还要看长期黄变和析出物附着。
合规。 阻燃通常要求 UL94 V0，不少场合要无卤；靠近电器的位置还要看灼热丝（GWIT）。这些和"碰不碰介质"是两条独立的线，选料时要一起提。
六维里，温度、压力、介质、寿命都给了具体数字，这就是件级篇该有的精度。下面进入材料路线。
三、三条材料路线，代价各不同
把服务器液冷管路的候选路线并排放，看的是"代价"那一列，不是"优点"那一列。
| 路线 | 组成 | 给什么 | 代价 |
|---|
| PA12 挤出级 | 长碳链尼龙，本体或半硬管 | 低吸水、耐水解、尺寸最稳、柔韧 | 耐温上限约 80℃、单价高、刚性偏低 |
| PA612 / PA610 共聚 | 中长碳链，平衡型 | 性能介于 PA12 与 PA66 之间，成本更友好 | 长期泡水尺寸仍略逊 PA12 |
| PA12-GF / PA6T-GF | 玻纤增强，硬管段与歧管 | 刚性、耐压、抗蠕变 | 吸湿后尺寸变化、玻纤处可能析出水痕 |
三条路线都没有"谁更好"，只有"哪个件的哪条账更紧"。
PA12 在这件上的理由很直接：吸水率低到 1% 以下，泡在去离子水里尺寸几乎不漂，接头密封面十年后的配合尺寸和出厂时差不离。 代价是贵、软、耐温不算高——但服务器回路温度本来就不高，软一点反而抗振动。
PA612 是降本的平衡点：性能够用，价格比 PA12 好接受，适合管身这类应力温和的位置。
玻纤增强那一行用在硬管段和歧管——要的是刚性和耐压。但它的吸湿和蠕变比长碳链纯料明显，软硬过渡的位置恰恰是应力集中点，这点在第四节专门讲。
一句话：服务器液冷管路，碰介质的位置往长碳链走；纯结构、不接触冷却液的支架类，可以留在 PA66 体系。这条分界线一画清，选料范围立刻缩小一半。
四、选型判据表：长期静液压和尺寸稳定是主角
把上面的约束落成可核对的指标。下表的门限值是方向性建议，不是验收标准——实际数值必须由具体项目、具体工况和实测确定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 长期静液压强度（外推） | 设计温度下环应力按 50 年校核 | ISO 9080 外推 + ISO 1167 静液压 | 十年后蠕变渗漏 | 选低蠕变基材 + 控壁厚 | 抗氧剂（热氧稳定） |
| 管径 / 壁厚（爆破） | 按 PN 与管系列定，爆破 ≥ 数倍工作压力 | ISO 1167 爆破试验 | 壁厚偏薄、环应力超 | 重算管系列、加壁厚 | 材料本征，不靠助剂 |
| 吸水率与尺寸稳定 | 平衡吸水 ≤ 1.5%，浸泡尺寸变化小 | ISO 62 吸水 + 浸泡量测 | 接头密封面涨缩漏 | 长碳链基材 | 材料本征，不靠助剂 |
| 冷却液相容 / 离子析出 | 浸泡后失重与电导率增量可控 | 工况介质浸泡 + 电导率法 | 电导率升高、系统报警 | 低迁移配方 + 选材 | 润滑剂（低析出选型） |
| 环向蠕变 | 长期承压形变率低 | ISO 899 蠕变 + 管内压法 | 管径鼓胀、密封失效 | 低蠕变体系 | 抗氧剂（抑制老化蠕变） |
| 耐水解（水-乙二醇） | 1000 h 强度保持率达标 | 乙二醇浸泡 + 力学复测 | 内壁龟裂、渗漏 | 长碳链 + 稳定化 | 耐水解稳定剂（可选） |
| 低温韧性 | -40℃ 冲击不脆 | ISO 179 低温冲击 | 寒区运输开裂 | 增韧或选韧基材 | — |
怎么用这张表：不要逐行打分。先看第一行和第三行——长期静液压和尺寸稳定过不了，后面的都不用谈。管路渗漏是慢变量，串联在这两个指标上。
一个提醒：表里"长期静液压"这一项，靠的是 ISO 9080 的外推方法——用高温短时数据和 20℃ 长时数据，外推到设计温度下的五十年强度。没有这份外推曲线，只拿爆破压力说事，等于用瞬间成绩替十年表现背书。
五、四条常见误判，和它们的真实根因
判反一：把爆破压力当合格线。
这是管路选型里最贵的一课。客户拿一段样管来，标签上写"爆破 4.0 MPa"，就以为能用了。爆破测的是瞬间承压，管路实际工况是 0.3 MPa 压着十年。长期静液压外推才是真门槛，爆破只是入场券。 我们接这类询盘，第一句一定先问"有没有五十年外推曲线"，没有的话，建议先做浸泡加内压的耐久验证再定型。
判反二：用 PA66 省成本，赌它温度低。
服务器回路确实只有 40–55℃，水解慢。但 PA66 吸水率在 8% 上下，泡在去离子水里尺寸会漂、长期承压蠕变也明显。温度低只缓解水解，不缓解吸湿带来的密封面漂移。 接头位置渗不渗，往往和这点尺寸变化直接相关。要省，省在管身平衡料上，别省在接触介质的密封段。
判反三：只看强度，不看离子析出。
去离子水回路对电导率极敏感。某些润滑剂、稳定剂是小分子，长期泡水会被慢慢抽提出来，抬高介质电导率，严重时触发系统绝缘报警。这不是料的强度问题，是配方里低迁移组分的选型问题。 选料时把"离子析出"单列一项验证，比多测几次拉伸有用。
判反四：软硬管一段料走到底。
PA12 软料做管身，PA12-GF 硬料做歧管，过渡位置刚性差一大截，应力集中比管身大得多。很多开裂不发生在管身，发生在软硬过渡的焊缝或接头根部。 这个位置要单独算应力、单独做验证，不能套管身的结论。
一条时间线（行业里常见的失效路径，不是某一家的个案）：样管爆破合格 → 装线上线 → 第三个月接头微潮 → 半年后密封面尺寸漂移、间歇性渗 → 满一年批量渗液、追溯发现是长期静液压下的蠕变 + 吸湿叠加。问题从一开始就在，只是慢。
六、加工与验证：挤出和注塑要分开盯
服务器液冷管路通常是"挤出管材 + 注塑接头"两段工艺拼起来的，两段的坑不一样。
干燥。 尼龙必烘，挤出也不例外。PA12 吸水率低，但粒子在包装和车间里照样会受潮；含水率超标，挤出时内壁银纹、强度掉。干燥窗口按实测含水率定，不照抄牌号推荐值。
挤出与壁厚。 管径和壁厚不是随便给的，按工作压力反算管系列。壁厚偏薄，环向应力就超；偏厚，成本和柔韧都吃亏。壁厚公差要比普通管更紧，因为密封配合就靠那零点几毫米。
接头注塑。 注塑接头的浇口、排气、保压决定密封带质量。密封面有流痕或缺料，卡尺量不出来，放大镜才看得出。这一件必须做密封带外观全检，不能只靠尺寸。
验证顺序。 建议这样排：
1. 材料级：长期静液压外推 + 爆破（先确认基材底线）
2. 介质级：去离子水 / 水-乙二醇浸泡，测失重、尺寸、电导率增量
3. 接头级：与对配件一起做插拔和密封测试（单测一个接头看不出问题）
4. 组合级：介质浸泡 + 温度循环，复测密封与尺寸
5. 系统级：上整机前最后再验
顺序不能换。 前一项没过就往下走，后面测出来的数据没有解释意义。
七、边界：什么时候这件事不该用改性尼龙
这一段可能比前面更值钱。
其一，长期温度超过 120℃ 的水路。 长碳链尼龙的耐温上限摆在那里，这种位置要换金属或 PPS 类方案。
其二，大口径、长期高压（比如持续超过 10 bar）的主回路。 大口径高压下金属更稳，尼龙去做反而要不断加壁厚、加增强，性价比倒挂。
其三，强酸碱或特殊化学介质。 这类要走专门的耐化学体系，不是通用改性尼龙能兜底。
其四，年用量小到摊不平挤出和注塑的专用投入。 管路要开挤出模具、接头要开注塑模、还要跑长期验证。年用量只有几百米，从钱上不成立。
其五，要求管路完全透明、长期无任何析出可见。 尼龙即便低析出，长期泡水仍可能有极轻微附着，这种视觉洁癖场景要提前说清预期。
把这五条写在前头，不是劝退，是省时间。样品阶段一路顺、最后卡在介质或压力边界上、整个方案回退的项目，见过不止一个——回退的代价，比当初不做高得多。
八、换料风险清单（从橡胶管 / 金属管换到改性尼龙管路，要动什么）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 挤出模具 | 按目标管系列重算壁厚与公差 | 只按旧管外径套，壁厚偏薄 |
| 干燥 | 按实测含水率定窗口，不用热风干燥机 | 回用料掺入带入水分 |
| 料温 / 模温 | 接头注塑按 PA12 窗口调，不套通用参数 | 模温低导致密封带粗糙 |
| 保压与脱模 | 接头密封带位置重点控，防缺料流痕 | 密封面缺陷卡尺量不出 |
| 调湿 | 尺寸报告按泡水 / 调湿态出，不按干态 | 干态尺寸漂亮、湿态漂移 |
| 色差 | 半透明件色板提前确认 | 长期黄变预期未对齐 |
| 验证顺序 | 外推 → 浸泡 → 接头 → 组合 → 系统 | 前一项未过就往下走 |
九、一页纸汇报表（给要向上汇报的人）
`
项目：服务器液冷管路 · 材料路线评估
结论方向：长碳链尼龙可作为候选，能否落地取决于三项前置条件
一、必须守住的三条
1. 长期静液压按 50 年外推校核，不拿爆破压力替代
2. 接触介质的密封段用低吸水基材，尺寸报告按湿态出
3. 离子析出单列验证，不并入口径强度
二、前置条件（任一不满足则建议暂缓）
· 长期工作温度 ≤ 80℃ 量级
· 系统对去离子水电导率有明确要求且可测
· 年用量足以摊薄挤出与注塑专用投入
三、下一步动作
1. 取实际介质做浸泡，测失重与电导率增量
2. 做管系列反算，定壁厚与公差
3. 接头与对配件一起送插拔 + 密封测试
风险提示：本路线的主要不确定性在长期静液压下的蠕变与吸湿尺寸，不在初始强度。
`
十、读者常问的两句
问：和进口长碳链料差在哪？
只讲两件能对照的事：同一指标，看它标没标测试状态（干态还是湿态、20℃ 还是设计温度）；同一件上，看它给没给长期静液压外推曲线。管路类指标对状态特别敏感，状态不明的数字不宜直接比。有些位置走国产长碳链路线已经比较成熟，有些高压密封段目前仍建议谨慎——具体到你的管径和压力，要看温度和环应力两样。
问：能不能用 PA66 先把成本压下来？
看位置。纯结构、不碰冷却液的支架可以留在 PA66；只要接触介质、要靠尺寸保密封，PA66 的吸湿和蠕变就是长期隐患。 省下来的料钱，可能不够一次机房渗液事故的处置成本。这不是"能不能"，是"值不值"。
把料倒进机器之前，其实该做的事已经做完了。
增强多少、加不加阻燃、耐温做到哪一档、尺寸稳不稳——这些判断一旦定了，粒子只是把结论执行一遍。
宁波市科隆新材料有限公司，做改性尼龙（PA6 / PA66 / PA46 / PA11 / PA12 / PA6T / PA9T 及尼龙合金）、改性 PPO / PPS / 热塑性弹性体，以及各大化工巨头尼龙树脂、副牌料、大包料现货。另：长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
配方里的助剂体系按件的工况配——常规助剂常备现货，特殊型号按需配套；你报工况和牌号，料和助剂一次配齐。
Last week, a client who works on server liquid cooling pipelines came to us with a sample of modified nylon tubing to ask about.
The tube is translucent, with a handwritten label stuck on the outer wall that says 'Burst 4.0 MPa.' The first thing he said after sitting down was: 'The burst pressure is high enough, so why has it still been leaking after three months?'
There is a typical misjudgment hidden in this sentence: taking 'indestructible' as 'leak-proof'.
The failure of liquid cooling pipelines is, in the vast majority of cases, not due to bursting, but to slow leakage after long-term pressurization. This article will cover this one topic—server liquid cooling pipelines—by breaking down and explaining four aspects: pipe diameter and wall thickness, long-term hydrostatic pressure, coolant compatibility, and creep and joint stress.
1. The difficulty with the pipeline lies in 'pressing continuously' rather than 'pressing once'.
First, clarify the position of the server liquid cooling pipes in the system.
It is connected between the chilled water distribution unit (CDU) and the cabinet manifold, through which runs deionized water or low-concentration water-glycol, with a temperature usually between 40–55°C and not high pressure, commonly just 1–3 bar. It seems much milder than automotive liquid cooling.
Mild does not equal easy to do.
What car liquid cooling pipelines fear is hydrolysis at high temperatures, while server pipelines fear another thing: long-term, continuous, low-amplitude static pressure, combined with dimensional drift caused by contact with the medium. The former tests instantaneous strength, the latter tests whether it will fail over ten years.
This is why the selection of pipeline materials cannot be based solely on 'whether the strength is sufficient.' What truly determines whether it can be used are the following four factors:
The pipe diameter and wall thickness determine how much hoop stress this pipe can withstand; long-term hydrostatic strength determines whether it will creep and leak over ten years; coolant compatibility and ion precipitation determine whether soaking it in deionized water will raise the system's conductivity; joint stress determines whether the position where it mates with metal cold plates and sealing rings will crack first.
Among these four quantities, the latter three were partially discussed in old articles on 'battery liquid cooling,' but servers have their own considerations—low temperature, low pressure, and even more stringent requirements for cleanliness. The following section lays out the operating conditions.
In one sentence: When selecting materials for server liquid cooling pipelines, the first question is not 'is it sturdy,' but 'after ten years under pressure, immersed in deionized water, can it still maintain a seal?'
2. Operating Condition Six Dimensions: What constraints are applied to this pipeline
Break down the working conditions into six dimensions; missing one means that all subsequent material selection is just guessing.
Temperature. The cold plate liquid cooling loop is generally 40–55°C, which is a bit lower than automotive liquid cooling. But don't relax because of this—the biggest hidden danger in this loop is not heat, but 'being constantly soaked.' Low temperature only means hydrolysis is slow, it does not mean dimensional issues and creep disappear.
Load (pressure). A common circumferential pressure is 1–3 bar. To convert: a DN10 pipe (inner diameter about 10 mm) with a wall thickness of 1.5 mm, under an internal pressure of 0.3 MPa, has a circumferential stress of about 1.0 MPa (formula σ = p·D / 2e). This number looks small, but it is constant, twenty-four hours a day, over thirty-one million seconds a year, never unloaded.
Medium. Deionized water is the main component, though sometimes a water-ethylene glycol mixture is used. Deionized water is pure but has a drawback: its own conductivity is extremely low (usually required to be below 0.1 μS/cm), which in turn can 'draw' ions and additives out of the materials. Once impurities precipitate in the pipeline, the conductivity of the entire loop rises, triggering a system alarm.
Lifespan. Data centers start with a service life of ten years. The criterion is not 'when will it fail,' but 'after ten years, can the seal still hold, and how much of the strength remains?'
Appearance and cleanliness. The machine room is a working environment, requiring low smoke, low toxicity, and low deposits. Transparent or translucent pipes also need to consider long-term yellowing and attachment of deposits.
Compliance. Flame retardancy usually requires UL94 V0, and in many cases, it must be halogen-free; for locations close to electrical appliances, the glowing wire test (GWIT) also needs to be considered. These are independent issues from 'whether it contacts the dielectric,' and both should be mentioned when selecting materials.
In six dimensions, temperature, pressure, medium, and lifespan are all given specific numbers; this is the level of precision that a component-level article should have. Next, we move on to the material route.
3. Three material routes, each with different costs
Place the candidate routes for the server liquid cooling pipes side by side, looking at the 'Cost' column, not the 'Advantages' column.
| Route | compose; consist of | Give what | Cost |
|---|
| PA12 Extrusion Grade | Long carbon chain nylon, solid or semi-rigid tube | Low water absorption, hydrolysis resistant, most dimensionally stable, flexible | Temperature resistance upper limit about 80℃, high unit price, relatively low rigidity |
| PA612 / PA610 Copolymer | Medium-long carbon chain, balanced type | Performance is between PA12 and PA66, with a more cost-friendly price | The size after long-term soaking is still slightly inferior to PA12 |
| PA12-GF / PA6T-GF | Glass fiber reinforced, rigid pipe segment and manifold | Rigid, pressure-resistant, creep-resistant | Dimensional changes after moisture absorption, water stains may appear at the glass fiber locations |
None of the three routes have 'which one is better,' only 'which item's account is tighter.'
The reason for using PA12 in this part is very straightforward: it has a water absorption rate of less than 1%, so its dimensions hardly change when soaked in deionized water, and the mating dimensions of the joint sealing surfaces remain almost the same even ten years later as they were when leaving the factory. The trade-offs are that it is expensive, soft, and not very heat-resistant—but server circuit temperatures are not high to begin with, and being softer actually helps resist vibration.
PA612 is the cost-reduction balancing point: it is functional, the price is more acceptable than PA12, and it is suitable for locations like pipe bodies where the stress is moderate.
The fiberglass reinforced type is used in rigid pipe sections and manifolds—it requires rigidity and pressure resistance. However, its moisture absorption and creep are more pronounced than those of long-chain pure materials, and the position where the softness transitions to hardness is precisely the stress concentration point, which is explained in detail in Section Four.
In one sentence: For server liquid cooling pipelines, areas that come into contact with the medium should move toward long carbon chain materials; purely structural brackets that do not contact the coolant can remain in the PA66 system. Once this dividing line is drawn, the range of material selection is immediately halved.
4. Selection Criteria Table: Long-term Hydrostatic and Dimensional Stability Are the Main Factors
Translate the above constraints into verifiable indicators. The threshold values in the table are directional suggestions, not acceptance criteria—the actual figures must be determined by specific projects, specific working conditions, and actual measurements.
| Indicator | Directional Threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary agent system |
|---|
| Long-term static hydraulic strength (extrapolated) | The circumferential stress at the design temperature is checked according to a 50-year period | ISO 9080 extrapolation ISO 1167 hydrostatic | Creep leakage after ten years | Choose low-creep substrate and control wall thickness | Antioxidant (thermal oxidative stability) |
| Pipe Diameter / Wall Thickness (Burst) | According to PN and pipe series, the bursting pressure ≥ several times the working pressure | ISO 1167 Burst Test | Wall thickness is too thin, hoop stress is excessive | Recalculate pipe series, increase wall thickness | Intrinsic properties of the material, without relying on additives |
| Water absorption and dimensional stability | Water absorption balance ≤ 1.5%, minimal dimensional changes after soaking | ISO 62 Water Absorption Soaking Measurement | Joint sealing surface expansion and contraction leakage | long carbon chain substrate | Intrinsic to the material, not dependent on additives |
| Coolant Compatibility / Ion Precipitation | Weight loss and conductivity increase after soaking are controllable | Operating Condition Medium Soaking Conductivity Method | Increased conductivity, system alarm | Low migration formula Material selection | Lubricant (low deposit selection) |
| Circumferential creep | Low long-term creep rate | ISO 899 Creep Internal Pressure Method | Pipe diameter swelling, seal failure | low-creep system | Antioxidant (inhibits aging creep) |
| Hydrolysis resistant (water-ethylene glycol) | 1000 h intensity retention rate meets the standard | Ethylene glycol soaking Mechanical retest | Inner wall cracking and leakage | Long carbon chain Stabilization | Hydrolysis-resistant stabilizer (optional) |
| Low-temperature toughness | Not brittle at -40℃ | ISO 179 Low Temperature Impact | Cracking in cold region transportation | Toughen or select a tough substrate | — |
How to use this table: Do not score line by line. First look at the first and third rows — if long-term static hydraulic and dimensional stability fail, there is no need to discuss the rest. Pipeline leakage is a slow variable, linked in series with these two indicators.
A reminder: The item "long-term static hydraulic" in the table relies on the ISO 9080 extrapolation method—using high-temperature short-term data and 20°C long-term data, extrapolated to fifty-year strength at the design temperature. Without this extrapolation curve, just talking about burst pressure is equivalent to endorsing ten-year performance with instantaneous results.
Five, four common misjudgments, and their true causes
Misjudgment One: Treating the blasting pressure as the pass line.
This is the most expensive lesson in pipeline selection. A customer brings a sample pipe, and the label says 'burst 4.0 MPa,' and they think it can be used. The burst test measures instant pressure tolerance, while the actual pipeline condition is 0.3 MPa for ten years. Long-term static hydraulic extrapolation is the real hurdle; bursting is just a ticket to enter. When we receive such inquiries, the first thing we always ask is 'Do you have a fifty-year extrapolation curve?' If not, we recommend conducting soak plus internal pressure durability testing before finalizing the design.
Counter-argument two: Use PA66 to save costs, betting that its temperature is low.
The server circuit indeed only reaches 40–55°C, so hydrolysis is slow. But PA66 has a water absorption rate of around 8%, so it will swell in deionized water, and long-term stress can also cause noticeable creep. Low temperature only slows down hydrolysis, it doesn’t reduce the dimensional drift caused by moisture absorption. Whether a joint leaks or not often directly relates to this dimensional change. If you want to save costs, save on the body of the pipe with balanced material, not on the sealing section that comes into contact with the medium.
Counter reaction three: Only consider the intensity, not the ion precipitation.
The deionized water circuit is extremely sensitive to conductivity. Some lubricants and stabilizers are small molecules that are slowly extracted from prolonged soaking, increasing the dielectric's conductivity and, in severe cases, triggering system insulation alarms. This is not a matter of material strength, but of the selection of low-migration components in the formula. When selecting materials, listing "ion precipitation" as a separate item for verification is more effective than multiple tensile tests.
Reverse Four Judgment: A segment of soft and hard pipes goes all the way to the end.
The tube body is made of PA12 soft material, and the manifold is made of PA12-GF hard material. The rigidity at the transition area is much lower, and stress concentration is much higher than in the tube body. Many cracks do not occur in the tube body but at the weld or joint root of the soft-hard transition. This position needs to be calculated for stress separately and validated individually; conclusions applicable to the tube body cannot be applied here.
A timeline (common failure path in the industry, not a case specific to any one company): sample tube passes burst test → installed online → third month, joint slightly damp → after six months, sealing surface size drifts, intermittent leakage → after one year, batch leakage, trace-back finds it’s creep under long-term static hydraulic pressure combined with moisture absorption. The problem was there from the beginning, just slow.
6. Processing and Verification: Extrusion and injection molding need to be monitored separately
Server liquid cooling pipelines are usually assembled from two processes: 'extruded tubing' and 'injection-molded connectors', and the defects in the two segments are different.
Drying. Nylon must be dried, and extrusion is no exception. PA12 has a low moisture absorption rate, but the pellets can still get damp during packaging and in the workshop; if the moisture content exceeds the limit, silver streaks appear on the inner wall during extrusion and strength decreases. The drying window should be determined based on the measured moisture content, not simply copied from the grade's recommended value.
Extrusion and Wall Thickness. Pipe diameter and wall thickness are not given arbitrarily; they are calculated in reverse according to the working pressure. If the wall is too thin, the circumferential stress will exceed the limit; if it is too thick, both cost and flexibility suffer. The wall thickness tolerance must be tighter than that of ordinary pipes because the seal fit relies on those fractions of a millimeter.
Connector injection molding. The gate, venting, and holding pressure of the injection-molded connector determine the quality of the sealing strip. If the sealing surface has flow marks or missing material, it cannot be measured with a caliper and can only be seen with a magnifying glass. This piece must undergo a full visual inspection of the sealing strip; it cannot rely on dimensions alone.
Verification order. It is recommended to arrange it like this:
1. Material Level: Long-term static hydraulic expansion blasting (confirm the baseline of the substrate first)
2. Medium level: Soaking in deionized water / water-ethylene glycol, measuring weight loss, dimensions, and conductivity increase
3. Connector stage: Perform plug-in and sealing tests together with matching parts (testing a connector alone cannot reveal problems)
4. Assembly Level: Media Soak, Temperature Cycling, Retest Sealing and Dimensions
5. System level: Final inspection before assembling the complete machine
The order cannot be changed. If the previous item fails, moving on means the data measured afterwards has no explanatory significance.
7. Boundaries: When this matter should not use modified nylon
This section might be more valuable than the previous one.
First, water passages where the long-term temperature exceeds 120°C. The upper temperature limit of long-chain nylon is set, and for such applications, metal or PPS solutions need to be used.
Secondly, main circuits with large diameters and long-term high pressure (for example, sustained pressure over 10 bar). Metals are more stable under large-diameter high pressure, whereas using nylon would require continuously increasing wall thickness and reinforcement, resulting in a reversed cost-performance ratio.
Third, strong acids and bases or special chemical media. This type needs specialized chemical-resistant systems; general modified nylon cannot cover it.
Fourth, the annual usage is too small to justify the specialized investment for extrusion and injection molding. The piping requires the opening of extrusion molds, the joints require the opening of injection molds, and long-term validation tests are also needed. With an annual usage of only a few hundred meters, it is not financially viable.
Fifth, it requires the tubing to be completely transparent and free of any visible deposits over the long term. Even low-extraction nylon may still have extremely slight adhesion after prolonged soaking in water, so it is necessary to clearly communicate expectations in scenarios where visual purity is critical.
Writing these five points at the outset is not to dissuade, but to save time. I've seen more than one project that went smoothly in the sample stage, only to get stuck at the interface or pressure boundaries, causing the entire plan to be rolled back—the cost of rolling back is much higher than not doing it in the first place.
8. Material Change Risk List (What needs to be done when switching from rubber/metal pipes to modified nylon piping)
| link; segment; part | What do you want to move? | Points that are easy to overlook |
|---|
| Extrusion die | Recalculate wall thickness and tolerance according to the target pipe series | Only fits according to the outer diameter of the old pipe, with a relatively thin wall |
| Dry | Set the window according to the measured moisture content, without using a hot air dryer | Incorporate recycled materials with the carried water content |
| Material Temperature / Mold Temperature | The connector injection molding should be adjusted according to the PA12 window, without using general parameters. | Low mold temperature causes the sealing strip to be rough |
| Pressure Holding and Demolding | Focus on controlling the position of the joint sealing tape to prevent material shortage and flow marks | The sealing surface defect cannot be measured with calipers |
| Humidity control | The size report is based on soaking/wet condition or humidity-adjusted state, not dry condition. | Good dry-state dimensions, wet-state drift |
| Color difference | Confirm the color swatch of the translucent parts in advance | Long-term yellowing expectations are not aligned |
| Verification order | Extrapolation → Soaking → Joint → Combination → System | If the previous item fails, just move on. |
9. One-page report form (for those who need to report upward)
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Project: Server Liquid Cooling Pipeline · Material Route Evaluation
Conclusion direction: Long-chain nylon can be considered as a candidate, and whether it can be implemented depends on three prerequisite conditions.
1. Three Rules That Must Be Followed
1. Long-term static hydraulic pressure is extrapolated and checked according to 50 years, without substituting it with blasting pressure.
2. The sealed section in contact with the medium uses a low water absorption substrate, and the size report is based on the wet state.
3. Single-column verification of ion precipitation, without merging the inlet diameter strength
2. Precondition (It is recommended to postpone if any are not met)
· Long-term operating temperature ≤ 80℃ range
· The system has clear requirements for the conductivity of deionized water and it can be measured
· Annual usage sufficient to dilute the dedicated inputs for extrusion and injection molding
3. Next Steps
1. Use the actual medium for soaking, measure weight loss and conductivity increase
2. Perform reverse calculation for the pipe series, determine wall thickness and tolerance
3. Connectors are delivered together with matching parts for plug and play, sealing test
Risk Warning: The main uncertainties of this route lie in creep and moisture-induced dimensional changes under long-term static hydraulic conditions, not in the initial strength.
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10. Two Questions Frequently Asked by Readers
Question: How does it differ from imported long-chain materials?
Let's only talk about two comparable things: for the same indicator, see whether it marks the test condition (dry state or wet state, 20°C or design temperature); for the same item, check whether it provides a long-term static hydraulic extrapolation curve. Pipeline indicators are particularly sensitive to state, and numbers with unclear states shouldn't be directly compared. Some positions using domestic long carbon chain routes have become relatively mature, while some high-pressure sealing sections are still recommended to be cautious—specifically for your pipe diameter and pressure, you need to consider both temperature and hoop stress.
Question: Can we use PA66 to bring the cost down first?
Look at the location. Brackets that are purely structural and do not touch coolant can remain in PA66; as long as they come into contact with the medium and need to maintain a seal through precise dimensions, the moisture absorption and creep of PA66 are long-term risks. The money saved on materials may not be enough to cover the cost of handling a single data center leakage incident. This is not a question of 'can it be done,' but 'is it worth it'.
Before pouring the material into the machine, what needed to be done was actually already completed.
How much to enhance, whether to add flame retardant, which level of temperature resistance to achieve, whether the size is stable—once these judgments are made, the particles just execute the conclusions.
Ningbo Kelon New Materials Co., Ltd. specializes in modified nylon (PA6 / PA66 / PA46 / PA11 / PA12 / PA6T / PA9T and nylon alloys), modified PPO / PPS / thermoplastic elastomers, as well as nylon resins from major chemical companies, secondary materials, and bulk material in stock. Additionally, we have long-term procurement of nylon raw materials, sprue material, and various nylon waste, with formal disposal channels.
The auxiliary system in the formula is matched according to the working conditions per item — conventional auxiliaries are kept in stock, and special models are matched as needed; you report the working conditions and grade, and the material and auxiliaries are prepared together at once.
